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Proceedings Paper

Corneal epithelium, visual acuity, and laser refractive keratectomy
Author(s): Gabriel Simon; Jean-Marie A. Parel; Gerard N. Kervick; Pascal O. Rol; Khalil Hanna; Keith P. Thompson
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Paper Abstract

Photorefractive keratectomy (PRK) using an argon fluoride excimer laser for photoablation of the cornea shows potential for the precise correction of refractive errors in patients. Usually, the epithelium is mechanically removed, and Bowman's layer and stromal tissue are photoablated to precomputed depths and shapes that are based on known ablation rates for these tissues. After four day's time, the epithelium has regrown. Assuming the epithelium to be preoperatively uniform in thickness across the central optical zone, and assuming that it regrows to the same thickness, a theoretical precision of +/- 0.05 diopters is achievable with PRK. Keratometric measurements of the epithelium and of Bowman's layer were made at the 2.0 and 3.6 mm optical zones on 10 fresh cadaver eyes (<21 hours postmortem). In the eyes studied, the epithelium thickness was found to vary across the central optical zone, accounting for the measured refractive differences of 0.5 to 1.8 diopters. Bowman's layer was found to be more prolated than the epithelial surface (ratios: 1.005 compared to 1.033). In addition, the surface of Bowman's layer had a larger degree of astigmatism. Other studies have shown that the epithelium regrowth is a function of the newly exposed corneal topography as the wing cells compensate for irregularities in Bowman's surface. As the preoperative topography of the epithelium cannot be used as a reference surface when computing photoablation depth, intraoperative keratometry of Bowman's surface becomes a necessity in PRK.

Paper Details

Date Published: 1 June 1991
PDF: 3 pages
Proc. SPIE 1423, Ophthalmic Technologies, (1 June 1991); doi: 10.1117/12.43974
Show Author Affiliations
Gabriel Simon, Bascom Palmer Eye Institute/Univ. of Miami (France)
Jean-Marie A. Parel, Bascom Palmer Eye Institute/Univ. of Miami (United States)
Gerard N. Kervick, Bascom Palmer Eye Institute/Univ. of Miami (United States)
Pascal O. Rol, Swiss Federal Institute of Technology and Univ. of Zuerich (Switzerland)
Khalil Hanna, Univ. of Paris Hotel-Dieu (United States)
Keith P. Thompson, Emory Univ. (United States)

Published in SPIE Proceedings Vol. 1423:
Ophthalmic Technologies
Carmen A. Puliafito, Editor(s)

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