When we discuss or consider blindness, this is what most people visualize: a complete darkness or absence of any vision.

In reality, less than 15% of all the people who are defined as legally blind have no usable remaining vision. That means approximately 85% of those who are considered legally blind do possess some remaining vision.

The definition of legal blindness is 20/200 or less visual acuity in the better eye with best correction, or if the visual field is restricted to 20° or less. What that means is 20/200 visual acuity is a comparison of what the normal eye sees at 200 feet in distance — this individual needs to be within 20 feet to see the same detail. The large "E" on the Snellen Acuity chart — which is used in most doctor's offices, is the 20/200 line. The better eye in the definition means the eye with the best vision and it has to be 20/200 or less acuity. For example, a person could be totally blind in one eye, with just slightly better than 20/200 acuity, and would not be considered legally blind. The best correction in the definition means while wearing glasses or contact lenses to correct the refractive error. Visual field restriction means that a person could possess 20/20 visual acuity, but if vision is affected in the peripheral fields to 20° or less, then that person is still considered legally blind.

Sometimes the vision is referred to as "tunnel vision" and is similar to looking through a straw where only the central vision is usable. Due to the definition of legal blindness which is a national and in fact, an international standard, it has led one pioneer in the field of blindness and visual impairment to comment, "More people are blinded by definition than by any other cause."