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S.M. Mathews, J.C. Bradley, J.G. George, K.T. Xu; Predicting the Rigid Contact Lens Base Curve Using Corneal Topography in Keratoconus . Invest. Ophthalmol. Vis. Sci. 2005;46(13):860.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Rigid contact lenses often provide the best vision for keratoconic patients. Achieving a comfortable stable fit that also provides both good vision and maintains corneal health can be arduous. Previous studies have looked at pre–fit corneal topography to try to find indicators of the proper base curve. These prior studies involved few patients and were, therefore, of limited use as a fitting guide. We compiled topographical data from a much larger sample of keratoconic patients and compared this data to the patients’ best fit base curves to learn to better predict the base curve in keratoconus. Methods: A retrospective chart review was done on all keratoconic patients successfully fit with rigid corneal contact lenses at Texas Tech UHSC in the last 5 years. Pre–fit Keratron Scout or Tomey TMS–1 corneal topography data and best fit contact lens base curve were gathered on 200 keratoconic eyes. Topographic variables included: flat and steep simulated keratometry readings, flat and steep curvatures from the normalized scale, Maloney best fit sphere, irregularity index, and asymmetry index. Linear regression yielded a formula and R2 value that described the relationship between each topographical variable and the best fit base curve. Results: The best predictors of base curve were the Maloney best fit sphere and simulated keratometric readings from the Keratron Scout topographer. All linear regressions had non–unity slopes and non–zero Y–intercepts. R2 values were higher for the Keratron versus the Tomey topographer, for central versus peripheral apices, and for simulated keratometry readings versus curvatures from the normalized scale. Interestingly, the Tomey irregularity and asymmetry indices were better predictors than either the Tomey simulated keratometry readings or curvatures from the normalized scale. Conclusions: Practitioners equipped with the formulas from this study should be able to choose an initial trial lens base curve that will be closer to the best fit base curve. Choosing a better initial trial lens should reduce the number of trial lenses evaluated with fluorescein per eye and shorten the time needed to arrive at the final fit.
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