Have you ever asked yourself what 20/20 eyesight really stands for? 20/20 vision is a term to express a normal level of clarity of vision also known as visual acuity assessed from a 20 feet distance. That is to say that an individual with such vision will be able to see an object clearly from 20 feet away which is regarded as normal to see clearly from that distance.
For those who cannot see an object clearly at 20 feet away, the number is determined according to the first point at which they are able to see clearly, in relation to the norm. As an example, 20/100 vision indicates that you must be at a distance of 20 feet to see what a person with normal eyesight would be able to see at a distance of 100 feet.
One can also have better than 20/20 vision. For instance someone with 20/10 eyesight can see clearly at 20 feet what most can only see at 10 feet. Members of the animal kingdom particularly birds of prey have more acute vision in comparison to what humans are capable of. A hawk for example can have 20/2 vision, designed for spotting prey from great heights.
A typical eye screening is done by using an eye chart most commonly the classic Snellen eye chart designed by Dutch eye doctor, Herman Snellen in the 1860's. While there are now a number of versions, the chart generally shows 11 rows of capital letters which get smaller in size as one looks downward. The chart begins with one uppercase letter - ''E'' with letters being added subsequently as you move down the chart. During the vision test, the eye doctor will assess the smallest line of letters you can make out. Each line is assigned a distance, with the 20/20 row typically being assigned forth from the bottom. In cases in which the patient can't read, such as young children or handicapped individuals, the ''Tumbling E'' chart is used. At the same scale as the traditional Snellen chart, this variation portrays only the uppercase letter E in different rotations. The eye doctor asks the patient to indicate which rotational direction the ''fingers'' of the E are pointing: right, left top or bottom. Both charts must be placed 20 feet away from the patient's eyes.
While 20/20 eyesight does show that the person's distance vision is average, this metric alone doesn't suggest that a person has perfect vision. There are many other essential elements to make perfect vision such as side or peripheral sight, perception of depth, color vision, near vision and focusing and coordination between the eyes amongst others.
While an eye exam with a Snellen chart can establish if you need a visual aid for better distance vision it will not provide the eye doctor a full understanding of the total health of your eyes and vision. It's recommended that you still schedule a yearly comprehensive eye exam which can diagnose potential diseases. Contact our office today to schedule an eye exam in Phoenix, AZ.