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R.A. Applegate, K. Pesudovs, J.D. Marsack, W.J. Donnelly III; Optical quality metrics of backscatter, foward scatter and wave aberration account for over 50% of the variance in low luminance high contrast visual acuity in cataract patients with nuclear opalescence . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1747.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To investigate the ability of a combination of back scatter, forward scatter, and wave aberration metrics of optical quality to predict visual acuity in a population with varying degrees of cataract due to nuclear opalescence. Methods: We obtained Shack/Hartman (S/H) images from 149 patients (age 22 to 84 years) in the University of Houston's Visual Optics Institute Cross–Sectional Cataract Study. Optical quality metrics included grading of backward scatter using the Lens Opacities Classification System (LOCSIII): nuclear opalescence (NO) (range 0.8 to 5.6). Significant cortical and posterior sub–capsular cataract were excluded. 37 optical quality metrics were calculated from wavefront error. Scattering was quantified by 11 metrics characterizing light spread beyond the center of each S/H lenslet point spread function (PSF). Visual acuity (VA) was measured with high (HC) and low contrast (LC) letters at both high (HL) and low luminance (LL). The wavefront aberration, nuclear oplaescence and scatter metrics of optical quality along with age were tested for their ability to predict variance in each measure of visual acuity by stepwise multiple linear regression. Results: The strongest explanation of the variance occurred for high contrast VA at low luminance using three metrics: cataract severity (NO), a scatter metric (the lenslet image with the highest standard deviation in the tails of the PSF), and a wavefront metric (the ratio of the central circular area below a wavefront error of λ/4 to the total pupil area) r^=0.56). This pattern of nuclear opalescence, scatter and wavefront variables were similar for high luminance VA measures (HCHLVA r^2 = 0.39 and LCHLVA r^2 = 0.51) and did not require scatter for the LCLLVA (r^ = 0.45). Conclusions: Shack–Hartmann wavefront sensing provides a fast noninvasive method of quantifying aberration and scatter in a single test that when combined with clinical cataract grading accounts for a large percentage of the variance in VA.
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