Oculomotor dynamics in emmetropes, myopes, and hyperopes: A behavioral perspective

The oculomotor system, which controls eye movements, is closely linked to visual processing. While refractive errors are common, their influence on oculomotor behavior remains underexplored. This study compared oculomotor performance among emmetropic, myopic, and hyperopic individuals.

In this cross-sectional, single-visit study, 67 participants (33 myopes, 10 hyperopes, 24 emmetropes; mean age 25.9 ± 3.0 years) completed fixation and visually guided saccade tasks at a viewing distance of 57 cm. A centrally positioned black, disc-shaped target (0.50° in diameter) was displayed on the screen for 45 seconds, after which it shifted to a predetermined location to elicit visually guided saccades. Clinical measures were included in the correlation analysis to ensure the findings were clinically relevant and to examine relationships between research variables and patient outcomes. Eye movements were recorded using the EyeLink 1000Plus. Fixation stability was quantified using Bivariate Contour Ellipse Area (BCEA). Fixational saccade metrics, vergence stability, and saccadic behavior were analyzed. Axial length and corneal power were measured using a portable ultrasound scanner.

Fixation stability differed significantly across groups, with myopes exhibiting larger BCEA values compared to emmetropes (H[2] = 10.6, p < 0.05). Analysis of fixational saccades revealed that myopes demonstrated significantly greater amplitude (H[2] = 507.4, p < 0.001), peak velocity (H[2] = 595.7, p < 0.001), and frequency (H[2] = 9.0, p < 0.05) relative to the other groups. Vergence stability was also poorer in myopes than in emmetropes (H[2] = 8.7, p < 0.05). In contrast, saccadic behavior during visually guided tasks showed no significant group differences in latency (H[2] = 1.9, p = 0.38) or gain (H[2] = 5.59, p = 0.06). Finally, correlation analyses indicated no significant associations between fixation stability and spherical equivalent, axial length, or corneal power.

Myopes exhibited more unstable fixation, characterized by larger, faster, and more frequent fixational saccades. These findings suggest distinct oculomotor behavior in myopia, potentially reflecting altered spatiotemporal processing during visual development.