OCT valuable for evaluating treatment effects in CNV

Miami-Optical coherence tomography (OCT) can be a valuable tool for evaluating the status of choroidal neovascularization (CNV) in patients with wet age-related macular degeneration (AMD), particularly when new drugs are being used to treat the disease, said Philip J. Rosenfeld, MD, PhD, associate professor of ophthalmology, Bascom Palmer Eye Institute, Miami.

Several advantages

Used to identify pathology in the macula, OCT can pinpoint areas of fluid accumulation responsible for decreased vision in patients with neovascular AMD.

"It is these cases with macular fluid that have the best chance of vision improvement if the fluid were eliminated using anti-VEGF therapy. It is clearly a qualitative technique that is very valuable for detecting anatomic changes, particularly the accumulation of fluid and structural alteration of the macula. In addition, it can be used quantitatively with certain caveats," Dr. Rosenfeld said.

OCT is also advantageous because it is rapid, noninvasive, and does not require an experienced ophthalmic photographer. A different skill set is required for an OCT operator.

Often times technicians with video game experience make the best OCT operators; they adapt to the technology very quickly, Dr. Rosenfeld stated.

In his practice, he uses both the fast and the slow radial scan modes that take six diagonal sections through the central macula at 30° increments. The fast scan takes 128 A-scans per diagonal, which he uses for quantitative analysis, and the slow scan takes 512 A-scans per diagonal, which he uses for qualitative analysis. Overall, this is about 3,840 A-scans.

He emphasized the benefits of using OCT to evaluate the onset of the treatment effect, its durability, and the response to re-treatment in either established or experimental treatments.

At the Bascom Palmer Eye Institute, physicians have used OCT to study two new pharmaceuticals, both from Genentech: ranibizumab (Lucentis) and bevacizumab (Avastin). Both drugs inhibit VEGF. Genentech has submitted a Biologics License Application to the FDA seeking a priority review of ranibizumab for treatment of neovascular AMD. Bevacizumab, approved for treatment of colorectal cancer, is being used off-label in patients with neovascular AMD.

To gain more information on ranibizumab, Dr. Rosenfeld is conducting an investigator-sponsored study called PrONTO (Prospective Optical Coherence Tomography Imaging of Patients with Neovascular Age-Related Macular Degeneration Treated with Intra-Ocular Lucentis) in which patients with all types of AMD receive three monthly intravitreal injections of the drug.

OCT is used to determine how quickly central retinal thickness decreases following ranibizumab therapy and whether this decrease correlates with improved visual acuity. OCT is used to determine when re-treatment is necessary with ranibizumab.

OCT provides a cross-sectional view of the gradual changes that occur in and under the retina, while fluorescein angiography is harder to quantitate and it is more difficult to assess where the fluid is accumulating when leakage is detected, Dr. Rosenfeld said.

"When we use OCT to quantitate the retinal thickness over the first 3 months, we can see a decrease in fluid that's significant by the first day after the injection, and this decrease, which plateaus by day 90, is associated with an overall improvement in visual acuity," he added.

Dr. Rosenfeld has also used OCT to study the effects of bevacizumab following systemic use of the drug. Most patients received two infusions and were followed for 24 weeks. With OCT, he was able to track resolution of the fluid and neovascularization, the reappearance of fluid after the treatment was stopped, and the impact of re-treatment in these patients.