Imaging method identifies glaucoma risk

FDOCT systems operating at a central wavelength of 1310 nm have been tried in glaucoma diagnosis before, but the increased sensitivity of the Fourier-domain approach comes at the price of limited usable imaging depth, partly due to the presence of a symmetric overlapping image artefact in the images. This artefact, referred to as the complex conjugate artefact, complicates image acquisition and prevents the technique from looking deeper than 3 to 4 mm into the critical anterior chamber of the eye; not deep enough for a firm diagnosis.

The Duke University team has developed a novel approach using interferometers constructed from 3 x 3 optical couplers for simultaneous acquisition of phase-separated spectral interferometric data, as well as a high-speed algorithm to correct for imperfect or miscalibrated phase shifts. This combination provides high-resolution, quantitative imaging in vivo at a scan rate of more than three times higher than that attainable with time-domain OCT systems, and is also able to image at greater depths.

"Resolution of the complex conjugate artefact permitted a scan depth in excess of 6.3 mm, allowing imaging of the entire depth of the anterior chamber while reducing artefacts," said Asrani. "The combination of this depth resolution and the detailed viewing possible with FDOCT technology represents a novel breakthrough in this field."

In addition to imaging the drainage angle region and iris, the system permits visualization of other areas of in the eye in both two-dimensional and volumetric cross-sectional images, suggesting a wide range of potential clinical applications. Use of this adapted FDOCT method in glaucoma treatment may permit accurate diagnosis even by a general eye care practitioner without any specialist training.

Asrani predicted that the technique would be available at teaching or university hospitals within five years.