DARK ADAPTATION AND VITAMIN A DEFICIENCY
A N E W TECHNIC*
A. G. SHEFTEL
From the Department of Medicine of the College of Medical Evangelists and the
Laboratories of Los Angeles County Hospital, Los Angeles, Calif.
There has been much controversy regarding the practical value
of dark adaptation tests in determining the degree of Vitamin A
deficiency, the accumulated results of which can be classified into
two groups.
In group 1, a considerable degree of vitamin deficiency among
various classes of the population was detected by means of a
photometer. When vitamin deficient subjects were given adequate amounts of Vitamin A over a certain period of time, the
deficiency disappeared, as was indicated by higher photometric
readings. Thus Jeans and Zentmire1, using the Birch-Hirschfeld
photometer in a study of the dark adaptation of 213 children,
found that 45 were subnormal, and when Vitamin A was added
to their diets, the photometric readings returned to normal. In
another study 2 , using the same technique, these authors found
that 26 per cent of rural, 53 per cent of village, and from 56 to 73
per cent of city children, presented evidence of vitamin deficiency. Again, after addition of Vitamin A to the diet, the readings became normal.
Adopting a new apparatus, the bio-photometer, Jeans,
Blanchard and Zentmire 3 found that 35 per cent of children in an
orphanage had Vitamin A deficiency.
Jeghers4 investigated the dark adaptation of three groups of
subjects with a Birch-Hirschfeld photometer. Members of group
A were on a varied diet, abundant in Vitamin A (young doctors
in a Boston hospital). Group B consisted of healthy individuals
whose diet, while apparently not so abundant in Vitamin A as
group 1, was probably somewhat representative of the average
* Received for publication April 3,1939.
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low income class American diet (workers on relief, technicians,
students). Group C represented ambulatory patients convalescent from the usual run of diseases.
All members of group A, with the exception of two, gave normal
photometric readings. In group B, 65 per cent gave normal
photometric readings, 42 per cent showed mild deficiency, 4.6
per cent showed moderate, and 1.4 per cent showed severe deficiency. In group C, 33 per cent gave normal readings, 41.7
per cent showed mild deficiency, 7.6 per cent moderate, 7.7 per
cent severe deficiency. In many cases of deficiency, the photometric readings became normal when adequate amounts of
Vitamin A were added to the diet.
Similar observations were described by Park 5 •6, Corlett, Youmans, Frank and Corlett 7 , and Schuck and Miller8. It is the
opinion of all these investigators, that the degree of Vitamin A
deficiency can easily be measured by means of photometers, and
that the addition of Vitamin A to the diet results in higher
photometric readings.
Group 2. Another group of investigators, using the same
apparatus, were unable to demonstrate a relationship between
dark adaptation and Vitamin A deficiency. Snelling9, using the
Birch-Hirschfeld photometer, found this instrument unsatisfactory in determining Vitamin A deficiency. Palmer10 using the
bio-photometer, made an intensive study of 106 children, who
during previous tests had given low photometric readings. These
children were divided at random into two groups. The children
of group 1 were given an average daily supplement of 18,000 units
of Vitamin A; children of group 2 were used as controls and
photometric readings were taken at weekly intervals. After
five weeks, two facts were noted. Marked improvement occurred
in the average photometric readings in successive tests in both
groups, those fed on vitamin concentrate, and those receiving
none. In addition, all measurements showed a high degree of
variability above and below the means. Isaaks, Young and Ivy 11
studied the dark adaptation by means of the bio-photometer on
two groups of healthy individuals, in order to determine whether
any given subject would give constant readings and whether the
apparatus was sufficiently reliable to permit detection of day to
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A. G. SHEFTBL
day variations. They found that no correlation could be found
between dietary Vitamin A deficiency and bio-photometric
readings. Also, that in the bio-photometer technique, the most
important step, namely, the threshold reading, taken 30 seconds
after exposure to bright light, was the most unreliable.
Palmer and Blumberg12 in reviewing each step of the biophotometer technique, discovered certain fallacies. The first
of these concerns the "bleaching" step. In the technique under
discussion, this consists of instructing the subject "to look
steadily with both eyes open, for a period of three minutes, at a
brightly illuminated ground glass screen within the bio-photometer. A subject may or may not follow these simple instructions
completely, and the operator has no definite way of knowing just
how precisely the standard conditions of the test are being
followed. With cooperative subjects, particularly adults, this
part of the test probably is reasonably well controlled. Without
the operator's knowledge, however, a subject may look at the
black surfaces of the sides of the bio-photometer or may even
close the eyes during all or part of the period that he is instructed
to gaze at the illuminated screen. Three minutes may seem a
long time to some individuals, especially to children, and there
can be little doubt that a considerable amount of variability in
the results is possible and probable because of lack of rigorous
control over this bleaching procedure. The bio-photometer
test does not provide for the control of this variation, and it is
difficult or perhaps impossible to make a quantitative evaluation
of the amount or importance of this source of variability in
routine use of the present instrument."
Another important consideration arises in connection with
the determination of the exact thresholds. The subject is asked
to tell the operator at what intensity the light is visible. But
the operator has no way of knowing when the subject sees the
critical spot of light. Some individuals may state that they
perceive the light when it is very indistinct, and even when there
may be some doubt in their minds that they actually see it.
Others may report seeing the test light only if it is very distinctly
visible. This explains why the measurements obtained by
Palmer showed such a high variability above and below the
means.
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In the method herein described, the intensity of the light can
be controlled by increasing or decreasing the height of a column
of dark colored fluid through which the light passes. The liquid
used is a solution of Prussian blue, which is freshly made by
adding equal amounts of a 0.45 per cent solution of Potassium
Ferrocyanide and Ferric Iron solution, prepared according to
Folin's method for blood sugar determination13. For measuring
the intensity of light, the author's colorimeter14 has been suitably
adapted.
FIG. 1. COLOBIMETER
The colorimeter (fig. 1) consists of two opaque cups with transparent bottoms. Directly beneath these cups, there is a light of uniform intensity. One
cup is attached to a hypodermic syringe, so that liquid can be easily removed
or added, thus decreasing or increasing the column of liquid, consequently
augmenting or diminishing the intensity of light which passes through the
colorimeter.
The reasons prompting the use of this colorimeter for photometric purposes
are that the optical system at the top of the colorimeter is detachable thereby
presenting a larger visual field; and that the colorimeter light is closely attached
to the cups, permitting comparatively little light to escape. To insure against
any light escaping through one of the joints, the colorimeter should be covered
with a piece of dark rubber sheeting, having two holes through which the cups
can be passed. The cup not in use should be covered with a rubber stopper.
The entire apparatus (fig. 2) for measuring dark adaptation consists of a stand-
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A. G.
SHEFTEL
ard size x-ray viewing box (16 x 19 inches), with a frosted white glass, and a
250 watt bulb. To be certain that the subject is looking directly at the light,
a sheet of thin white paper with stenciled letters is pasted in the center of the
frosted glass, which the subject reads aloud. This is an extremely important
factor in performing dark adaptation tests in children, as it enables the operator
to know definitely that the conditions of the test are being followed.
The x-ray viewing box is inserted into a tight-fitting heavy white cardboard
box or a wooden box with white walls. On the left of the wooden box, 7 inches
from the bottom, a notch is cut, large enough for the subject to rest his thumb.
F I G . 2. APPABATUS FOR DARK ADAPTATION MEASUREMENTS
The technique of the test is as follows: 2 cc. of the Prussian Blue solution is
introduced into the cup connected with the hypodermic syringe, and the plunger
of the syringe pulled out to the 100 mark, thus leaving 1 cc. in the cup. The
colorimeter is then placed in the middle of the box, about half an inch from the
border. The subject is seated close to the apparatus (fig. 3), the height of the
seat adjusted so that the forehead touches the upper part of the wooden box at a
distance 2 finger breadths above the eyebrows. This position is maintained
throughout the test. The room is kept in complete darkness for five minutes.
The operator may use a flashlight for timing purposes. Then the bright light
in the x-ray box is turned on for two minutes, and the subject reads aloud the
letters pasted on the front of the glass. At the end of this two-minute period,
the colorimeter light is turned on and the bright light extinguished. The
VITAMIN A DEFICIENCY
173
subject having previously placed his thumb in the notch, looks directly at the
tip of his thumb, and signals the operator as soon as he perceives the light from
the colorimeter, which is at an angle of about 35 degrees. The time is noted by
means of a stop watch. Immediately thereafter, the subject looks down in the
direction of the colorimeter. The light which he previously saw disappears,
but reappears later, and the time is again noted. Two minutes after the bright
light has been extinguished, and at two minute intervals thereafter, continuing for eight minutes, the subject is instructed to find the light threshold.
He does this by pushing the plunger in until the light disappears, and then
FIG. 3. POSITION OF SUBJECT FOR DARK ADAPTATION MEASUREMENT
gently pulling it out again, until he sees the light. The operator notes each
reading on the syringe, using a flashlight, the subject always closing his eyes
while the flashlight is on. It is advisable that the subject become accustomed
to finding the threshold before performing the test, and to discard the results of
the first test, until the technic has been learned.
The following data are important:
1. Rapidity of regeneration of the visual purple to the periphery
of the eye, i.e., the length of time taken for the subject to perceive
the light passing through a column of liquid, 10 mm. high (1 cc.)
at an angle of approximately 35 degrees.
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A. G. SHEFTEL
2. Rapidity of regeneration of visual purple at the fovea. Both
of these values are expressed in seconds, the intensity of light
and the column of Prussian Blue being constant.
3. The regeneration of the visual purple at consecutive twominute intervals is expressed in terms of the height of the column
of Prussian Blue, i.e., in millimeters. Each ten mark on the
hypodermic syringe corresponds to 1 mm.
For normal controls, eight healthy individuals with no ocular
defects, were chosen. These controls were on a normal and varied
diet, and had received 32,000 additional units of Vitamin A daily
in the form of Halliver oil, for several weeks. After being
exposed for two minutes to the bright light, these subjects presented the following:
a. Time required for the Periphery of the Eye (at an approximate angle of 35 from Fovea) to perceive a dim light,
passing through a column of Prussian Blue, 10 mm. high:
15-25 seconds.
b. Time required for the Fovea to perceive the same light:
40-70 seconds.
c. Light threshold after 2 minutes of darkness (expressed in
mm. of a column of Prussian Blue, through which the
light passes): 11-12.5 mm.
d. Light threshold after 4 minutes of darkness (expressed in
mm. of a column of Prussian Blue, through which the
light passes): 12-14 mm.
e. Light threshold after 6 minutes of darkness (expressed in
mm. of a column of Prussian Blue, through which the
light passes): 15-17 mm.
f. Light threshold after 8 minutes of darkness (expressed in
mm. of a column of Prussian Blue, through which the
light passes): 16.5-18.5 mm.*
* Since this article went to press, the manufacturers have introduced
a new light filter for the colorimeter lamp, which produces a dimmer light.
As this technic was developed with the old type filter (i. e., the one with the
brighter light), normal individuals may show a delayed perception of light with
the new filter. Therefore, those intending to use the colorimeter for photometric determinations, should inquire of the manufacturers with which type
light filter their colorimeter is equipped.
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175
t)uring the entire period of observation, the readings of each
individual were consistently uniform.
This is a preliminary report, as work is being continued on
relationship of dark adaptation to Vitamin A in health and disease. This technic is being presented now in the hope that other
investigators may determine whether or not it is adequate for the
diagnosis of Vitamin A deficiency.
SUMMARY
A new technic for determination of Vitamin A deficiency is
described having the following features:
1. A means for control of the bleaching process of the visual
purple is provided.
2. The degree of dark adaptation is measured by the intensity
of light passing through a solution of Prussian Blue, the height
of which can be decreased or increased, thereby modifying the
intensity of light, and thus dispensing with rheostats.
3. The rapidity of regeneration of the visual purple is measured
separately at the periphery of the eye, and at the fovea.
4. The threshold of light is determined by the subject rather
than the operator, permitting him to modify the intensity until
the exact threshold is obtained.
5. The apparatus herein described can be quickly and inexpensively constructed in any laboratory.
1915 Wilshire Blvd.
Los Angeles, Calif.
REFERENCES
Owing to their number references are omitted but will be included in the
author's reprints.