May 2004
Volume 45, Issue 13
Free
ARVO Annual Meeting Abstract  |   May 2004
Astigmatism redefined as a form of ectasia based on corneal Orbscan studies
Author Affiliations & Notes
  • O. Fass
    Cornea, University of California San Diego, La Jolla, CA
  • T. Pham
    Cornea, University of California San Diego, La Jolla, CA
  • D.J. Schanzlin
    Cornea, University of California San Diego, La Jolla, CA
  • C. Heichel
    Cornea, University of California San Diego, La Jolla, CA
  • R. Angeles
    Cornea, University of California San Diego, La Jolla, CA
  • Footnotes
    Commercial Relationships  O. Fass, None; T. Pham, None; D.J. Schanzlin, None; C. Heichel, None; R. Angeles, None.
  • Footnotes
    Support  none
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 2877. doi:
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      O. Fass, T. Pham, D.J. Schanzlin, C. Heichel, R. Angeles; Astigmatism redefined as a form of ectasia based on corneal Orbscan studies . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2877.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Abstract: : Purpose:It is known that areas of the cornea that are thinned can result in a change of shape of the cornea called an ectasia. The purpose of this experiment is to measure the thickness of a normal cornea along the meridians of astigmatism showing that the flatter axis is thinner and hence bulges outward. This would redefine astigmatism as a primary form of ectasia. Methods:Fifty eyes were selected at random on the orbscan data bank with greater than 2.5 diopters of astigmatism. The flattest and steepest meridians of astigmatism were identified and the thickness recorded at intervals of 1,2,2.5,3, and 4 mm from the central cornea in both directions. The data was averaged and the steep meridian compared to the flat in terms of thickness. Results:At 4mm and 1mm from the central cornea in either direction there was no significant difference between the thickness of the flat and steep meridians. At 3mm the flatter cornea was thinner by an average of 19.3 microns with a p value of .000766. At 2.5mm the flatter meridian was thinner by 16.6 microns p=.002173. At –2mm the flat axis was thinner by 9.4 microns p=.035245. And at –2.5mm the flat axis was thinner by 10.36 microns p=.035421. Conclusions: This preliminary study shows that in astigmatism over 2.5 diopters the flatter axis is thinner in the paracentral cornea suggesting an ectasia like component to common astigmatism.

Keywords: astigmatism • cornea: basic science • anterior segment 
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