THE PREVALENCE OF VISUAL ACUITY IMPAIRMENT AND
COLOR BLINDNESS ON SCHOOL AGE CHILDREN OF TWO
PRIMARY SCHOOLS IN ADDIS ABABA.
A Thesis Submitted to the School of Graduate Studies of Addis Ababa
University in Partial Fulfillment of the Requirements for the Degree of
Masters of Science in Physiology.
By
Haile Fentahun Darge
March, 2014
Addis Ababa, Ethiopia
ADDIS ABABA UNIVERSITY
SCHOOL OF GRADUATE
THE PREVALENCE OF VISUAL ACUITY IMPAIRMENT AND COLOR
BLINDNESS ON SCHOOL AGE CHILDREN OF TWO PRIMARY
SCHOOLS IN ADDIS ABABA.
A Thesis Submitted to the School of Graduate Studies of Addis Ababa
University in Partial Fulfillment of the Requirements for the Degree of
Masters of Science in Physiology.
By
Haile Fentahun Darge
Advisors
1. Dr. Getahun Shibru, Department of Physiology.
2. Dr. Abiy Mulugeta, Department of Ophthalmology
March, 2014
Addis Ababa, Ethiopia
Addis Ababa University
School of Graduate Studies
This is to certify that the thesis prepared by Haile Fentahun entitled: The Prevalence of Visual
Acuity Impairment and Color Blindness on School Age Children of Two Primary Schools In
Addis Ababa and submitted in partial fulfillment of the requirements for the Degree of Master of
Science in Physiology complies with the regulations of the university and meets the accepted
students with respect to originality and quality.
Signed by the Examining Committee.
Examiner
Prof. Yekoye Abebe: Signature _______________________ Date _____________________
Advisors
Dr. Getahun Shibru: Signature ________________________Date_____________________
Dr. Abiy Mulugeta: Signature ________________________ Date______________________
___________________________________________________________________________
Chair of Department or Graduate Program Coordinator
ACKNOWLEDGEMENTS
Foremost, I would like to express heartfelt gratitude to my advisors Dr. Getahun Shibru and Dr.
Abiy Mulugeta for their positive, valuable, reliable professional guidance, constructive
comments, suggestions and encouragement starting from proposal development up to the
completion of this thesis. They spent countless hours trying to make sense out of my work and
critique my progress along the way.
I am also very much grateful to Professor Yekoye Abebe for his valuable comments and idea
during proposal development and Dr.Adugna Lisanework from Department of Ophthalmology,
Menelik Hospital for her best cooperation in providing brief guidance and explanation about
Snellen chart and Ishihara’s test.
I would like to extend my gratitude to Betewulign Kassa (Lecturer at Axum University), Aemro
Mekonen (MSc. Student at AAU), and Birhanu Dessie (MSc. Student at AAU) for their technical
support during data collection.
I am also indebted to directors and staff members of ‘The Holy Trinity Cathedral and ‘Zeray
Deres’ Primary Schools for their positivity and cooperation during data collection.
I also wish to thank the Research and Publication Office, Addis Ababa University for financial
assistance and Samara University for sponsored me and covering my living expense throughout
the study period.
I am also very much grateful to the Department of Medical Physiology, Addis Ababa University
and all my instructors in the Department for their significant contribution to my academic career.
My special thanks again go to my uncle Muluken Bayih. It is because of him that I got courage
to proceed with my education, felt confident and dreamed more.
Above all, I like to thank my family as a whole for their key and principal role in the success of
my life. I am proud of them.
And finally, I am so much grateful to my all friends who supported me in one way or another
making this research possible.
i
TABLE OF CONTENT
CONTENTS
PAGE
ACKNOWLEDGMENT-------------------------------------------------------------------------------------i
TABLE OF CONTENT -------------------------------------------------------------------------------------ii
LIST OF TABLE --------------------------------------------------------------------------------------------iv
LIST OF FIGURE --------------------------------------------------------------------------------------------v
LIST OF APPENDIX ---------------------------------------------------------------------------------------vi
LIST OF ABBREVIATION-------------------------------------------------------------------------------vii
ABSTRACT ------------------------------------------------------------------------------------------------viii
1. INTRODUCTION.................................................................................................................... 1
1.1. Statement of the problem .................................................................................................... 5
2. LITERATURE REVIEW ........................................................................................................ 6
2.1. Definition ........................................................................................................................... 6
2.2. Visual impairment worldwide ............................................................................................ 7
2.3. Causes of visual impairment .............................................................................................. 8
2.4. Color blindness .................................................................................................................. 9
2.4.1. Inherited Vs. acquired color blindness ......................................................................... 9
2.5. Significant of the study ..................................................................................................... 14
3. OBJECTIVE OF THE STUDY ............................................................................................. 15
3.1. General objective ............................................................................................................. 15
3.2. Specific objectives ........................................................................................................... 15
4. MATERIALS AND METHODS ............................................................................................ 16
4.1. Study area and period....................................................................................................... 16
4.2. Study design .................................................................................................................... 16
4.3. Population........................................................................................................................ 16
4.4. Sampling technique and sample size. ............................................................................... 17
4.5. Data collection instrument and procedure......................................................................... 19
ii
4.6. Data entry and analysis procedure .................................................................................... 20
5. ETHICAL CLEARANCE ...................................................................................................... 22
6. RESULTS .............................................................................................................................. 23
6.1. Visual acuity .................................................................................................................... 23
6.2. Color vision ..................................................................................................................... 31
7. DISCUSSION ........................................................................................................................ 35
8. CONCLUSION AND RECOMMENDATIONS .................................................................... 41
8.1. Conclusion ....................................................................................................................... 42
8.2. Recommendations............................................................................................................ 43
9. REFERENCES ...................................................................................................................... 44
Appendix I: Information sheet and consent form for study subjects ............................................ 49
Appendix II: Questionnaires ..................................................................................................... 53
Appendix III: Numerals on each plate and answers which would be given by normal color vision
and color defective individuals .............................................................................. 56
iii
LIST OF TABLES
Table
Page
Table 2.1. Category of blindness and low vision (visual impairment) (WHO, ICD-9, 10) ............. 6
Table 4.1: Sample size calculation for each school estimates. ..................................................... 18
Table 4.2. Distribution of class population and sample size determination for each class ……...18
Table.6.1: Distribution of participants by grade, school and sex. ................................................ 23
Table 6.2: Frequency of different activities by individuals who have VA≤ 6/12 ......................... 25
Table 6.3: Socio-demographic features of parents of students who have VA ≤ 6/12.................... 26
Table 6.4: The frequency of visual impairment (VA ≤6/12) by sex and schools. ......................... 27
Table 6.5: Bivariate logistic regression analysis of factors associated with VAI.......................... 28
Table 6.6: Frequency of visual acuity with the worse eye ........................................................... 29
Table 6.7: Distribution of VAI by sex in one and both eyes ........................................................ 29
Table 6.8: Socio-demographic feature of color blind individuals and their parents. ..................... 33
Table 6.9: Bivariate logistic regression analysis of factors associated with CVD. ...................... 34
iv
LIST OF FIGURES
Figure
Page
Fig. 2.1. Cause of visual impairment in Ethiopia ( Berhane et al., 2006) ....................................... 8
Fig 4.1. Students in the field after VA test. ................................................................................. 18
Fig.4.2: Snellen chart ................................................................................................................. 19
Fig.4.3: Samples of plates used for color blindness test. ............................................................. 20
Fig.6.1: Distribution of participants by age. ................................................................................ 24
Fig 6.2: Causes of low vision ..................................................................................................... 30
Fig.6.3: Pie-chart that shows the distribution of color blindness................................................. 31
Fig.6.4: Distribution of color vision by sex ................................................................................. 32
v
LIST OF APPENDIX
Appendix
Page
Appendix I: Information sheet and consent form for study subjects---------------------------------49
Appendix II: Questionnaires -----------------------------------------------------------------------------------53
Appendix III: Numerals on each plate and answers which would be given by normal color vision
and color defective individuals------------------------------------------------------------57
vi
LIST OF ABBREVIATIONS
CNS
Central Nervous System
CVD
Color Vision Disorder
Fig
Figure
FVL
Functional Visual Loss
ICD-10
International Statistical Classification of Diseases, 10th revision.
LGN
Lateral Geniculate Nucleus
LP
Light Perception
NLP
No Light Perception
nm
nanometer
RE
Refractive Error
SNNP
South Nation Nationality and People
VA
Visual Acuity
VAI
Visual Acuity Impairment
VI
Visual Impairment
WHO
World Health Organization
vii
ABSTRACT
Vision is the primary means of integration between individuals and the external
environments. For a normal eye, light is focused on the retina. This message would then be sent
to the brain to be interpreted as a message. There are different factors that will affect normal
vision such as infection, malnutrition, lack of vitamin A rich food, refractive error, cataract, etc.
Visual impairment is major cause of blindness and mortality in developing countries where there
is no enough health care services and because of malnutrition.
The main aim of this study was to determine the prevalence of visual acuity impairment and
color blindness in school children.
The study was conducted in randomly selected one governmental and one private primary
schools in Addis Ababa from Sep.10 to Nov.30, 2013. A cross sectional study design was utilized
and using random sampling with estimated sample size calculation, 378 students in two schools
were involved in the study. All the school age children in the selected schools who have a
written consent from their parents were included.
Snellen chart was used for visual acuity test and color blindness was determined using
Ishihara’s tests. Students who have visual acuity ≤ 6/12 and color blindness were further
interviewed and diagnosed by ophthalmologist to identify the causes of visual acuity impairment.
Structural questionnaires were also prepared and filled by parents to know the socio
demographic features. The collected data was manually cleared and checked and the result was
presented in the form of table and graph using SPSS version 20.
Although prevalence of blindness is high as people aged, it is also a major problem in
children in developing countries like Ethiopia because of malnutrition and limitation of health
service. The study found the prevalence of visual acuity impairment; VA ≤ 6/12 in either eye was
5.8% (3.2% female, 2.6% male); VA< 6/18 in either eye was 1.1% and VA < 6/18 in better eye
was 0.53%. The prevalence of color blindness in this study was 4.2% (1.6% female, 2.6% male);
2.9% deutran, 1.1% protan and 0.3% color weakness.
Although the prevalence of visual impairment in children was very low, priority should be
given to them because the health of children would have high cost for economic, social and
educational development of the community. Most visually impaired children showed low
compliance with the use of spectacle. Thus, Ministry of Health, Ministry of Education and other
stakeholders should look at different strategies among students to have behavioral change about
the use of spectacles. Further studies to be done to determine magnitude and severity of CVD using
anomaloscope, visual impairment of near vision using jaeger eye chart and risk factors for
visual problems. Early detection of visual defect of an individual is very important in life to make
decision on future career or to take correction.
Key words: visual acuity, color blindness, prevalence and visual impairment.
viii
1. INTRODUCTION
The visual system is one of our most important sensory systems. It is the primary means of
integration between individuals and the external environments. It results from entrance of light
into the eye and the interpretation of this stimulus by the brain. For a normal eye, light is focused
to a spot on the retina. This message would then be sent to the brain to be interpreted as a
message (Tonks, 1993). The overall visual function of an individual has four major components;
communication, mobility, daily living activities and sustained near vision tasks like reading and
writing, including color vision and contrast sensitivity assessment. This is achieved through an
optical system in the eye that refracts light onto the retina, where the first step of visual
processing occurs (Krebs et al., 2012).
There are two types of photoreceptor cells; rods and cones on the retina. Each photoreceptor cell
has an outer segment where the detection of light occurs. The outer segments of rods and cones
differ in their morphology, but each contains discs that contain a vitamin A–linked photopigment
(rhodopsin in rods, iodopsin in cones). Activation of this photopigment by the absorption of light
(photons) initiates the signal transduction cascade (Krebs et al., 2012).
From the photoreceptor cell, the visual pathway consists of a four neuron chain that processes
visual information and conveys it to the cortex. The first two neurons in the chain are in the
retina: the bipolar cells and the retinal ganglion cells. From the retina, the visual pathway
projects to the third neuron, which is located in the lateral geniculate nucleus (LGN) of the
thalamus. Axons from the thalamus project via the optic radiations to the primary visual cortex
(Krebs et al., 2012).
If there is any defect on the anatomy and physiology of the visual system, it will cause visual
impairments such as low vision and blindness. According to the International statistical
classification of diseases, injuries and causes of death, 10th revision (ICD-10), low vision is
defined as visual acuity of less than 6/18, but equal to or better than 3/60, or a corresponding
visual field loss to less than 20 degrees in the better eye with best possible correction and
blindness is defined as visual acuity of less than 3/60, or corresponding field loss to less than 10
1
degrees in the better eye with best possible correction (ICD-10, 1992, The Oslo invitational
workshop, 2005).
Visual acuity is defined as the clarity or sharpness of vision, which is the ability of the eye to see
and distinguish fine details (Tonks, 1993). It is estimated that 1.6 billion people in the world
suffer from impaired visual acuity and the incidence is increasing (Fredrick, 2002).
Color blindness is also a visual problem. Visual system allows us to appreciate the visual world
around us in form, motion and color, with visual acuity. Objects do not have color as a physical
attribute. In fact, color is light, which is carried as specific wavelengths that the eye absorbs and
the brain converts into ‘messages’ so that we ‘see’ colors. An object that appears blue actually
absorbs all the other color wavelengths except blue. The unabsorbed wavelength is reflected
back to the eye and the brain interprets the object as blue (Krebs et al., 2012).
Color vision begins in the retina where different types of cones are sensitive to photons of
different frequencies and it is analyzed through the comparison of cell activations in the retina
and in the primary visual cortex (Krebs et al., 2012).
The color of any object we are looking at depends on the wavelength of light reflected by the
object. Our brain recognizes the color of an object by interpreting the combination of signals
coming to it from the three different color cones or color pigment (Silverthorn et al., 2010).
These color pigments are called, respectively, red-sensitive pigment (L-type cones): detect lowfrequency photons (555–565 nm), green-sensitive pigment (M-type cones): detect middlefrequency photons (530–537 nm) and blue-sensitive pigment (S-type cones): detect high
frequency photons (415–430 nm). Mixing the information of those three different types of cones
makes up our color vision, which allows us to detect the millions of colors visible to the human
eye (Krebs et al., 2012, Guyton and Hall, 2006).
Color vision deficiency, commonly called color blindness, manifests itself in everyday life in the
confusion of or blindness to one or more primary colors and its origins may be congenital or
acquired (Linksz, 1964).
2
There are two recognized types of color vision deficiency; red-green color blindness and blue
color blindness. Most cases are hereditary (congenital), while others are acquired, mainly caused
by ocular or neurological disease, drug toxicity or exposure to certain solvents.
Different
scientific studies show, that roughly 9% of all men and 0.5% of all women are color blind
(Agamemnon et al., 2003). This numbers are supported by different studies and are about the
same all around the world. The high difference between men and women is resulting from the
facts that the most common form, red-green color blindness, is a recessive sex-linked trait
(Emslie-Smith et al., 1998). In reality, we are all color deficient to a greater or lesser degree
because our perception of color is somewhat limited and never 100 percent complete.
Employment in certain professions like working in the capacity of pilots, drivers and a few
others necessitates a normal color vision and hence color blind persons are likely to be rejected
from such professional jobs (Rahman et al., 1997).
Other visual problems, blindness and low vision, lead to loss of functional ability and selfesteem. They have considerable social, psychological and economic implications for the patient
and their care giver.
Prevalence of visual impairment is high in developing countries compared with developed one.
In Canada, the prevalence rate of blindness and low vision were estimated about 0.038% and
0.36% respectively (Maberley et al., 2006), while national eye survey done in Malaysia, found
that the prevalence of visual impairment was 2.7%. The prevalence was higher in rural areas
(2.9%) as compared to urban areas (2.5%) (Zainal et al., 2002).
According to World Health Organization (WHO, 2009), Sub-Sahara Africa has an estimated 5-6
million blind and 16-18 million persons with low vision. Around 60% of them live in twenty
African countries including Botswana, Eritrea, Ethiopia, Gambia, Ghana, Kenya, Lesotho,
Liberia, Malawi, Mauritius, Namibia, Nigeria, Seychelles, Sierra Leone, South Africa,
Swaziland, Uganda, the United Republic of Tanzania, Zambia and Zimbabwe.
Eye problems in Ethiopia are among the major public health challenges of the country and pose
huge economic and social impact for affected individuals and to the society and the nation at
large. The major causes of low vision and blindness include cataract, refractive error, and
3
trachomatous corneal opacity. All major causes of low vision and blindness are either
preventable or treatable (Berhane et al., 2006).
The prevalence of low vision and blindness in Ethiopia is 3.7% and 1.6% respectively with
considerable regional variations. The prevalence of childhood blindness is 0.1%, which accounts
for over 6% of the total blindness burden nationwide The large proportion of low vision (91.2%)
and blindness (87.4%) are due to avoidable (either preventable or treatable) causes (Berhane et
al., 2006, Kello and Gilbert, 2003). Therefore, the main aim of this study was to determine the
prevalence of visual impairment in early stage and to suggest possible ways to prevent or treat
those individuals who have visual impairment.
4
1.1.
Statement of the problem
Visual impairment and vitamin A deficiency is a major cause of blindness and mortality in
developing countries including Ethiopia. According to WHO 285 million people are visually
impaired worldwide and one individual becomes blind in each minute and a child in each 5
minute (WHO, 2013). A National Survey on Blindness, Low Vision and Trachoma in Ethiopia
estimates that the prevalence of blindness and low vision is 1.6% and 3.7%, respectively
(Berhane et al., 2007). This indicates that burden of eye disease in Ethiopia is believed to pose
huge economic and social impacts on individuals, society and the nation at large. Visual problem
have negative effect on learning and social interaction, thus affecting the natural development of
academic and social abilities. It has been estimated that 75-90% of all learning in the classroom
comes to the students either wholly or partially via the visual pathway (Naresh, 1995). In the
classroom, blocks or other teaching tools may be color coded as well as being of different size. A
child with color vision problems may have to rely on size differences alone. Therefore, in
children, vision impairment can affect school performance and other functions, such as ability to
safely participate in sports. Poor performance at school may contribute to the child's selfconfidence and their career. Some occupational groups such as drivers will also not allow getting
driving license if he/she is color blind. Thus, this study would fill knowledge gap to detect visual
defect early and suggest possible methods of prevention and treatment to visual problems in
children.
5
2. LITERATURE REVIEW
2.1.
Definition
According to WHO, blindness is defined as best corrected vision of less than 3/60 in the better
eye or a visual field no greater than 10° in radius around central fixation (Resnikoff et al., 2004).
Low vision is defined as visual acuity of less than 6/18 but equal to or better than 3/60 or a
corresponding visual field loss to less than 200 in the better eye. Visual impairment (VI) includes
both blindness and low vision and severe visual impairment (SVI) is defined as best corrected
visual acuity worse than 6/60 but better or equal to 3/60 in the better eye (Resnikoff et al., 2004).
Based on recommendations from WHO study group on the prevention of blindness, visual
impairment has been divided into six strata by the International Statistical Classification of
Diseases and Related Health Problems, 10th revision (ICD-10, 1992) (Table 2.1).
Table 2.1. Category of blindness and low vision (visual impairment) (WHO, 1992)
Category of Visual
impairment
Low vision
Blindness
Visual acuity with best possible correction
1
Maximum less than
6/18
Minimum equal to or better than
6/60
2
6/60
3/60
3
3/60
1/60
4
1/60
Light perception (LP)
5
No light perception (NLP)
9
Undetermined or unspecified
6
2.2.
Visual impairment worldwide
The number of people with visual impairment worldwide in 2002 was in excess of 161 million,
of whom about 37 million were blind (Resnikoff et al., 2004). The burden of visual impairment
is not distributed uniformly throughout the world: the least developed regions carry the largest
share. Visual impairment is also unequally distributed across age groups, being largely confined
to adults 50 years of age and older. A distribution imbalance is also found with regard to gender
throughout the world: females have a significantly higher risk of having visual impairment than
males (Resnikoff et al., 2004).
A larger survey conducted in 2008 across standardized populations in Asia, Africa and Latin
America, found an overall prevalence of functional visual loss (FVL) of 1.52 in 1000 children.
Retinal lesions and amblyopia were the commonest causes in which FVL was significantly
associated with age and low education level of the parents (Gilbert, 2008).
A study conducted in Malaysian on prevalence of visual acuity impairment and its associated
factors among secondary school students (77), 25.0% had visual acuity impairment. Females
and those who have been watching television at a distance of less than two meters were
significantly associated with visual acuity impairment (Aniza et al., 2012).
The poorest regions of Africa and Asia are where three quarters of the world's blind children live
(Gilbert and Foster, 2001). Out of the 1.4 million blind children globally, about 300,000 live in
Africa. The prevalence of blindness in children in a country is related to the nutritional, health
and socioeconomic status of that country (Gilbert and Foster, 2001).
As is true in most sub-Saharan African countries there is no adequate eye care service delivery
system in Ethiopia. Many reasons can be given for this. The country lacks sufficient number of
skilled eye care professionals at all levels of hierarchy and service delivery. The number of eye
care professionals is very limited and inadequate for the large population of Ethiopia.
Ethiopia has one of the highest prevalence of blindness in the world (Berhane et al., 2006). The
national blindness survey which was conducted in 2006 revealed that the prevalence of blindness
in the country was 1.6%. There are about 1.2 million blind people in the country which means
7
that Ethiopia alone contributes for 2.7% of the total blindness worldwide. The prevalence of low
vision (presenting vision less than 6/18 but equal to or better than 3/60 in the better eye) is also
high at 3.7% (Berhane et al., 2006).
2.3.
Causes of visual impairment
The World Health Organization (WHO) estimates that trachoma accounts for 3.6% of global
blindness; if 3.6% of visual impairment globally is due to trachoma, then an estimated 5.8
million people are visually impaired by it (Resnikoff et al., 2004).
Studies from Cameroon (Ote et al., 2006), Nigeria (Patrick et al., 2005) and Mali (Kortlang et
al., 1996) also reported that the main causes of blindness and low vision were cataract,
accounting for 60% of all bilateral blindness and 51.7% of all low vision.
Another study done in Ethiopia (Berhane et al., 2006), states that the major causes of blindness
are as follows: cataract accounts for 49.9% of the blindness followed by corneal opacity (mainly
trachomatous) 19.3%, refractive error 7.8%, glaucoma 5.2%, and macular degeneration 4.8%.
The three commonest causes of low vision as shown in figure 2.1 below are cataract accounting
for 42.3%, refractive error 33.4% and corneal opacity 13.6%.
Fig. 2.1. Causes of visual impairment in Ethiopia (Berhane et al., 2006)
8
Beside to the above factors, a study done in Melbourne, states that the main factor causing
impaired visual acuity would be close distance activity such as reading and usage of a computer.
It is estimated that 1.6 billion people in the world suffer from impaired visual acuity and the
incidence is increasing (Fredrick, 2002).
All major causes of low vision and blindness are either preventable or treatable (Berhane et al.,
2006). The study from Butajira, Ethiopia, also indicated that blindness is either preventable or
curable in 74% of the cases (Alemayehu et al., 1995).
2.4.
Color blindness
Color blindness is the inability to distinguish certain colors. Molecular studies have shown that defects in
color vision result from the absence, malfunction, or alteration of one (dichromatism), two
(monochromatism) or all (achromatism) of the photopigments. (Diez et al., 2001).
2.4.1. Inherited Vs. acquired color blindness
There are two ways a person can be visually color deficient: they can inherit color blindness at
birth or they can acquire it later in life. Acquired color vision defects are the less common forms
and do not involve inherited alterations to the opsin genes. Aquired color vision defects are
caused by toxins, inflammation or detachment of the retina, macular degeneration, optic nerve
diseases, ageing and many other causes (Cohen, 1968). A form of total color blindness,
dyschromatopsia, can develop because of brain fever, cortical trauma, or cerebral infarction.
There are other forms of acquired color blindness related to things such as: fundus detachment,
glaucoma, CNS diseases, macular degeneration, and optic atrophy (Bowmaker, 1998).
Inherited color blindness is much more common than acquired color blindness and develops
from an alteration to the opsin genes. The resulting color deficiencies occur because opsin genes
are lost, altered, or debilitated. These losses and alterations typically take place on the Xchromosome, but have also been shown to take place on as many as 19 different human
chromosomes. This leads us into describing the different color vision defects and their causes
(Sharpe, 2001).
9
2.4.1.1.
Anomalous Trichromacy
Anomalous trichromacy includes the milder forms of red-green color blindness: protanomaly and
deuteranomaly are most common. In this category of color blindness the spectral sensitivity of
one of the three cone pigments is altered. The spectral sensitivity is shifted in one of three cones,
typically in the L- and M- cones, in a way that the M-cone may develop more like the L-cone
and vice-versa (Neitz et al., 2000). It affects approximately 5.5% of males and 0.39% of females,
with approximately 11% of females with normal color vision carrying genes for red-green
anomalous trichromacy (Squire, 2009)
A. Protanomaly
Those suffering from protanomaly have trichromatic color vision, but lack the normal L-cone
photopigments. This means that their trichromatic vision is not based on the classic L-, M-, and
S-cone photopigments, but because the L-cone photopigments are lacking they rely on 2 M-cone
photopigments and 1 S-cone photopigment. One M-cone, which processes green pigment, and
the S-cone, blue pigment, are normally functioning, but the function of the L-cone is lost and is
replaced by another M-cone. These 2 M-cone photopigments differ slightly in their spectral peak
(Neitz et al., 2000)
B. Deuteranomaly
Deuteranomaly is the most common type of the inherited color vision defects and has been
shown to affect about 5% of men in the United States. In this type of anomalous trichromacy the
M-cone photopigment is nonfunctional and the S-cone is joined by 2 spectral subtypes of L
cones. Those with this defect possess a reduced sensitivity to the color green because of the Mcone shift to L-cone photopigments. In approximately two thirds of men with deuteranomaly the
M-genes are present, but have lost their function (Neitz et al., 2000).
2.4.1.2.
Dichromacy
Dichromacy is the most serious red-green type of color blindness and is based on 2 pigments
instead of 3 and occurs at a rate of 1 in 100 in white males, it is much rarer in women. Usually in
dichromacy the inactivation or loss of one of the opsin genes encoding a cone photopigment
10
class is the cause of the color vision defect. The opsin gene can be negatively altered by point
mutations, sequence deletions, or unequal crossing over during meiosis (Neitz et al., 2000)
A. Deuteranopia
Those with deuteranopia lack the M-cone photopigment function and the majority does not have
any M-opsin genes at all. Those lacking the M-opsin genes have lost them by sequence deletions,
but those with the nonfunctional M-opsin genes have suffered a point mutation. People with this
defect are unable to receive the color green (Neitz et al., 2000).
B. Protanopia
Protanopia is similar to deuteranopia except that those with the defect are missing the L-cone
photopigment function. In most cases of protanopia, the deletion of genes that could encode Lcone pigments is to blame for the color vision defect. When these genes are deleted variants are
created in which the L-cone gene sequences are replaced by M-cone gene sequences, these
variances are called chimeric genes. (Neitz et al., 2000)
C. Tritanopia,
Tritanopia is the form of dichromacy resulting from the complete loss of S cone function, is
much more rare and shows equal incidence across gender since the S pigment gene is located on
an autosome (chromosome 7) (Squire, 2009).
Red-green color vision defects are the most common form of color vision deficiency. Among
Caucasians, about 8% of males and 0.5% of females have red-green color vision defects, and
15% of females are heterozygous carriers. Red-green color vision defects are significantly less
frequent among males of African (3%-4%) or Asian (3%) origin, largely because of the presence
of more deuteranomalous individuals among Caucasians (5%) (Motulsky et al., 2001).
Study of color blindness is usually undertaken more out of an academic interest than for its
clinical relevance. However, some occupations such as forensic science, driving, armed forces,
color matching in textile, paints & cosmetics, electrical work and a few others require perfect
11
color vision and hence color blind persons are likely to be rejected from such professional jobs
(Rahman et al., 1997).
The incidences of color blindness vary from race to race and are, therefore, different in the
different geographical regions of the world inhabited by people of different ethnicity. The
maximum incidence of color blindness has been reported from the Caucasian population
consisting mostly of the European Whites (Clements, 1961) and the minimum incidence from
certain regions of Africa (Applemans, 1953), the incidences from the various Asian countries
being in between these two extremes (Naresh, 1995).
A study done in Australia showed prevalence of 7.4% in males and 0.7% in females (Mann I.
and Turner C., 1956). In the USA, the average incidence of red-green color blindness was found
to be about 8.0% among males and 0.4–0.7% among females (Mueller et al., 1995).
However, the incidence of red-green color blindness is significantly higher in North Africa than
in sub-Saharan Africa which displays a very low incidence but lower than the usual European
incidence of 7% to 9%. The overall incidence of red-green color blindness in sub-Saharan
population was reported to be 2.63% (Sunderland and Rosa, 1976) Studies in some of the
countries of North Africa reported a prevalence of 6.56% in Algerians, 5.6% in Tunisians, and
5.99% in Libyans and 10.5% in Moroccans among studied male population which is
(Sunderland and Rosa, 1976).
The study of color blindness in Ethiopian population is scarce with only two published studies.
According to these studies, the prevalence of congenital color blindness among Ethiopians was
reported to be 4.2% among males and 0.2% among females (Adam, 1962, Zein, 1990). All the
studies invariably report a much higher incidence amongst the males as compared to the females
that is only to be expected since color blindness is a genetic disorder transmitted through the sexlinked recessive X-chromosome (Emslie-Smith et al., 1988).
Color is routinely used to code and convey information as well as finding extensive application
in the educational system. Currently, no treatment exists for congenital color vision defects.
However, studies showed that diagnosis of these defects early in life may help children adjust
better to tasks at school and may help adults understand their limitations at work. Undiagnosed
12
color vision defect (CVD) could pose a handicap to the scholarly performance of an affected
student (Gnadt and Amos, 1992). It is therefore important that children of school age,
particularly boys, should be tested early.
13
2.5.
Significant of the study
This study helps for early determining the status of visual acuity and color blindness and possible
factors for visual impairment. Because about 91.2% of low vision and 87.4% of blindness are
due to avoidable or either preventable or treatable causes. Therefore, finding from this study
helps to prevent and treat the visual impairment in an early stage. Most visual impairment found
at old age (>50 years) but early detection and correction of visual problem at children is found to
have educational and behavioral benefits, and certainly enhances quality of life in general.
Screening for visual impairment of the children and encouraging them to take corrective
measures can also play an important role in preventing long- term visual disability.
14
3. OBJECTIVES OF THE STUDY
3.1. General objective
Determining the prevalence of visual impairment and describe the possible risk factors
among school age children in two elementary schools in Addis Ababa.
3.2. Specific objectives
To assess the status of visual acuity among school children.
To estimate the prevalence of color blindness among school children.
To suggest the possible causes of low vision and recommend the suitable measures to
prevent visual impairment among them.
15
4. MATERIALS AND METHODS
4.1. Study area and period
The study was conducted in The Holy Trinity Primary School around Arat Kilo and Zeray Deres
Primary School around Teklehaimanot in Addis Ababa. It was conducted from Sep.10 to
Nov.30, 2013.
4.2. Study design
Cross sectional study design was utilized.
4.3. Population
Source population: School age children in Addis Ababa
Study population: school age children in The Holy Trinity Primary School and Zeray Deres
Primary School during the study time. Based on the registrar statistical data in the academic year
2013/2014, total number of about 1071 students in The Holy Trinity Primary School (521
females and 550 males) and about 510 students in Zeray Deres Primary School (260 female and
250 male) have been enrolled.
Fig 4.1. Students in the field after VA test.
16
Inclusion criteria
All elementary school students in The Holy Trinity Primary School and Zeray Deres Primary
School who have a written consent from the parents or adult guardians were included.
Exclusion criteria
Students, who do not give full cooperation, have not written consent from parents, who are on
leave during the collection of data, who have difficulty in communicating; who usually wear
eyeglasses and non-Ethiopian citizens during the study period was excluded.
4.4. Sampling technique and sample size.
A convenient non-probability sampling technique was applied to select two schools in Addis
Ababa. To get appropriate sample from selected schools, the investigator used random sampling
methods in all sections from grade 1-8 in the study period.
The total sample size was estimated by using a single proportion formula and calculated as
follows.
Prevalence of low vision in Ethiopia is 3.7% (Berhane et al, 2006). (P= 0.037, q= 1-0.037 =0.963
at 95 CI by assuming a margin of error 2 % =0.02).
n = Z2pq
d2
n = Sample size
p = Proportion of low vision =0.037
d = Margin of error =0.02
q = 1-p = 0.963
Z = 1.96 at 95% Confidence Interval (CI)
n= (1.96)2 X0.037 X 0.963 = 343
(0.02)2
To avoid non-response rate 10% is added so that the total sample was 378. The total sample size
of the population was distributed proportionally to the selected schools.
17
Table 4.1: Sample size calculation for each school.
Primary Schools
Total
population
% of total
Expected prevalence Sample
of low vision (%)
size
The Holy Trinity Cathedral
1071
67.74
3.7
256
Zeray Deres
510
32.26
3.7
122
Total
1581
100
378
Thus the total sample size of the population calculated for each school was again distributed to
their classes based on their population size; sample allocation using probability proportional to
size (PPS) technique.
Table 4.2: Distribution of class population and sample size determination for each class.
School
Grade
The Holy Trinity 1st
Cathedral
2nd
Primary School
3rd
4th
5th
6th
7th
8th
Total
Zeraye
Deres 1st
Primary School
2nd
3rd
4th
5th
6th
7th
8th
Total
Grand Total
Total
pop.
100
100
108
110
112
159
162
220
1071
67
70
55
63
62
61
57
75
510
1581
Pop. as percentage Probability proportion
of total
to size (PPS)
6.33
24
6.33
24
6.84
26
6.96
26
7.09
27
10.06
38
10.25
39
13.92
52
67.74
256
4.24
16
4.43
17
3.48
13
3.99
15
3.92
15
3.86
14
3.61
14
4.75
18
32.26
122
100
378
The estimated sample size in each class was selected randomly using lottery method.
18
4.5. Data collection instrument and procedure
Snellen chart for visual acuity
6m notation was adopted for measuring the visual acuity. The subjects in this study were
considered to have visual impairment (abnormal vision), if their visual acuity was below 6/9 in
either eye. Visual acuity <6/9 to ≥6/18(mild visual impairment), <6/18 to ≥6/48 (moderate visual
impairment), < 6/48 to ≥3/60 (sever visual impairment), < 3/60 to > 1/60 (profound visual
impairment) and ≤1/60 (blind) (low vision -ICD 9, 10). Visual acuity was measured in a
properly illuminated quiet room, using snellen chart at 6 m to discriminate different letters. .
Each eye will be tested separately and repeat the procedure three times then the best was taken.
The person who could identify the letters of the size 6 at 6m (20 at 20 feet) was said to have 6/6
(20/20) vision. The numerator expressed the distance between the observer and the letters while
the denominator expresses the distance at which they could be distinguished by the normal eye.
Fig.4.2: Snellen chart
Children with visual acuity ≤ 6/12 in either eye were interviewed and referred to ophthalmologist
for further diagnosis about the cause of abnormal vision. Their parents were also asked to fill
questionnaires to know family history.
19
Color blindness test
The color vision was tested with the help of Ishihara test, (Ishihara, 1968 edition: 38 plates). The
subjects were able to read the numerals at reading distance (30-34 cm). So, out of 38 plates, plate
numbers 1 to 25 were used in the present study. Plate numbers 1 to 21 were used to determine if
any red-green color vision defects existed in a given subject. If 17 or more plates were read
normally, the color vision was regarded as normal. If 13 or less than 13 plates were read normal,
color vision was regarded as deficient, thereafter, plate numbers 22 to 25 were used to determine
the precise type of color vision defects (protan and deutan). The numerals which were seen on
plate 1-25 were read without more than three seconds delay. The test was conducted in the room
which is lit adequately by daylight. There was no direct introduction of sunlight or use of electric
light on the plate during examination because it would have an alteration in the appearance of
shades of color on the plate.
b) plate No.5
a) Ishihara’s test, 1968 edition
c) Plate No. 19
d) plate No. 24
Fig.4.3: Samples of plates used for color blindness test.
20
Questionnaires
Structural questionnaires were prepared and filled by children who have visual acuity, VA ≤ 6/12
and their parents to know the socio-demographic characteristics of children and their family. All
the questionnaires were translated in to Amharic version.
4.6. Data entry and analysis procedure
All data obtained were entered manually into a computer on excel sheet and subsequently
transferred to SPSS version 20 for further analysis. The collected data was manually cleared and
checked. Frequency distributions, cross-tabulations and a graph were used to describe the
variables of the study and for numerical variables we used mean value, and standard deviation.
The significance level was set at P < 0.05.
21
5. ETHICAL CLEARANCE
The study was conducted after ethical approval was obtained from Department Research and
Ethics Review Committee (DRERC) of Medical Physiology, College of Health Science, School
of Medicine, Addis Ababa University and after informed consent was obtained from study
subjects. The informed consent form was translated in to Amharic version for simple
understanding by parents. All study participants were duly acknowledged.
22
6. RESULTS
6.1. Visual acuity
A total of about 378 students from randomly selected one private and one governmental school
of grade 1-8 were participated in the study. Among these, 255 (67.5%) were from Holy Trinity
Cathedral Primary School (private school) and 123(32.5%) were from Zeray Deres Primary
School (governmental school). Participants ranged in age from 5 to 16 years with mean age
11.05 ±2.58 and 162 (42.9%) were from 1st -4th grade and 216 (57.1%) were from 5th - 8th grade.
The frequency of females and males among participants were 192 (50.8%) and 186 (49.2%)
respectively (Table 6.1).
Table.6.1: Distribution of participants by grade, school and sex.
Grade
Primary Schools
Sex
F
1st-4th
5th-8th
Total
Total
M
Holy Trinity Cathedral
48 (12.7%)
53 (14.0%)
101 (26.7%)
Zeray Deres
29 (7.7%)
32 (8.5%)
61 (16.2)
Total
77 (20.4%)
85 (22.5%)
162 (42.9%)
Holy Trinity Cathedra
86 (22.8%)
68 (18.0%)
154 (40.7%)
Zeray Deres
29 (7.7%)
33 (8.7%)
62 (16.4%)
Total
115 (30.4%)
101 (26.7%)
216 (57.1%)
Holy Trinity Cathedra
134 (35.4%)
121 (32.0%)
255 (67.5%)
Zeray Deres
59 (15.7%)
64 (16.9%)
123 (32.5%)
Grand Total
192 (50.8%)
186 (49.2%)
378 (100%)
23
Age
Fig.6.1: Distribution of participants by age.
Socio-demographic features of visually impaired children and their parents.
Among the total participants, 22 children have visual acuity ≤ 6/12 and their rate of TV watch,
distance at which they watch TV, rate of playing computer games, previous visual status and
color vision deficiency is describe in the table below (Table 6.2).
Majority 15(68.2%) of visually impaired individuals watch TV 2-5 hrs/day; 6(27.3%) of them
watch TV < 2 hrs/day and 1(4.5%) watch 6-8 hrs/day. Half of them watch TV at a distance of <1
m; 9(40.9%) at a distance of 1-2 m and 2(9.1%) at a distance of 3.4 m.
Regarding rate of playing TV or computer game, majority 18(81.8%) of them did not play any
game; 1(4.5%) play game 2-5 days/weak and 3(13.6%) play game < 2 days/weak.
24
Table 6.2: Frequency of different activities by individuals who have VA≤ 6/12
Rate of TV watch
N
% (n=22)
<2 hrs/day
6
27.3%
2-5 hrs/day
15
68.2%
7-10 hrs/day
1
4.5%
<1 m
11
50.0%
1-2 m
9
40.9%
3-4 m
2
9.1%
<2 days/weak
3
13.6%
2-5 days/weak
1
4.5%
No, they did not play computer game
18
81.8%
Distance at which they watch TV
Rate of playing TV/computer game
Previous visual status
No, (I have not gotten any disease)
11
Yes, (I have gotten eye disease)
50.0%
11
50.0%
Protan
2
9.1%
Deutan
5
22.7%
Normal
15
68.2%
Color vision deficiency
VA= visual acuity, TV= television
25
Table 6.3: Socio-demographic features of parents of students who have VA ≤ 6/12.
Age
N (%)
25-40
41-55
56-70
Educational background
15 (68.2%)
4 (18.2%)
3 (13.6%)
Illiterate
Elementary school
Secondary school
College diploma
University degree
Income/month
1 (4.5%)
5 (22.7%)
12 (54.5%)
3 (13.6%)
1 (4.5%)
150-800
801-1500
1501-2500
2501-3500
5 (22.7%)
6 (27.3%)
8 (36.4%)
3 (13.6%)
Visual status
Blind
Color blind
Long sighted
Short sighted
Tearing
No eye problem
Eye care to their child
1 (4.5%)
1 (4.5%)
1 (4.5%)
7 (31.8%)
1 (4.5%)
11 (50.0%)
Washing with soap.
11 (50%)
No care to the eye of their child.
11 (50%)
From the total participants, 22 (5.8%) had abnormal visual acuity, (VA≤ 6/12 in either eye) and
356 (94.2%) of them were normal (VA > 6/12 in the worse eye) (Table 6.4).
14 (63.6%) of visually impaired students were from Holy Trinity Cathedral Primary School and
8 (36.7%) of them were from Zeray Deres Primary School. The frequency of females and males
were 12 (54.5%) and 10 (45.5%) respectively (Table 6.4). However, the difference between
26
female and male is not statistically significant (P =0.38) (Table 6.5). Among visually impaired
students 6 (27.3%) were 5-8 years old, 9 (40.9%) were 9-12 years old and 7 (31.8%) were 13-16
years old (Table 6.4)
Table 6.4: The frequency of visual impairment (VA ≤6/12) by sex and schools.
Primary
Holy Trinity Cathedral
Zeray Deres
Total (n=22)
% (n=378)
Schools
(n=22)
(n=22)
8 (36.4%)
4 (18.2%)
12 (54.5%)
3.2
6 (27.3%)
4 (18.2%)
10 (45.5%)
2.6
14 (63.7%)
8 (36.4%)
22 (100.0%)
5.8
5-8
5(22.7%)
1(4.5%)
6 (27.3%)
1.6
9-12
6 (27.3%)
3 (13.6%)
13-16
3 (13.6%)
4 (18.2%)
7 (31.8%)
Total
14 (63.7%)
8 (36.4%)
22(100%)
F
Sex M
Total
Age
27
9 (40.9%)
2.4
1.9
5.8
Table 6.5: Bivariate logistic regression analysis of factors associated with VAI.
Variables
Visual acuity
n
%
Total
VA ≤6/12
VA > 6/12
n
%
n
%
OR (95% CI)
P- value
0.38
Sex
Female
Male
180
176
47.6
46.6
12
3.2
10
2.6
192
186
50.8
49.2
1
0.65 (0.25-0.67)
0.26
Age
5-8
75
19.8
6
1.6
81
21,4
1
0.10
9-12
158
41.8
9
2.4
167
44.2
4.57 (0.74-28.34)
0.19
13-16
123
32.5
7
1.9
130
34.4
2.73 (0.58-12.964)
0.74
School
HTCPS
241
63.8
14
3.7
255
67.5
1
ZDPS
115
30.4
8
2.1
123
32.5
0.84 (0.30-2.34)
0.01*
Grade
1-4
147
38.9
15
4.0
162
42.9
1
5-8
209
55.3
7
1.9
216
57.1
0.12 (0.03-0.58)
0.00*
Color vision
Normal
347
91.8
15
4.0
362
95.8
1
Defective
9
2.4
7
1.9
16
4.2
19.65 (6.01-64.33)
Note: * statistically significant at 95% CI, P < 0.05; 1 = reference.
HTCPS=Holy Trinity Cathedral Primary School
ZDPS =Zeray Deres Primary School
VA= visual acuity
VAI= visual acuity impairment
28
Table 6.6: Frequency of visual acuity with the worse eye
VA of the ICD-9,10-CM WHO Age group (in year)
worse eye categories
-
1
-
1
0.3%
1
2
-
3
0.8%
6/18 Mild VI
1
2
2
5
1.3%
6/12 Mild V I
4
4
5
13
3.4%
6
9
7
22
5.8%
75
158
123
356
94.2%
81
167
130
378
100.0%
Low
Normal vision
Normal
6/6
vision
13-16
Total
Grand Total
VI= visual impairment, VA= visual acuity
Table 6.7: Distribution of VAI by sex in one and both eyes
Sex
Total
VA
Male
Female
(n=378)
≤6/12 - ≥ 6/18
Bilateral
8(2.1%)
10(2.6%)
18 (4.7%)
Unilateral
0 (0%)
0 (0%)
0 (0%)
Bilateral
1(0.3%)
1(0.3%)
2 (0.5%)
Unilateral
1(0.3%)
1(0.3%)
2 (0.5%)
Total
10 (2.6%)
12 (3.2%)
22 (5.8%)
< 6/18 - ≥ 6/60
VA= visual acuity
29
%
total(n=378) (n=378)
9-12
6/36 Moderate VI
VAI
% out of
5-8
6/60 Sever VI
Normal
Total
1.1%
98.9%
100.0%
Visual acuity impairment was caused by different factors. Refractive error was the leading cause
of visual acuity impairment in this study that accounts 17/22 (77.3%) of the cause. Cataract,
allergy, amplyopia, and strabismus each accounts 1/22(4.5%) of the causes. The cause of
abnormal vision for one student was not explained because he was absent at the time of diagnosis
(Fig.6.2)
No. of individuals (n)
77.3%
4.5%
4.5%
4.5%
4.5%
4.5%
Cause of VAI
Fig 6.2: Cause of low vision
After diagnosis the cause of VAI by ophthalmologist, more than three-fourth causes were
refractive error (RE). Those who have refractive error were advised to use spectacles for
correction and others were motivated to be visited by doctors from any hospital nearest to their
home for further treatment. However, most of them, mainly females respond that they were not
volunteer to use spectacles.
The main reasons reported for non-purchase or non uses of
spectacles were: discomfort, financial constraints, anticipation of teasing from other students,
unable to recognize their visual problems and believes about the harmful effect of glasses on
vision. Fearing in getting sexual partner was also one of the major reasons reported by adult
females for their reluctance in using spectacles.
30
6.2. Color vision
The color vision was tested with the help of Ishihara test. The subjects were able to read the
numerals at reading distance. So, out of 38 plates, plate numbers 1 to 25 were used in the present
study. Plate numbers 1 to 21 were used to determine if any red-green color vision defects existed
in a given subject and plate numbers 22 to 25 were used to determine the precise type of color
vision defects (protan and deutan).
From the total participants, 362 (95.8%) were normal color vision and 16 (4.2%) had color vision
defect. Of 16 cases of color blind, 4 (1.1%) were protan, 11(2.9%) were deutan, 1 (0.3%) had
color weakness (Fig 6.3). The prevalence of red-green color blindness excluding color weakness
subjects was 4.0%.
.
2.9%
0.3%
95.8%
Fig.6.3. Pie-chart that shows the distribution of color blindness
31
From the total color vision defect students, 5(31.3%) (1 protan and 4 deutan) were females and
11(68.8%) (3 protan, 7 deutan and 1 color weakness) were males (Fig.6.4). This implies that
more than two-third males had color vision defect than females. The frequency of color blindness
with age was 4(25%) aged from 5-8, 5(31.3%) aged from 9-12 and 7(43.8%) aged from 13-16
and 10(62.5%) of the total color blind students were from Holy Trinity Primary School and
6(37.5%) were from Zeray Deres Primary School.
43.8%
25 %
18.8%
6.3%
6.3%
Note: n=16, F= female, M= male
Fig.6.4: Distribution of Color vision defect by sex
32
Table 6.8: Socio-demographic feature of color blind individuals and their parents.
School of the participants
N
%
HTCPS
ZDPS
Grade level of the participants
1st-4th
5th-8th
Sex of the participants
Female
Male
Age of the participants
5-8
9-12
13-16
Educational background of parents
Elementary
Secondary
College Diploma
University Degree
Visual problem of parents
Color Blind
Short Sighted
Eye tearing
No visual problem
Eye care of parents to their child
Wash with soup
No care to their child
10
6
62.5
37.5
8
8
50.0
50.0
6
10
37.5
62.5
4
5
7
25
31.3
43.8
3
11
2
0
18.8
68.8
12.5
0.0
1
2
1
12
6.2
12.5
6.2
75.0
10
6
62.5
37.5
HTCPS = Holy trinity Cathedral Primary School
ZDPS = Zeray Ders Primary School.
33
Table 6.9: Bivariate logistic regression analysis of factors associated with CVD.
Color vision
Normal
Defective
Total
n
Variables
n
%
n
%
OR (95% CI)
P- value
%
0.15
Sex
Female
186
49.2
5
1.3
191
50.5
1
Male
176
46.6
11
2.9
187
49.5
0.43(0.14-1.36)
0.48
Age
5-8
77
20.4
4
1.1
81
21,4
1
0.75
9-12
162
42.9
5
1.3
167
44.2
0.70(0.08-5.98)
0.28
13-16
123
32.5
7
1.9
130
34.4
0.41(0.08-2.04)
0.89
School
HTCPS
245
64.8
10
2.6
255
67.5
1
ZDPS
117
31.0
6
1.6
123
32.5
0.92(0.29-2.91)
0.94
Grade
1-4
154
40.7
8
2.1
162
42.9
1
5-8
208
55.0
8
2.1
216
57.1
1.066(0.18-6.35)
0.00*
Visual acuity
VA> 6/12
347
91.8
15
4.0
362
95.8
1
VA ≤ 6/12
9
2.4
7
1.9
16
4.2
20.14(5.95-68.13)
Note: * statistically significant at 95% CI, P < 0.05; 1 = reference, VA= Visual Acuity,
HTCPS= Holy Trinity Cathedral Primary School, ZDPS= Zeray deres Praymar School.
34
7. DISCUSSION
WHO fact sheet (WHO, 2013) on visual impairment and blindness stated that globally 285
million people were visually impaired and about 90% of the world’s visually impaired lived in
developing countries. More than 80% of all visual impairments could have been avoided or
cured. However, if it is not detected early, it may cause irreversible blindness. When vision loss
is present at a young age, the adverse impact is felt over the many remaining years of life.
This study focus on the prevalence of visual acuity impairment and color blindness on school
children to make correction and make adjustment in instructional methods and career choices.
Visual acuity
The study found that the prevalence of visual acuity impairment; VA ≤ 6/12 in either eye, was
22(5.8%), VA < 6/18 in either eye was 4 (1.1%) and VA < 6/18 in the better eye was 2 (0.53%)
which is much less than the study done nationally in Ethiopia by Berhane which was 3.7%
(Berhane et al., 2006, 2007). The low prevalence of visual acuity impairment may be due to the
difference in study area; our study was conducted in Addis Ababa where accessibility of health
service and quality of life is better than anywhere else in Ethiopia. There was also a difference in
age of the participants between our study and the study done by Berhane; as age increase the
prevalence of visual acuity impairment will increase (Goh et al., 2005, Livingston, 1997).
Study done in Malaysia and Indonesia (Goh et al., 2005, Saw et al., 2003) showed that reduction
in visual acuity had a linear relationship with increasing age. However, in our study it is shown
in Table 6.4, 9(2.4%) of children between 9-12 years old had VA ≤ 6/12 in either eye which is
greater than children aged 5-8 and 13-16 years old that accounts 6(1.6%) and 7(1.9%)
respectively; there was no statistically significant association between age and visual acuity
impairment (OR=4.57, 2.73, p > 0.05). This may be due to the fact that in this study the sample
size comprised of a small age difference which was between 5 and 16 years old with mean age
11.05 ±2.58, therefore the association between age and reduction of visual acuity may not be
seen. The result is in line with another study done in Malaysia which state age factor was not
associated with reduction of visual acuity (Aniza et al., 2012).
35
The prevalence of VA ≤ 6/12 was slightly higher among females as compared to males
(12(3.2%) in female and 10(2.6%) in male) It is supported by the study done in India (Hetal et
al., 2011). This may be due to the fact that females commonly suffer social and economic
vulnerability in many societies, which contributes inequalities in health and access to health care.
However, the difference was not statistically significant (OR = 0.65, P = 0.38).
From Table 6.2, half of the participants who have VA ≤ 6/12 responded that the distance of TV
watch was < 1m.
The study conducted in Malaysia (Aniza et al., 2012), suggest that there was a significant
association between distance of watching television and prevalence of impaired visual acuity.
Aniza reported that, there was significant difference between visual acuity impairment among
respondents who had a distance of watching television of less than 2 meters with respondents
who had a distance of watching television of more than 2 meters. It is also supported by another
research conducted by Ministry of Health Malaysia 2002 (Zainal et al., 2002). It also showed
that there was a weak correlation between duration of watching television and reduced visual
acuity. There was a positive coefficient correlation indicated that the longer the duration of
watching television, the visual acuity will be further impaired (median duration was 5 hrs/day).
In our study from Table 6.2, 15(68.2%) of the participant who have VA ≤6/12 in either eye
reported that the duration of TV watch was 2-6 hrs/day, 6(27.3%) < 2 hrs/day , and 1(4.5%) 7-8
hrs/day.
Different studies showed a significant association between visual acuity impairment in children
and income, educational background and visual status of parents. A study done in South Africa
(Thomas et al., 2008) showed that poor in protein, fruit, and vegetable intake led to poor visual
acuity in the subject. In our study (Table 6.3), income of majority of the parents of visually
impaired children 8(36.4%) were from 1501-2500 birr/month and only 3(13.6%) had more than
2500 birr/month. These shows that the incomes of most parents are low and their children may
not have balanced diet and this may contribute for poor visual acuity.
36
Regarding educational background of parents, only 4(18.1%) had college diploma and university
degree. More than 81% of them had no college diploma; they have certificate of secondary
school and primary school and 4.5% illiterate (Table 6.3). Studies done in India, China and
Nepal reported that visual problems were found around three times more in those who have no
schooling than those who have schooling (Murthy et al., 2001, Zhao et al., 1998, Pokharel et al.,
1998).
In our study half of the parents of visually impaired children had visual problems like short
sighted, long sighted, tearing, color blind and blind and others had no visual problems. A study
done by Mutti, stated that the risk of inheriting impaired visual acuity was increased if parents
had similar problems (Mutti, 2001). In contrast to this the study done by Aniza (Aniza et al.,
2012) showed that there was no association between family histories and impaired visual acuity
among the respondents.
The prevalence of VA ≥ 6/12 in Holy Trinity Primary School (private school) and Zeray Deres
Primary School (governmental school) was 3.7% and 2.1% respectively (Table 6.5). The
investigator assumed that parents of children who learn in private school will have better income
and then better visual acuity of their children (Thomas et al., 2008). However, there was no
statistically significant difference between two schools (OR=0.84, P= 0.74). These may be due to
small sample size; only one private and one governmental school were taken in the study. Other
possible reason may be due to the fact that the incomes of the parents in the two schools have no
such difference (Table 6.3).
In this study, 31.8% of individuals who had VA ≤ 6/12 had color vision defect and from Table
6.5, the study showed that there was a strong association between visual acuity impairment and
color blindness. (OR=19.65, P< 0.01). This implies that being color vision defective is more at
risk to visual impairment than individuals who have normal color vision. In the same way, being
visual impaired is more at risk to color blindness than individuals who have normal visual acuity
(OR = 20.14, P < 0.01) (Table 6.9). This is the fact that people with total color blindness usually
have reduced visual acuity at the same time because missing, dead or damaged cone cells result
37
in loss of both acuity and color perception (NIRE, 2002). Another study done by Delpero
suggested that acquired CVD may escape detection, but if severe, is also associated with loss of
visual acuity and/or visual field (Delpero et al., 2005).
A study done in India (Dandona et al., 2001), Malaysia (Zainal et al., 2002), China (Li et al.,
1999) and a study done in African children (Raghunandan et al., 2003) suggested that
uncorrected refractive error as the main cause of visual impairment in school children. Our study
also showed that uncorrected refractive error was the main cause for defective vision. From the
total individuals with VA ≤ 6/12, 17 (77.3%) of them were because of refractive error. It is
consistence with another study done in India which states that refractive error accounts 77% of
the total cause of visual impairments (Amruta et al., 2009). It also showed that refractive error
caused 5.2% of visual impairment, amplyopia (0.8%), cataract (0.07%), strabismus (0.01%).
This is slightly comparable with the results found in our study; refractive error (4.5%),
amplyopia, cataract, strabismus and allergy each constitute 0.3% of the cause of visual
impairment. Another study done by Anmol found the prevalence of refractive error was 4.2%
(Anmol et al., 2012)
Color vision
Screening of color vision deficiencies was done using Ishihara’s test 38 plate edition which is
generally considered to be the most efficient for screening red and green congenital defects.
The prevalence of color blindness was 16 (4.2%); 1.3% female and 2.9% male. Of 16 cases of
color blind, 11(2.9%) were deutan, 4 (1.1%) were protan, and 1 (0.3%) had color weakness (Fig.6.3).
This finding is consistent with the study done in central Ethiopia in 2009 (Mulusew et al., 2009)
that states the prevalence of color blindness was 44 (4.2%). Of these 30 cases (2.89%) involved
deutan, 6 cases (0.58%) protan, 6 cases (0.58%) unclassified, and 2 cases (0.19%) of totally color
blind. The lower prevalence of protan may be due to unclassified 6 cases in the study. Another
study on licensed car drivers in Addis Ababa indicated a prevalence rate of 4.5 %, which is
nearly the same as the prevalence of color blindness described in our study (Abebe and
Wondmikun, 2002).
38
Another study conducted by Zein (Zein, 1990) in 954 boys and 1064 girls attending two schools
in North-west Ethiopia in 1988 using the Ishihara 24 plate edition reported a total of 40 color
blind (4.2%) among males and 2 (0.2%) among females (average prevalence, 2.08%) and there
were 33(1.6%) deutans and 9 (0.45%) protons which is almost lower by half than our study. This
low prevalence may be due to the old version of Ishihara plate (Ishihara 24 plate edition).
However, the prevalence of color blindness found in our study (4.2%) was less than other studies
done in Africa including Algerians (6.56%), Tunisians (5.6%) Libyans (5.99%) and Moroccans
(10.5%) (Sunderland and Rosa, 1976) and the study done in Nigerian dental practitioners (6.3%)
(Cornelius et al., 2007). The possible reason may be due to the difference in race.
The study done in immigrant populations in Punjab in 2012 (Khushdeep et al., 2012) found a
prevalence of 2.48% color blindness in male and 0.00% in female (0.78% protan, 1.28% deutan,
0.05% tritan and 0.25% unclassified) which is much lower than the result found in our study.
This may be due to the fact that the study population came from different ethnic group
(immigrant people from different area). The incidences of color blindness vary from race to race
and are, therefore, different in the different geographical regions of the world inhabited by
people of different ethnicity (Naresh, 1995).
The most common type of color vision defect was deutan than protan. The ratio of deutan with
protan in this study was 2.8:1.0 which is slightly lower than the study done by Zein (3.7:1.0)
(Zein, 1990).
Because the most common type of color blindness is red-green color blindness which is
congenital and a sex-linked recessive trait, it is more common in males than females. All the
studies invariably report a much higher incidence amongst the males as compared to the females
which is only to be expected since color blindness is a genetic disorder transmitted through the
sex-linked recessive X-chromosome (Emslie-Smith et al., 1988). In our study the incidence of
color blindness was also comparatively higher in males (2.9%) than females (1.3%) (Fig.6.4).
39
This study found that one individual (0.3%) had color weakness/ totally color blind which is
caused by the total absence of either 2 or 3 of the pigmented retinal cones (L, M, and S). This
type of color vision defect is reported to occur very rarely. In 2009, Mulusew found 0.2% totally
color blind individuals for the first time in Ethiopia (Mulusew and Yilikal, 2009).
The prevalence of getting colour vision defects was reported to increase with age (Davies et al.,
1998). Although the age range is narrow in this study, there was a corresponding increased in the
prevalence of color vision defect with increasing age (25%, 31.3% and 43.8% in the age group
of 5-8, 9-12 and 13-16; respectively). However, the difference was not statistical significant
because the age variable of the population exhibited small variation with mean age of 11.05
±2.58 and all of them were children (OR = 0.70, 0.41, P > 0.05) (Table 6.9).
Early detection of color vision defect of an individual is very important in life to make decision
on future career. It is also important for parents and teachers to make necessary adjustments
during teaching for effective learning. But most of color blind individuals do not aware of their
color vision status which will negatively affect their future career. According to our study almost
all of the participants, except one were not aware of their status of color vision. Among about 7%
of male population with color vision deficiency, about 40% of that population appeared to be
unaware of the defect prior to leaving secondary school (Weir, 1998).
40
Limitations of the study
•
Ishihara plate test used only for red-green color test. Thus it is difficult to estimate other
color defects like tritanopia
•
Parents were involuntary to give appropriate information to know their sociodemographic feature.
•
Some private schools were not voluntary to be the study subject in this study and,
•
Time and financial constraint were some of the limitations of the study.
41
8. CONCLUSION AND RECOMMENDATIONS
8.1. Conclusion
 The prevalence of VA ≤ 6/12 in either eye was 22 (5.8%), VA < 6/18 in either eye was
4(1.1%) and VA < 6/18 in the better eye was 2 (0.53%).
 Although the prevalence of visual impairment in children was very low, priority should be
given to them because the health of children would have high cost for economical, social and
educational development of the community.
 The prevalence of color blindness was 16 (4.2%). 11(2.9%) were deutan, 4 (1.1%) were
protan, and 1 (0.3%) had color weakness.
 Most of the children who had visual impairment showed low compliance with the use of
spectacles. This calls for another research to explore different strategies among students to
spread awareness about eye health and to have behavioral change about the use of spectacles.
 These findings are essential for visual health program planners as studies reveal that barriers
other than economic constraints are present which prevent adoption of desired behaviors and
utilization of accessible eye services
42
8.2. Recommendations
 Screening of the children for vision at the time school admission, periodical eye examination
of the children is recommended for early rectification of impaired vision in school children.
This will help to adjust learning strategies and to find out children’s future career.
 Children and parents should be educated and aware regarding visual problem for early
correction.
 Ministry of Health, Ministry of Education and other stakeholders should look at different
strategies among students to have behavioral change about the use of spectacles.
 We also recommend further studies to be done to determine the magnitude and severity of
color vision defects using anomaloscope and visual impairment of near vision using jaeger
eye chart and to assess the possible risk factors for visual impairment.
43
9. REFERENCES
Abebe Y, Wondmikun Y. Defective colour perception among car drivers in Addis Ababa,
Ethiopia. Traffic Injury Prevention. 2002; 3(4): 294-297
Adam A. A survey of some of the genetic characteristics in Ethiopian Tribes: Part VII: color
vision. Am J Phy Anthrop. 1962; 20:194- 195.
Agamemnon Despopoulos, Stefan Silbernagl, stried Rothenburger. Color Atlas of Physiology, 5th
edition, completely revised and expanded, 2003
Alemayehu W., Tekle-Haimanot R., Forsgren L., Erkstedt J., Causes of visual impairment in
central Ethiopia. Ethiop Med J. 1995; 33(3):163-74.
Amruta S, Rajiv Khandekar, Sheetal Dharmadhikari, Kuldeep Dole, Parikshit Gogate, and
Madan Deshpande. Prevalence of Uncorrected Refractive Error and Other Eye Problems among
Urban and Rural School Children, Middle East Afr J Ophthalmol. 2009 Apr-Jun; 16(2): 69–74
Aniza I, Azmawati MN, Jamsiah M, Idayu BI, Mae Lynn CB, Prevalence of Visual Acuity
Impairment and its Associated Factors Among Secondary School Students in Beranang,
Selangor, Malaysian Journal of Public Health Medicine 2012, Vol. 12(1): 39-44
Anmol Gupta, Ram Lal, S.R. Mazta, Deepak Sharma. Prevalence of Refractive Errors, Color
Vision Defects and Other Ocular Disorders in School-going Children: Primary Screening by
School Teachers. Shimla district, India. 2012, JIMSA Oct-Dec. 2012 Vol. 25(4)
Applemans M., Color defects among the natives of Congo. Bull Soc Beige Opthal, 1953; 103:
226-229.
Berhane Y., Worku A., Bejiga A., Adamu L., Alemayehu W., Bedri A., Haile Z., Ayalew A.,
Adamu Y., Gebre T., Kebede T., West E. Prevalence and causes of blindness and Low Vision in
Ethiopia. Ethiop.J.Health Dev. 2007; 21(3):204-210.
Berhane Y., Worku A., Bejiga A. National Survey on Blindness, Low Vision and Trachoma in
Ethiopia, Federal Ministry of Health of Ethiopia with support from and in collaboration with a
consortium of NGOs (The Carter Center, CBM, ITI, ORBIS Intl. Ethiopia and LfW),
Ophthalmological Society of Ethiopia, and the Ethiopian Public Health Association, Addis
Ababa, Ethiopia, 2006.
Bowmaker, J.K., Visual Pigments and Molecular Genetics of Color Blindness. News
Physiological Science 1998 Vol. 13: 63-69.
Clements F. Racial differences in color blindness. Amer J Phys Anthrop 1961; 4: 189-204.
Cohen J. Weighted kappa: nominal scale agreement with provision for scaled disagreement or
partial credit. Psychol Bull. 1968; 70: 213-220
44
Cornelius Tokunbo Bamise, Temitope Ayodeji Esan, Patricia Adetokunbo Akeredolu, Onakpoya
Oluwatoyin, Elizabeth Obhioneh Oziegbe. Color vision defect and tooth shade selection among
Nigerian dental practitioners.2007; Rev. Clín. Pesq. Odontol. 2007 set/dez; 3(3):175-182.
Dandona L, Dandona R, Srinivas M, et al. Blindness in the Indian state of Andhra Pradesh.
Invest Ophthalmol Vis Sci 2001; 42:908–916.
Davies IRL, Laws G, Corbett GG, Jerrett DJ. Cross-cultural differences in colour vision:
Acquired colour blindness in Africa. Personality and Individual differences. 1998; 6:1153-1162.
Delpero WT, O'Neill H, Casson E and Hovis J. Aviation-relevent epidemiology of colour vision
deficiency. Aviation Space and Environmental Medicine 2005; 76(2): 127-133.
Diez MA, Luque MJ, Capilla P. et al. Detection and assessment of colour vision anomalies and
deficiencies in children. J Pediatr Ophthalmol Strabismus. 2001; 38: 195–205.
Emslie-Smith D, Paterson CR, Scratcherd T, Read NW. Textbook of Physiology 1998; 11th
Editions; 456-457.
Foster, D. H. Inherited and acquired color vision deficiencies: fundamental aspects and clinical
studies. Macmillan Press: London; 1991.
Fredrick DR., Myopia, British Medical Journal, 2002; 324: 1195-1209.
Gilbert C., Ellwein LB. Prevalence and causes of functional low vision in school age children:
results from standardized population surveys in Asia, Africa and Latin America. Invest
Ophthalmology Vis Science 2008; 49(3): 877-81.
Gilbert C. and Foster A. Childhood blindness in the context of VISION 2020-The Right to Sight.
Bulletin of the World Health Organization, 2001. 79: 227-232.
Gnadt GR, Amos JF. Dichromacy and its effect on a young male. J Am Optom Assoc. 1992; 63:
475-480.
Goh PP, Yahya A, Pokharel GP, Ellwein LB. Refractive error and visual impairment in school
age children in Gombak district, Malaysia. American Academy of Ophthalmology 2005; 112(4):
678-85.
Guyton A. and Hall J. A Textbook of Medical Physiology, 2006, 11th Edition: 372-378
Hetal K. Rathod, Pankaja R. Raghav, Sidharth Mittal. Profile of School Going Children with
Visual Impairment, India, Indian Medical Gazette 2011.
Human development report: Oxford University press, New York: United nation development
program, 2000.
45
International Statistical Classification of Diseases and related Health Problems, 10th revision.
Geneva: World Health Organization 1992: 456-57.
Kello A B., Gilbert C., Causes of severe visual impairment and blindness in children in schools
for the blind in Ethiopia; Br J Ophthalmol 2003;87:526–530.
Khushdeep Singh Arora, Ruchika Garg, Naveenta Gupta and Nitin Bansal. Comparative Study
of Colour Blindness Among Various Immigrant Populations In Punjab; An Online International
Journal Available at http://www.cibtech.org/jms.htm 2012 Vol. 2 (2)
Kortlang C., Koster JC., Coulibaly S., Dubbeldam RP. Prevalence of blindness and visual
impairment in the region of Segou, Mali. A baseline survey for a primary eye care programme.
Top Med Int Health. 1996; 1(3):314-9.
Krebs C., Weinberg J., Akesson E. Lippincott’s Illustrated Review of Neuroscience, 2012, 291 302.
Li S, Xu J, He M, et al. A survey of blindness and cataract surgery in Doumen County, China.
Ophthalmology 1999; 106:1602–1608.
Linksz A. An Essay on Color Vision and Clinical Color Lesion Tests. New York. Grune and
Stratton, 1964.
Livingston P M., McCarty C A. and Taylor H R. Visual impairment and socioeconomic factors.
Br J Ophthalmol 1997; 81: 574-577
Maberley DAL., Hollands H., Chuo J., Tam G., Konkal J., Roesch M., et al. The prevalence of
low vision and blindness in Canada. Eye 2006: 20: 341-346.
Mann I, Turner C. Color vision in native races in Australasia. Am J Ophthalmol.1956; 41: 797800.
Motulsky AG, Deeb SS. Color vision and its genetic defects. In: Scriver CR, Baudet AL, Sly
WS, Valle D, editors. The metabolic and molecular bases of inherited disease. 8th ed. McGrawHill: New York; 2001; vol. 4: 5955- 5976.
Mueller RF, Young ID. Emery’s Elements of Medical Genetics, 9th. edition. Edinburgh:
Churchill Livingstone, 1995; 317.
Mulusew A. and Yilikal A. Prevalence of congenital color vision defects among school children
in five schools of Abeshge District, Central Ethiopia, 2009; East African Journal of
Ophthalmology July 2013 .
Murthy GVS, Gupta S, Ellwein LB. A population based eye survey of older adults in a rural
district of Rajasthan: central vision impairment, blindness, and cataract surgery. Ophthalmology
2001; 108: 679–85.
46
Mutti DO. Can we conquer myopia? Review of Optometry 2001; 138: 80-92.
Naresh S. Study of colour blindness in J at Sikhs. Indian J Physiol Pharmacol 1995; 39: 127-130.
Negerel A.D., Maul G.P., Pokharel J., Zhao and Ellwein. Refractive error study in
children:
sampling and measurement methods for a multicountry survey. Am.J.Ophthalmol, 2000;
129:421-426
Neitz Maureen and Neitz Jay., Molecular Genetics of Color Vision and Color Vision
Defects.Archives of Ophthalmology 2000; Vol. 118; 691-700.
Ote JE., Kuper H., Dineen B., Befidi-Mengue R., Foster A. Prevalence and causes of blindness
and visual impairment in Muyuka: A rural health district in South West Province, Cameroon. Br
J Ophthalmol 2006; 90(5):538-542.
Patrick-Ferife G., Ashaye AO., Qureshi BM. Blindness and low vision in adults in Ozoro, a rural
community in Delta State, Nigeria. Niger J Med 2005; 14(4):390-395.
Pokharel GP, Regmi G, Shrestha SK. Prevalence of blindness and cataract surgery in Nepal. Br J
Ophthalmol 1998; 82: 600–605.
Raghunandan A, Mashige KP, Govender P, Holden BA, Pokharel GP, et al. Refractive error and
visual impairment in African children; J. Ophtalmol Vis Sci. 2003; 44:3764-3770.
Rahman SA, Singh PN, Nanda PK. Comparison of the incidence of colour blindness between
sections of Libyan and Indian populations. Indian J Physiol Pharmacol. 1997; 42 (2): 271- 275
Regina K., Pamela A., Charles C., Dapeng Z., Berga L. and Fina O. Vitamin-A Partnership for
Africa: A Food Based Approach to Combat vitamin A Deficiency in Sub-Saharan Africa through
Increased Utilization of Orange-fleshed Sweetpotato, Chronica horticulturae, 2005, vol. 45.
.Resnikoff S., Pascolini D., Etya’ale D., Kocur I., Pararajasegaram R., Pokharel G., Mariotti SP.
Global data on visual impairment in the year 2002. Bulletin of the World Health Organization,
2004, 82844-82851.
Saw S-M., Husain R., Gazzard G M., Koh D., Widjaja D., Tan D T H. Causes of low vision and
blindness in rural Indonesia. Br J Ophthalmol 2003; 87:1075–1078
Sharpe Lindsay T., Stockman Andrew, and Nathans Jeremy. Color Vision: From Genes to
Perception. Chapter 1: Opsin genes, cone photopigments, color vision, and color blindness.
Cambridge University Press. 2001.
Silverthorn D., Johnson B., Ober W., Silverthorn A.
Approach, 2010; 5th Edition: 372-378
47
Human Physiology: An Integrated
Sommer A. & West Jr KP. Vitamin A Deficiency: Health, Survival and Vision. New York:
Oxford University Press, 1996.
Squire Larry R. Encyclopedia of neuroscience ,USA, Elsevier Ltd, 2009: 661- 668
Sunderland E, Rosa PJ. The incidence of red- green color blindness in the population of
Tripolitania, cyreniaca, & Fezzan in Libia and of the Kikuyu, Kamba, Taita, Taveta & Luo tribes
of Kenya. Am J Phys Anthrop. 1976; 44: 151- 156.
The National Institute for Rehabilitation Engineering (NIRE). Vision Aids for People with
Impaired Color Perception, 2002
The Oslo invitational workshop. Toward a reduction in the global impact of low vision. The
International Society for Low Vision Research and Rehabilitation, New York, NY USA 2005.
Thomas B., Umapathy E., and Iputo J. effects of nutritional deficiency on visual acuity. Journal
of Biological science 2008; 8(7): 1246-1250.
Tonks A. Children who sleep with light on may damage their sight. British Medical Journal,
1993; 18: 1369.
Weir R, Kirk R, Bidwell S, Hinder P. et al. Color vision screening. A critical appraisal of the
literature. New Zealand Health Technology Assessment Clearing House. Report 7, 1998.
World Health Organization. Global prevalence of vitamin A deficiency in population at
risk1995-2005; WHO, 2009. available from: http://www.who.int/vmnis/vitamina/prevalence/report/en/
World Health Organization. Prevention of childhood blindness, Geneva, WHO, 1992.
World Health Organization (WHO) fact sheet 2013.
Zainal M., Ismail SM., Ropilah AR. et al. Prevalence of blindness and low vision in Malaysian
population: result from the National Survey 1996. British Journal Ophthalmology 2002; 86(9):
951-956.
Zein ZA. Gene frequency and type of color blindness in Ethiopians. Ethiop Med J. 1990;
28(2):73-75.
Zhao J., Jia L., and Sui R. Prevalence of blindness and cataract surgery on Shunyi county, China.
Am J Ophthalmol 1998; 126: 506–514.
.
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Appendix I
Information sheet and consent form for study subjects
My name is Haile Fentahun. I’m second year MSc student at Addis Ababa University, College of
Health Sciences, Department of Medical Physiology and I’m doing my MSc research on Visual
Acuity and Color Blindness in School Age Children of The Holy Trinity Primary School and
Zeray Deres Primary School in Addis Ababa, Ethiopia. This study has been approved by the
ethical and review committee of the Department of Medical Physiology, school of Medicine,
Addis Ababa University.
Dear client, you are kindly requested to give permission for your child to participate in this
study. Here is some important information which helps you to decide whether your child to
participate or not to participate in the study.
1. Objective of the study: the objective of this study is to determine the prevalence of visual
acuity impairment and color blindness and associated factors in school children.
2. Procedures to be carried on: the children will be requested to read letters in snellen chart for
measuring visual acuity and identify colors in pseudoisochromatic plate for measuring color
vision.
3. Risk and discomfort: there is no risk or discomfort during the tests.
4. Expected benefit: this study ensures whether there is visual acuity impairment and color
blindness in the children. If there are visual problems there will be further examination by
ophthalmologist without fee and possible treatment and advice will be given. So the children
will be benefit from the results obtained in order to solve visual problems.
5. Confidentiality: The information given by the children will serve only for this study not for
any other purpose and will be kept confidential.
6. Termination of the study: participation in the study is voluntary, and refusal to participate
involves no penalty or loss of benefits to which you are otherwise entitled. You have every
right to accept or refuse participation in this study at any time.
If you have any question about the study you can reach the principal investigator at:
Department of Medical Physiology, School of Medicine, Addis Ababa University
Mob. No: +251910058330, E-mail: [email protected]
49
Consent form
Code no---------------------Information about the study has been explained to me by the investigator. I understood that the
objective of this study is to determine the prevalence of visual acuity impairment and color
blindness and associated factors in school children and the information given by the children will
serve only for this study not for any other purpose. It has also been explained to me that children
have the right to stop participation at any time in between and there is nothing they will lose if
they refuse to participate. I agree that my children to participate in the study and I hereby
approve my agreement with my signature.
Participant’s name & signature-----------------------------------------------------------Date--------------Investigator’s name & signature--------------------------------------------------------------Date-----------
50
የጥናቱ ተሳታፊዎች የመረጃ እና የስምምነት ቅጽ በአማርኛ
ስሜ ኃይሌ ፈንታሁን ይባላል፡፡ በአ.አ ዩኒቨርሲቲ ሕክምና ፋካልቲ፡ ፊዚዮሎጂ ት/ክ የድኅረምረቃ ተማሪ ስኾን የመመረቂያ
ጽሑፌን በጥራት የማየት ችግር ያለባቸዉ እና ቀለሞችን በትክክል የመለየት ችግር ያለባቸዉን 1ኛ ደረጃ ተማሪዎች ስርጭት
ማወቅ እና ለዚህ አጋላጭ የሆኑ ምክንያቶችን መለየት በሚል ርዕስ በቅድስት ስላሴ ካቴድራል የመጀመሪያ ደረጃ ት/ቤት እና
ዘራይ ደረስ የመጀመሪያ ደረጃ ት/ቤት በአዲስ አበባ ከተማ ውስጥ ላይ እሠራለሁ፡፡ እርስዎም በዚህ ጥናት ልጅዎ እንዲሳተፍ
ፍቃድዎን በአክብሮት እጠይቃለሁ፡፡
ውድ የተሳታፊ ተማሪ ወላጆች
ልጅዎ በጥናቱ ለመሳተፍም ሆነ ላለመሳተፍ ለመወሰን እንዲያስችልዎት ስለ ጥናቱ
የሚከተሉትን ማብራሪያዎች እባክዎ ይመልከቱ፡፡
1. የጥናቱ ዓላማ፡- የዚህ ጥናት ዓላማ በጥራት የማየት ችግር ያለባቸዉ እና ቀለሞችን በትክክል የመለየት ችግር ያለባቸዉን
1ኛ ደረጃ ተማሪዎች ስርጭት ማወቅ እና ለዚህ አጋላጭ የሆኑ ምክንያቶችን መለየት ይሆናል፡፡
2. አጠቃቀም፡- የልጅዎን የማየት አቅም ለማወቅ በሰሌዳ ላይ ያሉ ፊደሎችን እንዲያነብ ይደረጋል፡፡ ቀለሞችን በትክክል
መለየቱን ለማወቅ ደግሞ የተለያዩ ቀለሞችን እንዲለይ ይደረጋል፡፡
3. ሊደርስ የሚችል አደጋ፡- በጤናው ላይ ምንም አይነት አደጋ ወይም ችግር አያስከትልም፡፡
4. ከጥናቱ የሚገኘው ጥቅም፡- በጥናቱ በጥራት የማየት ችግር ያለባቸዉ እና ቀለሞችን በትክክል የመለየት ችግር ያለባቸው
ልጆች ተለይተው ይታወቃሉ፡፡ ችግር ያለባቸው ልጆች ለተጨማሪ ምርመራ የዓይን ስፔሻሊስት ያለምንም ክፍያ
እንዲያየው/ያት ይደረጋል፡፡ ውጤቱም ለችግሩ መፍትሔ ለመፈለግ ይረዳል፡ ተገቢውን ህክምና እንዲያገኝም ሁኔታዎችን
አመቻቻለሁ፡፡ ልጅዎም ከመፍትሔው ተጠቃሚ ይሆናል፡፡
5. ምስጢራዊነት፡- የማንኝውም የጥናቱ ተሳታፊ መረጃ በምስጢር ይያዛል፡፡ የእያንዳንዱን ግለሰብ መረጃ ከዋናው
ተመራማሪና አማካሪው በስተቀር ማንም ሊያዉቀዉ አይችልም፡፡
6. ፈቃደኝነት፡- የእርሶ ልጅ በጥናቱ ለመሳተፍ ፈቃደኛ ያለመሆን፡ ማንኛውንም መረጃ እና ናሙና ያለመስጠት እንዲሁም
ጥናቱን በማንኛውም ጊዜ የማቋረጥ መብቱ የተጠበቀ ነው፡፡
ጥናቱን በተመለከተ ምንም ዐይነት ጥያቄ ካለዎት በሚከተለው አድራሻ ሊያገኙኝ ይችላሉ፡፡
ስም፡ ኃይሌ ፈንታሁን ፣ ፊዚዮሎጂ ት/ክፍል ፣ ሕክምና ፋካልቲ፣ አ.አ ዩኒቨርሲቲ
ስልክ፡ 0910058330፣ ኢሜል፡ [email protected]
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የስምምነት መጠየቂያ ቅጽ በአማርኛ
የጥናቱ ተሳታፊ መለያ ቁጥር------------ጥናቱን በተመለከተ በቂ ማብራሪያ ተደርጎልኛል፡፡ የጥናቱንም አላማ በሚገባ የተረዳሁ ሲሆን፤
የምሰጠውም መረጃ ለዚህ ጥናት ብቻ የሚውል በመሆኑ በልጀ ላይም ሆነ በኔ ላይ ምንም አይነት ጉዳት
እንደማያደርስ እና የምሰጣቸው ማንኛውም መረጃዎች በሚስጥር እንደሚጠበቁ ስለተገነዘብኩ በጥናቱ ልጄ
እንዲሳተፍ መወሰኔን በፊርማዬ አረጋግጣለሁ፡፡
የጥናቱ ተሳታፊ ወላጅ ወይም አሳዳጊ ስም------------------------------------------------------------ፊርማ----------------------------የመረጃ ሰብሳቢው ስም----------------------------------------------------------ፊርማ---------------------------------ቀን---------/---------/------------
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Appendix II: Questionnaires
Addis Ababa University, School of Medicine, Department of Medical Physiology
This is a questioner designed to be filled by parents in order to know the effect of socioeconomic status on the vision of their children. You are not forced to write your name and
address so that the result will not have any consequence on your life as well as your children.
The questioner will take about 10 minutes. Please fill it properly and in patience because the
outcomes will have a great value to suggest the cause of visual impairment in children and to
give possible solutions to it.
Thank you for your time and cooperation.
Part I: Personal information
1. ID-------------------------2. Sex :
Male
Female
3. Nationality :Mother-------------------------Father ---------------------------------4. Age:
Mother-------------------------Father ----------------------------------
5. Educational background: Mother-------------------------Father ---------------------------------6. Job : Mother-------------------------Father ---------------------------------7. Marital status:
single
married
divorced
widowed
8. Salary or income per month: Mother-------------------------Father -------------------------------
9
Have you any eye problem listed below? (Mother or Father)
Shortsighted
Color blindness
Longsighted
10. Have you got any eye disease before?
Mother : Yes/No ; if your answer is “yes” please specified the disease --------------------------Father : Yes/No ; if your answer is “yes” please specified the disease --------------------------11. Do you take care for your children’s eye? Yes/No. If yes how?----------------------------------
53
አዲስ አበባ ዩኒቨርሲቲ፣ የህክምና ፋካልቲ፣ ሜዲ ካ ል ፊ ዚ ዮ ሎጅ ት /ክ ፍ ል
ይ ህ በ ወ ላ ጆ ች ወይ ም አ ሳ ዳ ጊ ዎ ች እ ን ዲሞላ የ ተ ዘ ጋ ጀ የ 10 ደ ቂ ቃ መጠይ ቅ ነ ዉ፡ ፡ መጠይ ቁ ን
ለ መሙላ ት ስ ምዎ ን ም ሆ ነ
አ ድ ራ ሻ ዎ ን መጻ ፍ አ ይ ጠበ ቅ ብ ዎ ት ም፡
በ መሆ ኑ ም በ ሚሰ ጡት መረ ጃ
ምክ ን ያ ት በ እ ር ስ ዎ ወ ይ ም በ ል ጅ ዎ ምን ም አ ይ ነ ት ች ግ ር አ ይ ኖ ር ም፡ ፡ መጠይ ቁ ን በ ት ክ ክ ል
በ መሙላ ት ዎ የ ል ጆ ች ን በ ጥ ራ ት የ ማየ ት እ ና ቀ ለ ሞች ን በ ት ክ ክ ል የ መለ የ ት ች ግ ር ምክ ን ያ ቶ ች
ለ ማወ ቅ ና
ተ ገ ቢዉን
መፍ ት ሄ
ለ መስ ጠት ስ ለ ሚያ ስ ች ል በ ት ክ ክ ል
እ ን ዲሞሉ በ አ ክ ብ ሮ ት
እ ጠይ ቃለ ሁ፡ ፡
ለ ት ብ ብ ር ዎ አ መሰ ግ ና ለ ሁ፡ ፡
ክ ፍ ል 1፡ የ ተ ሳ ታ ፊ ዉን ቤ ተ ሰ ብ ማን ነ ት የ ተ መለ ከ ተ መጠይ ቅ
1. የ ተ ሳ ታፊ ዉ መለ ያ ቁ ጥ ር -----------------2.
ጾ ታ፡
3. ዜ ግ ነ ት ፡
4. እ ድ ሜ፡
ወን ድ
እ ና ት -----------------------------------አ ባ ት --------------------------------------እ ና ት -----------------------------------አ ባ ት ---------------------------------------
5. የ ት ምህ ር ት ደ ረ ጃ ፡
6. ሥራ ፡
ሴት
እ ና ት -----------------------------------አ ባ ት ------------------------
እ ና ት -----------------------------------አ ባ ት ---------------------------------------
7. የ ጋ ብ ቻ ሁኔ ታ? ሀ . ያ ገ ባ
8. ወ ር ሀ ዊ የ ገ ቢ ሁኔ ታ፡
ለ.ያላገ ባ
ሐ. አ ግ ብ ቶ የ ፈ ታ
መ. ባ ለ ቤ ት የ ሞተ በ ት
እ ና ት -----------------------------------አ ባ ት ----------------------------
9. ከ ዚ ህ በ ታች የ ተ ዘ ረ ዘ ሩ ት የ ዓ ይ ን በ ሽ ታዎ ች አ ለ በ ዎ ት ? እ ና ት ወ ይ ም አ ባ ት
ሀ . ከ ር ቀ ት የ ማየ ት ች ግ ር
ለ . ከ ቅ ር ብ የ ማየ ት ች ግ ር
ሐ. ቀ ለ ሞች ን በ ት ክ ክ ል የ መለ የ ት ች ግ ር
10. ከ ዚ ህ በ ፊ ት ዓ ይ ን ዎ ን ታመዉ ያ ዉቃሉ ?
እ ና ት = አ ዎ / አ ሞኝ አ ያ ዉቅ ም፡ ፡ መል ስ ዎ አ ዎ ከ ሆ ነ በ ሽ ታዉን ይ ግ ለ ፁ ል ን -------------------አ ባ ት = አ ዎ / አ ሞኝ አ ያ ዉቅ ም፡ ፡ መል ስ ዎ አ ዎ ከ ሆ ነ በ ሽ ታዉን ይ ግ ለ ፁ ል ን -------------------11. ለ ል ጅ ዎ ዓ ይ ን እ ን ክ ብ ካ ቤ ያ ደ ር ጋ ሉ ?
አ ዎ / አ ላ ደ ር ግ ም;; መል ስ ዎ አ ዎ ከ ሆ ነ በ ምን አ ይ ነ ት
መን ገ ድ እ ን ደ ሚን ከ ባ ከ ቡ ይ ግ ለ ፁ ፡ ፡ ----------------------------------------------------------------------------------------------------------------------------------------------------------------------
54
Addis Ababa University, School of Medicine, Department of, Medical Physiology
It is a questioner filled by participants.You is not forced to write your name and address so that
the result will not have any consequence on your life or health. The questioner will take about 10
minutes. Please fill it properly and in patience because the outcomes will have a great value to
suggest the cause of visual impairment in children and to give possible solutions to it.
Thank you for your time and cooperation.
Part I: Personal information
1. ID No. -------------------------2. Sex:
male
Female
3. Nationality :----------------------------4. Age: ----------------------------------5. Grade : -------------------------------Part III: Day-to-day activity questions.
1. Do watch TV? Yes/ No. If your answer is yes, how often do you watch television?
A. More than 8 hrs/ day
hrs/day .
B. About 6-8 hrs/day
C. About 2-5 hrs/day
D. Less than 2
2. If your answer is yes for question number 1, at what distance do you watch it?
A. Less than 1 m,
B. 1 -2m,
C. 3-4 m
D. More than 4 m
3. Are you playing TV or computer games? Yes / No., if your answer is yes, how often do you
play?
A. Daily
B. 4-6 days/week
C. 2-5 days/week
D. less than 2 days/week
4. How often do you wear eyeglass?
A. Always
B. usually
C. sometime
D. never wear eyeglass.
5. Do u have visual acuity problem or color blindness? Yes/ No._________________________
6. Do you have diabetes? Yes/ No
7. Ethnicity --------------------------------55
አ ዲ ስ አ በ ባ ዩ ኒ ቨ ር ሲ ቲ ፣ የ ህ ክ ምና ፋ ካ ል ቲ ፣ ሜዲ ካ ል ፊ ዚ ዮ ሎጅ ት /ክ ፍ ል
ይ ህ የ 10 ደ ቂ ቃ መጠይ ቅ ቤ ተ ሰ ቦ ቻ ቸ ው ሙሉ ፈ ቃደ ኛ በ ሆ ኑ ተ ሳ ታፊ ተ ማሪ ዎ ች እ ን ዲ ሞላ የ ተ ዘ ጋ ጀ መጠይ ቅ
ነ ዉ፡ ፡ መጠይ ቁ ን ለ መሙላ ት ስ ምዎ ን ም ሆነ አ ድራ ሻ ዎ ን መጻ ፍ አ ይ ጠበ ቅ ብ ዎ ት ም፡ በ መሆኑ ም በ ሚሰ ጡት
መረ ጃ ምክ ን ያ ት የ ሚደ ር ስ ብ ዎ ምን ም አ ይ ነ ት ች ግ ር አ ይ ኖ ር ም፡ ፡
መጠይ ቁ ን በ ት ክ ክ ል በ መሙላ ት ዎ
የ ል ጆ ች ን በ ጥ ራ ት የ ማየ ት እ ና ቀ ለ ሞች ን በ ት ክ ክ ል የ መለ የ ት ች ግ ር ምክ ን ያ ቶ ች ለ ማወ ቅ ና ተ ገ ቢዉን
መፍ ት ሄ ለ መስ ጠት ስ ለ ሚያ ስ ች ል በ ት ክ ክ ል እ ን ዲ ሞሉ በ አ ክ ብ ሮ ት እ ጠይ ቃለ ሁ፡ ፡
ለ ት ብ ብር ዎ አ መሰ ግ ና ለ ሁ፡ ፡
ክ ፍ ል 1፡ የ ተ ሳ ታ ፊ ዉን ማን ነ ት የ ተ መለ ከ ተ መጠይ ቅ
1. መለ ያ ቁ ጥ ር -----------------2.
ጾ ታ፡
ወን ድ
ሴት
3. ዜ ግ ነ ት ፡ ------------------------------4. እ ድ ሜ፡ ---------------------5. የ ት ምህ ር ት ደ ረ ጃ /ክ ፍ ል /--------------ክ ፍ ል 2፡ የ ተ ሳ ታ ፊ ዉን የ ቀ ን ተ ቀ ን እ ን ቅ ስ ቃ ሴ ን የ ተ መለ ከ ተ መጠይ ቅ
1. ቴ ሌ ቪዥን ይ መለ ከ ታሉ ?
ይ መለ ከ ታሉ ?
ሀ. ከ8ሰዓት በላይ
አ ዎ / አ ል መለ ከ ት ም ፣ መል ስ ዎ አ ዎ ከ ሆነ
ለ . ከ 6-8 ሰ ዓ ት
ሐ. ከ 2-5 ሰ ዓ ት
በ ቀ ን ለ ምን ያ ህ ል ሰ ዓ ት
መ. ከ 2 ሰ ዓ ት በ ታች
2. ለ ጥ ያ ቄ ቁ ጥ ር 1 መል ስ ዎ አ ዎ ከ ሆ ነ ፣ በ ምን ያ ህ ል እ ር ቀ ት ይ መለ ከ ታሉ ?
ሀ . ከ 1 ሜት ር በ ታች
ለ . ከ 1-2 ሜት ር
ሐ. ከ 3-4 ሜት ር
መ. ከ 4 ሜት ር በ ላ ይ
3. የ ቴ ሌ ቪዥን ወ ይ ም የ ኮ ምፒ ተ ር ጨዋ ታ ተ ጫዉተ ዉ ያ ዉካ ሉ ? አ ዎ / አ ላ ዉቅ ም፡ ፡
በ ሳ ምን ት ለ ምን ያ ህ ል ሰ ዓ ት ይ ጫወታሉ ?
ሀ.በየ ቀኑ
ለ . ከ 4-6 ቀ ን
ሐ. ከ 2-5 ቀ ን
መል ስ ዎ አ ዎ ከ ሆ ነ
መ. ከ 2 ቀ ን በ ታች
4. መነ ፅ ር ይ ጠቀ ማሉ ?
ሀ . ሁል ጊ ዜ እ ጠቀ ማለ ሁ ለ .ብዙ ጊ ዜ እ ጠቀ ማለ ሁ ሐ.አ ል ፎ አ ል ፎ እ ጠቀ ማለ ሁ መ. ተ ጠቅ ሜ አ ላ ዉቅ ም
5. በ ጥ ራ ት የ ማየ ት ወይ ም ቀ ለ ሞች ን በ ት ክ ክ ል የ መለ የ ት ች ግ ር በ ሽ ታዎ ች አ ለ በ ዎ ት ? አ ዎ / የ ለ ብኝ ም ፡
6. የ ስ ኮ ር በ ሽ ታ አ ለ ብ ዎ ?
አ ዎ / የ ለ ብኝ ም
56
Appendix III
Table I: Numerals on each plate and answers which would be given by normal color vision and
color defective individuals.
Number Normal
Person with Red-Green Person with Total Color
of Plate Person
Deficiencies
Blindness and Weakness
1
12
12
12
2
8
3
X
3
6
5
X
4
29
70
X
5
57
35
X
6
5
2
X
7
3
5
X
8
15
17
X
9
74
21
X
10
2
X
X
11
6
X
X
12
97
X
X
13
45
X
X
14
5
X
X
15
7
X
X
16
16
X
X
17
73
X
X
18
X
5
X
19
X
2
X
20
X
45
X
21
x
73
X
Protan
Deutran
22
26
6
2
23
42
2
4
24
35
5
3
25
96
6
9
X= The plat can not read.
57