Integration of corneal topography, wavefront analysis useful for customized treatment decisions

Integrating data derived from corneal topography and wavefront analysis can help clinicians validate decisions about customized refractive surgery treatments, said Stephen D. Klyce, PhD, professor of ophthalmology, Louisiana State University, New Orleans, United States.

"Wavefront data that's presented in diopters is analogous to topography and can be used to determine the internal aberrations of the eye," Dr. Klyce said. "Wavefront data expressed in microns can be presented with a scale that correlates with corneal topography in diopters. Zernike decomposition can be useful with this proper scaling, but only in eyes that have minimal aberrations."

A challenge facing clinicians is that "corneal topography is measured on the surface of the cornea and is expressed in units of diopters," Dr. Klyce said, whereas "many of the Hartmann-Shack units that are used to measure wavefront aberrations of the whole eye are expressed at the pupil plane in units of microns. So how do we make the wavefront maps and the corneal topography maps present themselves in a way that we can really understand their meaning?"

To answer that question, "we went back to what we did for corneal topography and the development of a wavefront scale. What we learned is that if we measure the range of clinical data; adopt a contrasting, color-coded set; show only clinically relevant aberrations; and use a fixed, standard scale, then there is a possibility to really be able to interpret what's going on. And also, if we use standard clinical terminology, you can start to understand some of these more complicated concepts."

Dr. Klyce said he and colleague Michael K. Smolek, PhD, developed a wavefront scale to enable comparison between corneal topography and wavefront analysis data.

"That goes a long way helping the clinician realize wavefront information, that in fact it's correct," he said.

An alternative to using this scale, Dr. Klyce said, is technology that combines a scanning slit autorefractor with a corneal topographer (e.g., OPD-Scan, Nidek; KR-9000PW, Topcon). Such a device can present data directly in diopters, allowing the clinician to compare wavefront data with the corneal topography map using the same unit of measure.

"The advantage of this is that, by doing a simple subtraction, one can find out what's going on inside the eye," he said. In most patients, he added, the inside of the eye can appear normal, with almost all of the aberrations emanating from the corneal surface.

Corneal topography should be used for diagnostic purposes, Dr. Klyce recommended.

"If we think we can diagnose all keratoconus cases by looking at wavefront, we are mistaken. And why is that? Because wavefront has limited extent coverage," he said.

Dr. Klyce is a paid consultant to Nidek.