The authors utilized optical coherence tomography (OCT) with enhanced depth imaging (EDI) with the OCT anterior segment module to visualize the microarchitecture of Schlemm's canal before and four weeks after selective laser trabeculoplasty (SLT). Thirteen primary open-angle glaucoma eyes, average age 68 years, were included for analysis. Both 180 and 360-degree treatments were utilized, but the proportion is unknown. Intraocular pressure decreased on average 5 mmHg. The majority of the eyes were phakic.
The authors found the nasal cross-sectional area (CSA) of Schlemm's canal increased by 8% after SLT and was correlated with IOP drop along with an increase in the volume of the canal.
If technically feasible, a recommendation would be to include OCT of the temporal portion of the angle as well. For the patients that only underwent nasal SLT, the temporal angle OCT microarchitecture could be important from a non-treated viewpoint. For example, if the authors found an increase in cross-sectional area of the nasal canal but not temporally, this would imply the increase in canal area was mainly the result of increased aqueous flow in the region induced directly by the SLT as opposed to an increase in canal diameter due simply to a lower IOP. This would better delineate the mechanism of how SLT lowers IOP in glaucoma patients.
Clearly, a great deal of information can be learned about the canal and its surroundings with non-invasive OCT. With similar methodology in a study of the CSA of Schlemm's canal measured by OCT, these same authors found a 24% increase in the CSA of the canal after the instillation of pilocarpine 2%. As the technology improves, our delineation of the anatomy and physiology of the outflow system will ultimately lead to better canal-based surgical outcomes. Glaucoma surgeons and outflow researchers eagerly await these technologically challenging imaging advancements.