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.