Link seen between corneal elasticity and glaucomatous damage

SAO PAULO, Brazil — The physiology of the cornea, not only its anatomy, appears to be strongly correlated with glaucomatous damage, according to a study presented here.

Nathan Congdon, MD, presented a paper that examined physiologic factors such as corneal bioelasticity as predictors of glaucomatous damage.

“Parameters besides the thickness of the cornea, related to deformability or the physiologic state of the cornea, may also be related to glaucoma risk,” Dr. Congdon said.

The study by Dr. Congdon and colleagues at Johns Hopkins University was named one of the “Best National Papers” here at the World Ophthalmology Congress.

Clinical studies have confirmed a relationship between corneal thickness and glaucomatous damage, but the nature of the relationship is not yet clear, Dr. Congdon said.

“We know that measured IOP varies with central corneal thickness for all modalities,” he said. “Yet this relationship has not been quantified and may or may not be linear.”

Because the significance of central corneal thickness is still not entirely clear, Dr. Congdon said it is “important to look at the physiology and not just the anatomy.”

Among the physiologic factors to be considered are hydration, connective tissue composition and bioelasticity, he said.

Dr. Congdon and associates conducted a retrospective review of the charts of one or two eligible eyes of 230 participants, 85% of whom were glaucoma patients or suspects. From the patients’ charts they recorded age, race, gender, diagnosis, number of years since diagnosis, baseline and current IOP, and cup-to-disc ratio. They also recorded visual field data including mean defect, pattern standard deviation, visual field progression and hemifield test.

Hysteresis was then measured in these subjects using the noncontact Ocular Response Analyzer from Reichert. Dr. Congdon and colleagues found that low corneal bioelasticity, also known as hysteresis, was associated with the presence of visual field progression, while central corneal thickness was not.

Dr. Congdon acknowledged that the study was not able to establish causality and was limited by the fact that much of the data were attained retrospectively. However, he said, it is “one of the first studies to suggest the link between corneal deformability and glaucoma damage.”