Abstract
Abstract: :
Purpose: Test the hypothesis that rod cell and rod–mediated retinal and visual sensitivity are low in infants and children with hypopigmentation due to oculocutaneous albinism (OCA). In experimental ocular hypopigmentation, the number of rod photoreceptors and rhodopsin content are low1. In normal development, rod cell sensitivity (S) is scaled by rhodopsin content2. Methods: Rod photoreceptor and post–receptoral responses were derived from ERG responses to full–field stimuli. Rod–mediated visual sensitivity was tested in selected, small retinal regions using a two–alternative, spatial, forced–choice method and staircase procedure. Infants and children (N=21; aged 2.5 months to 7 years) with graded hypopigmentation due to oculocutaneous albinism (OCA) were tested. Not every subject was tested with both procedures. The data of the subjects with ocular hypopigmentation were compared to those of age–matched controls. Results: Rod photoreceptor sensitivity, derived from the ERG a–wave in 17 subjects, was within the 95% prediction interval of normal for age in all but 3 subjects. However, postreceptoral sensitivity, b–wave log σ, was normal in only 6 of these 17 subjects. The dark–adapted visual thresholds were normal in all 10 tested. Conclusions: Although the psychophysical procedure did not demonstrate deficits in dark–adapted scotopic visual sensitivity in these children with ocular hypopigmentation, mild deficits in rod and rod mediated retinal sensitivity are found in many. This may be a human correlate of rod deficits found in animals with hypopigmentation. 1 Donaten P & Jeffery G. IOVS 2002. 43(3): 1198–1203. 2 Fulton AB & Hansen RM. IOVS 2000. 41(6): 1588–1596.
Keywords: visual development: infancy and childhood • electroretinography: non–clinical • photoreceptors: visual performance