Ever ask why 20/20 is the standard for ''perfect'' eyesight and what it really stands for? The term 20/20 eyesight represents a normal level of clarity of vision or visual acuity calculated from a 20 feet distance. In other words an individual with such eyesight will be able to see an object clearly from 20 feet away which is considered normal to see clearly from that distance.
In cases of individuals that cannot see at 20 feet away, the number is assigned according to the first point at which they are able to see clearly, in relation to what is normally expected. For instance, if your acuity is 20/100 that indicates that at 20 feet you can only see what the standard would see at 100 feet .
It's also possible to have vision that is above the norm. For example a person with 20/10 eyesight can see sharply at 20 feet what most can see only at 10 feet. Members of the animal kingdom particularly birds of prey have been known to have incredibly acute eyesight in comparison to humans. For example, hawks have been known to have 20/2 vision, designed for locating prey from great heights.
Most optometrists use some version of the Snellen eye chart, which was invented by Dutch eye doctor, Herman Snellen in the 1860's, to perform an eye test. While there are now quite a few versions, the chart generally shows 11 rows with capital letters which get progressively smaller as they move toward the bottom. The chart begins with the capital letter - ''E'' with letters being added subsequently as you move down the chart. During the eye exam, the optometrist will examine which is the smallest line of letters you can see clearly. Each line is assigned a distance, with the 20/20 line usually being ascribed the eighth row. For small children, illiterate or handicapped persons who are not able to read or vocalize letters, the ''Tumbling E'' chart is employed. Similar to the traditional Snellen chart, this variation shows only the uppercase E in different spatial orientations. The eye doctor tells the person being tested to mimic which rotational direction the arms of the E are pointing: right, left top or bottom. Either chart needs to be placed 20 feet away from where the patient is viewing it.
Despite what many think, 20/20 visual acuity doesn't mean an individual has perfect eyesight but only that their distance vision is normal. There are many other essential abilities needed that contribute to your overall vision such as peripheral vision, depth perception, color vision, near vision and focusing and eye coordination to name a few.
While a vision screening using an eye chart can determine whether you require a visual aid to see far away it doesn't provide the eye doctor a full picture of the complete health of your eyes and vision. You should still go in for a yearly comprehensive eye exam which can diagnose potential diseases. Contact our office now to schedule a Fayetteville, NC eye exam.