The ocular effects of spitting cobras: I. The ringhals cobra (Hemachatus haemachatus) venom-induced corneal opacification syndrome.

Venom from the ringhals cobra (H. haemachatus) caused extensive chemosis, prolonged corneal edema and marked miosis when applied locally to the eyes of two strains of rabbits: Buskat (albino) and Chinchilla (pigmented). In the pigmented rabbits, the corneal edema progressed to complete corneal opacification with corneal and conjunctival neovascularization that remained unchanged until the end of the experiment (70 d). In the albino rabbits the corneal cloudiness and conjunctivitis cleared within three weeks of venom instillation. Treatment with heparin and tetracycline markedly improved the corneal opacification syndrome, while treatment with specific antivenom resulted only in partial improvement. It is postulated that the venom owes its ocular effects to its cardiotoxin, the only venom fraction capable of inducing the corneal opacification syndrome. The protective effect of heparin is probably through its electrostatic binding to the cardiotoxin in the venom. Tetracycline could form ionic bonding at several sites in the strongly basic cardiotoxin. The corneal opacification syndrome was associated with the ability of the snakes to spit since venoms from the other non-spitting cobras were devoid of this activity.