Impact of monochromatic aberrations on visual function

Purpose. My PhD studies emphasize the characteristics of monochromatic aberrations in normal and abnormal human eyes, the clinical applications of wavefront aberrometry and the quantification of visual quality based on wavefront aberration measurements. Methods. Using the Shack-Hartmann aberrometer (SH), I measured monochromatic aberrations in normal human eyes with refractive error, keratoconic eyes with and without contact lens correction, and developing chick eyes. I validated the first clinical SH aberrometer using model and human eyes and examined the variation of aberration measurements. Using computer simulations, I evaluated the visual impact of aberrations and compared the visual quality measures to objective image quality metrics to identify those metrics that best predict subjective visual quality. Results. Higher order aberrations were uncorrelated with refractive errors. Highly myopic and hyperopic eyes could have as good optical quality as emmetropic eyes. Keratoconic eyes had significantly larger aberrations that limited their best-corrected vision. Current RGP contact lens correction significantly reduced aberrations in most keratoconic eyes, but was not sufficient to reduce them to normal levels. The chick eye's study indicated that higher order aberrations might not play an active role in normal emmetropization. Carefully controlled validation studies showed that a clinical aberrometer could measure higher order aberrations accurately, repeatedly, and with good tolerance to misalignment. Studies on repeated measures of human eye's higher order aberrations provided detailed descriptions of the magnitudes and sources of aberration variations, and their impact on image quality and aberration correction. Finally, using the carefully verified computational and psychophysical paradigm, I examined the impact of higher order aberrations on visual acuity and subjective judgement of best focus, and found neural-weighted image plane metrics were good predictors for vision. Conclusion. My studies help to further understand the optical characteristics of human eyes and provide useful information about validity of clinical aberrometry. The psychophysical studies emphasizing understanding the visual impact of aberrations and searching for optimized metrics image quality bring the aberration studies further from quantifying optical quality to visual quality, which have valuable clinical implications in achieving the ultimate goal of improving vision better than 20/20.