Independence of Optokinetic Nystagmus Asymmetry and Binocularity in Infantile Esotropia

Abstract

Children with congenital esotropia, amblyopia, or early visual deprivation have persistent asymmetric monocular pursuit, as measured by optokinetic nystagmus (OKN), and favor targets moving in a temporal to nasal direction. Previous studies suggest that binocular visual development is necessary for the development of symmetric monocular OKN. We recently treated patients with congenital esotropia with unconventionally early surgery to establish good binocularity. We wished to determine if mature symmetric OKN responses could develop in patients with congenital esotropia following the acquisition of good stereopsis. Electro-oculographic recordings documented horizontal eye movements in response to an electronic OKN stimulus. The recordings of three patients with congenital esotropia that had been surgically aligned before age 20 weeks and who had achieved high-grade stereopsis with random dot and Titmus stereographic testing were studied. We compared this group of children with groups of age-matched controls, including the following: (1) three patients with congenital esotropia who underwent surgical alignment after age 6 months and who had no amblyopia but poor stereopsis; (2) three children with accommodative esotropia, good ocular alignment when wearing spectacles, and good stereopsis; and (3) three normal children. The normal children and those with accommodative esotropia demonstrated normal symmetrical OKN. The patients with congenital esotropia showed poor nasal to temporal OKN regardless of the degree of stereopsis or timing of surgery. Our results indicate that good binocularity, as measured by stereopsis, is not sufficient for the development of symmetric OKN in patients with congenital esotropia.