Differences in Sensitivity of Various Ophthalmological Methods of detecting Light-induced Retinal Damage in Rats

Abstract

Albino (Slc: SD) and pigmented (ACI/N) rats were exposed to continuous illumination (120Å`190 lux) for 14 days. Pupillometry, fundoscopy, electroretinography, and histopathological examination were performed periodically throughout the study. Retinal damage induced by continuous light was observed only in albino rats. In pupillometry, mydriasis was noted in albino rats after 3 days of continuous light. The pupillary diameter reached a maximum level after 5 or 7 days of continuous light and then tended to gradually contract. The retinal arteries and veins showed narrowness, fundal reflectivity increased, and the optic disc was clearly seen by fundoscopy in albino rats after 7 or 10 days of continuous light. Electroretinography revealed prolongated peak latency and lowered amplitude in the a-wave after only 1 day (24 hours) of continuous light. Similar changes were recorded in the b-wave after 3 days of treatment. The a and b-waves showed more pronounced changes with further treatment. The electroretinogram was almost flat after 7 days of exposure. Histopathologically, dark bodies appeared in the outer segment zone after 1 day of exposure. Regressive changes developed by degrees, and the receptor cells and external granular layers partially disappeared after 14 days of treatment. The abnormalities detected in ophthalmological examinations never returned normal even when animals were housed under diurnal cyclic lighting. In conclusion, among the types of ophthalmological examination used in this study, electroretinography detected retinal damage at the earliest stage. In addition, the alteration in pupillometry appeared at a comparatively early stage of retinal damage. However, further investigation is needed to elucidate the relationship between retinal damage and change of pupillary diameter.