Visual acuity

In the US, the Snellen Eye Chart is the chart most commonly used by ophthalmologists and optometrists to measure a person's distance visual acuity. The chart is used to measure how well you can see at a distance of 20 feet away from the chart. For example, if the eye doctor tells you your distance visual acuity is 20/20 this is determined to be 'normal' vision. However if your distance visual acuity is measured at 20/200, this means that a person with 'normal' (20/20) vision will correctly identify an object from 200 feet, but you will need to be as close as 20 feet to identify the same object.

Few people today are totally without sight. In fact, 85% of all individuals with eye disorders have some remaining sight — and approximately 15% are totally blind.

Legal Blindness

In the United States, legal blindness [link opens in new window] refers to the criteria used to determine eligibility for government disability benefits and do not necessarily indicate a person's ability to function. In the United States, the criteria for legal blindness are:

• Visual acuity of 20/200 or worse in the better eye with corrective lenses (20/200 means that a person at 20 feet from an eye chart can see what a person with normal vision can see at 200 feet); or
• Visual field restriction to 20 degrees diameter or less (often known as 'tunnel vision') in the better eye.

Total blindness

Total blindness is the complete lack of form and light perception and is recorded as "NLP", an abbreviation for "no light perception."

Low Vision

The term "low vision," also known as "partial sight," is defined as "a degree of vision that is functional but limited enough to interfere with the ability to perform everyday activities and that cannot be corrected with standard eyeglasses or contact lenses."