instrumental strategies
Diagnosis Made Easy
The Stratus OCT3 eliminates much of the mystery in glaucoma detection.

WALTER D. WEST, O.D., F.A.A.O.

For years I recognized, as many of you have, the challenges in diagnosing and managing glaucoma patients. Early on, the primary clinical indicators I used in diagnosing and managing glaucoma were patient history, family history, ethnicity, IOP, cup-to-disk ratio and perimetry. I recognized that IOP was a key indicator for glaucoma, but that it certainly wasn't by itself diagnostic. In normal tension glaucoma, for instance, we couldn't rely on tonometry alone for diagnosis, and in fact it was misleading in many cases.

So I searched for every possible way to improve the accuracy and reliability of the data that were available at the time. I also evaluated new technologies as they became available to identify any other variables for making earlier diagnoses and improved management decisions.

Looking for help

In my practice one of the first major improvements in equipment relative to diagnosing and managing glaucoma came in the form of the Humphrey Field Analyzer, which allowed me to automate and thereby more consistently evaluate visual fields and monitor changes that occurred. Although a great improvement, I recognized that perimetry wasn't an early indicator for glaucoma as a result of the neurological makeup of the retina. Regardless of how well any perimeter performs, before it can begin to quantify or qualify field loss glaucoma has to have compromised or damaged 50% of the retinal ganglion cells.

Nerve fiber layer is the key

In the late 1980s and early 1990s, much attention was given to the relationship of the integrity of the nerve fiber layer and glaucoma. Many of us began to incorporate a new variable in our clinical evaluation for glaucoma: the identification and monitoring of dropout in the nerve fiber layer, primarily in the superior and inferior papillomacular bundles as they left the margin of the optic nerves. While those early evaluations were crude and subjectively performed with a red-free filter on a binocular indirect ophthalmoscope or by using a 90D pre-corneal lens and slit lamp, we began to appreciate the diagnostic value of identifying dropout in the nerve fiber layer in glaucoma patients and/or glaucoma suspects.

At this time, the assessments we made were purely subjective; any appreciation of serial differential was subject to our memory, the quality of drawings in the patients record or attempts to photo-document with slit lamp photography. Yet even with these shortcomings -- plus the fact that there was no way to quantify what we observed -- we recognized that changes in the density of the nerve fiber layer within 2 to 3 disk diameters of the optic nerve was an important variable in potentially providing an earlier diagnosis. At the same time, it allowed us to be more proactive in our approach to treatment.

The OCT3 provides the measure of nerve fiber density and the volumetric evaluation of the optic nerve.

Meeting the OCT3

Continuing my quest for additional diagnostic capability, I purchased an OCT3, the most recent model of the Stratus OCT, in the fall of 2002. I wanted to be able to assess more accurately the density of the nerve fiber layer in evaluating my existing glaucoma patients as well as in those patients who were glaucoma suspects. The OCT3, manufactured by Carl Zeiss Meditec, is an optical coherence tomographer. It's similar in performance to ultrasound but uses a light source of broadband super luminescent light instead of sound. The result is an image with resolution that's 100 times greater than that of ultrasound.

The OCT3 provides me with two important pieces of information for my glaucoma and glaucoma suspect patients.

1. A volumetric representation of optic nerve cupping. This representation of the optic nerve topography is more meaningful to me than the typical cup-to-disk ratio because its representation is three-dimensional. As a result, it enhances the appreciation of the "bean pot" cupping with which some patients present. (The cupping of the optic nerve visible at its surface isn't always the largest diameter associated with the cupping.) Even a stereoscopic view of the optic nerve with a binocular indirect ophthalmoscope or slit lamp doesn't reveal the full effect that the cupping might present to the individual nerve head.

I find that the three-dimensional volumetric representation gives me a better appreciation for the health of the rim of the optic nerve. The serial appreciation of changes over time are more exacting as well.

2. An objective measure of the density of the retinal never fiber layer previously unavailable. The fact that the assessment of the density of the nerve fiber layer using the OCT3 is objective makes this in and of itself an advantage over the subjective format used in gathering perimetry data. With the measure of nerve fiber density and the volumetric evaluation of the optic nerve provided by the OCT3 as part of my glaucoma evaluation, I can make an earlier and more confident diagnosis and identify potentially sight-threatening clinical changes relative to glaucoma.

The OCT3 multitasks

As with any investment in capital equipment, the improvement in patient care is my prime concern, but I must also know that the use of the equipment justifies the cost of providing this service to my patients. In my practice, using the OCT3 for glaucoma alone justifies the cost, but this instrument isn't limited to diagnosing and managing glaucoma.

The OCT3 is also a valuable tool for evaluating lesions and abnormalities in the macular area and throughout the posterior pole of the retina. The imaging and improved qualification of macular irregularities such as macular pucker, cystoid macular edema and macular degeneration provide for even greater opportunities to employ the OCT3 to the patient's benefit.

It makes a difference

Providing patients with the most advanced clinical diagnostics available is an integral part of my clinical practice as well as my business plan. The OCT3 has been a valuable addition to my practice and has enhanced the level and the consistency of my patient care.

DR. WEST IS A PARTNER IN THE PRIMARY EYECARE GROUP OF BENTWOOD, TENN., AND A FELLOW OF THE AMERICAN ACADEMY OF OPTOMETRY. DR. WEST IS ALSO THE CHIEF OPTOMETRIC EDITOR OF OPTOMETRIC MANAGEMENT MAGAZINE. YOU CAN REACH HIM AT WWEST@PRIMARYEYECARE.COM.