Retinal expansion during myopia progression affects changes in spherical equivalent (SE), axial astigmatism, and ocular misalignments, according to a study published in Vision Research. The effects of retinal expansion are stronger for larger eccentricity.
Researchers simulated retinal expansion by translating retinal points along the chief rays in the vitreous humor. The primary objective was to investigate the impact of retinal expansion on axial and peripheral aberrations while factoring in axial astigmatism and ocular misalignments. They constructed a realistic eye model with astigmatism, misalignments and other irregular features according to measurement data. The team performed 3-dimensional ray tracing on this model and its 2 symmetric versions to analyze the changes of axial and peripheral aberrations caused by retinal expansion.
The investigators found that spherical equivalent refraction changes the most during retinal expansion with a rate of −4 to −3 D/mm — approximately 10 times larger than the plus cylinder power. They also found that axial astigmatism determined the retinal effect on peripheral astigmatism, and observed unique patterns near the 2 peripheral field locations with 0 cylinder power. They note that ocular misalignments mainly affect higher-order aberrations, particularly third-order coma.
“For most optical features, the impacts of retinal expansion are stronger for larger eccentricity,” according to the researchers. “The impacts of retinal expansion on the lower- and higher-order aberrations have been systematically characterized for the two-dimensional visual field, showing unique patterns in the presence of astigmatism and ocular misalignments.”
This study is limited by the failure to provide a benchmark predicting the change of a standard eye during myopia progression.
Li Q, Fang F. Contribution of the retinal contour to the peripheral optics of human eye. Vision Res. Published online May 5, 2022. doi:10.1016/j.visres.2022.108055.