Low vision is a general medical term used to describe impaired vision in both eyes that cannot be corrected to normal with medical treatment, surgery, or eyeglasses. The term low vision does not refer to any particular disease, it refers to the visual impairment itself, which can be caused by any of a wide variety of eye, optic nerve, and brain disorders. The leading causes of low vision are age-related eye diseases such as macular degeneration, glaucoma, and diabetic retinopathy. Although these diseases can be treated to slow or prevent further vision loss, any damage already done to the nerves in the eye or vision part of the brain cannot be undone, so in most cases the low vision is permanent.