When monitoring for glaucoma progression, there is often a lack of agreement between results from visual field and structural imaging tests. Such discordance can occur for a number of reasons, with a variety of approaches for reconciling these differences.
This article was reviewed by David S. Greenfield, MD
Structural and functional measurements are both necessary to monitor for glaucoma progression, but their findings often do not coincide.
David S. Greenfield, MD, has reviewed data on the frequency of test discordance, contributing factors, and strategies to help reconcile the differences and improve agreement.
A common phenomenon
Dr. Greenfield, professor of ophthalmology, Douglas R. Anderson Chair in Ophthalmology, Co-Director Glaucoma Service Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, said mechanisms for discordance emphasized that structural and functional assessments in glaucoma often disagree.
Supporting his comment were data from a recently published study conducted at Bascom Palmer Eye Institute, [Nguyen AT, et al. Ophthalmol Glaucoma. 2019;2:36-46].
The study analyzed data from 147 eyes that were followed annually for a mean of almost six years with visual field testing and OCT measurements of the retinal nerve fiber layer (RNFL) and macula. It found that progression was documented by all three metrics in only 7% of eyes.
“Longitudinal changes in retinal nerve fiber layer thickness should agree with changes in macular ganglion cell measurements, which should agree with serial changes in visual function using standard automated perimetry,” Dr Greenfield said. “Yet many patients with glaucoma progression will develop isolated changes in structural tests without detectable changes in visual function, and vice versa.”
The fact that there is a nonlinear relationship between structure and function is one factor that contributes to discordance between the findings of their respective diagnostic tests.