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Proceedings Paper

Computed estimation of visual acuity after laser refractive keratectomy
Author(s): Pascal O. Rol; Jean-Marie A. Parel; Khalil Hanna M.D.
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Paper Abstract

A number of surgical techniques has been developed to correct ametropia (refractive defaults) of the eye by changing the anterior corneal radius. Because the air-cornea interface makes up for about two-third of the refractive power of the eye, a refractive correction is obtained by a suitable photoablation of the cornea. For this purpose, e.g., an ArF excimer laser which emits a wavelength of 193 nm is being used. After a mechanical removal of the epithelium, the Bowman's layer and the corneal stroma are photoablated on typically 50% of the central surface of the cornea with various precomputed shapes. Methods using a variable diaphragm1 or a scanning slit2 are being utilized. After regrowth of the epithelium, a smooth interface with air develops itself, which can be attributed to a mechanical equilibration. Yet, SEM studies have shown that with such kind of treatments, irregularities can remain in the new stromal surface (Fig. 1). A possible explanation for this effect is associated with an inhomogeneous energy distribution of the laser beam profile3. To some extent, the stromal surface is equalized by the epithelial layer during healing& However, as the corneal epithelium and stroma have different refractive indices, a scatter of the incident light may result causing a haze in the cornea and a blur of the image at the retina. In such a case the resolution and the contrast performance of the eye which is expected from a successful operation, may be reduced. This study is an attempt to quantify the vision blur as a function of the deformation observed at the epithelium-stroma interface.

Paper Details

Date Published: 1 June 1991
PDF: 5 pages
Proc. SPIE 1423, Ophthalmic Technologies, (1 June 1991); doi: 10.1117/12.43966
Show Author Affiliations
Pascal O. Rol, Swiss Federal Institute of Technology and Univ. of Zuerich (Switzerland)
Jean-Marie A. Parel, Bascom Palmer Eye Institute/Univ. of Miami (United States)
Khalil Hanna M.D., Emory Univ. (USA) and Univ. of Paris Hotel-Dieu (France) (United States)

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

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