During a comprehensive eye examination or vision screening you will be asked to read the smallest row of letters on a chart to determine if your vision is “normal.” In the United States 20/20 vision is accepted as what the typical human being can see. But what exactly does this mean?
The top number of 20/20 indicates a distance, typically the distance an eye chart is from the person reading it. The bottom number indicates the size of the letter on the chart that can be read. For example, if your vision is 20/40, that means that the smallest letter you can see 20 feet away is twice as big as one a person with 20/20 vision can see at that same distance.
You can measure visual acuity with correction (with glasses or contact lenses) or without correction. Most often your eye doctor wants to determine what your “BCVA” or Best Corrected Visual Acuity is. When 20/20 can’t be achieved with glasses or contact lenses then a reason for this must be found. There are many reasons someone may have less than 20/20 BCVA. Congenital conditions, disease processes, or just not receiving corrective lenses early enough in life can all lead to permanently reduced acuity. Some conditions of the eye like cataracts cause temporarily reduced acuity until they can be removed with surgery.
A comprehensive examination with an optometrist is recommended as early as 6 months old in order to diagnose problems that could lead to permanently reduced visual acuity. Regular eye examinations throughout adult life may help prevent decreased BCVA as well by making early diagnosis and treatment intervention possible.
By Dr. Melissa Sterling
Eye Doctor | Greenville
Doctors Vision Center