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Jason Marsack, Lingyan Anderson, Ayeswarya Ravikumar, Heather Anderson, Raymond Applegate; Optimizing spectacle correction for keratoconus patients with the visual quality metric VSX. Journal of Vision 2013;13(15):P26. doi: https://doi.org/10.1167/13.15.61.
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Background: Spectacles often have limited efficacy in keratoconus (KC) due to elevated higher-order aberrations (HOA). However, aberrations interact, providing an opportunity to use sphere and cylinder to optimize visual image quality and reduce deleterious effects of HOA.
Purpose: To objectively search for the sphero-cylindrical condition that maximizes visual image quality in the presence of uncorrected HOA in KC.
Methods: Uncorrected 5mm wavefront error through the 8th order was obtained for right eyes of 56 KC subjects. For each subject, 8177 unique sphero-cylindrical conditions were produced near the correction defined by the low order Zernike terms (range ±2.00D of sphere and 2D of cylinder). Resulting Zernike descriptions were used to find the maximal value of the visual image quality metric VSX (which ranges from 0 to 1, with 1 being best).
Results: Twenty-two eyes achieved a maximal VSX value within the range of sphero-cylindrical conditions studied, indicating a larger search range is required. For the 22 eyes, the median best VSX was 0.189 (1Q: 0.091; 3Q:0.227) compared to 0.041 (1Q: 0.015; 3Q:0.075) when low order Zernike's are set to 0.
Conclusions: Selecting proper sphero-cylinder corrections in the presence of higher-order aberrations optimizes visual image quality. Objectively defined sphero-cylindrical corrections allow evaluation of infinite conditions per eye, which is not feasible with subjective refraction. Future work will compare visual performance and optical quality of objectively and subjectively-defined corrections.
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