May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
Gender Differences in Cone Apex Location in Keratoconus
Author Affiliations & Notes
  • T.T. McMahon
    Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, IL
  • R.J. Anderson
    Biostatistics & Epidemiology, School of Public Health, University of Illinois at Chicago, Chicago, IL
  • L.B. Szczotka–Flynn
    Ophthalmology, University Hospitals, Case Western University, Cleveland, OH
  • D. Libassi
    SUNY College of Optometry, New York, NY
  • R. Gundel
    SUNY College of Optometry, New York, NY
  • C. Roberts
    Ophthalmology, The Ohio State University, Columbus, OH
  • A.M. Mahmoud
    Ophthalmology, The Ohio State University, Columbus, OH
  • CLEK Study Group
    Ophthalmology & Visual Sciences, University of Illinois at Chicago, Chicago, IL
  • Footnotes
    Commercial Relationships  T.T. McMahon, None; R.J. Anderson, None; L.B. Szczotka–Flynn, None; D. Libassi, None; R. Gundel, None; C. Roberts, None; A.M. Mahmoud, None.
  • Footnotes
    Support  NIH Grants EY12656, NEI Core Grant EY1792 (UIC), Research to Prevent Blindness, New York, NY
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 2894. doi:
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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)

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Abstract

Abstract: : 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.

Keywords: keratoconus • cornea: clinical science 
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