Ever question what 20/20 eyesight truly represents? The phrase 20/20 eyesight describes normal visual acuity or sharpness of vision. In other words an individual with such vision can see an object clearly at a distance of 20 feet that most individuals are expected to be able to see from that distance.
For those who cannot see an object clearly at 20 feet away, the number is assigned according to where they begin to see clearly in relation to the norm. For instance, 20/100 acuity indicates that you have to be as close as 20 feet to see what someone with normal eyesight would see at 100 feet away.
It's also possible to have better than 20/20 vision. For example a person with 20/10 vision can see sharply at 20 feet what the average person can see only at 10 feet. Certain animals particularly birds of prey have been known to have incredibly acute eyesight compared to what humans are capable of. A hawk for example can have 20/2 vision, enabling them to spot prey from high in the air.
An average eye test is performed with the use of an eye chart most commonly the familiar Snellen eye chart developed by Hermann Snellen, a Dutch eye doctor in the mid-1800's. While there are a number of versions, the chart typically has eleven lines with capital letters which get progressively smaller as one looks toward the bottom. The top of the chart usually shows one uppercase letter – ''E'' and subsequently adds more letters on the lines as they get smaller. During the vision test, the optometrist will assess the smallest line of letters you can make out. Each row is assigned a rating, with the 20/20 row typically being ascribed forth from the bottom. In cases where the patient isn't able to read, such as young children or handicapped persons, a different version of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, this version is composed of only the uppercase E in different directions. The optometrist asks the patient to point to the right, left, top or bottom to show which direction the E is facing. Either chart needs to be positioned at a distance of 20 feet from where the patient is viewing it.
While 20/20 visual acuity does indicate that the person sees at the norm from a distance this metric on its own doesn't mean that the individual has perfect vision. There are a number of other necessary elements that contribute to your overall vision such as side or peripheral sight, depth perception, focus for near vision, color vision and coordination between the eyes amongst others.
While a vision screening using a Snellen chart will establish if you need glasses to see clearly at a distance it will not provide the eye doctor a full perception of your overall eye health. It's recommended that you still book an annual comprehensive eye exam to screen for any more serious conditions. Call us today to schedule a Hamburg, MI eye test.