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Larry N. Thibos, Arthur Bradley, Raymond A. Applegate; Where is the far-point in aberrated eyes?. Journal of Vision 2002;2(10):41. doi: 10.1167/2.10.41.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: We sought a method for deducing the far-point of an aberrated eye from an aberration map. Such a method is necessary for successful implementation of wavefront-guided treatments. Method. Accommodation was paralyzed and pupils dilated in both e yes of 100 subjects. Subjective refractions determined the spectacle correction needed to maximize visual acuity for high-contrast letters. Sphero-cylindrical refractive errors were corrected with trial lenses when measuring monochromatic abe r rations (633nm) with a Shack-Hartmann aberrometer. Resulting aberration maps were fit with spherical wavefronts four ways to yield four different estimates of the far point for each eye. Method 1 minimized the RMS error b etween the given wavefro nt and the s pherical 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 wavefron t 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 sinc e all eyes were emmetro pic when t ested. 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=0.0 23 , std=0.296. Metho d 3: mean =0.05 , std=0.33. Method 4: mean=0.004 , std=0.55). Methods 2 and 3 yield standard deviations close to the expected minimum (0.25D) set by the variability of subjective refraction. Conclusion: Three successful methods for u sing an aberration map to locate the far point of the eye have been found. One unsuccessful method is equivalent to the Zernike coefficient for defocus.
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