FD-OCT shows promise as advance in glaucoma diagnosis

March 1, 2007
Cheryl Guttman

Las Vegas-Early results from the ongoing prospective Advanced Imaging for Glaucoma Study (AIGS; see www.AIGStudy.net) indicate that Fourier-domain optical coherence tomography (FD-OCT; also called spectral-domain OCT) is a valuable addition for glaucoma diagnosis, according to research presented here at the annual meeting of the American Academy of Ophthalmology.

In the glaucoma free-paper session, Vikas Chopra, MD, assistant professor, Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, presented findings from analyses evaluating the glaucoma discrimination capabilities of time-domain OCT (TD-OCT; Stratus, Carl Zeiss Meditec) and a newly introduced FD-OCT platform (RTVue, Optovue). The study involved an AIGS subset of 30 subjects with normal eyes and 31 patients with perimetric glaucoma.

Circumpapillary and macular scanning were performed with both systems to obtain thickness measurements of the circumpapillary retinal nerve fiber layer (cpRNFL) and macula. In addition, macular inner retinal layer (IRL) thickness was determined using FD-OCT. Glaucoma discrimination capability was determined based on construction of area under receiver operating curves (AROCs) for each of the parameters.

"Both of these OCT systems demonstrated excellent ability to differentiate glaucomatous eyes from normal controls using cpRNFL thickness measurements," said Dr. Chopra. "However, unlike the [TD-OCT device], this FD-OCT platform allows reliable retinal segmentation analysis in all eyes. By determining thickness of the macular IRL, FD-OCT can objectively measure changes to the retinal anatomy that are specifically affected by glaucoma damage for improved discrimination.

"However, based on these early results, we believe FD-OCT measurement of the macular IRL thickness should not be considered a substitute for circumpapillary anatomy measurements, but rather it might serve as an additional complementary parameter for improved detection of glaucoma," he added.

Previous studies with TD-OCT have shown that the macular retinal thickness measurement was not as sensitive as cpRNFL thickness in detecting glaucoma, Dr. Chopra noted. That finding, however, does not necessarily mean that the macula does not contain as much diagnostic information as the cpRNFL, he said.

"In fact, our own research and a study reported by Ishikawa et al. show that measurement of the inner retinal complex instead of the overall retinal thickness improves the diagnostic power of macular mapping with the [TD-OCT device] to a level equivalent to circumpapillary NFL evaluation," Dr. Chopra said. "Unfortunately, only 65% of glaucomatous eyes had a good enough signal-to-noise ratio to perform the macular segmentation using the time-domain technology. FD-OCT overcomes that obstacle."

Improved speed, resolution

David Huang, MD, PhD, associate professor, Doheny Eye Institute, is the principal investigator in the AIGS and a co-inventor of OCT. Compared with TD technology, he said, FD-OCT offers both an exponential increase in imaging speed (65-fold) and better resolution.

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