Glaucoma is a disease that causes damage to the optic nerve from excess pressure inside the eye.  The nerve fibers that connect the retina to the optic nerve are slowly damaged causing areas of poor vision.  This damage occurs in the periphery, particularly the lower field of vision.  It also occurs very slowly so the person is not really aware of the visual loss.  It is very common for a person with glaucoma to go without any help for a long time because they do not realize how bad the vision has become.  The central vision is usually good for a long time so reading and distance vision remain intact.

Many people have high pressure that is controlled with eyedrops.  This is usually not a serious condition as long as the drops are used correctly to keep the pressure down.  Glaucoma is worse when the pressure cannot be controlled or has been high for a long time before it is detected. Sometimes laser treatment is used to open drainage channels in the eye to allow excess fluid to escape, sometimes surgery to insert shunts to drain the fluid is necessary.  The fluid is internal and does not show up as tears or drain outside the eye.  It drains into the blood stream through channels in the front area of the eye.