Symmetry of Visual Motion Processing and Vergence Eye–Movements in Infantile Esotropia

Abstract

Abstract: : Purpose:To determine whether sensory cortical binocular mechanisms predict motor binocular functions in subjects with infantile esotropia. Sensory cortical binocular functions were assessed using motion visual evoked potentials (mVEPs) which are considered to be capable of selectively accessing binocular motion pathways and binocular motor functions tested in the study were fusional vergence eye movements. Methods:Six children with infantile esotropia (age 11 to 17) viewed disparity vergence visual stimuli that were displayed on a computer screen through a pair of liquid crystal shutter glasses. Eye–movements were recorded using a binocular head mounted eye tracker. The criterion for the detection of vergence eye movements was a movement of the two eyes in opposite directions (disconjugate eye movements). In addition, each child underwent assessment of motion processing. Motion VEPs were measured monocularly in response to vertical sinusoidal gratings displayed on a video monitor. The grating shifted synchronously with the video frame between two positions separated by 90º of spatial phase (5 min arc for 3 c/deg gratings) at 10 Hz. The gratings were presented for 10 seconds and several trials recorded from each eye. Responses were declared asymmetric in the presence of a phase difference of 180º±40º between the two eyes in F1 (bow tie) and an asymmetry index higher than 0.4. Results: Bow ties were found in three out of six children. Asymmetry index was higher than 0.4 in all of the children. Five children showed evidence of vergence eye movements. Fischer’s exact test showed no association between symmetry of motion response (presence of bow tie) and evidence of vergence eye movements (p = 0.333). Conclusions:Although previous studies support the assumption that the motion VEP provides evidence of binocular integrity the current study suggests that the ability to demonstrate vergence eye movements in infantile esotropia is multifactorial. Continuing studies are investigating other factors that contribute to vergence eye movement responses in infantile esotropia.

Keywords: strabismus • electrophysiology: clinical • vergence