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Retinal tomography measurements associated with POAG development, study shows
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For the first time, measurements from a laser imaging device have been shown to be associated with the development of glaucoma, an ancillary Ocular Hypertension Treatment Study shows.
Using the Heidelberg Retina Tomograph (HRT), Linda M. Zangwill, PhD, and colleagues were able to show that optic disc topographic measurements are associated with the development of primary open-angle glaucoma (POAG) in patients with ocular hypertension.
The Confocal Scanning Laser Ophthalmoscopy (CSLO) Ancillary Study involved seven of the 22 study centers that participate in OHTS.
“This is one of the few studies that looks at baseline measurements to predict the development of glaucoma,” Dr. Zangwill said in an interview. “This ancillary study included this extra test with the HRT and was designed not to interfere with the main OHTS.”
Combined with baseline clinical factors, baseline topographic measurements were significantly associated with the development of primary open-angle glaucoma, according to Dr. Zangwill.
“The main OHTS found that corneal thickness, visual field, stereophoto and IOP at baseline were significantly associated with the development of glaucoma. Similarly, the Heidelberg Retina Tomograph measurements were, at baseline, significantly associated with the development of glaucoma,” Dr. Zangwill said.
How the instrument functions
According to a Heidelberg Engineering press release, the HRT produces a topography image of the patient’s optic disc and measures the cup, rim and retinal nerve fiber layer and stores the information. During follow-up visits the HRT can then measure changes in those variables that might indicate possible signs of glaucoma progression.
“This is an imaging instrument that provides quantitative information about the optic nerve head,” Dr. Zangwill said.
Study eligibility requirements
To be eligible for the ancillary study, participants were required to have an IOP of 24 to 32 mm Hg in at least one eye and 21 to 32 mm Hg in their other eye. They were also required to have normal-appearing optic disc images.
Baseline measurements were taken with the HRT, and participants received annual follow-up visits over the course of 8 years.
HRT study results
“This is the first time a laser imaging device has been shown to predict glaucoma,” said Gerhard Zinser, PhD, managing director and head of research and development for Heidelberg Engineering, in a company press release. “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.”
Researchers studied 865 eyes in 438 patients by taking a baseline measurement of their optic disc and comparing values among participants who developed glaucomatous optic disc and visual field damage according to the OHTS protocol with those who did not develop glaucomatous damage.
“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 press release stated.
The study, published in the September issue of Archives of Ophthalmology, reported that 36 patients developed POAG in one or both eyes during the 8-year study.
Monitoring glaucoma
“These data suggest that CSLO topographic optic disc measurements, when combined with other known predictive factors such as age, IOP and central corneal thickness, could assist the eye care professional in assessing the likelihood of developing POAG,” the authors wrote.
The authors also reported that they are unable to recommend a single CSLO parameter to diagnose or monitor glaucoma. “It clearly is not sufficient or prudent to rely on a single parameter when making clinical decisions,” they wrote. In addition, the authors state that “although a baseline outside normal limits classification was significantly associated with the development of POAG, most of the participants with values outside normal limits did not develop POAG within the time frame of this report. It is also important to determine whether the participants with POAG end points and CSLO and MRA classifications within normal limits at baseline had measurements outside normal limits during their later follow-up examinations.”
The authors recommend that longer follow-up studies are required to evaluate the true diagnostic accuracy of the CSLO measurements.
Analysis of the study
Primary Care Optometry News Editorial Board member Murray Fingeret, OD, FAAO, discussed with PCON an editorial by GA Cioffi and JM Liebmann published in the October 2002 issue of the Journal of Glaucoma. The editorial addressed the OHTS results and how they may be used in clinical practice.
“Included in their discussion were several points regarding the OHTS enrollment process,” Dr. Fingeret said in an interview. “They point out that 20% of enrolled OHTS patients had a SWAP visual field deficit at the time of entry, indicating some functional deficit may have been present in some individuals.”
The editorial further discusses study logistics, particularly in terms of the selection process for enrollment, Dr. Fingeret said.
“In particular, the optic disc reading center was aware that the stereo optic nerve photographs being evaluated came from individuals with full visual fields, and that the enrolling physician considered the nerves to be non-glaucomatous,” he said. “The authors raise the question that if the optic nerve photographs were now analyzed in a different, masked fashion, some of the optic nerves considered normal at the time of entry may be deemed abnormal.”
Dr. Fingeret said some of the OHTS optic nerve photographs are available on the OHTS Web site (https://vrcc.wustl.edu/photo/photos.htm), adding that, “Upon review, some do appear suspicious, if not downright abnormal.”
Dr. Fingeret said that in the editorial, Drs. Cioffi and Liebmann point out that the confocal scanning laser ophthalmoscopy ancillary study being done at a few centers “Will likely provide additional information about optic nerve structure at the time of entry.”
Dr. Fingeret said the HRT ancillary OHTS study “adds insight to the questions proposed.
“Was the HRT recognizing ‘optic nerve risk factors’ predictive of the development of glaucoma or detecting unrecognized glaucomatous damage?” Dr. Fingeret asked. “I would argue for the latter. It is often difficult to detect subtle glaucomatous optic nerve damage on one evaluation, even in the hands of experts.”
Dr Fingeret said the use of instrumentation such as the HRT may alert the clinician to an abnormally thin rim or loss of retinal nerve fiber layer, even when it escapes photographic inspection. “Turning the data around, very few of those who were not flagged (normal evaluation) went on to convert to glaucoma,” he said.
Dr. Fingeret said the Zangwill paper does not indicate that the HRT or any other imaging device may replace optic nerve evaluation, as there is no data indicating sensitivity or specificity rates in this study.
“Rather, it makes the case that imaging can be valuable when used in conjunction with optic nerve evaluation and other tests to alert the clinician to suspicious optic nerves that may have been initially overlooked,” he said.
For Your Information:
- Linda M. Zangwill, PhD, associate professor at the University of California, San Diego, can be reached at Hamilton Glaucoma Center, 9415 Campus Point Drive, La Jolla, CA 92093; (858) 534-7686; fax: (858) 534-1625; e-mail: zangwill@glaucoma.ucsd.edu. Dr. Zangwill has no direct financial interest in the products she mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Murray Fingeret, OD, FAAO, is chief of the optometry section at the Department of Veterans’ Affairs Medical Center in Brooklyn and Saint Albans, N.Y., and a professor at SUNY College of Optometry. He is also a member of the Primary Care Optometry News Editorial Board. He may be contacted at St. Albans VA Hospital, Linden Blvd. and 179th St., St. Albans, NY 11425; (718) 526-1000; fax: (516) 569-3566; e-mail: murrayf@optonline.com. Dr. Fingeret has received research support and honoraria for lecturing for Heidelberg Engineering.
- Heidelberg Engineering, maker of the Heidelberg Retina Tomograph, can be reached at 1499 Poinsettia Ave., Suite 160, Vista, CA 92081; 760-598-3770; fax: 760-598-3060; e-mail: contactusa@heidelbergengineering.com; Web site: www.heidelbergengineering.com.