Ciliary muscle thickness and intraocular pressure before and after latanoprost

To test the hypothesis that a larger, latanoprost-induced intraocular pressure (IOP) reduction is associated with a thicker ciliary muscle.

Participants (N = 31) were healthy with the following details: mean ± SD age 24.8 ± 3.3 years. The ciliary muscle was imaged with anterior segment optical coherence tomography and Goldmann IOP was measured at baseline and 12-18 h after latanoprost instillation. Linear regression models of baseline IOP and IOP reduction as predicted by baseline ciliary muscle thickness were performed. Partial correlation coefficients were calculated for model predictor variables.

The mean ± SD latanoprost-induced IOP reduction was -2.6 ± 2.1 mmHg (t = -7.1, p < 0.0001). A larger reduction in IOP was significantly associated with thicker baseline maximum ciliary muscle thickness (CMTMAX) after controlling for age and baseline IOP (R² = 0.37; CMTMAX: -0.02, p = 0.01; age: 0.23, p = 0.08; baseline IOP: -0.39, p = 0.003), and was also significantly associated with thicker baseline ciliary muscle thickness 1 mm posterior to the scleral spur (CMT1) after controlling for age and baseline IOP (R² = 0.44; CMT1: -0.02, p = 0.002; age: 0.22, p = 0.06; baseline IOP: -0.43, p = 0.0008). Partial correlation coefficients between IOP reduction and baseline CMTMAX or CMT1 were -0.47 and -0.56, respectively.

Thicker baseline CMTMAX/CMT1 was associated with larger latanoprost-induced IOP reductions and lower baseline IOP. Future studies should determine the clinical usefulness of ciliary muscle dimensions as a predictor of the response to latanoprost in glaucoma patients.