Cyclopentolate 1% Decreases Schlemm’s Canal Dimension in Normal Subjects

Abstract

Purpose: To characterize the in vivo effect of cyclopentolate 1%, an anticholinergic agent, on the structure of Schlemm’s canal (SC) in normal eyes.

Methods: Healthy subjects with no ocular or systemic diseases known to affect the iridocorneal angle or trabecular aqueous outflow structures were prospectively recruited. Eighty-one serial horizontal enhanced depth imaging (EDI) optical coherence tomography (OCT) B-scans (interval between B-scans, ~35 µm) of the nasal corneoscleral limbal area were obtained before and 1 hour after cyclopentolate 1% administration. With conjunctival vessels and iris anatomy as landmarks, the same limbal area was scanned before and after cyclopentolate administration. The SC cross-sectional area was measured in each selected EDI OCT B-scan. After three-dimensional reconstruction, SC volume was determined.

Results: Eight eyes (5 men, 3 women; mean age, 27±4 years) were included. Mean intraocular pressure was 13.4±1.3 mmHg before and 13.8±1.1 mmHg after cyclopentolate administration (p=0.17). All patients developed mydriasis after administration. Schlemm’s canal was continuous in the scanned area in all eyes and was successfully delineated and reconstructed 3-dimensionally pre- and post cyclopentolate administration. Mean SC cross-sectional area decreased after cyclopentolate administration (6855±658µm² vs. 5848±791µm²; p<0.01). Mean SC volume also decreased (11852607±1145016 µm³ vs. 10117350±1368343 µm³; p<0.01).

Conclusions: Cyclopentolate 1% decreases SC dimension in healthy subjects. Whether this results from a direct anticholinergic effect on the canal or secondarily from its effect on the ciliary musculature and/or decreased trabecular outflow remains to be determined. EDI OCT of Schlemm’s canal may prove useful in evaluating the mechanisms of action of pharmacologic agents in glaucoma.