Diagnostic imaging  

Retina tomography shown to predict Glaucoma

20 September 2005

Dossenheim, Germany. Researchers at the Hamilton Glaucoma Center and Department of Ophthalmology at the University of California at San Diego have demonstrated that measurements taken using the Heidelberg Retina Tomograph (HRT) can predict the development of glaucoma. The study was conducted on patients with elevated inner eye pressure whose eyes otherwise appeared normal by standard clinical assessment.

"This is the first time a laser imaging device has been shown to predict glaucoma," said Dr. Gerhard Zinser, Managing Director and head of R&D for Heidelberg Engineering. "In this study, the HRT's method of analyzing optic discs was shown to be a powerful and accurate predictor of glaucoma in patients with elevated eye pressure. It is important to note that the results are based on measurements taken at an initial visit, and we expect that follow-up examinations will give us even higher predictive values."

The results, published in the September issue of Archives of Ophthalmology, show that the HRT offers new diagnostic information, overcoming some of the limitations of current methods, such as the familiar "air puff" test or the visual field test in which the patient looks for white lights projected onto a white screen. The study was sponsored by the National Eye Institute (NEI).

Glaucoma is the name given to a collection of diseases that damage the eye's optic nerve, which if left untreated can lead to blindness. The NEI estimates that 2.2 million adults 40 years of age and older in the United States have glaucoma, and it expects this number to climb to 3.3 million in 2020. Furthermore, glaucoma is the most common cause of blindness among Hispanics and one of the two leading causes of blindness among African-Americans (the other being cataracts), according to NEI.

The HRT scans the patient's eye with a beam of light, producing a topographical or surface image of a patient's optic disc, and then measures the key structures known as cup, rim and retinal nerve fiber layer. The instrument then stores each patient's images, and on a follow-up visit the device checks for signs of statistical change that are presented to the clinician as signs of a possible disease progression. This enables the clinician to make a better decision on a course of therapy.

Researchers, led by Linda Zangwill, Ph.D., and Robert Weinreb, M.D., studied 438 participants (865 eyes) in a prospective, multicenter study that is ancillary to the previously reported landmark Ocular Hypertension Treatment Study (OHTS). Each participant had baseline optic disc images taken using the HRT at the start of the study and had follow-up images taken annually. Although all the participants had ocular hypertension or elevated pressure inside their eyes, none of them showed evidence of disease using stereo optic disc assessment or visual field testing at initial assessment. The patients were then followed for up to eight years, during which time 36 patients developed primary open-angle glaucoma (POAG) in one or both eyes (in 41 eyes total).

Researchers found that several of the HRT's topographic optic disc measurements were significantly associated with development of POAG. The measurements included larger cup-to-disc area ratio, mean cup depth, mean height contour, cup volume, reference plane height, smaller rim area, rim area to disc area, and rim volume. The HRT's classification of results as "outside normal limits" and its Moorfields Regression Analysis were also found to be strong indicators of glaucoma.

The HRT's Moorfields Regression Analysis of the superior temporal region had the highest positive predictive value for glaucoma, at 40 percent. That means 40 percent of those eyes that were flagged as "outside normal limits" at the baseline examination went on to develop glaucoma. This compares favorably with the previous OHTS results establishing central corneal thickness (CCT) as a risk factor for glaucoma. In the earlier study a thin cornea, combined with high intraocular pressure, had a positive predictive value of 36 percent.

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