Adult albino mammals have specific retinal defects, including
reduced numbers of rod photoreceptors. To examine when
this rod deficit arises and whether it exists in nonmammalian
albinos, we have used absorbance spectrophotometry to measure
photopigment levels in dark-adapted eyes taken from three
groups of pigmented and albino animals: adult rodents (rats
and mice), developing rats, and mature Xenopus
frogs. Rhodopsin concentrations were consistently and significantly
reduced in mammalian albinos compared to their wild-type
counterparts from before the time of eye opening, but photopigment
levels were similar in frogs of both pigmentation phenotypes.
The results strongly suggest that deficits in the rod cell
population arise early in development of the mammalian
albino retina, but do not generalize to nonmammalian mutants
lacking retinal melanin.