Differential effect of ischemia/reperfusion on pigmented and albino rabbit retina

The purpose of the study was to compare the retinal sensitivity of pigmented and albino rabbits to ischemia/reperfusion-induced electroretinogram (ERG) alterations and optic nerve morphological changes. High intraocular pressure (HIOP) was induced by applying a suction-cup on the eye and a depression with an ophthalmodynamometer. HIOP was maintained for lengths of time (30-75 min). Flash ERGs were recorded in dark-adapted animals for ischemia and 2 h reperfusion periods. Two weeks later, histological examination of the retinas and optic nerves was done. Albino rabbits submitted to 45 min HIOP failed to recover b-wave ERG amplitude after 2 h reperfusion, whereas pigmented animals presented a total ERG recovery even if ischemia was maintained as long as 75 min. Intravenous treatment of albino animals with Lazaroid U74389G led to significant ERG recovery at reperfusion. Histological studies show that pigmented rabbit optic nerves suffered less damage than the albino ones. These results emphasize the role of the pigmentary status of the animals in the retinal sensitivity to ischemia. Neuroprotection afforded by the antioxidant U74389G suggests that ocular pigments could also protect the retinal functional integrity through a free radical scavenging activity.