Ophthalmologists discuss: Can OHT be differentiated from glaucoma?

Are the two entities clearly different? The highlights of a panel at an international meeting are presented here.

Issue: September 15, 2001

PRAGUE, Czech Republic — Advancements in visual field testing and the recent introduction of optic nerve imaging instruments are allowing clinicians to evaluate signs of glaucoma earlier. They are also permitting precise differentiation between glaucoma and ocular hypertension (OHT) in many patients, according to a well-known glaucoma specialist.

“We do have the tools available to diagnose glaucoma in most of our patients, but not in all of our patients,” Robert N. Weinreb, MD, told ophthalmologists in attendance at the 3rd International Glaucoma Symposium. He took the “pro” stance in a discussion of whether modern ophthalmic medicine can differentiate OHT from glaucoma.

The “anti” position was taken by Ivan Goldberg, FRACO, FRACS.

New, specialized visual field tests that are more sensitive to specific types of retinal ganglion cells can, in many cases, detect functional changes of the optic nerve before they would be detected with standard perimetry, Dr. Weinreb said.

“Fortunately, there are a number of tests available that allow us to recognize functional change, even in the presence of a standard automated visual field test that is within normal limits,” Dr. Weinreb said.

The different tests permit early recognition of glaucomatous loss, and they should be conducted on patients with elevated eye pressure and normal standard perimetry, he said.

He cited a study by Pamela Sample, PhD, showing that patients with glaucomatous-appearing discs but normal standard visual fields often had abnormal, repeatable visual fields when tested with the newer neuron-specific tests, such as short wavelength, frequency-doubling and motion-automated perimetry.

“We should perform at least one of these tests in patients who have OHT with normal visual fields,” he said. Functional change is detectable at a much earlier stage than has been previously possible.

Direct measurement of the nerve fiber layer by scanning laser technology can further aid clinicians in differentiating between glaucoma and OHT, Dr. Weinreb added. Scanning laser polarimetry, confocal scanning laser ophthalmoscopy and optical coherence tomography often permit experienced glaucoma clinicians to “sensitively recognize loss of nerve fiber layer thickness or neuroretinal rim area. This still requires the input of the ophthalmologist to recognize that the changes are most compatible with glaucoma.”

Structural and functional changes in many OHT patients can be identified.

“[However,] there is probably a group of patients with OHT in whom we cannot recognize structural and functional changes, regardless of the testing employed. Those patients should continue to be called OHT patients and should be followed as suspect for glaucoma” Dr. Weinreb said.

Too much overlap

Taking the contrary position, Dr. Goldberg, of Sydney, Australia, argued that there is too much overlap between the two entities.

“If we are intellectually honest, then we must admit we do not have the tools to differentiate the two entities,” Dr. Goldberg said.

OHT cannot be separated from glaucoma, and even normals cannot be separated from ocular hypertensives, he said.

“My colleague has essentially argued my case for me,” he said. Clearly separating the entities of glaucoma and OHT “depends critically on our technology …, which is in a constant stage of evolution and development.”

The clinician’s ability to assess structural and functional damage has changed dramatically with the development of new tests, Dr. Goldberg said.

“We know for example, based on Dr. Weinreb’s own research as well as the work of Chris Johnson, PhD, that blue-on-yellow perimetry can pick up damage up to 5 years earlier than white-on-white perimetry,” he said.

“That being the case, we know that damage is occurring ahead of our current technologies, and therefore, in being intellectually honest, we must agree that this is an evolving paradigm and we cannot, at this point, make the separation between the overlapping entities.”

For Your Information:

Robert N. Weinreb, MD, can be reached at Shiley Eye Center, 9500 Gillman Drive, La Jolla, CA 92093-0946; (858) 534-8824; fax: (858) 534-1625; e-mail: weinreb@eyecenter.ucsd.edu.

Ivan Goldberg, FRACO, FRACS, can be reached at 187 Macquarie St. Park House, Floor 4, Suite 2 Sydney, NSW 2000 Australia; +(61) 2-9247-9972; fax: +(61) 2-9232-3086 e-mail: rauaroha@medeserv.com.au.