Ever wonder why 20/20 is the standard for ''perfect'' vision and what it truly means? 20/20 vision is a term to describe a normal level of clarity of eyesight (visual acuity) assessed from 20 feet away from the object. That is to say that an individual with 20/20 vision can see an object clearly at a distance of 20 feet that the majority of people should be able to see from such a distance.
In cases of individuals that don't have 20/20 vision, their visual acuity score is designated based on where they begin to see clearly in comparison to the norm. For instance, 20/100 vision indicates that you have to be at a distance of 20 feet to see what a person with normal vision can see at 100 feet away.
An individual can also have vision that is above the norm. For instance a person with 20/10 vision can see sharply at 20 feet an object that most can only see at 10 feet. Members of the animal kingdom have more acute vision in comparison to what humans are capable of. A hawk for instance can have 20/2 vision, enabling them to spot prey from great heights.
Most optometrists use a form of the Snellen eye chart, which was invented by Hermann Snellen, a Dutch eye doctor in the 1860's, to perform a vision exam. While there are quite a few variations, the chart generally shows eleven rows of uppercase letters which get progressively smaller as they move toward the bottom. The chart begins with one capital letter - ''E'' with letters being added subsequently as you move down the chart. During the eye exam, the eye doctor will assess the line with the smallest lettering you can see clearly. Every row is assigned a distance, with the 20/20 row usually being assigned the eighth row. For young children, illiterate or disabled persons who can not read or vocalize letters, the ''Tumbling E'' chart is employed. At the same scale as the regular Snellen chart, this variation portrays only the capital letter E in different spatial orientations. The person being tested uses their hand to point to the right, left, top or bottom according to the 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 mean that an individual's distance vision is normal, this measure on its own does not mean that a person has flawless vision. ''Perfect'' vision includes many other necessary competencies such as peripheral sight, depth perception, color vision, near vision and focusing and coordination between the eyes amongst others.
While an eye exam with a Snellen chart can establish whether you need glasses to improve distance vision it will not give the optometrist a comprehensive understanding of your complete eye health. You should still schedule a yearly comprehensive eye exam which can identify any more serious conditions. Call our office now to book a Virginia Beach, VA eye test.