Tomograph a powerful predictor for glaucoma progression

January 15, 2008

A proprietary retina tomograph (Heidelberg Retina Tomograph 3, Heidelberg Engineering) can help ophthalmologists differentiate patients at risk of progression to glaucoma from those patients who are not, based on structural and functional findings in the optic nerve and visual fields.

Key Points

New Orleans-The features of an enhanced retina tomography platform (Heidelberg Retina Tomograph 3 [HRT 3], Heidelberg Engineering) can help ophthalmologists differentiate patients who are at risk of progression to glaucoma from those who are not. Using structural information about the optic nerve from the retina tomograph with functional findings from visual fields, clinicians can have more confidence about whether to treat patients, said Robert Noecker, MD, MBA, at the annual meeting of the American Academy of Ophthalmology.

As reported in the Ocular Hypertension Treatment Study (OHTS), some of the risk factors for developing glaucoma are an increased cup-to-disc ratio, decreased central corneal thickness, increased IOP, race, and advanced age. During the course of the 5-year OHTS, in about 50% of patients who developed glaucoma, the disease was diagnosed based on changes in the optic nerve only. Visual field testing identified only about 35% of patients whose conditions progressed to glaucoma, Dr. Noecker said.

"Importantly, both structural and functional parameters need to be evaluated in order to detect changes," said Dr. Noecker, vice chairman and associate professor, Department of Ophthalmology, University of Pittsburgh School of Medicine. "In many patients, the structural changes may actually indicate glaucomatous changes substantially earlier than the functional ones."

He also said that in the ancillary OHTS, a patient with ocular hypertension and a normal retina tomograph image had a 93% chance of not developing glaucoma within the follow-up period. The relative predictive value of developing glaucoma with the retina tomograph was 8.88 as determined by the Moorfields Regression Analysis (temporal superior). Other smaller studies seem to indicate that the retina tomograph seems to be comparable, if not superior, to optical coherence tomography in its predictive powers, he said.

Two goals exist in evaluating patients, Dr. Noecker said. The first is the use of baseline images to compare patients with subjects in a normal population at the initial diagnosis.

"The [retina tomograph] has become more refined and more powerful over time," he said. "Initially, the database used was relatively small, but now, with the expansion of the database, the [device] offers specific database variations within various ethnic groups and provides, for example, a normal range for African-American patients. The more sophisticated the software becomes, the more targeted the possible analysis."

The probability of structural abnormality (Glaucoma Probability Score, Heidelberg Engineering) is calculated via software using three-dimensional measurements of the optic disc and retinal nerve fiber layer. This feature of the device aims to reduce reliance on subjective clinician drawings of the disc margins, which has been characterized as tedious and time-consuming.

The second goal is detection of progression by looking at measurements of variations in the cup and rim of the optic nerve. The strength of the retina tomograph is its ability to detect minute changes over time when following patients. The device analyzes topographic change, which allows clinicians to compare changes in the areas of the optic disc in the same patient over time. This follow-up is key in patients who are at high risk of developing glaucoma, according to Dr. Noecker.

"[The proprietary retina tomograph] has the best progression software currently available with which to analyze changes after two to three examinations," Dr. Noecker said. "Red-and-green color scales demonstrate the magnitude of changes over time. This is extremely helpful for clinicians to assess changes quickly in the optic nerves of patients with glaucoma."