A recent theory posits that ocular drifts of fixational eye movements serve to reformat the visual input of natural images, so that the power of the input image is equalized across a range of spatial frequencies. This “spectral whitening” effect is postulated to improve the processing of high-spatial-frequency information and requires normal fixational eye movements. Given that people with macular disease exhibit abnormal fixational eye movements, do they also exhibit spectral whitening? To answer this question, we computed the power spectral density of movies of natural images translated in space and time according to the fixational eye movements (thus simulating the retinal input) of a group of observers with long-standing bilateral macular disease. Just as for people with normal vision, the power of the retinal input at low spatial frequencies was lower than that based on the 1/f2 relationship, demonstrating spectral whitening. However, the amount of whitening was much less for observers with macular disease when compared with age-matched controls with normal vision. A mediation analysis showed that the eccentricity of the preferred retinal locus adopted by these observers and the characteristics of ocular drifts are important factors limiting the amount of whitening. Finally, we did not find a normal aging effect on spectral whitening. Although these findings alone cannot form a causal link between macular disease and spectral properties of eye movements, they suggest novel potential means of modifying the characteristics of fixational eye movements, which may in turn improve functional vision for people with macular disease.
Despite their abnormal characteristics, fixational eye movements exhibited by people with macular disease also demonstrate spectral whitening, although the magnitude of whitening is less (and is limited to lower spatial frequencies) than that observed in people with normal vision. The less-than-normal whitening should not be interpreted as indicating that the benefits of fixational eye movements, especially those due to ocular drifts, are smaller for people with macular disease. Rather, it just means that spectral whitening occurs for a range of spatial frequencies lower than that for normal vision, which is reasonable given that people with macular disease must rely on their peripheral retina for vision. Using a mediation analysis, we found that the eccentricity of the PRL adopted by these observers and the diffusion constant of ocular drifts are the important factors limiting the amount of whitening. These findings offer novel potential means of improving the characteristics of fixational eye movements, which may, in turn, improve functional vision for people with macular disease. Finally, we did not find a normal aging effect on spectral whitening.