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OCT essential to glaucoma work-up
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Optical coherence tomography helps in the follow-up process of glaucoma as well as the diagnosis of other related diseases, according to a presenter.
“Optical coherence tomography is an essential part of the glaucoma diagnostic work-up, without question. It has changed our diagnostic way of treating this disease,” OSN Glaucoma Board Member Richard A. Lewis, MD, said at Kiawah Eye 2013. “[It has] enhanced understanding of glaucoma, as well as other optic nerve diseases.”
Correlating data
Spectral domain OCT automatically quantifies parameters of the optic disc and borders without being dependent on operator measurement, Lewis said, and that data can now be compared with a normative database.
“We now have automated quantitative information that is reliable visit to visit,” he said.
The key parameters of the optic nerve head and retinal nerve fiber layer thickness are displayed in a table format and compared with normative data, which can distinguish normal or abnormal relationships between the patient’s measurements and the normative database.
Richard A. Lewis
Even so, there must be correlation across all aspects of the examination, according to Lewis, particularly between the optic disc appearance and the visual field.
“If the two don’t correlate, if it doesn’t make sense … you’ve got to be able to explain it,” he said.
When there are discrepancies — such as when the SD-OCT data are normal and the visual field data are abnormal, or vice versa — correlation becomes even more important.
For example, when the visual field is relatively normal but there is extensive nerve fiber layer damage and cupping shown on OCT, the clinician needs to reconcile the findings to manage the patient.
“It isn’t always easy,” Lewis said. The optic cup and nerve fiber layer may have deteriorated in advance of the visual field, or the patient may have been a poor visual field test taker.
This patient represents the intermediate category of patients who may transition into glaucoma, and the question is whether visual field loss or optic nerve cupping is detected first.
With regard to such a patient, Lewis said, “The nerve fiber layer is a very good early indicator of glaucoma, more so than the visual field. … At the moment, I put more confidence in the objective nature of the OCT.”
One cannot always depend on only the OCT, however. Lewis presented a case of a 67-year-old patient with hypotony whose OCT data indicated that, at 2 years after cataract surgery with implantation of an IOL and canaloplasty, the patient was “cured” of glaucoma.
“Did I really cure his glaucoma?” Lewis asked. “No. What I got was disc swelling from hypotony.”
Other diagnoses
In one case of disc drusen in a 74-year-old man whose MRI scan results were normal, OCT showed a nerve fiber layer with values that far exceeded those in the normative database. Such elevated values are normal in any kind of defect that causes elevation of the optic nerve, such as drusen and hypotony, and do not necessarily mean the patient has glaucoma.
“There are a lot of diseases that can give us thickening and elevation of the nerve fiber layer,” Lewis said.
Disc drusen can be seen in a variety of ways on OCT, be it discrete or subtle. When diagnosed by OCT, disc drusen would be seen as occurring at a much higher incidence than the expected 2%, Lewis said.
“OCT is a very effective indicator of optic nerve head drusen, and that isn’t glaucoma,” Lewis said. – by Cheryl DiPietro and Patricia Nale, ELS