The Human Fovea Is Relatively Horizontally Elongated in Infantile Nystagmus.

Purpose: Infantile nystagmus (IN) is characterized by primarily horizontal, repetitive eye movements. IN develops in the first few months of life, in tandem with the postnatal development of the fovea. This study tested the hypothesis that the foveal pit is horizontally elongated in adults with IN, corresponding to the streak of the retina over which the image constantly oscillates. Methods: In 12 adults with IN (without associated conditions known to affect the fovea) and 12 healthy controls (age, sex, and ethnicity-matched), horizontal and vertically-orientated foveal images were acquired with a long-wavelength (λc 1040 nm) optical coherence tomography system. Horizontal and vertical foveal pit diameters were measured and the ratio between them (foveal shape factor). Results: Foveal shape factor (vertical/horizontal pit diameter ratio) was significantly lower (more horizontal) in participants with IN compared to controls (0.89 vs. 0.96, P = 0.006, BF10 = 4.14). Conclusions: IN is associated with significant relative horizontal elongation of the anatomical fovea. These results indicate that early-onset nystagmus and foveal structure could have a direct impact on each other during development. Future work should investigate whether these differences are present at the photoreceptor level.