Glaucoma is a group of diseases that cause damage to the optic nerve as a result of increased eye pressure. It is the second most blinding eye disease in the world. A large percentage of patients have no symptoms in the early stages of the disease, and only when the disease progresses to an advanced stage do they develop detectable symptoms, but by then a very important part of their vision has been irreparably lost. This is why it is also called the “thief of vision”. The eye is like a sink, with the faucet and drain always open. The intraocular fluid (i.e., atrial fluid) is constantly circulating through the anterior chamber. When the drain is blocked, the constantly generated atrial fluid cannot leave the eye quickly enough, resulting in a reservoir of atrial fluid. The stored fluid thus causes an increase in intraocular pressure [IOP] (The normal value of IOP is 10-21 mmHg.). To understand how the elevated pressure affects the eye, we can think of the eye as a balloon, and when too much gas hits the balloon, the rising pressure bursts the balloon. But the eye is relatively strong, not so easily broken. Instead, the pressure acts on the weakest point, which is the place where the optic nerve leaves the eye. High eye pressure damages every structure in the eye. The most important damage is optic nerve atrophy, which causes a diminishing range of vision and, in severe cases, blindness. Some advanced glaucoma vision may still be 1.5, but the range of seeing is very small. It is important to remember that visual acuity is not used as a criterion for good or bad glaucoma.