Optical and Visual Performance in Typically-sighted and Highly Aberrated Eyes

Purpose: This dissertation explores the manner in which typically-sighted individuals and individuals with keratoconus perform simulated, clinical and real-world visual tasks under varying levels uncorrected optical aberration. Methods: Study 1 tested the viability of a common (rather than an eye-specific) decentration rule for placement of wavefront-guided optics in a wavefront-guided scleral lens. Study 2 quantified threshold word acuity with and without accompanying flanking words at high (100%) and low (25%) contrast over 5 stimulus durations for habitually corrected individuals with keratoconus and typically-sighted individuals. Study 3 quantified the limits of agreement and intra-visit repeatability of the CamBlobs2 contrast sensitivity test and compared the results to the near Pelli-Robson contrast sensitivity test in individuals with keratoconus and typically-sighted individuals. Results: Study 1 demonstrated that decentering the wavefront-guided correction from the subject-specific location was predicted to lead to an appreciable increase in residual aberration and reduction in visual image quality. Study 2 demonstrated that there was a trend toward elevated threshold word acuity, when compared to visual acuity (which was more pronounced with near low contrast words). Study 3 demonstrated that in typically-sighted individuals, repeatability of both tests was within ± 0.20 logCS and the limit of agreement between near Pelli-Robson and CamBlobs2 scores was -0.08 ± 0.08 for right eyes and -0.05 ± 0.10 logCS for left eyes. The repeatability worsened to ± 0.30 logCS and the limit of agreement between near Pelli-Robson and CamBlobs2 scores was -0.05 ± 0.14 for the keratoconus group. Conclusions: The wavefront-guided correction must be placed at an eye-specific location to avoid reduction in optical and visual performance predicted to be noticeable to an individual. Larger font sizes are required for word recognition (especially low contrast words) than would be expected from common measurement of high contrast distance visual acuity. Both contrast sensitivity tests were repeatable and with a 0.05 correction, the CamBlobs2 scores showed an excellent agreement with those of the near Pelli-Robson contrast sensitivity test.