Wednesday, November 8, 2006

20/20 Vision

20/20 vision means perfect vision, right?  Wrong!  The term actually
signifies "normal" human vision.

Meaning of 20/20 Vision
"20/20 vision is a term used to express normal visual acuity (the
 clarity or sharpness of vision) measured at a distance of 20 feet.
 If you have 20/20 vision, you can see clearly at 20 feet what should
 normally be seen at that distance. If you have 20/100 vision, it
 means that you must be as close as 20 feet to see what a person with
 normal vision can see at 100 feet."

Wikipedia article on "Visual acuity"
"It is possible to have vision superior to 20/20: the maximum acuity
 of the human eye without visual aids (such as binoculars) is generally
 thought to be around 20/10 (6/3). Recent developments in optometry
 have resulted in corrective lenses conferring upon the wearer a vision
 of up to 20/10. Some birds, such as hawks, are believed to have an
 acuity of around 20/2, which is much better than human eyesight."

A Snellen Chart is often used in doctors' surgeries to determine
visual acuity.  If you're at work and want to make a dork of
yourself, use the following chart to estimate your visual acuity:
Read the instructions to work out how far to stand from your monitor,
and remember to test one eye at a time.

(It turns out that my right eye is better than my left eye.)