Abstract
Purpose :
Research in myopia and emmetropization traditionally focuses on the spatial characteristics of visual stimulation. However, the visual input to the retina is never stationary, as eye movement occur continually, even when attending to a single point, and retinal neurons are highly sensitive to input temporal changes. Previous research with emmetropes has shown that the spatiotemporal modulations from fixational eye movements facilitate neural encoding and enhance sensitivity to high spatial frequencies. Here we examine whether this oculomotor-induced space-time conversion of visual input signals is altered in myopia.
Methods :
We examined the eye movements of 26 observers, ranging in spherical refractive errors from +0.25D to -6.5D (measured with a Reichert Potec PRK-7000). Subjects engaged in two high-acuity tasks: discriminating the 20/20 line of a tumbling E eye chart and reporting the gaze direction (directed or not toward the observer) of a small (1 deg) image of a face. Axial length was measured with a Zeiss IOL Master. All subjects were corrected to the 20/20 line or better on the Snellen eye chart using a Badal lens apparatus. Eye movements were continually tracked at high resolution via digital Dual-Purkinje imaging.
Results :
Our data indicate that fixational drift, the smooth inter-saccadic eye motion, undergoes systematic changes in myopia. Notably, drift is faster (p = 0.014) and less curved (p = 0.006) in subjects with longer eyes. The angular speed of eye drift and curvature changed at similar rate, approximately 8% per millimeter of elongation in axial length. These oculomotor changes have important repercussions on how fixational drift converts spatial patterns into luminance modulations: as the eye length increases, drift enhances progressively lower spatial frequencies in the retinal input at the expenses of high spatial frequencies.
Conclusions :
By selecting the range of spatial frequencies enhanced by luminance modulations, eye movements enable spatial filtering in the temporal domain. Our results show that this process is altered in myopia in a way that attenuates luminance modulations at high-spatial frequencies. As high-frequency attenuation is known to induce eye elongation in animal models, our finding not only demonstrates a visual consequence of myopia, but also raises the possibility that oculomotor factors contribute to its causation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.