Software enhances detection of glaucoma progression

Glaucoma progression is relatively easy to detect with visual fields and is made easier now using software (Glaucoma Progression Analysis [GPA], Carl Zeiss Meditec) with a proprietary diagnostic device (Humphrey Field Analyzer II, Carl Zeiss Meditec), said Donald L. Budenz, MD, MPH, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.

“The GPA program is based on principles for determining progression from a large clinical trial,” Dr. Budenz said. “It judges progression in a sensitive and, hopefully, specific way and is easy to use, but is underutilized.”

The software adjusts for reduced hill of vision that occurs with cataract and other media opacities and works with both baseline full threshold or Swedish Interactive Thresholding Algorithm fields. It was developed using criteria for diagnosing visual field progression in the Early Manifest Glaucoma Trial (EMGT). In that study, progression was defined as deterioration of three or more test points at a p < 0.05 level at the same location on three consecutive fields, he said.

The GPA printout is also simple to understand. Deterioration from a baseline field at p < 0.05 on one occasion appears as an open (empty) triangle. If that finding is confirmed on a second consecutive field, the location is identified with a half-filled triangle. Deterioration at the same location on three consecutive tests is noted with a completely colored triangle. Based on the EMGT progression criteria, the report will note “possible progression” if three or more points are changed at the same location on two consecutive tests and “likely progression” if three or more points changed at the same location on three consecutive tests.

Dr. Budenz pointed out a number of factors that can confound visual field test results, however. These include the learning effect in visual field testing, the possibilities of long-term fluctuation and a patient simply having a “bad day,” the limitations of identifying change in a patient with advanced glaucoma, and the likelihood that other pathologic conditions may be the cause of the true visual field changes.

“Remember that you always must start with good baseline information and clinical correlation is always advised,” Dr. Budenz said.