Have you ever wondered why 20/20 is the benchmark for ''perfect'' eyesight and what it actually means? The phrase 20/20 vision expresses a normal level of clarity of eyesight or visual acuity determined from 20 feet away from the object. In other words someone with such eyesight can clearly see an object at a distance of 20 feet that the majority of people are expected to be able to see from such a distance.
For those who cannot see at 20/20, their visual acuity score is assigned based on the first point at which they are able to see clearly, compared to what is normally expected. For instance, if your vision is 20/100 that means that at a distance of 20 feet you can only see what the standard would see from 100 feet distance.
It's also possible to have vision that is better than 20/20. For instance a person with 20/10 vision can see sharply at 20 feet what the average person can only see at 10 feet distance. Certain animals particularly birds of prey have more acute eyesight compared to man. For example, hawks have been known to have 20/2 vision, enabling them to spot prey from high in the air.
An average eye test is performed by using an eye chart such as the classic Snellen eye chart developed by Hermann Snellen, a Dutch eye doctor in the mid-1800's. While today there are a number of variations, the chart generally has 11 lines with 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 examine which is the smallest line of letters you can make out. Every line is assigned a distance, with the 20/20 row usually being ascribed forth from the bottom. In instances in which the patient can't read, such as young children or disabled persons, the ''Tumbling E'' chart is employed. Similar to the standard Snellen chart, the ''Tumbling E'' is composed of only the capital E in different directions. The patient uses their hand to show the direction the ''fingers'' of the E are facing.. Either chart needs to be placed 20 feet away from where the patient is viewing it.
Even though 20/20 visual acuity does mean that the person is able to see at the norm from a distance this measure on its own doesn't imply that someone has flawless eyesight. ''Perfect'' eyesight involves a number of other important abilities such as side or peripheral vision, depth perception, focus for near vision, color vision and coordination between the eyes to name a few.
It's important to remember that even though a vision screening using a Snellen chart can conclude if you require eyeglasses to correct for distance vision it doesn't provide the optometrist a complete perception of your complete eye and vision health. You should still go in for an annual comprehensive eye exam which can identify potential conditions. Contact our office today to book an eye exam in Plymouth, MI.