Biology Reference
In-Depth Information
8
6
4
2
10
20
30
Time in darkness (min)
Fig. 19.1 Dark-adaptation curves of a rod monochromat K. N. (● ) and a
normal trichromat (○) following a full bleach. Wavelength of test stimulus
was 550 nm; size, 1 x 2º; duration of exposure, 0.5 sec; and retinal location
7 º in the nasal field of view.
of bleached rhodopsin and sensitivity during dark adaptation could
then be calculated.
In agreement with Hecht (
1921
/1922) and Dowling (
1960
), the
results from the photanope showed a close linear relationship between
the fraction of rhodopsin still bleached and the logarithm of the rod
threshold. The result obtained was assumed to be also representative
for normal trichromats, since their rhodopsin regeneration curve and
the last 2-log unit part of their rod dark-adaptation curve (the only
part that could be measured in trichromats) coincided closely with
those of the photanope.
Complications intruded however. Thus, Rushton found the
simple linear relationship obtained to be restricted in two important
