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

The purpose of this study is to compare how two FDA-approved eye drops: netarsudil (Rhopressa) and timolol, protect nerve cells in the eye of adults with open-angle glaucoma. Both medications lower pressure inside the eye, but researchers want to learn if Rhopressa is more effective at slowing down or preventing the loss of retinal ganglion cells. These cells are essential for sight because they carry visual signals from the eye to the brain. Participants in this study will complete a total of 6 study visits over 12 months: * Participants will spend 6 months using Rhopressa eye drops and 6 months using Timolol eye drops. The order of the two eye drops will be chosen randomly. * At scheduled study visits, researchers will examine participants' eyes and measure eye pressure. * Researchers will take detailed pictures of the back of the eye using a specialized high-resolution camera called adaptive optics optical coherence tomography (AO-OCT). * Participants will also complete specialized visual field testing to measure eye function. Researchers will count and track individual nerve cells over time to determine if one medication offers better protection against cell loss than the other.

Inclusion Criteria: * All subjects will be 18 years of age or older * Subjects must be diagnosed with open-angle glaucoma and have had an eye exam within the past year * Subjects with glaucoma will have structural (optic nerve and retinal nerve fiber layer) and functional (visual field testing) defects consistent with the diagnosis of glaucoma * Subjects will have a corrected acuity of 20/50 or better and be able to fixate * Naïve to medication subjects or post washout IOP between 18 and 34 mmHg * Spherical equivalent from +3 diopters to -6 diopters, with a cylinder of \