Structural testing effective in monitoring glaucoma cases

Expert says HRT appears to give accurate information about the optic nerve head with fewer testing variability issues.

Using a tomograph on borderline and other challenging glaucoma cases can assist physicians in monitoring structural changes and abnormalities that could affect disease classification, a glaucoma expert said.

Malik Y. Kahook, MD, told Ocular Surgery News in a telephone interview that the Heidelberg Retina Tomograph (HRT, Heidelberg Engineering) is his default test for clinical testing in glaucoma cases. He still uses optical coherence tomography and GDx with variable corneal compensation (Carl Zeiss Meditec) in his practice but much less frequently than HRT and usually for clinical research or trials.

“In a perfect world, we’d be able to have all three tests done because they each offer unique information that the other is not capable of offering. But if I had to choose one — one that had the most utility as far as glaucoma diagnosis or follow-up or just collecting data as I follow patients — then HRT is the one,” Dr. Kahook said.

OCT is a viable testing tool, in his experience, and is especially helpful in examining changes around the optic nerve and beneath the nerve fiber layer. OCT provides information about the various retina layers that the other machines do not and has great potential for further development as the technology advances, he said. Spectral domain OCT is currently being studied to better understand how reproducible and accurate these devices might be in following glaucoma patients.

But Dr. Kahook said he prefers HRT as his main test for glaucoma structural testing because it appears to give accurate information about the optic nerve head with fewer variability issues.

“In my clinic, with my patient population and with my technicians, HRT is easier to use, and we notice less issues with misalignment that are more common with OCT retina nerve fiber layer scans.”

He also said incorrect mapping of the optic nerve by his technician can be compared with his clinical exam of the optic nerve and corrected easily using the HRT software.

“The structural information that you get from HRT, either along a continuum looking at the optic nerve rim or a single test showing you the actual disc area of the optic nerve, makes you a little bit more comfortable about the absence of disease or the presence of disease in that case,” he said.

“Ultimately, the diagnosis of glaucoma is made on clinical exam, taking all diagnostic information into account. The HRT may help in cases of subtle rim changes in patients with suspect optic nerves or in patients with large nerves who have correspondingly larger optic nerve cups,” Dr. Kahook said.

Effectiveness

Dr. Kahook said HRT is helpful in patients with normal and abnormal visual fields.

For instance, in patients with normal visual fields, whose optic nerves appear to have glaucomatous cupping, HRT helps him assess the situation. Patients in those cases sometimes simply have a physiologically large optic nerve that is not glaucomatous, he said.

The structural testing tool is also effective for patients with abnormal visual fields, Dr. Kahook said. He encountered a case of a patient with nonspecific visual field changes and suspicious-appearing optic nerves.

“In this scenario, where we’re talking about a patient who has an abnormal visual field, nonspecific changes or changes that are slightly worrisome but then we do an HRT and it looks absolutely normal, we can continue to follow these patients using structural testing like HRT. This is helpful in patients who have a hard time with visual field testing,” Dr. Kahook said. “If HRT testing continues to remain normal, then we’re a bit more comfortable in the fact that there is no progressive disease, despite the fact that the patient might not be a good visual field test taker.”

Features

The HRT3 device has added a large multiracial database, making the device more versatile, Dr. Kahook said.

“Our patient population in Denver is not homogenous, so we can use the database and sort of tailor it to our patients, so we’re getting more accurate information,” he said.

The HRT3 progression analysis is also an effective technological advance, with enhanced software that provides helpful information on patients who have multiple scans. With the scans, the HRT3’s neural network can analyze changes within the optic nerve head rim tissue and aid in detecting glaucomatous progression in the optic nerve, Dr. Kahook said.

“It could potentially help me decide whether I needed to advance therapy or whether the current IOP was the correct goal pressure or whether we need to lower the pressure further,” he said.

The HRT3 model has also been easier for technicians to use in his office, Dr. Kahook said. The testing can be performed in a highly reproducible manner with fewer fluctuations. He attributed the device’s lower level of variability issues to its scanning speed and more user-friendly applications.

“It takes minimal training to teach a technician how to do a good HRT,” he said.

For more information:

Malik Y. Kahook, MD, is assistant professor of glaucoma and cataract and director of clinical research at the Rocky Mountain Lions Eye Institute, University of Colorado at Denver and Health Sciences Center. He can be reached at 1675 N. Ursula St., Aurora, CO 80045; 720-848-2500; fax: 720-848-5014; e-mail: malik.kahook@gmail.com. Dr. Kahook has consulted for Heidelberg Engineering.

Heidelberg Engineering, maker of Heidelberg Retina Tomograph, can be reached at 1499 Poinsettia Ave., Suite 160, Vista, CA 92081-8543; 800-931-2230; fax: 760-598-3060; Web site: www.heidelbergengineering.com.

Erin L. Boyle is an OSN Staff Writer who covers all aspects of ophthalmology.