Structure/function discordance analyzed

SAN DIEGO – A study aimed at understanding the reasons for discordance between structural measurements and functional tests in glaucoma was presented on Friday here at the annual Academy of Optometry meeting.

Jerome Sherman, OD, FAAO, said that while in many cases structural observations and measurements are in agreement with functional tests, discrepancies do occur. “We’re very interested in why this discordance occurs,” he said.

In this study, Dr. Sherman and colleagues looked at 70 indisputable cases of glaucoma. In cases with little correlation between structure and function, attempts were made to analyze and categorize the reasons for discordance.

Through this analysis, the cases were divided into four groups: 1) superior structure/function agreement, 2) moderate structural abnormalities with moderate correlating functional abnormality, 3) structural abnormalities with no correlating functional defects and 4) functional abnormalities with no matching structural anomalies.

In cases where structural abnormalities but no corresponding functional defects existed, the study found that this was largely due to structural defects at or very near the vertical meridian or nasal to the disc or nasal disc zone. In cases where functional abnormality existed with no correlating structural defect, the analysis showed that these field defects were within the central 10 to 15 degrees.

Dr. Sherman discussed how this discordance might reveal the weaknesses and strengths of function and structure tests. “Function tests are better if it (visual field defect) is confined to the papillomacular bundle,” Dr. Sherman said, “and structural tests are better if the retinal nerve fiber layer defect is in the vertical meridian, or if the retinal nerve fiber layer defect is nasal to the disc.”

Dr. Sherman added that tests of both structure and function are advised for the early detection of glaucoma.