Nerve fiber layer examination can be valuable in diagnosis

Examination is recommended in cases of suspected disk abnormality, and in patients with risk factors for glaucoma.

BySue Marrren

LOS ANGELES — There are at least two situations in which nerve fiber layer analysis can supply significant information necessary for the diagnosis of glaucoma, according to Joseph Caprioli, MD, of the Jules Stein Eye Institute here.

“So to answer the question, ‘should I examine the nerve fiber layer in glaucoma?’” he said, “the answer, unfortunately, is ‘Sometimes.’”

The first instance in which nerve fiber layer analysis is helpful is in verifying a suspected disk abnormality when the disk appearance and static perimetry are equivocal, he said. Second, “if you have a patient with risk factors for glaucoma, perhaps a young black male with a strong family history, the visual field is normal, you’re really looking for evidence of damage that may trigger a decision to treat this patient — that is probably the best place for nerve fiber layer examination.”

Evaluation of structure

---The superior rim is thin, but the inferior rim appears nearly normal on the disk photo (Figure 1). Corresponding nerve fiber layer dropout (Figure 2) reveals expected losses to the nerve fiber layer superiorly, but unexpected loss inferiorly.

Dr. Caprioli addressed the issue of evaluation of structure in glaucoma. Given standard static perimetry with a sensitive strategy and analysis such as short wavelength automated perimetry (SWAP), what structural evaluations can be used? Disk photography is the standard to which all other methods must be compared, he said. Cup-to-disk ratio is of little use and disk drawings, although superior to the cup/disk ratio, are not as useful as photography. Sequential disk photography can be very convincing evidence.

Dr. Caprioli noted that nerve fiber layer analysis can bring additional information. “We can identify diffuse and localized defects with red-free ophthalmoscopy, with specialized photography and, finally, with image analysis,” he said.

Viewing photographs makes identification of defects much easier than using red-free ophthalmoscopy on the patient in the examination room. He showed slides of cases in which nerve fiber layer imaging merely confirmed defects that could be predicted by the appearance of the optic nerves.

Following these, he produced an exception — a nerve head with a thin superior margin and unremarkable inferior margin — that proved to have nerve fiber layer defects corresponding to the superior margin defect and, surprisingly, to the inferior margin (Figures 1, 2). He added, “I can show you maybe a dozen or so examples from my collection of slides of nerve fiber layer defects where the appearance of the disk was either downplayed or actually appeared pretty good.”

Quantitative means of analysis

Instruments available for quantitative disk analysis include the Optical Coherence Tomographer (Humphrey Systems, Dublin, U.S.A.), the Heidelberg Retina Tomograph (Heidelberg Engineering, Carlsbad, U.S.A.), and the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, San Diego).

Dr. Caprioli reviewed several cases using these diagnostic instruments as well as with routine qualitative testing. The special tests, in his words, “are certainly corroborative or confirmatory, but will they be complementary to the standard examination standards? That requires some additional study and perhaps some additional evidence of investigation.”

Dr. Caprioli added that what remains to be done with the new technologies is to try to take them in new directions. As an example, he cited his work with colleagues that was published in Investigative Ophthalmology and Vision Science. He and co-workers used the Heidelberg Retina Tomograph (HRT) and developed software to calculate the slope of the nerve fiber layer in the peripapillary region of the optic nerve.

This slope is significantly steeper in glaucoma patients than in normal patients, and further analysis of this small portion of the HRT image may well be useful in glaucoma diagnosis, he said.

For Your Information:

Joseph Caprioli, MD, can be reached at the Jules Stein Eye Institute, 100 Stein Plaza, Los Angeles, CA 90095-7006 U.S.A.; +(1) 310-825-0146; fax: +(1) 310-206-7773. Dr. Caprioli has no direct financial interest in any of the products mentioned in this article, nor is he a paid consultant for any companies mentioned.

For more information on the Laser Diagnostic Technologies GDx, contact Robert Damstra, Laser Diagnostic Technologies, 9550 Waples St., Ste. 105, San Diego, CA 92121 U.S.A.; +(1) 858-558-9144; fax: +(1) 858-558-9145; Web site: www.laserdiagnostic.com.

For more information on the Heidelberg Engineering Retina Tomograph, contact John A. Hawley, vice president, Heidelberg Engineering Inc., 5661 Palmer Way, Ste. G, Carlsbad, CA 92008 U.S.A.; +(1) 760-930-3570; fax: +(1) 760-930-3575; Web site: www.Heidelbergengineering.com.

For more information on the Humphrey Systems Optical Coherence Tomographer, contact Paul Kealey, marketing manager, Humphrey Systems, 5160 Hacienda Drive, Dublin, CA 94568 U.S.A.; +(1) 925-557-4442; fax: +(1) 925-557-4319; Web site: www.humphrey.com.

Reference:

Caprioli J, Park HJ, Ugurlu S, Hoffman D. Slope of the peripapillary nerve fiber layer surface in glaucoma. Invest Ophthalmol Vis Sci. 1998;39(12):2321-2327.