Optokinetic asynunetry in esotropia

Abstract

Laboratory evidence suggests that the interruption of binocularity produced by early onset strabismus inhibits normal development of cortical inputs to the brainstem optokinetic pathway, producing an asymmetry in monocular optokinetic responses. It has been proposed that this optokinetic asymmetry can be useful in evaluating the presence of binocular vision. We studied 134 strabismic and 16 orthotopic patients to determine the clinical prevalence of asymmetric optokinetic responses. Cooperative children and adults were tested. For each subject, the observer made a judgment about the presence or absence of symmetry in the nasally directed versus temporally directed monocular optokinetic responses to motion of a hand-held drum.Clinical evidence of significantly greater nasally than temporally directed optokinetic responses was observed in 58% of esotropie patients who developed strabismus before the age of 6 months; in 22% of esotropie patients with onset between 6 and 12 months of age; in 9% of esotropie patients with onset between 12 and 24 months of age; and in only 5% of esotropie patients with onset of esotropia after the age of 24 months. No asymmetry was observed in any of the exotropic patients or in the hypertropic patient and was present in only 6% of orthotropic patients. Statistical analysis indicates that in this population the finding of monocular optokinetic asymmetry in an esotropie patient implies an 85% chance that the onset of esotropia occurred in the first 6 months of life. Quantitative electro-oculographic recording demonstrated that the clinical evaluation of optokinetic asymmetry can detect high degrees of asymmetry, but may miss subtle ones. Dissociated vertical deviation and latent nystagmus were not consistently associated with asymmetry of the monocular optokinetic responses.It may be concluded that clinically evident asymmetry of monocular optokinetic response is strong evidence for esotropia of early onset, while the absence of such asymmetry does not rule out early onset. Other manifestations of infantile esotropia, such as latent nystagmus and dissociated vertical deviation, are not invariably associated with optokinetic asymmetry.