Precis:Lower response of aqueous outflow pathway structures after pilocarpine could be observed in primary open angle glaucoma (POAG) patients, which is likely to be helpful for understanding intraocular pressure (IOP) evaluation in glaucoma. Purpose:To evaluate the morphologic changes in the trabecular meshwork (TM), Schlemm canal (SC), scleral spur (SS), and ciliary muscle after miosis in patients with POAG and healthy individuals. Methods:A total of 30 patients with POAG and 26 healthy controls were recruited. All participants underwent complete ophthalmologic examinations, including IOP and swept-source optical coherence tomography (OCT), before and 1 hour after the local administration of pilocarpine (2%). OCT measurements included TM thickness and width, SC diameter and area, SS length, ciliary muscle thickness, and ciliary muscle angle (CMA). Results:Pilocarpine administration induced a decline in IOP (15.6 & PLUSMN;2.3-14.6 & PLUSMN;2.2 mm Hg), decrease in nasal SS length (196.31 & PLUSMN;47.75-171.52 & PLUSMN;33.93 & mu;m), decrease in TM thickness (90.18 & PLUSMN;16.43-83.02 & PLUSMN;13.74 & mu;m), and increase in SC diameter (134.84 & PLUSMN;32.28-162.08 & PLUSMN;48.67 & mu;m) and SC area (3851.37 & PLUSMN;1455.07-4801.39 & PLUSMN;1762.37 & mu;m(2) ) among healthy controls. In contrast, no significant changes in IOP and OCT measurements were found in patients with POAG. At baseline, CMA was independently correlated with IOP in normal eyes. After miosis, the change in TM thickness was independently correlated with changes in IOP in normal eyes; in eyes with POAG, changes in SS length and CMA were independently associated with changes in IOP. Conclusions:Topical pilocarpine-induced morphologic changes to outflow pathway structures in healthy individuals without significant changes in POAG. The lower response observed in patients with glaucoma may be relevant to understanding IOP changes.