Chicago?Optical coherence tomography (OCT) is an important imaging technology that allows high-resolution, cross-sectional imaging of microstructures in the eye. Since the technology was first introduced, successive generations have improved considerably.
Jay S. Duker, MD, described prototype ultra-high-resolution OCT and high-speed spectral OCT during the retina subspecialty day at the American Academy of Ophthalmology annual meeting. He also noted the contributions of researchers at the New England Eye Center, the Massachusetts Institute of Technology, both in Boston, and the University of Pittsburgh Eye Center, Pittsburgh.
Ultra-high-resolution OCT became available in 2002 and the resolution increased to 2 µm from 10 µm in the previous generation (Stratus OCT3, Carl Zeiss Meditec). This was achieved by a five-fold increase in bandwidth in the new light source. Another advance is scanning speed that uses new spectral technology. Spectral OCT has a scanning speed 40 times greater in the Stratus OCT3. Thus, the problem of the long acquisition times has been resolved, according to Dr. Duker. He demonstrated a side-by-side comparison of images obtained with the OCT3, which provided excellent delineation of the retinal layers, and the ultra-high-resolution OCT, which provided even better resolution than OCT3 and in a much shorter scanning time.
Foveal thickness measurements
He explained that to test the utility of the ultra-high-resolution prototype system, he and his colleagues conducted a study in which they compared retinal thickness measurements in normal patients and retinal thickness measurements in patients with retinitis pigmentosa (RP). In the study, total foveal thickness was defined as the distance from the inner retina to the outer retinal pigment epithelial (RPE) layer. Outer foveal thickness was defined as the thickness from the inner/outer photoreceptor junction to the outer RPE layer.
Data from 36 patients with normal vision were compared with data from nine patients with RP. Dr. Duker showed a patient with RP and normal central visual acuity in whom there was thinning of the outer retina and another patient with RP and reduced central visual acuity.
"The results of the study showed that overall central foveal thickness was not predictive of the presence of RP; the outer foveal thickness, however, did correlate with the diagnosis of RP in a statistically significant fashion. We do not believe that the outer retinal thickness measurement can be obtained reliably with the resolution of a Stratus OCT3," he reported.
Dr. Duker also reported that there was no correlation between central foveal thickness and visual acuity, but the visual acuity was highly correlated with the outer foveal thickness.