Oxyopia Abstract

March 12, 2004
Friday, 4 PM
489 Minor Hall

Jaime McLellan, PhD
Schepens Eye Research Institute and Harvard Medical School, Boston
Host: Stan Klein

Title

"Wave Aberrations: Planned Imperfection?"

Abstract

The optics of the eye are subject to both chromatic and monochromatic aberrations, but the interactions between these aberrations have received little quantitative scrutiny. Conventional wisdom has long held that chromatic aberration so blurs the retinal image of short-wavelength light that it can contribute little to spatial vision, and this assumption has been used to explain both the presence of macular pigment and the sparse mosaic of S-cones in the retina. While this could be true if the eye were free of monochromatic aberrations, our work shows that when the effects of all the eye’s aberrations are taken into account, retinal image quality, as measured by the modulation transfer function (MTF), is roughly constant across the visible spectrum. Wave aberrations were measured at multiple wavelengths using a psychophysical technique. When the eye is optimally focused for mid-spectral wavelengths, monochromatic aberrations degrade the MTFs at these wavelengths, but actually improve the MTFs for the spectral extremes, thereby decreasing the variability in image quality with wavelength that would be expected from chromatic aberration alone.

These results suggest that there may be visual benefits to having “imperfect” optics, and have led us to consider whether aberration development may be “guided” in some way. We have explored this possibility with Monte Carlo simulations to determine whether the eye’s wave aberrations are random. MTFs for an eye’s measured aberrations were compared to a distribution of MTFs for aberrations of equal RMS error but randomized signs. Results for a large group of subjects show that the eye’s optical quality is better than would be expected if the aberrations were random. Furthermore, while this is true for the eye’s total aberrations, it is not true for corneal aberrations alone, suggesting the possibility of an active developmental process. These results could have relevance to the continued development of corneal refractive surgery techniques, and they raise questions about what visual mechanisms could guide aberration development.