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J. Marsack, A. Roorda, W.L. Miller, J.A. Jackson, N.E. Leach, R.A. Applegate; Development of a Shack - Hartmann Wavefront Sensor for a Study of Keratoconus . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4084.
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Purpose: The purpose of this study was to extend the operating range of a Shack-Hartmann wavefront sensor (SHWS) in order to quantify higher order aberrations in keratoconus (KC) subjects enrolled in a rigid gas permeable (GP) contact lens study at the University of Houston, College of Optometry (UHCO). Methods: Subjects' corneal aberrations were subjectively graded by clinical experts on a scale of 1-10, where 1 was the most mild and 10 was the most severe case of overall corneal anomaly. The grade was based on three criteria: best corrected visual acuity, pachymetry and corneal topography. Subjects were enrolled in the study if the magnitude of their wavefront aberration excluded them from measure by the current UHCO SHWS which was designed with a lenslet array spacing of 400µm, 24 mm focal length and 100% fill factor. The main operating constraint that was identified as excluding a subject from successful measurement was overlap of spots on the imaging device. A modified lenslet array spacing of 300µm, focal length of 7.6mm and 100% fill factor were chosen by computing simulated spot patterns from wavefront error based on corneal topography of a KC subject with a subjective score of 9. Results: Previous UHCO SHWS designs were incapable of completely measuring this set of subjects. The first six orders of wavefront aberrations for five eyes with varying subjective scores were recorded. Clinical subjective scores of 2, 4, 5, 6 and 9 corresponded to higher order wavefront RMS values (3rd to 6th order modes) calculated for a 3mm pupil of 0.49, 0.47, 0.55, 0.91, 0.69µm respectively. Conclusions: Improvements in wavefront sensor instrumentation increases the number of subjects with large amounts of keratoconic-induced wavefront aberrations that can be quantitatively classified.
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