Ever ask what 20/20 eyesight really means? 20/20 vision is a term to express a normal level of clarity of vision (visual acuity) calculated from a 20 feet distance. In other words an individual with such vision will be able to see an object clearly at a distance of 20 feet that most people should be able to see from that distance.
For those who cannot see an object clearly at 20/20, the number is assigned according to the first point at which they are able to see clearly, compared to the norm. For example, if your vision is 20/100 that indicates that you must be at a distance of 20 feet to see clearly what a person with normal eyesight would see at 100 feet away.
An individual can also have better than 20/20 vision. For example someone 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 been known to have incredibly acute vision compared to humans. A hawk for example can have 20/2 vision, designed for spotting prey from great heights.
Most optometrists utilize a version of the Snellen eye chart, which was created by Hermann Snellen, a Dutch eye doctor in the 1860's, to perform an eye test. While there are now many variations, the chart typically shows 11 lines of capital letters which get smaller in size as they move toward the bottom. The top of the chart usually shows the capital letter – ''E'' and subsequently adds more letters as they get smaller. During the vision screening, the eye doctor will assess the line with the smallest lettering you can see clearly. Every line is assigned a distance, with the 20/20 line usually being ascribed forth from the bottom. For small children, illiterate or handicapped persons who are not able to read or vocalize letters, an alternate version of the chart is used called the ''Tumbling E''. At the same scale as the standard Snellen chart, the ''Tumbling E'' shows only the capital letter E in different rotations. The optometrist asks the person being tested to show the rotational direction the arms of the E are facing: right, left top or bottom. In order for the results to be accurate the chart must be positioned at a distance of 20 feet from where the patient is viewing it.
Despite what many think, 20/20 vision does not indicate someone has perfect vision but only that they are able to see as expected from a distance. ''Perfect'' vision involves a number of other important skills such as side or peripheral vision, perception of depth, color vision, near vision and focusing and coordination between the eyes amongst others.
While a vision screening with a Snellen chart can establish whether you need eyeglasses to see clearly at a distance it will not provide the optometrist a full picture of your overall eye health. Make sure you still book a yearly comprehensive eye exam to screen for vision-threatening diseases. Contact our office today to schedule a Temecula, CA eye exam.