Having 20/20 vision doesn’t mean you have “perfect” vision, but it does mean your vision is sharp and clear. Other vision skills, such as peripheral awareness, eye coordination, depth perception, ability to see moving objects and to discern objects that are similar in brightness to their background, focusing ability and color vision also contribute to your overall visual ability.
Visual acuity, which refers to the sharpness or clarity of your vision, is measured by your ability to identify letters or numbers on a standardized eye chart from a specific viewing distance. 20/20 vision is the term used to express normal visual acuity measured at a distance of 20 feet. Basically, if you have 20/20 vision, you have no problem seeing clearly at 20 feet what should normally be seen at that distance. The “20/20” fractions refer to your distance (in feet) from an eye chart and the distance at which a person with normal eyesight can read the same line of letters on the chart.
Herman Snellen, a Dutch ophthalmologist, developed this visual acuity measurement system in 1862 (20/20 fractions are also called Snellen fractions).
At 20 feet away, the size of the letters on a Snellen eye chart, on one of the smaller lines near the bottom, has been standardized to correspond to “normal” visual acuity. This is the 20/20 line. If you can identify the letters on this line but none of the letters on the next smaller lines, you have 20/20 visual acuity (or “20/20 vision”). Having 20/15 vision is possible: you can see a line on the eye chart at 20 feet away that the average person can see when they are closer, at 15 feet away. 20/10 is also possible, which would mean your visual acuity is twice as sharp as that of a person with 20/20 vision.
The increasing larger letter sizes on the lines of the Snellen chart correspond to worse visual acuity measurements. Fractions such as 20/30 and 20/100 mean that you need to be as close as 20 feet to see what a person with normal vision can see at 30 feet or 100 feet. The big “E” at the top of a Snellen eye chart corresponds to 20/200 visual acuity.
Even if you have 20/20 vision, you need regular eye exams throughout your life, once a year. Your doctor isn’t just checking which lines on the Snellen eye chart you can read, they’re also evaluating your overall eye health, looking for signs of change in your vision or early signs of eye problems such as glaucoma, cataracts and diabetic retinopathy that you may not have noticed yet yourself.
Schedule your next eye exam here, or give us a call at 307-634-2020.