Abstract
Purpose :
Previous studies have established that fixational eye movements (FEMs), especially microsaccades and at least the vertical component of slow-drifts, are mostly conjugate in the two eyes. However, specifics of the properties of FEMs during binocular vs. monocular fixation are less well documented. The purpose of this study was to determine how the presence of visual input of a fixation target affects the properties of binocular fixation.
Methods :
We used a custom-built, high-resolution two-channel confocal scanning laser ophthalmoscope (bino-TSLO) in this study. The bino-TSLO allows us to deliver visual targets and to record movies of the retina of the two eyes simultaneously and independently. When aligned properly, subjects perceived a single 6°×6° red imaging field. Five adults with normal binocular vision were instructed to fixate at the center of a 1° cross presented at the primary gaze position while we captured videos of the retina of both eyes for trials of 10s each. Three conditions, each with multiple trials, were tested in random order: the cross was presented in both eyes (“both”) or in only one of the two eyes (“left” or “right”). Eye positions were extracted from the videos using a brute-force cross-correlation algorithm at a sampling rate of 540 Hz. Characteristics of FEMs, including (1) fixation stability, (2) rate, amplitude and direction of microsaccades; and (3) direction and amplitude of drifts, were determined for each trial and for each eye.
Results :
The two eyes demonstrated a high degree of conjugacy in terms of the occurrence, amplitude and direction of microsaccades, regardless of whether the fixation cross was presented in one or both eyes. Drift direction and amplitude were mostly similar between the two eyes only in the “both” condition; else, the eye that did not receive the cross demonstrated larger drift amplitudes with directions different from that of the fellow eye. Further, for the “left” or “right” conditions, fixation stability of the eye that received the cross was similar to that for the “both” condition; but fixation stability of the fellow eye worsened by ~1.6×.
Conclusions :
Despite the high degree of conjugacy of the two eyes during fixation, the lack of visual input to one eye affects the characteristics of drifts and stability in that eye, emphasizing the importance of the presence of visual input in fine oculomotor control.
This is a 2020 ARVO Annual Meeting abstract.