What is low-tension and normal-tension glaucoma?

Glaucoma is a group of eye diseases that cause vision loss through damage to the optic nerve. In low-tension or normal-tension glaucoma, the optic nerve (nerve fibers that transmit visual impulses to the brain) suffers damage typical of glaucoma, but at normal eye pressures. The diagnosis is often made after there has been some vision damage, but more sensitive diagnostic techniques are making it possible to detect this disease earlier, before peripheral vision is lost. After other possible causes of the optic nerve damage and visual loss have been eliminated, lowering the pressure even further with medication, surgery, or both will usually stabilize the condition.