Ever wondered why Glaucoma is called “ the sneak thief of sight”? The most common form of glaucoma has no warning signs. The effect is so gradual that you may not notice a change in vision until the condition is at an advanced stage. Glaucoma is a leading cause of irreversible blindness worldwide. It is a group of eye conditions that damage the optic nerve, which is vital to good vision. This damage is often caused by abnormally high pressure in your eye.