Researchers now suspect characteristics of the posterior sclera play a role in myopic normal-tension glaucoma. They even have a new method for measuring any misalignment between the posterior sclera and the optic disc, which may be a novel marker to predict myopic normal-tension glaucoma before its onset, according to Korean researchers.

Their study, published in the Journal of Glaucoma, used a new posterior scleral geometry parameter, the “misaligned angle” and the “absolute misaligned angle” to look at the alignment between the optic disc and posterior sclera. The study defined the misaligned angle as the degree of the deepest point of the eye deviated from a hypothetical line crossing the short axis of the optic disc either way, and the absolute misaligned angle was the absolute value of the misaligned value.

The study found the absolute misaligned angle along with the established parameter—the horizontal tilt angle—were significantly associated with myopic normal-tension glaucoma and greatly exceeded other measured parameters used in the study.

“Our result may be explained by the degree of absolute misalignment and the horizontal tilt representing a displaced direction of the optic nerve head to the posterior sclera, which may have occurred due to the altered configuration of the glaucomatous sclera. Diagnosis based on structural parameters alone can facilitate the prediction of progress to glaucoma before neuropathy occurs,” the researchers wrote in their paper.

The study included 203 eyes of 203 patients with myopia divided into two groups: myopic normal-tension glaucoma (113 patients) and non-glaucomatous myopia subjects (90 patients). Investigators analyzed the optic nerve head and posterior scleral parameters with swept-source OCT.

 The optic nerve head was classified as misaligned when the degree of misalignment was greater than 15 degrees in either direction.

Researchers found 20 (22.22%) out of 90 eyes in the non-glaucomatous group showed misalignment compared with 60 (53.09%) of the eyes in the myopic normal-tension group.

Additional studies are needed to predict the disease onset prior to glaucomatous damage, the researchers said. “Yet, our approach may have implications not only on the glaucoma diagnosis but also on the prediction before the onset,” they wrote.

Kim YC, Cho BJ, Jung KI, Park CK. Comparison of diagnostic power of optic nerve head and posterior sclera configuration parameters on myopic normal tension glaucoma. J Glaucoma. July 12, 2019. [Epub ahead of print].