Ever question why 20/20 is the standard for ''perfect'' eyesight and what it actually means? The term 20/20 vision represents a normal level of sharpness of vision or visual acuity calculated from 20 feet away from the object. That is to say that someone with such vision will be able to clearly see an object from 20 feet away that the majority of individuals are expected to be able to see from such a distance.
For those who cannot see at 20 feet away, the number is designated according to the first point at which they are able to see sharply, in relation to the norm. As an example, if your acuity is 20/100 that means that at a distance of 20 feet you can only see an object that someone with normal vision can see at 100 feet distance.
An individual can also have better than 20/20 vision. For example a person with 20/10 vision can see clearly at 20 feet an object that most can see only at 10 feet. Certain animals particularly birds of prey have been known to have incredibly acute eyesight in comparison to man. For example, hawks have been known to have 20/2 vision, designed for locating prey from high in the air.
Most eye doctors utilize a version of the Snellen eye chart, developed by Dutch eye doctor, Herman Snellen in the 1860's, to perform a vision screening. While there are now many variations, the chart typically shows 11 rows of uppercase letters which get progressively smaller as one looks toward the bottom. The top of the chart usually shows one capital letter – ''E'' with letters being added gradually as you move down the chart. During the eye exam, the optometrist will determine which is the line with the smallest lettering you can read. Every row is given a distance, with the 20/20 row usually being ascribed forth from the bottom. 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 regular Snellen chart, this variation is composed of only the uppercase E in different spatial orientations. The patient uses their hand to show which direction the ''fingers'' of the E are pointing.. Both charts needs to be positioned at a distance of 20 feet from the patient's eyes.
Although 20/20 vision does show that the person's distance vision is average, this metric on its own doesn't mean that the individual has perfect eyesight. Total vision includes a number of other important abilities such as side or peripheral sight, perception of depth, focus for near vision, color vision and coordination between the eyes to name a few.
Although a vision screening with a Snellen chart will determine whether you require a visual aid to see far away it doesn't provide the eye doctor a complete perception of the overall health of your eyes and vision. Make sure you still book a yearly comprehensive eye exam which can identify any more serious conditions. Call us today to book a Kenosha, WI eye exam.