Adjunctive safety tool available for laser vision correction

April 15, 2010

Eyes categorized as having keratoconus based on corneal topography and subsequently determined to be non-keratoconic by epithelial thickness profile criteria demonstrate good refractive stability after LASIK during up to 2 years of follow-up.

London-Eyes categorized as having suspected keratoconus based on corneal topography and subsequently determined to be non-keratoconic by epithelial thickness profile criteria demonstrate good refractive stability after LASIK during up to 2 years of follow-up, said Dan Z. Reinstein, MD, MA(Cantab), FRCSC, FRCOphth.

The study group was composed of 90 eyes with suspected keratoconus confirmed as non-keratoconic by epithelial thickness profile mapping. Their results were compared with those from a control group consisting of eyes matched within 0.50 D for preoperative sphere, cylinder, and spherical equivalent (SE), as well as for age and IOP.

Comparison of the refractive stability of SE and cylinder showed no statistically significant differences between the suspected keratoconus cases and matched controls at any time point during 2 years of post-LASIK follow-up. Analysis of corrected distance visual acuity (CDVA) outcomes also showed no statistically significant differences between groups.

"A diagnostic technique is needed that can definitively establish or rule out a diagnosis of keratoconus in eyes with abnormal topography when assessing patient suitability for LASIK, and I believe that epithelial thickness profiles can help provide the answer," Prof. Reinstein said.

Epithelial thickness profiles

In previous research, Prof. Reinstein and colleagues demonstrated that the epithelium of the average normal human cornea was not uniform in thickness, but rather, the epithelium was on average thinner superiorly and thicker inferiorly.2

This contrasted with keratoconic eyes, in which the epithelial thickness map exhibited a donut pattern characterized by thinning at the apex of the cone surrounded by an annulus of thicker epithelium.3

Prof. Reinstein and colleagues hypothesize that front and back corneal surfaces are generally yoked, meaning that any back surface ectatic change will be accompanied by a front stromal surface ectatic change.

"Because the Artemis can measure changes of as little as 1 µm within the epithelial layer, the very earliest changes in the epithelial thickness profile in response to a front surface stromal cone can be detected," he said. "Therefore, a localized zone of epithelial thinning overlying a posterior corneal surface eccentric apex would indicate an associated anterior stromal cone.

"Effectively, the epithelial thickness profile adds extra information to what is provided by front and back surface topography, making the diagnosis or exclusion of keratoconus more specific," he added.