PHILADELPHIA — Optic disc photography is the most useful method of identifying anatomic changes that portend glaucoma, a speaker said here.
Furthermore, changes to the optic disc are more effective than IOP and age in identifying glaucoma and tracking disease progression, George L. Spaeth, MD, OSN Glaucoma Board Member, said at the Wills Eye Institute Alumni Conference.
“In this digital age, we’ve forgotten the importance of analog evaluations,” Dr. Spaeth said. “Disc photographs are not obsolete. In contrast, most of the modern imaging techniques change every 3 or 4 years. It’s very difficult to import the old data into the new technique.”
Disc status trumps IOP, age
Contrary to conventional wisdom, measuring IOP alone is not a reliable method of diagnosing glaucoma, Dr. Spaeth said.
George L. Spaeth
“What proves the presence of glaucoma? We used to think it was pressure, but 95% of those with pressures over 21 mm Hg do not have glaucoma and won’t get it,” he said. “One-third to one-half of those with pressures below 21 mm Hg do have glaucoma. You can’t use pressure at that level to prove the presence of glaucoma.”
However, IOP still plays a key role in the diagnosis of glaucoma.
Generally, glaucoma is present if the IOP is greater than 35 mm Hg or IOP asymmetry is greater than 35 mm Hg. IOP lower than 30 mm Hg is essentially a useless measurement in diagnosing glaucoma, he said.
Progressive visual field loss and disc changes offer more unequivocal evidence of glaucoma.
“The disc is the basis for the diagnosis and care of patients with glaucoma,” Dr. Spaeth said. “Disc appearance is key. … The rate at which the field is changing is very important.”
Comparing image quality, utility
Observation of optic disc features hinges on the quality and repeatability of clinical images, Dr. Spaeth said.
OCT may become the preferred imaging modality but currently is not very useful for diagnosis.
“OCT is beautiful. It’s just wonderful,” Dr. Spaeth said. “But I don’t really know what to make of that. I get a beautiful image but it doesn’t tell me very much.”
Heidelberg Retina Tomograph (HRT) is a more accurate diagnostic tool than OCT, but it is difficult to obtain high-quality images. Neither OCT nor HRT shows pallor, disc hemorrhage or damage patterns, he said.
“Pattern is the most important clue to the health of the optic disc, and the only way to get pattern is with ophthalmoscopy or with photography,” Dr. Spaeth said.
Ophthalmoscopy may be the best method overall, but it is difficult to record objectively, he said. Conversely, disc photos provide a permanent record that can be imported into an electronic medical record, he noted.
Glaucoma is present if the rim of the optic disc is less than one rim-disc ratio, the rim narrows more rapidly than the patient is aging, or disc asymmetry cannot be attributed to other factors, he said. – by Matt Hasson
For more information:
- George L. Spaeth, MD, can be reached at Wills Eye Institute, 840 Walnut Street, Philadelphia, PA 19107; 215-928-3197; fax: 215-928-0166; email: firstname.lastname@example.org.
- Disclosure: Dr. Spaeth receives grant and research support from Allergan, Merck and Pfizer. He is a consultant for Merck and serves on the CME speakers’ bureau for Alcon, Allergan and Merck.