Adaptive Optics OCT Evaluation of Rhopressa's Effects on the Retinal Ganglion Cells in Glaucoma Patients

Glaucoma is a chronic, progressive optic neuropathy characterized by functional and structural alterations, specifically the degeneration and loss of retinal ganglion cells (RGCs). Currently, the main modifiable factor for intervention is aimed at lowering intraocular pressure (IOP). While IOP reduction slows disease progression, it does not halt neurodegeneration. Rho kinase (ROCK) inhibitors have been reported to provide benefit in neurodegenerative diseases. Netarsudil ophthalmic solution (Rhopressa) is a ROCK inhibitor approved for the treatment and management of open-angle glaucoma that lowers IOP and has reported protective effects on neural tissue. However, previous attempts to illustrate true cell loss or protection using clinical instrumentation have not demonstrated an effect to date. High-resolution retinal imaging based on adaptive optics optical coherence tomography (AO-OCT) enables direct visualization, tracking, and quantification of individual ganglion cell layer (GCL) somas in the living human eye. Leveraging the unique imaging capabilities and extraordinary sensitivity of ultra-high-speed AO-OCT, this study will test the hypothesis that treatment with netarsudil is more effective at reducing glaucomatous ganglion cell loss while producing comparable intraocular pressure reduction to that of the comparator. This prospective, randomized, investigator-masked, cross-over pilot study will compare RGC survival rates between two treatment groups (Rhopressa and Timolol). Thirteen subjects with open-angle glaucoma will be recruited. Following a screening assessment and medication washout period based on drug class, eligible subjects are randomized 1:1 into two age-matched cohorts: * Cohort 1: Receives Rhopressa (one drop once at night) for 6 months, then crosses over to receive Timolol 0.25% (one drop twice a day) for 6 months. * Cohort 2: Receives Timolol 0.25% (one drop twice a day) for 6 months, then crosses over to receive Rhopressa (one drop once at night) for 6 months. At Visit 2 (baseline), Visit 4 (6 months), and Visit 6 (12 months), subjects undergo imaging using the Indiana AO-OCT system along with Goldmann applanation tonometry, standard clinical OCT, and OCT-guided microperimetry (MP-3). AO-OCT imaging is performed at the same retinal regions surrounding arcuate defects to enable longitudinal cellular-level analysis. Primary and secondary endpoints evaluate differences in the rate of change of RGC soma density, individual RGC counts, and GCL thickness between treatment periods.