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Patients who have suspected keratoconus based on topography may be candidates for LASIK based on a study that showed refractive stability 1 year after LASIK in patients where keratoconus was excluded preoperatively using epithelial thickness mapping obtained with a VHF ultrasound eye scanner (Artemis 1, ArcScan).
Although refractive surgeons would not perform a procedure on a patient with keratoconus, refractive procedures have been performed on patients with topographically suspected keratoconus, with some surgeons offering surface ablation with special informed consent, as suggested in 2005 by the American Academy of Ophthalmology and International Society of Refractive Surgery Ectasia Committee.
"Once we excluded keratoconus," he said, "we performed refractive procedures to determine if the diagnosis by epithelial thickness mapping was correct. That is, we performed LASIK in cases in which we would not have performed it otherwise, protected by the fact that we have convinced ourselves that the patients do not have keratoconus based on the epithelial thickness profile."
Dr. Reinstein said that in eyes with confirmed keratoconus, the pattern of the epithelial thickness profile is different from that found in normal corneas. In a previous study of 110 normal eyes, he reported that the epithelial thickness was 53 µm centrally and that the superior epithelium was 6 µm thinner than the inferior epithelium.1
In a separate study of 40 keratoconic eyes, Dr. Reinstein reported an infero-temporal region of thin epithelium coincident with the cone on topography surrounded by a zone of epithelial thickening, with the thin and thick epithelium outside the range of epithelial thickness found in normal eyes.2
In early stages of keratoconus, there is forward bulging of the stroma and the back surface, Dr. Reinstein said. The epithelium is able to compensate for the sub-surface cone, topographically evident on the back surface, by thinning over the cone and thickening around the cone resulting in an apparently normal anterior surface, he added.
"There can be cases in which there is no change in the front surface of the cornea, but early keratoconic changes are occurring," Dr. Reinstein said.