Avoid specific benchmarks when using CCT to determine glaucoma risk

LAS VEGAS — When assessing a patient's risk of developing glaucoma, clinicians should categorize corneal thickness as "thick, thin or average," rather than attempting to use an absolute number, a speaker here said.

Odette V. Callender, MD, spoke on the role of central corneal thickness in evaluating glaucoma risk.

Central corneal thickness (CCT) can be affected by numerous factors, and therefore the use of a specific benchmark could be misleading, Odette V. Callender, MD, said at the OSN Las Vegas meeting.

"With all the things that can affect the actual measurement and number, it is probably best to look at it as a category of thick, thin or average and not focus on the exact pachymetry number you're getting," Dr. Callender said.

For example, it has been found, notably by the Ocular Hypertension Treatment Study (OHTS), that black patients tend to have thinner corneas than white patients. Other studies have found that factors such as corneal drying, diurnal variation, long-term variation, previous refractive surgery and contact lens use can all have a significant impact on CCT.

Race can also play a role in the measurement of cup-to-disc ratio, she said.

"African Americans have larger optic nerves. We know that the cup-to-disc ratio varies with the size of the nerve. All of this says it's important to assess the size of the disc itself and not just the ratio," she said.

Dr. Callender recommended using the ISN'T rule when evaluating the optic nerve because it does not vary according to racial characteristics.

"In OHTS, it was found that race is not really the issue, just that black [patients] have thinner corneas and larger optic nerves," Dr. Callender said. "Look at the ocular characteristics of your patients and not so much the racial characteristics."