Glaucoma is a condition in which there is raised pressure but it is NOT blood pressure, it is the cerebrospinal fluid known as CSF. It monitors the foreign bodies that enter and leave the blood. It forms barrier and prevents most of the dangerous bacteria to enter the blood - hence enter the brain. CSF is found in many places, from the brain to the spinal cord. so it is a guard for all these places. The eyes also come is this category. But when something goes wrong with the CSF like its not drained properly then there's raised CSF pressure in the eyes which affects the eye sight.