Background: The occurrence of monocular naso-to-temporal optokinetic nystagmus (OKN) asymmetry, as a reflection of the immature oculomotor system in infants, and its persistence with early onset monocular visual deprivation, is well known. This asymmetry has been linked with poor binocular function and attributed to disruption of the development of binocular cortical projections to the pretectum. Optokinetic nystagmus symmetry in patients with congenital uniocular total pattern vision deprivation has not been fully investigated.
Methods: The authors compared the optokinetic responses in six children with "profound" uniocular visual deprivation, who were born with untreated conditions (microphthalmos and persistent hyperplastic primary vitreous), with ten aphakic children treated early for congenital unilateral cataracts (nonprofound unilateral visual deprivation). Eye movements were recorded using dc-electro-oculography, and OKN was elicited using a full-field patterned curtain. Flash and pattern visual-evoked responses were also measured in each subject.
Results: Latent nystagmus was present in six children in the nonprofound group, whereas none was detected in the profound group. All children in the nonprofound group showed statistically significant monocular naso-to-temporal asymmetry for either eye. Subjects in the profound group had symmetric OKN.
Conclusions: The authors conclude that unequal input from the two eyes and interocular rivalry lead to OKN asymmetry. Their results suggest that if vision from one eye is so negligible that it does not compete with the neuroanatomic connections of the fellow eye, then the input from this eye remains undisturbed, and OKN remains symmetric.