Extent of foveal fixation with eye rotation in emmetropes and myopes

Purpose: This pilot study aimed to investigate the maximum extension of foveal fixation in the horizontal direction among young adults in both emmetropes and myopes. Methods: 35 participants (28 emmetropes and 7 myopes) were included. Participants with restricted extra-ocular mobility, end gaze nystagmus, and/or any other ocular pathology were excluded. Visual acuity (VA) was used as a surrogate measure of foveal fixation. VA was determined using a staircase procedure with 8 reversals. The average of the last 5 reversals was taken as the thresholds. VA acuity was measured at different gaze eccentricities along nasal and temporal visual field meridian. The eccentricity at which VA drops significantly was taken as the maximum extent of foveal fixation. A bilinear fit regression model was used to investigate the drop in the VA in both nasal and the temporal direction. Results: Emmetropes can foveate up to 35 +/- 2 degrees in nasal and 40 +/- 3 degrees in temporal direction and myopes can foveate up to 38 degrees in both nasal and temporal directions. Paired student t-test showed a significant difference in foveal fixation between nasal and temporal direction for emmetropes (P<0.001) but not in myopes (P = 0.168). An unpaired student t-test showed a significant difference in foveal fixation for nasal direction between myopes and emmetropes (P = 0.01). However, no statistically significant difference was found in foveal fixation for temporal direction between myopes and emmetropes (P = 0.792). Conclusion: The eye rotation does not necessarily match with the extent of foveal fixation at extreme eye rotation. Eyes can fixate only up to 35 degrees nasally and 40 degrees temporally maintaing their maximum visual acuity. (C) 2021 Spanish General Council of Optometry. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).