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S.M. Lee, S.D. McLeod, D.G. Hwang; Use of Elevation Topography in Rigid Gas Permeable Lens Fitting of Keratoconus . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1309.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the utility of scanning-slit elevation topography data for rigid gas permeable contact lens curvature selection in keratoconus. Methods: We obtained scanning-slit elevation data for 17 eyes of 12 patients with clincal keratoconus. We obtained the following values: average sim K, axial apical curvature, tangential apical curvature, and total mean curvature. We compared this data to the base curves of contact lenses fit using a minimal apical clearance philosophy. Results: Mean contact lens base curve for all patients was 48.71 +/- 3.84D. This value was significantly different (p<0.01) from axial apical (54.14 +/- 6.56D), tangential apical (58.37 +/- 7.17D), and mean power (52.68 +/- 6.49D) values. For mild cones (with sim K values <50D, n=9), the mean contact lens base curve was 46.27 +/- 2.21D. There was again a statistically significant difference (p<0.01) between this curvature and the three map-derived curvatures; axial (49.90 +/- 3.86D), tangential (54.04 +/- 3.70D), and mean curvature (49.02 +/- 2.34D). In the subgroup of moderate to advanced cones (any sim K value >50D, n=8), the mean base curve was 51.44 +/- 3.46D. There was some correlation with the mean curvature power (56.79 +/- 7.30, p=0.02), but no significant correlation with axial (58.91 +/- 5.66D) and tangential (62.84 +/- 7.67D) curvatures. Conclusions: Scanning-slit topography provides a representation of corneal surfaces independent of axial biases. Although mean curvature maps, based on scanning-slit data, resembled elevation float maps, the apex curvature derived from these displays were consistently steeper than acutal contact lens base curves. Therefore, scanning-slit topography does not appear to provide direct predictive value in base curve selection for keratoconus patients.
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