Ever wonder what 20/20 eyesight actually stands for? The term 20/20 vision expresses normal visual acuity or clarity of vision. In other words an individual with such visual acuity can clearly see an object from 20 feet away that the majority of people are expected to be able to see from that distance.
For those who cannot see an object clearly at 20/20, their visual acuity score is assigned based on where they begin to see clearly compared to what is normally expected. For instance, if your acuity is 20/100 that indicates that you have to be as close as 20 feet to see what a person with normal vision would see at 100 feet away.
Someone whose eyesight is 20/200 or worse is considered legally blind however, they can often see normally with the use of eyeglasses or contact lenses or by undergoing LASIK if they qualify.
A typical eye screening is done with the use of an eye chart such as the familiar Snellen eye chart invented by Hermann Snellen, a Dutch eye doctor in the mid-1800's. While there are now many versions, the chart generally has eleven lines with uppercase letters which get smaller in size as one looks downward. The chart begins with one uppercase letter - ''E'' with the addition of more letters as they get smaller. During the vision screening, the optometrist will look for the line with the smallest lettering you can see clearly. Your score is determined since each row is given a distance, with the 20/20 row typically being assigned forth from the bottom. In cases where the patient isn't able to read, such as small children or disabled persons, a varied version of the chart is used called the ''Tumbling E''. Similar to the regular Snellen chart, the ''Tumbling E'' is composed of only the capital letter E in different spatial orientations. The person being tested uses their hand to show the rotational direction the ''fingers'' of the E are pointing: right, left top or bottom. In order for the results to be accurate the chart should be positioned 20 feet away from where the patient is viewing it.
While 20/20 vision does mean that the person's distance sight is average, this metric on its own doesn't suggest that the individual has flawless eyesight. There are a number of other necessary abilities needed that contribute to your overall vision such as side or peripheral sight, perception of depth, focus for near vision, color vision and eye coordination to name a few.
While a vision screening using an eye chart will often conclude if you require a visual aid to see far away it will not give the optometrist a full perception of your total eye and vision health. It's recommended that you still schedule an annual comprehensive eye exam which can diagnose potential diseases. Call our office now to schedule an eye exam in North Reading, MA.