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K Zadnik, JT Barr, TB Edrington, TT McMahon, MO GordonCLEK Study Group; Flat vs. Steep: the Effect of Rigid Contact Lens Fitting Method in Keratoconus . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3225.
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Purpose: The idea that steep-fitting rigid contact lenses cause less corneal scarring in keratoconus comes from a small clinical trial on seven patients. The 12-month incidence of corneal scarring in the seven eyes randomized to flat-fitting contact lenses was 57% compared to 0% in the eyes wearing steep-fitting contact lenses. The purpose of this analysis is to compare the safety and efficacy of flat- and steep-fitting contact lenses in the management of keratoconus. Methods: Cross-sectional results at baseline were generated for the 1,091 subjects enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study who had not undergone corneal transplantation before study enrollment. Results: At baseline, 78% of eyes (1696 of 2177 eyes) habitually wore contact lenses. Twenty-seven percent of these contact lens-wearing eyes were scarred compared to 9% of eyes not wearing contact lenses (univariate odds ratio (OR) = 3.62, 95% confidence interval (CI) 2.53 - 5.17). Corneal scarring was associated with an 8% increase for each additional hour of contact lens wear per day (univariate OR=1.08, 95% CI 1.04 - 1.11). Of the 1505 eyes wearing rigid contact lenses, 87% (1309) were wearing flat-fitting lenses, while 13% (196) were wearing steep-fitting lenses. Further, among the rigid contact lens-wearing eyes, 31% (402/1309) of the eyes wearing flat-fitting contact lenses were scarred compared to 9% (18/196) of the eyes wearing steep-fitting rigid contact lenses (univariate OR=4.4; 95% CI = 2.7 - 7.2). Controlling for disease severity (corneal curvature as assessed by the first definite apical clearance lens), we found that the association of rigid contact lens wear and corneal scarring at baseline persisted (contact lens wear: adjusted OR=3.5; 95% CI=2.3 - 5.5) and that steeper corneal curvature increased the risk of corneal scarring by 29% per D of increased curvature (adjusted OR=1.29; 95% CI=1.25 - 133). Conclusion: Rigid contact lens wear is associated with corneal scarring in keratoconus, even when adjusting for disease severity. Corneal scarring is significantly associated with both disease severity and with flat-fitting rigid contact lenses, but this association does not imply causation.
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