Although researchers have yet to understand why only some highly myopic eyes develop postoperative IOP elevation and others with similar axial length do not, a new study may suggest that anatomical differences in the drainage passage may play a role. Researchers in China determined smaller vertical diameter of Schlemm’s canal and a thinner trabecular meshwork as two anatomical risk factors for early IOP elevation after cataract surgery in highly myopic eyes. The researchers believe that these principle sites of aqueous outflow warrant close attention.

The study included 88 highly myopic patients after uneventful cataract surgery, 31 of whom had early post-op IOP elevation and 57 of whom did not. The researchers used swept-source OCT to collect morphological features of Schlemm’s canal and trabecular meshwork for review.

In the highly myopic eyes, average Schlemm’s canal vertical diameter, Schlemm’s canal area, trabecular meshwork thickness and width all correlated negatively with the IOP elevation. Compared with the non-elevation group, these parameters were all smaller in the elevation group.

The researchers believe highly myopic eyes with these anatomical features are less capable of dealing with aqueous drainage during the early postoperative period, when the angle is obstructed by the sudden increase in surgically derived remnants. The narrowing of Schlemm’s canal may result from the reduced biomechanical properties of these eyes, which cause a weak and deformed Schlemm’s canal.

The study concluded that preoperative assessment of Schlemm’s canal and the trabecular meshwork with OCT on highly myopic cataract patients will ensure sufficient communication with patients, timely treatment and better clinical outcomes.

Qi J, He W, Lu Q, et al. Schlemm’s canal and trabecular meshwork features in highly myopic eyes with early intraocular pressure elevation after cataract surgery. Am J Ophthalmol. February 14, 2020. [Epub ahead of print].