Ever wonder why 20/20 is the benchmark for ''perfect'' vision and what it truly represents? 20/20 vision is a phrase used to describe normal visual acuity or clarity of vision. In other words someone with such eyesight can see an object clearly at a distance of 20 feet that the majority of people are expected to be able to see from such a distance.
In cases of individuals that cannot see at 20 feet away, the number is determined according to where they begin to see clearly compared to what is normally expected. As an example, if your vision is 20/100 that indicates that you must be at a distance of 20 feet to see clearly what someone with normal eyesight would see at a distance of 100 feet.
It's also possible to have better than 20/20 vision. For instance someone that has 20/10 vision can see clearly at 20 feet what most can only see at 10 feet distance. A number of animals have more acute vision compared to man. For example, hawks have been known to have 20/2 eyesight, designed for locating prey from great heights.
An average 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 many versions, the chart generally has eleven lines of capital letters which get smaller in size as they move downward. The chart begins with the uppercase letter – ''E'' and gradually includes more letters as they get smaller. During the vision screening, the optometrist will look for the smallest line of letters you can make out. Your score is determined since each line is assigned a rating, with the 20/20 line usually being assigned the eighth row. In cases where the patient can't read, such as young children or disabled individuals, the ''Tumbling E'' chart is employed. Similar to the traditional Snellen chart, this version is composed of only the uppercase letter E in different directions. The person being tested uses their hand to show which direction the ''fingers'' of the E are pointing: right, left up or down. Either chart should be placed 20 feet away from the patient's eyes.
Despite common conception, 20/20 eyesight does not indicate someone has flawless vision but merely that their distance vision is normal. There are many other necessary abilities needed to make perfect vision such as peripheral vision, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.
It's important to remember that even though an eye exam using an eye chart can determine whether you need a visual aid for better distance vision it doesn't provide the eye doctor a full picture of your complete eye health. You should still book an annual comprehensive eye exam to screen for potential conditions. Call us today to schedule a Lafayette, LA eye exam.