Pendular nystagmus was seen after intravenous infusion of fosphenytoin for the treatment of breakthrough seizure. The oscillations were conjugate, quasi-sinusoidal, and regular. The nystagmus was resolved within 12h. Phenytoin is known to cause conduction slowing. Such delays in the feedback between the cerebellum and the oculomotor neural integrator may cause instability of the integrator. An improvement in the conduction delay following post-ictal recovery may resolve the pendular nystagmus.
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