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T.T. McMahon, R.J. Anderson, L.B. Szczotka–Flynn, D. Libassi, R. Gundel, C. Roberts, A.M. Mahmoud, CLEK Study Group; Gender Differences in Cone Apex Location in Keratoconus . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2894.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Cone location has been previously described in a small number of keratoconus subjects. This report describes the location of the steepest region of the cornea in a large cohort of keratoconus subjects. Methods: 838 non–grafted, right eyes of CLEK Study subjects had two corneal topography images collected during year 5 of the study using Keratron Corneal Analyzers at 15 clinics (Optikon 2000, Rome, Italy). The two images were scrubbed to remove artifacts and graded for data quality (0–4 scale, 4 being best). Merged maps with quality scores grade 2 or better were analyzed reducing the sample size to 739. Using a new program, the Cone Location and Magnitude Index (CLMI), the steepest 1 mm zone of the cornea can be identified (based upon tangential curvature maps). The program identifies the steepest region that is 1mm in diameter and then references the average curvature of the steep region to the average curvature of the remaining area of the map. The search area currently is constrained to the central 6 mm of the map. We refer to this steep zone as the cone apex and CLMI can identify the distance from center (or the videokeratographic axis) and the meridian along which this area is located. Results: The mean increase in apex curvature compared to the remaining area was 7.95 D (range 0.08–38.79 D). The mean increase in apex steepening compared to the area outside the 1mm circles was 8.43 D for males and 7.36 D for females (p=0.005). The mean distance from center of the apex was 1.78mm (range 0.11–3.00mm). The mean distance of the apex from center by gender was 1.90mm and 1.63mm for males and females, respectively (p<0.0001). Cone apexes were grouped in 1mm annuli extending from center. Cone apexes located further than 1.9mm from center were more common in males (187/407, 46%) than females (97/332, 29%)(p<0.0001). The mean meridian of apex location was inferior temporal at 262 degrees. A majority of eyes (648, 87.7%) had cone locations inferior to the horizontal midline, and most commonly between the 240 and 270 degree meridians (right eyes only). Meridian location was similar for males and females. Conclusions:Keratoconus mostly results in inferior steepening as is classically described. Males were likely to have more decentered and steeper cone apexes. It should be noted that cone apex location can be along virtually any meridian.
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