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Yue Shi, Raymond Applegate, Ayeswarya Ravikumar, Harold Bedell; Optical quality metrics predictive of visual acuity for the design of wavefront guided corrections in the presence of dynamic registration uncertainty. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1279.
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When building a wavefront guided contact lens correction for highly aberrated eyes we would like to achieve the best visual acuity given dynamic registration uncertainty. To optimize the design of such a lens correction, it is useful to have optical quality metrics that are highly correlated with and predictive of visual acuity. The purpose here is to find optical quality metrics that are highly correlated with and predictive of acuity given the unusual aberration structures generated by misalignment of wavefront guided corrections.
Residual aberrations were generated by allowing 4 correction designs (3 wavefront guided and 1 sphero-cylinder for each eye) to undergo horizontal, vertical and rotary motion with respect to 3 keratoconic eyes (KC) for 2 pupil sizes (4 and 5mm). Then 77 aberrations were selected based on their log visual Strehl with the expectation that they would induce up to at least 5 lines loss of acuity [JOV, 12:1-13, 2012]. The point spread functions of the selected aberrations were convolved with unaberrated logMAR acuity charts to generate blurred charts, which were presented monocularly to 3 normal chart-readers with 20/15 best corrected acuity. For each chart, visual acuity was measured up to 5th letter missed through a 3 mm pupil placed conjugate and centered with the chart-reader’s dilated pupil. The measured change of acuity with respect to the unaberrated chart was regressed against the changes of acuity predicted by 29 optical quality metrics [JOV, 12:1-13, 2012].
Regression analysis revealed that only 3 of the 29 metrics (Fig.1) predicted change of measured logMAR acuity with a coefficient of determination (R2) of at least 0.9: logNS (R2=0.96), logVSX (R2 =0.96), and logVSMTF (R2=0.90). The slopes of predicted vs. measured change of acuity did not differ significantly from 1 (α=0.05) for 2 of the 3 metrics: logNS (p=0.28, Fig.2) and logVSX (p=0.13, Fig.3).
One can confidently use logNS or logVSX to design wavefront guided corrections that minimize the impact of registration uncertainty on visual acuity.
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