True blindness is when an eye is not capable of seeing any images or light. Even extremely bright lights directed right at the eye are not seen. Legal blindness refers to an eye’s ability to read a certain level on a Snellen eye chart. The Snellen eye chart is the standard eye chart that is used at an eye care provider’s office to measure and record vision. The large E on the Snellen eye chart refers to 20/400 vision, and the next line is recorded as 20/200 vision. Patients who are legally blind cannot read any further down on the eye chart than the 20/200 line. This means they may read the 20/200 line, the 20/400 line, or none of the eye chart. Legal blindness is determined by the best-seeing eye.
For patients to be declared legally blind, neither of their eyes would be capable of reading better than 20/200. Patients who are unable to read better than 20/200 in one eye but capable of better vision in their fellow eye are not considered legally blind. For instance, if the bad eye is 20/400 and the good eye is 20/80, then the patient’s best vision is considered 20/80, and he or she would not be considered legally blind. If legally blind, individuals may be eligible for certain benefits, including a possible deduction on income tax, as well as help from various businesses and organizations (such as unlimited directory assistance from the phone company or visual aids from state commissions for the blind).