Optokinetic nystagmus in strabismus: are asymmetries related to binocularity?

Strabismus may be associated with an asymmetry of monocular horizontal optokinetic nystagmus (OKN). It is unclear whether OKN asymmetries are associated with deficiency in binocular and/or stereovision. In the current study, patients with different degrees of binocularity were investigated.

OKN was examined in the dominant and nondominant eyes of four groups of patients: (1) no measurable binocularity (NB), (2) poor binocularity (PB)-that is, showing binocularity on the Bagolini Test and/or rudimentary stereovision, (3) good binocularity (GB) with good stereoacuity after squint surgery, and (4) a control group. Monocular OKN was elicited with black-and-white stripes moving temporally to nasally (TN) or nasally to temporally (NT) at velocities of 15, 30, 45, and 60 deg/s. Eye movements were recorded with infrared oculography.

Only subjects in the NB group showed a significant OKN asymmetry, with preference for TN stimulation in dominant and nondominant eyes. Subjects with PB did not have significant OKN asymmetries but reduced OKN gains in both stimulus directions. Subjects with GB had normal mean OKN gains without asymmetry. Larger OKN asymmetries were correlated with younger age at detection of strabismus if NB and GB were grouped together, but not if each group was analyzed separately.

For the first time, a large groups of patients classified by level of binocular vision has been investigated. The results show that OKN gain and asymmetry are associated with the development of binocular vision. OKN investigation may be helpful to identify patients with binocularity or binocular potential in strabismus.