Abstract
Purpose :
To better understand the relationship of fixational eye movements (FEM) between fellow eyes, we measured binocular FEM at different vergence demands in healthy subjects with a novel binocular scanning laser ophthalmoscope (bSLO).
Methods :
We designed and build a bSLO to record retinal images of both eyes of an observer with a single detector by splitting the imaging beam after scanning at a plane conjugate to the retina into two half-fields. Field size per eye was 3 x 3 degree of visual angle. Illumination wavelength was 788 nm (+-7nm) provided by a superluminescent diode. Spherical refractive errors were compensated by a Badal optometer, and controllable levels of binocular vergence (0-5 degree) were induced by a mirror on a motorized translatable rotational stage in front of each eye. Retinal motion was extracted by offline strip-wise image registration, providing motion traces at about 960 Hz. Torsional eye motion was estimated by analyzing the slope of sawtooth patterns in those traces at 30 Hz.
Results :
Spatial resolution of FEM estimation was tied to the digital sampling of the instrument and corresponded to about 2 arcsec for elevation, 4 arcsec for azimuth and about 1 arcmin for torsion. Monocular fixational stability as expressed as the bivariate contour elliptical area (BCEA) was generally high (71,70 ± 34,75 arcmin2) during attempted fixation. Binocular fixational stability expressed as difference of retinal motion between eyes was even higher (12,86 ± 7,89 arcmin2). Microsaccades occurred always simultaneously in both eyes with highly correlated amplitude and direction (R2Amp = 92,5%; R2α = 89,7%). Drift direction was often different in both eyes (R2α = 29,1%), while drift amplitude was comparable (R2Amp = 89,7%), reflecting micro-vergence movements. Ocular torsion was typically found with the onset of a microsaccade and varied about up to 60 arcmin within 10 seconds (SD= ± 5,41 arcmin). Torsional direction was typically counter-rotating between eyes (ØR2 = 68,6%), with a typical bias in one eye rotating up to ~15% more, reflecting cyclovergence. Increasing binocular vergence had an idiosyncratic impact on fixational stability.
Conclusions :
We measured binocular FEMs with high temporal and spatial resolution, and found that microsaccades, drift, and torsional motion were almost completely coordinated between the eyes during fixation. The neuronal control of binocular FEMs thus seems to resemble those of binocular eye movements in general.
This is a 2020 ARVO Annual Meeting abstract.