A CASE REPORT OF OCULAR CHANGES IN VIPER BITE

Abstract

Krait and cobra venom exhibit neurotoxicity and                    haematotoxicity. Viper venom is known to cause only              haematotoxicity. We report here a case of a 57 year old male of viper bite, presenting with iris atrophy with complicated cataract due to the neurotoxic effect of viper venom and  normal fundus findings. In healthy people, auto regulation is present in the retina, optic nerve head and the choroidal  vascular bed. In contrast there is no evidence of   autoregulation in the iris. Phospholipase A2 in viper venom binds and blocks presynaptic nerve terminal causing transient increase in acetylcholine in the vessel wall in iris, which is not sufficient enough to diffuse into the endothelium, causing unopposed vasoconstriction by acetylcholine leading to   anterior segment ischemia. Histology of the iris showed   inflammatory cell infiltration with no evidence of thrombotic or embolic phenomenon. Hence we hypothesize that the anterior segment ischemia is due to the neurotoxicity of viper venom.