Ocular Rotation, Foveal Fixation Not Always Correlated

The degree of ocular rotation does not always correlate with the extent of foveal fixation at extreme eye rotation, according to a study published in the Journal of Optometry.

Researchers enrolled 35 right eyes of 35 emmetropic and myopic participants in the study (n=28, 13 women, mean age 23.6±2.3 years and n=7, 4 women, mean age 24±2.2 years, respectively). They seated participants 1 meter from a computer monitor and confined head movement with a chin rest and head strap. Patients fixated on a series of targets as the investigators measured visual acuity (VA) at different eccentricities by moving the monitor in a horizontal arc. 

The VA at fovea was 0.0±0.03 logMAR for the emmetropic group and 0.03±0.02 logMAR for the myopic group at primary gaze. It remained consistent for all eccentricities in the emmetropic cohort until reaching 34.8°±2.0° nasally and 39.7°±2.7° temporally. Researchers observed a pattern in the myopic group in which VA began to change at 37.6°±2.0° along the nasal orientation and 37.8°±3.6° along the temporal direction.

These patterns indicated a significant difference in foveal fixation between nasal and temporal directions for the emmetropic (P <.001), but not the myopic (P =.168) group. Researchers found that participants in the myopia group foveated to a greater extent during nasal viewing (P =.01), but did not significantly differ in the temporal direction compared with the emmetropic group (P =.792).

Investigators believe their findings could possibly “help in customizing the ophthalmic instruments by fixing the endpoint of fixation and making it less cumbersome for the participant to not forcefully fixate the object in extreme gazes.” 

“In studies investigating peripheral visual acuity, peripheral refraction, or peripheral eye lengths participants were given a target at different eccentricities to fixate by eye rotation. It can now be noted that such measurements may not be accurate beyond +/- 35°,” researchers report.

This study was limited by failure to assess axial length and angle kappa, and the omission of older adults from the study.

Reference

Abdullah H, Verkicharla PK, Ganeshrao SB. Extent of foveal fixation with eye rotation in emmetropes and myopes. J Optom. Published online December 21, 2021. doi:10.1016/j.optom.2021.12.001