UC San Diego

Purpose

To use robotic visible-light optical coherence tomography (vis-OCT) to study circumferential segmental Schlemm's canal (SC) anatomy in mice after topical pilocarpine administration.

Methods

Anterior segment imaging using a robotic vis-OCT to maintain perpendicular laser illumination aimed at SC was performed. Sixteen mice were studied for repeatability testing and to study aqueous humor outflow (AHO) pathway response to topical drug. Pharmaceutical-grade pilocarpine (1%; n = 5) or control artificial tears (n = 9) were given, and vis-OCT imaging was performed before and 15 minutes after drug application. SC areas and volumes were measured circumferentially.

Results

Circumferential vis-OCT provided high-resolution imaging of the AHO pathways. Segmental SC anatomy was visualized with the average cross-sectional area greatest temporal (3971 ± 328 µm2) and the least nasal (2727 ± 218 µm2; P = 0.018). After pilocarpine administration, the SC became larger (pilocarpine, 26.8 ± 5.0% vs. control, 8.9 ± 4.6% volume increase; P = 0.030). However, the pilocarpine alteration was also segmental, with a greater increase observed superior (pilocarpine, 31.6 ± 8.9% vs. control, 1.8 ± 5.7% volume increase; P = 0.023) and nasal (pilocarpine, 41.1 ± 15.3% vs. control, 13.9 ± 4.5% volume increase; P = 0.045).

Conclusions

Circumferential noninvasive imaging of the AHO pathways was done in vivo. Segmental SC anatomy was seen, consistent with the known segmental nature of trabecular AHO. Segmental SC anatomical response to a muscarinic agonist was also observed. Segmental glaucoma drug response around the circumference of AHO pathways is an observation that may influence patient response to glaucoma treatments.