Functional damage is key to monitoring glaucoma

New York-The ideal monitor of glaucoma progression should have high sensitivity, high specificity, be resistant to fluctuations of the condition, require few confirmatory tests, have broad sensitivity at all stages of the disease, and be easy to interpret, according to David S. Greenfield, MD, who spoke at the Glaucoma 2004 meeting here.

At this time such a monitor is not yet available, but progress is being made, said Dr. Greenfield, associate professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami.

Seven trials conducted over the last 2 decades have described a number of risk factors for progression, he said, but with a bothersome lack of agreement among the findings.

Thus, it becomes essential to establish these confidence limits quantitatively to differentiate stable eyes from those in which glaucoma is progressing.

The Humphrey Glaucoma Progression Analysis software (Carl Zeiss Meditec) uses data collected from 16 clinical sites over 6 years from the Early Manifest Glaucoma Trial and represents "a new advancement in our ability to take some broad steps," Dr. Greenfield said.

"It allows one to evaluate a sequence of SITA [Swedish Interactive Threshold Algorithm] visual fields critically in a way that statistically assesses progression," Dr. Greenfield said.

In the creation of this software, significance limits were obtained by testing a patient four times within a period of 1 month. Glaucoma would not be expected to pro-gress in this period and repeated testing provides a means of creating variability estimates. Patient threshold values are compared with these estimates after creating a baseline image formed from two reliable visual fields.

Subsequent follow-up examination results are compared with the baseline examination in order to identify specific points that are suspected to have had progression. A significant change in three points on two consecutive visual fields indicates "possible progression"; a significant change in three points on three consecutive visual fields suggests "probable progression." Thus, five visual field tests are needed to determine progression.

Standard automated perimetry is an established technique that has many advantages, said Jody R. Piltz-Seymour, MD, director of glaucoma service and glaucoma fellowship at the Scheie Eye Institute, and associate professor of ophthalmology, University of Pennsylvania, Philadelphia.

The SITA test, using newer Humphrey perimeters, allows threshold testing in half the time of full threshold testing, Dr. Piltz-Seymour said.

The program uses information about many factors-age, different patterns of glaucomatous loss, and so on-to predict future responses continuously as the test proceeds.