Update on new methods of diagnosing glaucoma

Advances have been made recently in both structural and functional technologies for evaluating glaucoma. While many of these tools appear to perform better than earlier technologies, well-designed studies of their diagnostic abilities are still lacking, said Felipe A. Medeiros, MD, assistant professor of ophthalmology, University of California, San Diego.

Until recently, clinicians had to rely on time-domain optical coherence tomography (OCT) for structural assessment, but this technology was relatively slow and produced only a limited number of scans, Dr. Medeiros said. Now, spectral domain OCT has arrived, a technology in which a spectrum is measured with a spectrometer in the detection arm of the interferometer and converted to depth information by Fourier transformation.

"Spectral domain OCT has better resolution and faster image acquisition than time-domain OCT," Dr. Medeiros said. "Instead of just acquiring a limited number of points around the optic nerve, we can get a complete map of the nerve fiber layer."

A recent improvement in scanning laser polarimetry is the development of enhanced corneal compensation, a new software package that can be incorporated into a scanning laser polarimeter (GDx VCC, Carl Zeiss Meditec). This software can eliminate or reduce atypical retardation patterns.

Confocal scanning laser ophthalmoscopy has also been improved. The latest version of a particular tomographer (Heidelberg Retina Tomograph, Heidelberg Engineering GmbH) includes the glaucoma probability score. In a recent study, the glaucoma probability score predicted development of visual field loss in glaucoma suspects over time, and its reliability was similar to that of subjective assessment of optic disk photographs by glaucoma experts, Dr. Medeiros said.

Advances have also occurred in functional testing devices.

"With the introduction of SITA SWAP testing [Swedish interactive test algorithm short-wavelength automated perimetry], we have seen a reduction in testing time from SWAP and also reduced variability," Dr. Medeiros said.

Testing can be completed in about 5 minutes, compared with 15 minutes with SWAP.

Changes have been made as well in frequency-doubling technology. Smaller test stimuli are being used in the 24-2 program (incorporated into the Humphrey Matrix, Carl Zeiss Meditec), resulting in better characterization of visual field defects.