New analytic tools: backward compatibility enhances scanning laser tomography

Stability of technology is important when dealing with patients who have a progressive disease, said Balwantray Chauhan, PhD, professor and director of research, Department of Ophthalmology, Dalhousie University, Halifax, Nova Scotia.

When technology is continually upgraded, clinicians sometimes find that they are no longer able to view images taken years ago, which is clearly a disadvantage in dealing with slowly progressing conditions such as glaucoma, Dr. Chauhan said. Confocal scanning laser tomography (which was developed 25 years ago) lends itself to backward compatibility, however.

As a glaucoma specialist, Dr. Chauhan is interested in variability over a short period; when this is known, one can set limits that define change and establish criteria for change. Several techniques have been developed to help clinicians measure change with confocal scanning laser tomography.

Both statistic image mapping (SIM) and topographic change analysis (TCA) are effective techniques for detecting topographic change in series of images, Dr. Chauhan said.

"With both SIM and TCA, you can apply images that were captured in the early 1990s, for example, and start to reveal things that weren't really obvious at the time because of the backward compatibility," Dr. Chauhan said.

In evaluating images, it is also important to be able to correct for spatial correlation, Dr. Chauhan concluded. Doing so considerably decreases the amount of noise that may affect the accuracy of the interpretation.