Caffeine Consumption in Glaucoma Patients and Healthy Subjects

This trial is studying how caffeine consumption affects the tiny blood vessels in the eyes of people with glaucoma (a condition where the optic nerve is damaged due to high eye pressure) compared to people with healthy eyes, using a special type of eye scan called OCT angiography. **You may be eligible if...** - You are between 18 and 90 years old - You have been diagnosed with primary open-angle glaucoma (mild, moderate, or advanced), OR - You are a healthy person with no eye disease (for the control group) **You may NOT be eligible if...** - You have other eye or body conditions that would affect the scan results - You have more than a moderate cataract (clouding of the eye lens) - You have nystagmus (uncontrolled eye movement) - You have macular degeneration beyond very mild drusen or pigment changes - You have diabetes - You are unable to focus on a target during the scan Talk to your doctor to see if this trial is right for you.