Device offers hope of identifying patients with risk of ectasia before LASIK

Instrumentation (Ocular Response Analyzer [ORA], Reichert Inc.) may provide clinical measures of corneal viscoelasticity (corneal hysteresis) and rigidity (corneal resistance factor). The device provides clinical information on the dynamic biomechanical properties of the cornea and may be able to identify eyes at risk of developing ectasia, said Mitsugu Shimmyo, MD, Department of Ophthalmology, New York Medical College, New York.

"The goal of our research is to determine if we can predict which patients will develop ectasia using different means other than the size and shape of the cornea," Dr. Shimmyo said. "The viscoelasticity of the cornea is another important feature that we studied."

Dr. Shimmyo and colleagues used the measurements to predict the development of ectasia before LASIK. Corneal hysteresis and corneal resistance factors in normal eyes were measured before and after LASIK and in eyes with keratoconus.

In normal eyes the corneal hysteresis value and the corneal resistance factor value were 10.28 and 10.76 mm Hg, respectively, he said. In keratoconic eyes, the respective values were 8.30 and 7.15 mm Hg. After LASIK the respective values were 8.63 and 7.28 mm Hg. The corneal hysteresis and corneal resistance factor values were significantly smaller in the keratoconic eyes compared with normal eyes; these values were significantly smaller after LASIK compared with the pre-LASIK values.

"The importance question remains: Is there any way to identify those eyes that will develop ectasia?" Dr. Shimmyo said. "This will require a prospective long-term study. However, the [analyzer] provides the parameters to study the biomechanical properties of the cornea."

Dr. Shimmyo hopes the analyzer can be used to identify eyes that will develop ectasia before LASIK is performed. By doing so, these patients can undergo PRK and avoid the risk of developing ectasia.