Open-angle glaucoma. Fundoscopy image of the retina of the left eye of a patient with open-angle glaucoma. The retina is the light-sensitive layer at the back of the eye. The image shows glaucomatous papillary excavation of the optic disc with shifted blood vessels. Glaucoma is a condition in which the pressure of fluid inside the eyeball builds up to harmful levels. Open-angle glaucoma develops slowly over time and there is no pain. If untreated, it can cause blindness.