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Original Investigation |

Effect of Pilocarpine Hydrochloride on the Schlemm Canal in Healthy Eyes and Eyes With Open-Angle Glaucoma

Alon Skaat, MD1,2; Michael S. Rosman, BA1; Jason L. Chien, BS1; Rachel S. Mogil, BS3,4; Ruojin Ren, MD, PhD1; Jeffrey M. Liebmann, MD5; Robert Ritch, MD1; Sung Chul Park, MD3,4
[+] Author Affiliations
1Moise and Chella Safra Advanced Ocular Imaging Laboratory, Einhorn Clinical Research Center, New York Eye and Ear Infirmary of Mount Sinai, New York
2Goldschleger Eye Institute, Sheba Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
3Department of Ophthalmology, Manhattan Eye, Ear and Throat Hospital, New York, New York
4Department of Ophthalmology, Hofstra Northwell School of Medicine, Hempstead, New York
5Bernard and Shirlee Brown Glaucoma Research Laboratory, Harkness Eye Institute, Columbia University Medical Center, New York, New York
JAMA Ophthalmol. 2016;134(9):976-981. doi:10.1001/jamaophthalmol.2016.1881.
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Importance  The in vivo effect of pilocarpine hydrochloride on the Schlemm canal may help explain its pharmacologic mechanism of action and better indicate its clinical use.

Objective  To investigate the effect of pilocarpine on the structure of the Schlemm canal in vivo in healthy eyes and eyes with glaucoma.

Design, Setting, and Participants  In this case-control study, healthy individuals and patients with open-angle glaucoma were prospectively enrolled between September 1, 2013, and June 30, 2014, after a complete ophthalmologic examination at a tertiary glaucoma referral practice. Eighty-one serial, horizontal, enhanced depth imaging optical coherence tomographic B-scans (interval between B-scans, approximately 35 µm) of the nasal corneoscleral limbus were performed before and 1 hour after topical administration of pilocarpine, 1%, in 1 eye of healthy volunteers and pilocarpine, 2%, in 1 eye of patients with glaucoma. Fifty B-scans in the overlapping area (circumferential length, approximately 1.7 mm) between the 2 sets of serial scans (before and after pilocarpine administration) were selected for analysis based on the structures of aqueous and blood vessels as landmarks. The cross-sectional area of the Schlemm canal was measured in each selected B-scan. Volume of the Schlemm canal was calculated using commercially available 3-dimensional reconstruction software.

Main Outcomes and Measures  Mean cross-sectional area of the Schlemm canal.

Results  Enhanced depth imaging optical coherence tomographic scans of the Schlemm canal were performed successfully before and after administration of pilocarpine, 1%, in 9 healthy eyes (9 individuals) and pilocarpine, 2%, in 10 eyes with glaucoma (10 patients) (mean [SD] age, 31.9 [7.8] and 68.7 [13.2] years, respectively). Following pilocarpine administration, mean (SD) intraocular pressure decreased from 14.3 (1.3) to 13.7 (1.1) mm Hg in healthy eyes (P = .004) and from 17.5 (6.0) to 16.6 (6.1) mm Hg in eyes with glaucoma (P = .01). The mean (SD) cross-sectional area of the Schlemm canal increased by 21% (4667 [1704] to 5647 [1911] µm2) in healthy eyes (P < .001) and by 24% (3737 [679] to 4619 [692] µm2) in eyes with glaucoma (P < .001) (mean difference in percent increase, 2.2%; 95% CI, –8.5% to 12.9%). The mean (SD) volume of the Schlemm canal in the overlapping area increased from 8 004 000 (2 923 000) to 9 685 000 (3 277 000) µm3 in healthy eyes (P < .001) and from 6 468 000 (1 170 000) to 7 970 000 (1 199 000) µm3 in eyes with glaucoma (P < .001).

Conclusions and Relevance  These data suggest that pilocarpine expands the Schlemm canal in eyes with and without glaucoma. No differences in the effect were identified between the 2 groups. Enhanced depth imaging optical coherence tomography may be useful in investigating the effect of pharmacologic agents on the Schlemm canal.

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Figure 1.
Enhanced Depth Imaging (EDI) Optical Coherence Tomography (OCT) of the Schlemm Canal

A, The 15° × 5° rectangular area in the nasal limbus for 81 serial horizontal EDI OCT B-scans (box). B, Magnified horizontal EDI OCT B-scan with a clear visualization of the Schlemm canal (arrowhead). AC indicates anterior chamber.

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Figure 2.
Representative Enhanced Depth Imaging Optical Coherence Tomography B-Scans

A, The Schlemm canal (arrowhead) before administration of pilocarpine, 1%, to participant 2 (no glaucoma). B, The Schlemm canal (arrowhead) 1 hour after administration of pilocarpine, 1%, to participant 2. C, The Schlemm canal (arrowhead) before administration of pilocarpine, 1%, to participant 3 (no glaucoma). D, The Schlemm canal (arrowhead) 1 hour after administration of pilocarpine, 1%, to participant 3. AC indicates anterior chamber.

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