Glaucoma is an eye disease where the pressure inside the eye causes damage to the optic nerve at the back. Because this nerve connects the eye to the brain, damage to it will cause damage to vision..
There are various types of Glaucoma, but broadly they can be divided into chronic (open angle) where damage occurs slowly and painlessly- this is the most common type, and acute which is painful and characterised by a sudden dramatic rise in pressure. Most Glaucomas are bilateral, though frequently one eye is affected earlier or is more severely affected at discovery than the other.
The lens inside the eye and the cells on the back of the cornea do not have a blood supply- blood is opaque and would interfere with light getting into the eye- but being living tissue, they require oxygen and nutrients like any other. They are supplied these by the Aqueous Humour, a clear fluid which fills the frontal segment of the eye. Aqueous is derived from blood plasma and is produced by the Ciliary Body behind the Iris, flows through the pupil and eventually drains through a circular (Schlemm’s) canal between the Iris and Cornea, back into the bloodstream.
IntraOcular Pressure- the pressure inside the eye- is a balance between the amount of fluid produced, and the amount draining away- overproduction which is rare, or more commonly decreased drainage will increase pressure.