Abstract
Abstract: :
Background: Although an acuity chart may be readable after refractive surgery, the individual may not be happy with the visual quality. Purpose: To determine the level of aberration at which the normal individual feels the quality of vision is unacceptable. Method: 3 healthy volunteers with 20/16 or better acuity served as subjects. CTViewTM (Sarver and Associates, Inc.) was used to generate high-resolution simulated retinal images of aberrated high contrast log MAR charts having RMS error levels (0.0, 0.05, 0.10, 0.15, 0.20, and 0.25µ over a 6mm pupil) for each Zernike coefficients 3 - 14. Equivalent defocus ranged from 0.00 to 0.19 diopters. Subjects were dilated with 1% tropicamide. The foveal achromatic axis of the eye was aligned to a 3 mm pupil using an achromatic alignicator and a bite bar mounted to a 3 dimensional translator. Then the eye was optimally refracted for the 10' test distance (i.e., eyes are close to, if not, diffraction limited when optimally corrected and viewing through a 3 mm pupil diameter). Subjects were asked to rank the charts using a 10 point Likert scale to the first decimal place with 10.0 excellent, 7.5 good, 5.0 acceptable, 2.5 bad, and 0.0 unacceptable. A 0-aberration chart was used for refraction, and as a reference. Subjects were told to consider the 0-aberration chart a 10.0, the best their vision could be. There were three counter balanced trials for each set, with six sets. Between each set the "10.0" reference chart was shown again. Results: Subjects consistently ranked the charts with 0.25µ RMS error as unacceptable. 0.20µ ranked below 2.5 (below bad). Friedman's chi square test for level of aberration found a significant difference between levels, p < .0001. Nemenyi's post hoc test found that 0.25µ of aberration was significantly worse than 0.10, 0.05, and 0.0µ. 0.20µ was significantly worse than 0.10, 0.05, and 0.0µ. 0.15µ was significantly worse than 0.05 and 0.0µ. 0.05µ was no different than 0.0µ. Conclusion: This data suggest that refractive surgery should not induce more than 0.10µ of RMS error regardless of how readable the letters.
Keywords: 550 refractive surgery: optical quality • 500 optical properties • 620 visual acuity