Short- and long-term effects of transection of the ophthalmic nerve on optokinetic nystagmus in the rabbit.

The role of extraocular proprioception in optokinetic nystagmus (OKN) was examined, using adult pigmented rabbits following transection of the ophthalmic branch of the trigeminal nerve. OKN was induced by rotation of a drum at an angular velocity of 0.85 and 3.7 degrees/s. The eye on the operated side showed a delay in the transition from the OKN-induced quick phase to the slow phase regardless of closure of the eye on either the operated or unoperated side. In addition, the eye on the operated side showed an anticompensatory response in the vestibulo-ocular reflex (VOR) with an unstable drift in the dark. The above abnormalities in OKN and VOR following rhizotomy disappeared after 1-1.5 months. These results suggest that proprioception in the extraocular muscle plays an important role in the fine regulations of eye position for gaze accuracy. The recovery demonstrated appears to be due to a compensatory mechanism in the central nervous system.