The government defines legal blindness with the same terms eye care specialists use to describe low vision-acuity and visual field. BACK TO THE TOP 2. Acuity describes the amount of detail a given individual sees compared to what a person with normal vision sees. The smaller the second number, the more sight a person has. BACK TO THE TOP 3.
Visual field refers to how great an area a person can see and is measured, in degrees, as an angle.
The central one-third of the visual field is seen by both eyes. A visual deficit may be a central field loss, or may occur elsewhere in the visual field. A person is said to have low vision if she can only see a 40-20 degree field, or less, in her best eye. BACK TO THE TOP 4. Low vision can be caused by an accident, a disease, or a condition dating from birth or early childhood.