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GLAUCOMA TESTING AND REFRACTIVE SURGERY

OUR EXPERTS DISCUSS THE HOT TOPICS IN OPTOMETRY

Marc Bloomenstein, O.D., F.A.A.O.: Ben, we’ve been using pachymetry for a long time in the management of glaucoma and refractive surgery. What’s new in that world?

Ben Gaddie, O.D., F.A.A.O.: While pachymetry is still performed during my glaucoma workups, some new technologies are quickly becoming relevant. We know from the Ocular Hypertension Treat Study that thin corneas and elevated IOP don’t mix well, but corneal thickness alone doesn’t tell the story of why the cornea is so important for glaucoma. Some corneas, regardless of thickness, have a decreased corneal hysteresis (CH). Think of it as a structurally weak cornea and perhaps weaker-associated structures around the optic nerve. Robert Weinreb, M.D., and Felipe Medeiros, M.D., published a well-controlled prospective trial on the predictive value of CH in glaucoma progression. They found CH more predictive of patients who progressed vs. any other measure, including pachymetry and IOP. The Ocular Response Analyzer (ORA) (Reichert, Depew, N.Y.), which has CH measurement, is also being used in the cornea practice, particularly to diagnose keratoconus and pellucid marginal degeneration. In addition, CH is being used to determine the feasibility of LASIK in some practices — low CH could be a risk factor for long-term corneal complications. Speaking of refractive surgery, what other technologies are being used to better screen and predict problems after surgery these days?

M.B.: The landscape of refractive surgery has changed in these last few decades, though, as the old adage goes, things stay the same. The goal is to ensure that we place our patients in a position to get the best possible correction. Thus prevention, like the CH you described, is a great tool to help avoid ectasia. Research seems to be focused on avoiding this horrific complication.

For example, researchers at Emory University created a risk factor stratification scale intended to help prevent ectasia post LASIK. After analyzing the data, they assigned numerical scores to the various risk factors, which included topography pattern, residual stromal bed thickness, age, preoperative corneal thickness and preoperative spherical equivalent manifest refraction.

The technology in topography is the area that has really created a better sense of safety. Computerized Scheimpflug imaging has been used for corneal and anterior segment tomography in different commercially available instruments. Scheimpflug computes the 3D image of the cornea and anterior segment, enabling the characterization of elevation and curvature of the front and back surfaces of the cornea, pachymetric mapping, calculation of the total corneal refractive power and anterior segment biometry, all useful in the ectasia risk factor scale.

In thinking about glaucoma in these patients, one piece of equipment that I find invaluable is a handheld applanation tonometer that can acquire measurements outside the treated area of the cornea. Studies have shown that changes to the central thickness and curvature effect the measurement of post-surgical IOP. This is very similar to the corneal compensated IOP you mentioned with the ORA, without the CH value.

Keep in mind: The best predictor of problems is still being conservative and not performing surgery if there are any red flags. Another adage: An ounce of prevention is worth… well, in this economy, it isn’t really worth what it should be. OM

DR. BLOOMENSTEIN CURRENTLY PRACTICES AT SCHWARTZ LASER EYE CENTER IN SCOTTSDALE, ARIZ. HE IS A FOUNDING MEMBER OF THE OPTOMETRIC COUNCIL ON REFRACTIVE TECHNOLOGY. E-MAIL HIM AT MBLOOMESTEIN@GMAIL.COM.

DR. GADDIE IS THE OWNER AND DIRECTOR OF THE GADDIE EYE CENTERS, A MULTI-LOCATION, FULL-SERVICE PRACTICE IN LOUISVILLE, KY., AND IS CURRENTLY THE CHAIR OF THE CONTINUING EDUCATION COMMITTEE FOR THE AMERICAN OPTOMETRIC ASSOCIATION. E-MAIL HIM AT IBGADDIE@ME.COM, OR SEND COMMENTS TO OPTOMETRICMANAGEMENT@GMAIL.COM.

The authors report no financial interest in the products mentioned.