Paralytic Exotropia from Pit Viper Snakebite

ABSTRACT

PURPOSE: The authors report their experience with four cases of paralytic exotropia from a pit viper snakebite, accompanied with a literature review. METHODS: Four patients (two males and two females) visited the emergency room in the hospital with symptoms including diplopia, limitation of eye movement, exotropia, and blepharoptosis, after being bitten by a presumed pit viper, and were treated by antivenom. RESULTS: No visual disturbance was observed in the first examination, while limitation of adduction was found in four cases in the ocular movement test. As to the type of tropia, three patients showed intermittent exotropia and the other showed exotropia. The angle of strabismus in the distance was 20~30 prism diopters (PD) while that in the near was 18~35 PD. Two cases were accompanied with blepharoptosis. Except one case which was unavailable for follow-up observation, three cases became normal in diplopia, blepharoptosis, and limitation of ocular movement between the 4th and 11th day after the snakebite. CONCLUSIONS: Neurotoxicity induced by a pit viper snakebite is rare. However, neurotoxicity including strabismus and blepharoptosis can occur because extraocular muscles have a higher ratio of nerve fibers to the extraocular muscle fibers compared with skeletal muscles.