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J.D. Marsack, R.A. Applegate, K. Pesudovs; Retinal Image Quality Metrics Predict Visual Performance in Keratoconus Subjects Wearing RGP Lenses . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1506.
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© ARVO (1962-2015); The Authors (2016-present)
To examine the relationship between uncorrected ocular aberration and visual performance in keratoconus subjects wearing rigid gas permeable (RGP) contact lenses (CL).
Seven keratoconus subjects were recruited (avg: 42.71±11.38 yrs, range: 27 to 55 yrs). Central corneal scarring was an exclusion criterion. After pupil dilation, the visual performance (VP) measures logMAR visual acuity (VA), Pelli–Robson contrast sensitivity (PRCS) and the area under the letter contrast sensitivity function (LCSFa) were recorded through a 5mm artificial pupil while wearing their RGP correction. Wavefront error over a central 5mm pupil through 6th radial order was processed into four previously reported single value retinal image quality metrics: root mean square wavefront error (RMS); light in the bucket (LIB); average blur strength (Bave); and neural sharpness (NS). The three measures of visual performance were linearly regressed against each retinal image quality metric. Normative high order aberration data through 6th order was obtained from a previously recorded data set of 146 normal subjects. Normative VA and PRCS values were obtained from the literature.
VA (avg: 0.15±0.11, range: 0.0 – 0.3) and PRCS (avg: 1.61±0.14, range: 1.80 to 1.35) for keratoconus subjects demonstrates an average decrease when compared to normal performance data (VA= –0.13±0.05 for 40–44 years, PRCS= 1.74±0.13 for 40–49 yrs). Average higher order RMS (avg: 0.58±0.36µm, range: 0.31µm to 1.24µm) for keratoconus subjects was elevated when compared to normal RMS measures (avg: 0.24±0.10µm, range: 0.07–0.54µm). Linear regressions demonstrated strong relationships between VP measures and Bave, NS and logarithm of LIB with R2 values for VA= 0.56, 0.54 and 0.66, PRCS = 0.60, 0.54 and 0.64, LCSFa= 0.66, 0.85 and 0.87, respectively. RMS showed a much weaker correlation to VP with R2 values of VA= 0.11, PRCS = 0.08 and LCSFa= 0.32.
RGP corrections in these 7 keratoconus subjects did not reduce wavefront error to normal levels. This was reflected in sub–normal visual performance and implies that better optical solutions for keratoconus subjects should be sought. The impact of the uncorrected wavefront error on visual performance is poorly explained by the commonly used metric RMS wavefront error; better image quality metrics exist. Metrics predictive of VP provide a useful tool to objectively assess the retinal image quality provided by an optical correction.
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