Two-Dimensional Eye Movement Characteristics of Infantile Nystagmus in Eccentric Gaze

Purpose: Infantile nystagmus (IN) eye oscillations are usually predominantly horizontal. However, the contribution of the vertical component and its relationship with the horizontal component as a function of gaze angle remain unknown. This study aimed to quantify fixation performance at horizontal gaze angles, in two dimensions. Methods: Eye-tracking data from 17 participants with IN, fixating nine horizontal gaze positions spanning ±20°, were evaluated using a bivariate probability density function method, wherein the derived 68% isocontour of eye position samples were analyzed to quantify the accuracy and precision of fixation. In addition, the horizontal and vertical axis range (component) of this isocontour was evaluated using linear mixed models to determine how these vary across gaze angles. Results: From individual plots, the accuracy and precision of fixation varied between participants. There was a significant quadratic effect of gaze angle on the horizontal and vertical axis range of the 68% isocontour (β = 0.005, P < 0.001). Across participants, the gaze angle of highest fixation precision and least eye movement intensity showed a small mean difference of 0.29° but high variability. Also, mean values for fixation performance across eccentric gaze angles showed significant positive correlation with clinically measured visual acuity (accuracy: r = 0.659, P = 0.004; precision: r = 0.677, P = 0.003). Conclusions: Using this approach should enhance our understanding of the complexities of the null zone. These findings highlight the individual nature of IN oscillations and suggests that fixation precision may play a role in determining the preferred gaze position. Evaluating two-dimensional eye movements during eccentric gaze provides a more complete understanding of the relationship between fixation performance and visual acuity.