Does eye velocity due to infantile nystagmus deprive visual acuity development?

PURPOSE: To use eye movement recordings of young children to determine whether eye velocity from infantile nystagmus (IN) deprives the developing visual system of normal visual acuity.

METHODS: The video-oculography recordings and visual acuity measurements (including Teller cards) of 15 children ≤6.0 years of age with IN without visual sensory disease (idiopathic IN) were reviewed retrospectively. Eye velocity that would limit visual acuity development was predicted from both empirical adult data adjusted for age and a temporal limitation model using published photoreceptor density data with age. Foveal alignment onto a target was measured in 5 subjects using confocal retinal imaging.

RESULTS: All subjects had periods (85-2440 ms) during which eye velocity was below the limit that would reduce age-appropriate visual acuity. The percentage of time eye velocity was below the limit varied by 4%-54% across all eye movement recordings. Eye movement metrics (eye position variability, average eye velocity, maximum duration of foveation, and the nystagmus optimal foveation fraction) correlated poorly with age or with age-corrected visual acuity (r2  < 0.27 for each metric). Longitudinal visual acuity development overlapped between subjects with different nystagmus waveforms.

CONCLUSIONS: Eye velocity was not predicted to completely deprive visual acuity development in subjects with idiopathic IN. Nystagmus may decrease visual acuity development in children with idiopathic IN by interfering with visual-cortical development in the context of increased visual noise due to image motion with imprecise foveation.