Acute visual dysfunction following phenytoin-induced toxicity.

Purpose: To report that acute phenytoin toxicity may result in acute visual dysfunction. Methods: A 19-year old man with cryptogenic simple partial and secondary generalized epilepsy developed blurred vision and xanthopsia after phenytoin loading for status epilepticus. Color blindness was found on testing with Ishihara's pseudo-isochromatic charts and visual fields (Goldmann perimeter) showed gross concentric constriction in both eyes. Flash visually evoked potentials showed prolonged P1 latency in both the eyes. Serum free-phenytoin concentration revealed toxic levels of phenytoin and no other etiology for retinopathy or optic neuropathy. Results: Phenytoin was withheld and the patient experienced a partial recovery in conjunction with reduced serum levels of phenytoin. Ten months later flash visually evoked potentials were normal but electroretinogram confirmed diffuse bilateral cone and rod dysfunction. Conclusion: Phenytoin toxicity may result in acute visual dysfunction a previously unreported phenomenon.