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Proceedings Paper

Wavefront coherence area for predicting visual acuity of post-PRK and post-PARK refractive surgery patients
Author(s): Daniel D. Garcia; Corina van de Pol; Brian A. Barsky; Stanley A. Klein
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Paper Abstract

Many current corneal topography instruments (called videokeratographs) provide an `acuity index' based on corneal smoothness to analyze expected visual acuity. However, post-refractive surgery patients often exhibit better acuity than is predicted by such indices. One reason for this is that visual acuity may not necessarily be determined by overall corneal smoothness but rather by having some part of the cornea able to focus light coherently onto the fovea. We present a new method of representing visual acuity by measuring the wavefront aberration, using principles from both ray and wave optics. For each point P on the cornea, we measure the size of the associated coherence area whose optical path length (OPL), from a reference plane to P's focus, is within a certain tolerance of the OPL for P. We measured the topographies and vision of 62 eyes of patients who had undergone the corneal refractive surgery procedures of photorefractive keratectomy (PRK) and photorefractive astigmatic keratectomy (PARK). In addition to high contrast visual acuity, our vision tests included low contrast and low luminance to test the contribution of the PRK transition zone. We found our metric for visual acuity to be better than all other metrics at predicting the acuity of low contrast and low luminance. However, high contrast visual acuity was poorly predicted by all of the indices we studied, including our own. The indices provided by current videokeratographs sometimes fail for corneas whose shape differs from simple ellipsoidal models. This is the case with post-PRK and post-PARK refractive surgery patients. Our alternative representation that displays the coherence area of the wavefront has considerable advantages, and promises to be a better predictor of low contrast and low luminance visual acuity than current shape measures.

Paper Details

Date Published: 18 June 1999
PDF: 8 pages
Proc. SPIE 3591, Ophthalmic Technologies IX, (18 June 1999); doi: 10.1117/12.350591
Show Author Affiliations
Daniel D. Garcia, Univ. of California/Berkeley (United States)
Corina van de Pol, U.S. Army Aeromedical Research Lab. (United States)
Brian A. Barsky, Univ. of California/Berkeley and Univ. of California/Berkeley School of Optometry (United States)
Stanley A. Klein, Univ. of California/Berkeley School of Optometry (United States)

Published in SPIE Proceedings Vol. 3591:
Ophthalmic Technologies IX
Bruce E. Stuck; Pascal O. Rol; Michael Belkin M.D.; Karen Margaret Joos M.D.; Fabrice Manns; Bruce E. Stuck; Michael Belkin M.D., Editor(s)

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