Purpose. To examine the relationship between uncorrected residual wavefront error and visual performance (VP) in rigid gas permeable (RGP) contact lens-wearing keratoconic eyes.

Methods. Seven eyes from six subjects (six moderate, one severe) were studied (mean ± SD age: 42.71 ± 11.38 years). Significant corneal scarring was an exclusion criterion. Measurements were taken with RGP lenses in place. After pupil dilation, the VP measures of high contrast logMAR visual acuity (VA) and Pelli-Robson contrast sensitivity (PRCS) were measured through a 5-mm artificial pupil. Wavefront error was measured using a Shack–Hartmann wavefront sensor and calculated over 5 mm. For both VP and wavefront error, comparisons were made to previously collected normal values by calculating the interval encompassing 95% of normals, then reporting how many of the seven keratoconic eyes fell outside the normal interval. Additionally, second to sixth order aberrations were processed into four previously reported image quality metrics: root mean square of the wavefront (RMSw), root mean square of the slope (RMSs), average blur strength (Bave) and diameter containing 50% light energy (D50) and regressed against VP measures.

Results. Five of seven keratoconic eyes fell outside the normal interval (–0.23 to 0.09) for VA and two of seven fell outside the normal interval (1.59 to 2.03) for PRCS. Five of seven keratoconic eyes fell outside the normal interval (0.07 to 0.35 _m) for total higher order RMS. Linear regressions demonstrated relationships between both VA and PRCS and the image quality metrics RMSw, D50, RMSs, and Bave with R2 values for VA = 0.30, 0.30, 0.47, 0.62, and PRCS = 0.21, 0.15, 0.45, 0.75 respectively.

K1 and K2 from figure 1. Uncorrected ocular aberrations maps for two of the seven keratoconic eyes wearing RGP lenses. These maps are composed of the 2nd to 6th Zernike order aberration terms over a 5 mm pupil. Rotational asymmetry in the maps is a result of both high ord.

Conclusions. VP in RGP-wearing keratoconic eyes is reduced and higher order wavefront aberrations are elevated compared to normals. Metrics of retinal image quality demonstrate a relationship between keratoconic VP and residual wavefront aberrations. This relationship suggests developing corrections that more completely correct aberrations may improve visual performance in keratoconus.

Key Words: aberration, keratoconus, optical quality metrics, visual performance, Zernike polynomial

Optometry and Vision Science, Vol. 84, No. 6, June 2007; 463–470
Received May 20, 2006; accepted October 12, 2006.

Jason D. Marsack, MS, Katrina E. Parker, OD, FAAO, Konrad Pesudovs, PhD, FAAO, William J. Donnelly III, PhD, and Raymond A. Applegate, OD, PhD, FAAO

(JDM, KEP, WJD, RAA): Visual Optics Institute, College of Optometry, University of Houston, Houston, Texas, USA.
(KP): NH&MRC Centre for Clinical Eye Research, Department of Ophthalmology, Flinders Medical Centre, Flinders University, Bedford Park, South Australia,, Australia.

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