Glaucoma
Delving into glaucoma

At a glance

• Perimetry, gonioscopy, tonometry,visual fields, & other tests, still hold significant value in glaucoma detection
• Spectral domain OCT provides shorter scan times, fewer errors, & higher resolution than previous OCT methods

How imaging devices and long-used assessments help with glaucoma
detection, progression

Normal gonioscopy
Source: Karl Brasse, M.D., EyeLand Design Network

Newer methods to detect glaucoma strike a balance with the tried-and-true but less high-tech methods, a number of ophthalmologists said. Although state-of-the-art imaging methods to detect glaucoma earlier are now commonplace, glaucoma specialists said they don’t want to lose the value of perimetry, gonioscopy, tonometry, visual fields, and other detection tests.
For now, high-tech versus low-tech detection methods are used hand in hand. “The most common tests within glaucoma are perimetry and scanning computerized ophthalmic diagnostic imaging,” said Kevin J. Corcoran, C.O.E., C.P.C., F.N.A.O., president, Corcoran Consulting Group, San Bernandino, Calif. He bases his answer on an analysis of Medicare reimbursement trends. “The frequency of these services for glaucoma patients within the Medicare program is amazingly constant.” Of course, the actual tests performed depends on the type of glaucoma the patient may have, he added.
William B. Trattler, M.D., director, Cornea, Center for Excellence in Eye Care, Miami, said a new patient who is being tested for glaucoma at his practice initially will have tonometry and pachymetry performed. The patient is also sent for optical coherence tomography (OCT) to look at the retinal nerve fiber layer (RNFL), Dr. Trattler said. A visual field test is also usually performed, he added.
Here’s a closer look at how the newer glaucoma imaging techniques assist with glaucoma detection—and how they work in tandem with other detection methods.

OCT advances

Spectral-domain OCT (SD OCT), the newest generation of the OCT technology, attracts the attention of many ophthalmologists right now because it can serve both retina and glaucoma patients, said Douglas J. Rhee, M.D., assistant professor, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston. Shorter scan times and higher resolution available with SD OCT “together may make the utility of OCT better for glaucoma detection,” Dr. Rhee said.
Leon W. Herndon, M.D., associate professor of ophthalmology, Duke Eye Center, Duke University, Durham, N.C., added that SD OCT shows some improvement over the previous time-domain OCT. “I am becoming a big fan of spectral-domain OCT, especially Spectralis [Heidelberg Engineering, Vista, Calif.],” he said. “To this point with time-domain OCT, I have not been convinced that you can use this technology to follow patients over time. Now, with the faster image acquisition and better axial resolution we see with SD OCT, there is better quantitative peripapillary retinal nerve fiber layer measurement for glaucoma management. The improved accuracy of the OCT segmentation allows for better long-term evaluation of patients.”
“The newer higher-resolution OCT is more accurate and more useful,” Dr. Trattler said.
Specialists are now evaluating how SD OCT may assist in detecting glaucoma at its earlier stages.
For example, Dr. Herndon saw a presentation regarding early glaucoma detection at the 2009 American Academy of Ophthalmology meeting in San Francisco, presented by Masanori Hangai and colleagues at the Kyoto University Graduate School of Medicine, Kyoto, Japan. The investigators studied 28 patients with early glaucoma using the Spectralis device to image the ganglion cell layer. “They found that 73% of eyes with early glaucoma demonstrated foci of complete ganglion cell layer loss, making it possible to detect glaucomatous atrophy far sooner than retinal sensitivity loss is seen by standard perimetry,” Dr. Herndon said.
The newer OCT technology also helps correct for errors that may come about with eye movement. “Eye movement remains the greatest problem for constant precise multiple B-scan averaging, so a three-dimensional eye-tracking system employed in an SD OCT instrument enables the precise averaging of up to 50 to 100 B scans, which allows superior visualization of ganglion cell layer boundaries,” Dr. Herndon said.

Room for improvement

Although SD OCT is praised for early detection and higher resolution compared with the previous generation of the technology, there’s still room for improvement, many say.
For example, images taken with SD OCT cannot be compared to images from the earlier generation of OCT technology, Dr. Rhee said. An image with SD OCT may appear thinner, but it wouldn’t be obvious if the image is thinner because of actual progression or higher resolution possible with the new technology, he explained.In contrast, images taken with newer versus older versions of the Heidelberg Retinal Tomograph (HRT; Heidelberg Engineering, Calif.), another common high-tech glaucoma detection tool, can be compared, he added.
A study published online in December 2009 in Ophthalmology also noted that diagnostic classification as provided by the HRT and the Spectralis OCT may not always agree. “At a comparable level of specificity, Spectralis OCT RNFL measurement attained a higher sensitivity than HRT optic disc measurement,” wrote lead investigator Christopher Kai-shun Leung, M.D., M.B. Ch.B., Department of Ophthalmology and Visual Sciences, Chinese University of Hong Kong, Hong Kong. Investigators noted that agreement between the two machines was fair to moderate except for global and inferotemporal measurements.
Additionally, “I don’t think the technology has been around long enough to tell us if it’s better for detecting glaucoma progression,” Dr. Rhee said.
Some recent studies do demonstrate how OCT can assist with glaucoma progression. Dr. Leung was also the lead investigator of a study in the January issue of Ophthalmology that used the Stratus OCT (Carl Zeiss Meditec, Dublin, Calif.) to measure glaucoma progression analysis. Visual field tests were also performed. The investigators found that measuring the rate of change in RNFL thickness with the help of OCT could serve as a new way to observe and manage glaucoma patients.
Another study published in the December issue of Investigative Ophthalmology and Visual Science found that RNFL parameters as measured by the Stratus OCT discriminated between eyes progressing by visual fields or optic disc photographs. “Stratus OCT RNFL parameters were able to discriminate eyes with progressing disease by visual fields or optic disc photographs with eyes that remained stable according to these methods, and performed significantly better than [optic nerve head] and macular thickness parameters in detecting change over time,” wrote lead investigator Felipe A. Medeiros, M.D., Hamilton Glaucoma Center, Department of Ophthalmology, University of California, San Diego, La Jolla, Calif. The investigators added that the technology could be used to assist with measuring glaucoma progression.
Some of the study investigators, including Dr. Medeiros, have financial or consultative relationships with Carl Zeiss Meditec.

Remembering tried-and-true methods

Although high-tech imaging devices enhance glaucoma detection, they don’t eliminate the need for other detection methods, said Alan L. Robin, M.D., associate professor of ophthalmology and associate professor of international health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore. “Everybody wants to use the new toys, but let’s use what we already have,” Dr. Robin said.
Dr. Robin speaks of the value of using gonioscopy, visual field tests, pachymetry, and fundus photography to document other key indicators of glaucoma. He believes some physicians do not perform these tests as frequently as they should due to time or a lack of mastery for more complex tests such as gonioscopy. He said Web sites such as www.gonioscopy.org, developed by Wallace L.M. Alward, M.D., Frederick C. Blodi Chair in Ophthalmology and director, Glaucoma Service, Department of Ophthalmology and Visual Sciences, University of Iowa Carver College of Medicine, Iowa City, Iowa, may help specialists master that learning curve.
The tried-and-true low-tech tests are often reimbursed for, can provide detection cues that imaging devices cannot give, and can be performed by ophthalmic technicians, Dr. Robin said.
“Does the new technology replace what’s already done? No, it just supplements it,” Dr. Robin said.
Advances within glaucoma detection continue even beyond the imaging devices. For example, Dr. Herndon praises newer tonometers such as the Pascal Dynamic Contour Tonometer (DCT) (Ziemer Ophthalmic Systems, Alton, Ill.) and the Reichert Ocular Response Analyzer (Reichert, Depew, N.Y.) for their ability to give IOP values not affected by corneal parameters.
“I don’t utilize these new tonometers in every patient, as there is some extra time involved with generating an accurate measurement, particularly with the DCT,” he said. “Mainly I use these tonometers in a research mode at this point. Ultimately we hope to be able to utilize them to more accurately risk-stratify our patients to determine which patients are more likely to get worse over time.”

Editors’ note: Mr. Corcoran has no financial interests related to his comments. Drs. Trattler, Rhee, Herndon, and Robin have no financial interests related to their comments.

Contact information

Corcoran: 800-399-6565, kjc@corcoranccg.com
Herndon:919-684-6622, leon.herndon@duke.edu
Rhee: 617-573-3670, dougrhee@aol.com
Robin: arobin@glaucomaexpert.com
Trattler: 305-598-2020, wtrattler@gmail.com