Glaucoma

"Glaucoma is a group of eye diseases that gradually steal sight without warning. Although the most common forms primarily affect the middle-aged and the elderly, glaucoma can affect people of all ages.
There are two main types of glaucoma: primary open angle glaucoma (POAG), and angle closure glaucoma. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye. When optic nerve damage has occurred despite a normal IOP, this is called normal tension glaucoma. Secondary glaucoma refers to any case in which another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and subsequent vision loss."