Glaucoma May Decrease Structural Response to Pilocarpine

Fewer topical pilocarpine-induced changes to outflow pathway structures were observed among patients with primary open-angle glaucoma (POAG) compared with non-glaucoma eyes, according to results of an optical coherence tomography (OCT)-based study published in the Journal of Glaucoma. The researchers also evaluated intraocular pressure (IOP) changes. “Treatment with pilocarpine induced a decline in IOP, decrease in scleral spur length, decrease in trabecular meshwork thickness, and increase in [Schlemm canal (SC)] diameter and SC area in healthy controls. In contrast, no significant changes in OCT measurements were observed in patients with POAG.”

The researchers considered 30 patients with POAG (mean age 44.47±13.35 years; 22 men, 8 women) and 26 healthy controls (mean age 42.08±15.21 years; 16 men, 10 women)) were recruited for this study from the Tongji Hospital in China in 2019. All participants underwent swept-source OCT and the change of outflow pathway structures were evaluated before and one hour after 2% pilocarpine administration.

At baseline, the POAG cohort had elevated IOP(mean, 20.89 vs 15.56 mm Hg; P <.001) and decreased trabecular meshwork thickness (mean, 90.17 vs 104.30 μm; P <.001), scleral spur length (mean, 155.85 vs 185.44 μm; P <.001), retinal nerve fiber layer thickness (mean, 57.33 vs 97.50 μm; P <.001), SC diameter (mean, 134.84 vs 178.19 μm; P =.001), SC area (mean, 3851.37 vs 5091.60 μm2; P =.008), and mean deviation (mean, -13.75 vs 0.06 dB; P <.001) compared with controls, respectively.

In the multivariate analysis which adjusted for age, gender, and central corneal thickness, ciliary muscle thickness correlated with IOP among controls (β, 0.162; P =.012). No correlations between eye structures and IOP were observed among the POAG group.

Administering pilocarpine resulted in a decrease in IOP to 14.6 mm Hg among controls but no change among patients with POAG. Similarly, changes in scleral spur length, trabecular meshwork thickness, and SC diameter and area after pilocarpine administration was observed among controls but not among patients with POAG.

The change in IOP after pilocarpine administration was correlated with the change in the trabecular meshwork among controls (β, -0.519; P =.047) and with the change in scleral spur length (β, -0.609; P =.003) and in ciliary muscle angle (β, -2.550; P =.001) among the patients with glaucoma.

“Our results were consistent with those of previous studies, and we found that SC diameter and area were significantly smaller in patients with POAG than in healthy controls,” the researchers explain. “Although pilocarpine has been widely used to treat angle-closure glaucoma, its in vivo effects on the conventional outflow pathway of eyes with POAG remain unclear.”

The major limitation of this study was that outflow pathway changes after pilocarpine administration were time-dependent and may have differed between participants or groups on the basis of observation time.