 Where this angle is narrowed or closed, pressure increases over time, causing damage to the optic nerve, leading to blindness.Primary open-angle glaucoma (also, "primary glaucoma", "chronic glaucoma") refers to slow clogging of the drainage canals resulting in increased eye pressure which causes progressive optic nerve damage.This manifests as a gradual loss of the visual field, starting with a loss of peripheral vision, but eventually the entire vision will be lost if not treated.