Glaucoma is a group of eye conditions that damage the optic nerve, which is vital to good vision. This damage is often caused by an abnormally high pressure in your eye.Glaucoma is one of the leading causes of blindness in the United States.It can occur at any age but is more common in older adults.ultimedia. Glaucoma is a group of eye conditions that damage the optic nerve, which is vital to good vision. This damage is often caused by an abnormally high pressure in your eye. Glaucoma is one of the leading causes of blindness in the United States. It can occur at any age but is more common in older adults.