Impaired visual thresholds in hypopigmented animals.

Ocular hypopigmentation is associated with neurological defects in structure and function. This paper investigates the absolute visual thresholds in dark-adapted hypopigmented animals compared to their normally pigmented controls. Here we asked (1) whether the threshold elevation found in hypopigmented animals is a general consequence of the reduction in melanin content; (2) if so, which melanin components in the eye are likely to influence visual thresholds; and (3) whether similar threshold defects can be detected in orders other than rodents. By single-unit recordings from the superior colliculus, we compared incremental thresholds of normal black mice of the C57BL/6J strain to hypopigmented mutants: beige (bg/bg), pale ear (ep/ep), and albino (c2J/c2J) mice, three mutants in which melanin pigment throughout the body is affected; and Steel (Sl/Sld) and dominant-spotting/W-mice (W/Wv), two mutants with normal pigmentation in the retinal pigment epithelium (RPE) but without any melanin in the choroid or the rest of the body. We found that all mutants had elevated thresholds that varied with the reduction in melanin. The albinos were 25 times less sensitive than black mice, pale ear mice 20 times, beige mice 11 times, and Steel and W-mice 5 times. The mean thresholds of dark-adapted black mice were 0.008 cd/m2. Recordings from rabbits showed a similar impairment of visual sensitivity; incremental thresholds were elevated 40 times in New Zealand-White albino rabbits (0.0008 cd/m2) compared to Dutch-Belted pigmented controls (0.00002 cd/m2).(ABSTRACT TRUNCATED AT 250 WORDS)