in partial fulfil]ment of the - MSpace - University of Manitoba

test light.
68
The stimulus consisted of light flashed of 1 second duration
separated by'1 second intervals of darkness. The luminance of the
test light was increased or decreased depending on the response of the
subject. (en "ascending threshold" was the intensity at which the subject
first saw the test light as its luminance was increased; a
"descending threshofd" was the intensity at which the subject ceased to
see the tesL light as its luminance was lowered). Each threshold intensity
was mechanically plotted versus time, and the values were read off
the graph at the end of the session. Testing was continued until the
thresholds stabilized, i.e., until the final dark adapted threshold was
achi eved.
In the Rapid Dark Àdaptation Test, each subject was light adapted for
one minute immediately before the actual test began. 0n1y distance of
light source for Iight adapLation was recorded. Timing by stopwatch
started when the test light was dimmed to 0.0058 candela/mz. The subject
then sorted 5 white, 6 blue and 7 red discs until 100% accuracy of
sorting was achieved. Errors were reflected in the total amount of time
taken !o complete the test. Fasting serum Vitamin A (retinol) levels
were measured.
The resulls of this study indicated that in the Classical Dark
Adaptation Tesl, there rvas an elevated final dark adapted threshold and
an increased rod-cone break time in Vitamin À deficient subjects compared
to normal controls. The other interesting observation was that
Vitamin À deficient subjects had consistently increased test times in
all the lhree parameLers: in rapid test time (in the Rapid Dark
Adaptation Test), finat dark adapted threshold and rod-cone break time
compared to normal controls and Vitamin À sufficient patients. l.lhen the