By Sandra Duke
20/20 vision is normal visual acuity. Visual acuity is the ability to see symbols and objects clearly from a distance. Each line on the eye chart has a different bottom number usually from 20/200 down to 20/10. The top number represents the distance a person being tested stands from the eye chart. The bottom number represents how far away a person with normal vision can be from the chart and still read the letters. So, a person with normal vision can read the 20/20 line from 20 feet away, the 20/200 line from 200 feet away, and the 20/10 line from 10 feet away. A person with 20/10 vision can read from 20 feet what a person with normal vision must move up to 10 feet away to read, and therefore has better than normal vision. Conversely, a person with 20/200 vision can read from 20 feet away what a normal person can read from 200 feet away, so has extremely poor vision. The eye chart at your doctor’s office has been scaled down to fit the room, so while you may not actually stand 20 feet away, the ratios mean the same thing.
Visual acuity tests. The Snellen eye chart, developed by 1862 by Dutch Ophthalmologist Dr. Herman Snellen, is the original and most common eye chart. Other tests have been developed including the Tumbling E, the Broken Wheel, and the ETDRS tests. The Tumbling E and Broken Wheel tests were developed for small children and those adults who cannot read letters. The Tumbling E chart features a capital E facing up, down, left, and right. The person being tested is asked to respond with direction the E is facing. The Broken Wheel test uses cards with pictures of cars, some with whole wheels and some with broken wheels. The ETDRS test was originally developed for the Early Treatment of Diabetic Retinopathy Study. The ETDRS test uses letters, but is considered to be more accurate than the Snellen chart.
20/20 may not mean perfect overall vision. Since these tests only measure visual acuity, you can have 20/20 vision and still have vision problems. A person with 20/20 vision may have trouble seeing objects close up, poor depth perception, difficulty focusing, or poor peripheral vision. Eyes are tested separately and together. Many people have a different score for each eye.
What is best corrected vision? Your best corrected vision is the best visual acuity you can achieve with corrective lenses. Often people who cannot attain 20/20 vision with corrective lenses have better results with LASIK surgery because LASIK surgery can correct subtle imperfections in the vision system which corrective lenses cannot address.
What vision scores can mean to you. A person with 20/200 best corrected vision or worse (higher) is considered legally blind. 20/40 is the worst vision score you are allowed to have to obtain an unrestricted driver’s license. 20/50 is the limit for many professions.
Attaining 20/20 vision. Some people find that glasses and contact lenses are too uncomfortable and inconvenient, or simply do not want to be dependent on these things. Others find that corrective lenses are not enough and can benefit from a combination of LASIK surgery and corrective lenses. If you do not have 20/20 vision, or if you have 20/20 vision but still experience vision problems, your eye doctor can help you decide if corrective lenses or LASIK surgery is the best option for you. Any of the fine doctors at Professional Eye Associates in
Source: http://www.the-lasik-directory.com/article_2020.html