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Sophisticated imaging possible with current glaucoma diagnostic technology
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As technical advances allow more exact imaging of the posterior pole, opinions among clinicians vary as to whether imaging the optic nerve head or the retinal nerve fiber layer is more useful in diagnosing glaucoma.
Optic nerve head (ONH) cupping and defects in the retinal nerve fiber layer (RNFL) are two important indicators of glaucomatous optic nerve atrophy, said Jorge Alvarado, MD.
“Evaluation of the ONH clinically is a challenging task,” he said.
The size of the optic cup, according to Dr. Alvarado, is an important clue in glaucoma diagnosis. “You can have a large size with burying of the circumlinear vessel that you may think is glaucoma, but the patient could have a cup-to-disc ratio that remains essentially unchanged,” he said. When that occurs, the physician should re-examine the patients with standard nerve fiber layer analysis, Dr. Alvarado added.
RNFL is the most important structural endpoint in the detection of damage, said David Greenfield, MD. Technologies that generate information about the RNFL are “reproducible, quantitative and objective,” he said. If a physician uses only a topographer to assess structural damage of the ONH, it would be highly unlikely that damage at the superior pole of the neural rim would be seen, Dr. Greenfield said. The damage is visible using scanning laser polarimetry and optical coherence tomography (OCT).
Ultrahigh resolution OCT represents an improvement in resolution of about three to five times over conventional OCT, said Joel Schuman, MD, which gives physicians “an increased ability to differentiate between the layers of the retina.”
Robert Weinreb, MD, added visual function testing “is the least robust” of available diagnostic methods.
More details on the subject may be found in the May 15 print edition of Ocular Surgery News.