A: Injury, infection or tumors are all known to raise eye pressure, labelled secondary glaucomas, but the cause of eye drainage blockage without such issues is unknown. We do know that once this blockage occurs, fluid builds up within your eye, causing damaging pressure on the optic nerve. This pressure compromises the delicate optic nerve’s blood vessels and nerve fibers, causing vision loss. Cases of glaucoma that appear even with normal eye pressure are likely caused by poor blood flow to the optic nerve.