Statistical method may help detect corneas at risk for iatrogenic ectasia

PARIS — A new statistical method may be a valid tool for detecting corneas at risk of developing iatrogenic ectasia.

"Beware of false negatives, particularly in patients who have manifest keratoconus in the contralateral eye," Alain Saad, MD, of Fondation Rothschild, said at the meeting of the French Society of Ophthalmology.

Single topographic indices are often insufficient for classifying a patient and drawing reliable diagnostic conclusions.

"We need a statistical method with a discriminating power that might be useful in clinical situations," he said.

The new method that Dr. Saad proposed uses the Orbscan IIz (Bausch + Lomb) to obtain topographic and tomographic indices, a corneal thickness spatial profile, and anterior and posterior curvature spatial profiles. A specific calculation method is then used to determine the percentage of increase in thickness from the thinnest point to the periphery of the cornea. It also measures the percentage of variation in anterior and posterior curvature.

"In a large retrospective study, we were able to prove the validity of our method. Two indices in particular, the percentage of thickness increase and the variation of anterior and posterior curvature, had a high power to discriminate between normal corneas and corneas at risk of developing ectasia following refractive surgery," Dr. Saad said.

* Disclosure: Dr. Saad has no direct financial interest in the products discussed in this article, nor is he a paid consultant for any companies mentioned.