CLINICAL OPTOKINETIC NYSTAGMUS ASYMMETRY IN TREATED ESOTROPES

Background: Monocular optokinetic nystagmus (OKN) asymmetry is associa ted with disruption of early binocular visual development. Methods: Th ree groups of treated esotropic patients and a group of normal control s were evaluated for the presence of clinically detectable monocular O KN asymmetry. Clinical assessment of monocular OKN asymmetry was perfo rmed by observing eye movements in response to a hand-held rotating dr um. Asymmetry was quantitated on a scale of 0 to +3 OKN asymmetry. Cli nical OKN asymmetry was evaluated in the following groups of patients: those with congenital esotropia treated with very early surgery achie ving high-grade stereo acuity (group 1); those with congenital esotrop ia treated with late surgery achieving no stereopsis (group 2); those with acquired esotropia achieving high-grade stereo acuity after treat ment with spectacle correction (group 3); and normal controls (group 4 ). Results: Two of the three patients in group 1 showed +3 OKN asymmet ry despite having high-grade stereo acuity; the third one, who was sur gically aligned earliest (13 weeks), demonstrated +1 OKN asymmetry. Th is patient achieved orthotropia, 40 seconds stereo acuity, perfect Ran dot stereo acuity, and had no dissociated vertical deviation or latent nystagmus. All 10 patients in group 2 (those with late alignment-afte r 1 year-and no stereo acuity) showed +3 OKN asymmetry. All four patie nts in group 3 (those with acquired hypermetropic esotropia and high-g rade stereo acuity after treatment) and all 10 patients in the normal control group showed no OKN asymmetry. Conclusion: Clinically obvious monocular OKN asymmetry can occur in patients with congenital esotropi a who are aligned early and develop high-grade stereo acuity. Even bri ef periods of strabismus during the early period of binocular motor de velopment can result in persistent OKN asymmetry. This suggests that b inocular motor processing may develop distinct from, and prior to, the development of high-grade stereo acuity. OKN asymmetry appears to be a clinical sign of an insult to early binocular motor development.