INFLUENCE OF YELLOW FILTER ON CONTRAST SENSITIVITY FOR
FREQUENCY DOUBLING TECHNOLOGY PERIMETRY
PÉREZ M J1, SÁNCHEZ C1, PUELL C1, LANGA A1
INTRODUCTION
Nowadays, yellow filters are used because of the apparent improvement on brightness
perception (Chung et al., 1999; Kelly, 1990) as well as on the contrast sensitivity under
photopic illumination conditions (Yap, 1984; Rabin et al., 1996; Wolffsohn et al., 2000), and
also on several ocular pathologies (Rosenblum et al., 2000; Linnik et al., 1992, Kinney et al.
1983ª). However, under mesopic conditions the existent studies are scarce and that of Yap
(1984) does not find any improvements either.
The purpose of this investigation was to determine the effect of the yellow filter X-482,
with coated treatment, on photopic contrast sensitivity (CS) for frequency doubling
tchnology (FDT) perimetry in the central visual field (20º); with the intention of
psychophysically quantifying its influence on the visual performance.
METHOD
The sample studied consisted of 28 adult subjects :22 women (78%) and 6 men (22%)
with an average age of 38.39 years (max= 55 years; min= 21 years). They were all
emmetropic ( 0,5 D), had at least 6/6 Snellen visual acuity and absence of ocular
pathologies and pharmacological treatments. The contrast threshold was measured in the
right eye of the subjects.
The environmental photopic illumination was of 20
0,3 cd/m2. The measures of
luminance were obtained with the IL1400A 3448 photometer, calibrated to measure
illumination levels in cd/m2, in combination with the detector SPLO25Y 238.
The selected protocol to carry out the psychophysics measures with the interference of
yellow and neutral filters was the following: A 5-minute period of adaptation to the
illumination conditions, during which the process for the tests was explained. Then we
determined contrast thresholds. Measures were carried out with neutral filter first on half
of the subjects and with yellow filter first on the other half, so as to avoid the learning
effect.
The cut-off filter selected was the Essilor X-482 (yellow residual colour), with a
transmittance of 0,503 for 482 nm. and transmittance-matched neutral filter (ND), both
with a luminous transmittance of 0.71. The filters were subject to a multi-layer coated
treatment with a residual reflection of 0,4%. Figure 1 shows the X-482 spectral
transmittance curve obtained with the UV-SENSE Recording Spectrophotometer UV-2401
PC of Shimadizu Corporation Company of Japan. The filters were incorporated to a
spectacle frame adapted to the subjects or were worn over the subject’s best spectacle
correction.
Dept. Optics. Optic and Optometry School. UCM (Spain)
Frequency Doubling Technology is based on the premise that the low spatial frequency in
combination with the high temporal frequency of the stimulus will preferentially stimulate
Magnocellular (M- cell) mechanisms,which are believed to be primarily involved in the detection of
motion and rapid flicker or luminance change (Johnson et al.,1999; Adams et al.,1999)). The
frequency doubling percept is produced by a non-linear response to contrast, M-cells exhibiting nonlinear responses to stimulus contrast represent a small portion (aproximately 25%) of the total number
of M-cells. It is this non-linear response to contras that is believed to produce the frecuency doubling
appearance.
When a low spatial frequency sinusoidal grating
undergoes high temporal frequency counterphase
flicker, the stimulus display appears to have twice
as many light and dark bars than are actually
physically present (Figure 3).
Contrast sensitivity was determined at each
location by means of a modified binary search
(MOBS) staircase procedure
EVER 2002, Alicante
Total sample differences among the contrast sensitivity with the X-482 filter and ND filter gave
significant differences for the periphery area ( p= 0,0140). Figure 5 shows the differences between
men and women for the periphery area. Only the women’s group gave significant differences (p=
0,0067).
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CS (dD)
Figure 5. Differences among
the men and women contrast
sensitivity results with ND
filter and the yellow filter
for the periphery area.
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ND Filter
X- 482 Filter
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MEN
WOMEN
Table 1. Contrast sensitivity values obtained in younger and elder groups
p-value=
TOTAL
Figure 2. The Humphrey Systems FDT
Perimeter
The task did not take more than 5,1 minutes
on each subject’s eye.
The influence of the filter on the different
variables studied was analysed by means of
Student’s "t" for paired data.( Statgraphics
5.0)
Figure 1. Transmittance
curve of the filter X-482.
FOVEA
PERIPHERY
ND
X-482
ND
X-482
ND
X-482
Younger 29.7 3.6 29.4 2.5 31.7 10 29.0 3.7 29.2 2.4 29.5 2.6
p-value= 0.59
p-value= 0.38
p-value= 0.30
Elder 28.7 3.2 29.0 3.1 29.0 4.5 28.5 3.4 28.6 3.1 29.1 3.3
p-value= 0.28
p-value= 0.49
* p-value= 0.04
Figure 3. Frequency doubling of the
stimulus
RESULTS.
Figure 4 shows the contrast sensitivity mean obtained with yellow filter and ND filter in the
established areas of the visual field (20º). The results obtained with the yellow filter showed a
increase of the CS in the periphery area (29.39 3.241dB). However, no statistical significance was
found in the 5º central area (29.10 3.47dB). In the four quadrants, the CS values were higher than
those obtained with ND filter but without statistical significance.
Sample was divided in two age groups: Younger ( 35 years) and elder ( 36 years). Last group
( 36 years) CS had significant differences (p= 0.04) in the periphery area of the visual field (20º).
Rest of studied areas for the two groups, the contrast sensitivity measures didn’t give statistical
significance between the yellow filter and neutral filter (Table 1).
CONCLUSION
Photopic contrast sensitivity for frequency doubling tchnology (FDT) improved through the
coated yellow filter for the periphery area of the visual field (20º). Therefore, the effect of yellow
filter without residual reflections had a positive influence on the contrast perception of healthy
subjects at low spatial frequency.
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ACKNOWLEDGMENT.
The yellow filters used were kindly supplied by Essilor España, S.A.
CS (dB)
30
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29,6
Figure 4: Contrast
Sensitivity means in
the visual field (20º)
Contrast sensitivity was obtained for frequency-doubled stimuli (0.25 cycles per degree
sinusoidal grattings undergoing 25 Hz counterphase flicker) at 17 target locations (four
per quadrant (10º in diameter) of visual field (PERIPHERY area) and a central 5º circular
target (FOVEA area)) using the Humphrey Systems FDT perimeter (Figure 2). The
background luminance was 100 cd/m2..
E-mail: [email protected]
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