Optokinetic nystagmus in progressive retinal degeneration.

Studied optokinetic nystagmus (OKN) in normally pigmented and delayed amelanotic (DAM) strains of domestic chickens (N?=?18). The DAM line is characterized by postnatal feather and ocular depigmentation accompanied by progressive retinal degeneration that occurs, initially and most severely, in the central retina. Results indicate a close association between the extent of ocular pigment loss and relative reduction in OKN responsiveness in DAMs. The directional asymmetry of OKN responses, which normally occurs with monocular temporal-to-nasal (T–N) but not with N–T stimulation, was altered in relation to the extent of ocular amelanosis among DAMs. In particular, T–N OKN responses were progressively reduced as amelanosis of the central retina increased in severity. In DAMs with moderate to severe reductions in T–N responsiveness, relatively little reduction occurred in N–T responsiveness. The central retina, therefore, appears to play a major role in mediating responses to T–N stimulation, whereas the peripheral retina mediates both directions of response. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)