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J. Martin, L. N. Thibos, A. Bradley, B. Vasudevan, N. L. Himebaugh; Determination of the Optimum Weighting of Objective Refractions for Predicting Subjective Refraction. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3958.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of the study was to determine the optimum weighting of the 34 objective refractions for predicting acuity refraction.
This study was on 20 healthy subjects, cyclopleged with 1 drop of 1% cyclopentolate hydrochloride. In the psychophysical experiments the subject viewed a visual target through an afocal telescope that imaged an artificial pupil (6mm diameter) into the entrance pupil of the eye. Visual acuity was determined with a staircase paradigm for high (96%) contrast letters presented with quasi-monochromatic (635nm) light on a screen placed 2.5 meters from the artificial pupil of the telescope. Subjective refraction is the spherical lens power that maximized acuity. Ocular wavefront aberrations were measured, using a COAS aberrometer (Wavefront Sciences, Inc.) modified to use visible light (635nm). Objective wavefront refraction was performed computationally by determining the additional lens power required to maximize retinal image quality using 34 metrics (Thibos et al, JOV 2004).
Wavefront refractions agreed closely with acuity refractions obtained with 635nm light. A Partial least square (PLS) regression analysis was performed to reduce the number of objective predictors based on their ability to account for the variance in the subjective data. Taken together, the 34 metric-based refractions accounted for 99.26 % of variance in the data. The OTF metric (VNOTF) refraction accounted for about 97.9 of the variance in subjective refraction. Addition of a PSF-based metric-refraction (VSX) enabled the model to account for 98.74% of the variance. Adding a third metric refraction based on wavefront quality (PFWc) accounted for 98.9% of variance in subjective refraction. For this 3-component model, predicted refraction = 0.2094*(refraction based on VNOTF) + 0.1303*(refraction based on VSX) + 0.1167*(refraction based on PFWc).
Subjective refractive errors are accurately and precisely determined by wavefront-based objective refraction in monochromatic light.
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