WHERE IS THE FAR-POINT IN ABERRATED EYES?

Title WHERE IS THE FAR-POINT IN ABERRATED EYES?
Author, Co-Author Larry Thibos, Arthur Bradley, Raymond Applegate
Topic
Year
2002
Day
Friday
Program Number
Room
Room 1 SP
Affiliation
Abstract PURPOSE: We sought a method for deducing the far-point of an aberrated eye from an aberration map. Such a method must be found to successfully implement wavefront-guided treatments.

METHODS: Accommodation was paralyzed and pupils dilated in both eyes of 100 subjects. Subjective refractions determined the spectacle correction needed to maximize visual acuity for high-contrast letters. Indicated sphero-cylindrical refractive errors were corrected with trial lenses when measuring monochromatic aberrations (633nm) with a Shack-Hartmann aberrometer. The resulting aberration maps were fit with spherical wavefronts four ways to yield four different estimates (i.e. centers of wavefront curvature) of the far point for each eye. Method 1 minimized the RMS error between the given wavefront and the spherical wave over the full pupil. Method 2 determined the spherical wavefront which had the same paraxial curvature as the meridionally-averaged curvature of the given aberration map. Method 3 maximized the pupil area over which RMS wavefront error was less than a criterion level of 1/4 wavelength. Method 4 maximized the pupil area over which the absolute wavefront error was less than 1/4 wavelength.

RESULTS: A successful method will yield a far point at infinity since all eyes were emmetropic when tested. Method 1 was a clear failure, predicting a mean far point vergence of -0.26D for the study population. The other three methods all yielded far points which, on average, had vergence close to 0D (Method 2: mean=0.023 , std=0.296. Method 3: mean=0.05 , std=0.33. Method 4: mean=0.004 , std=0.55). Methods 2 and 3 produced standard deviations close to the expected minimum (0.25D) set by variability in subjective refraction.

CONCLUSIONS: Three successful methods for using an aberration map to locate the far point of the eye have been found. One unsuccessful method is equivalent to assigning the far point based solely on the Zernike coefficient for defocus.

ADDITIONAL COMMENTS: NEI Grant R01-EY05109
Affiliation of Co-Authors University of Houston, College of Optometry
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