Ever ask why 20/20 is the benchmark for ''perfect'' vision and what it really means? 20/20 vision is a phrase used to describe normal visual acuity or clarity of vision. That is to say that someone with such vision will be able to clearly see an object at a distance of 20 feet that the majority of people are expected to be able to see from that distance.
In cases of individuals that don't have 20/20 visual acuity, the number is determined based on the first point at which they are able to see clearly, in relation to what is normally expected. As an example, 20/100 acuity means 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 with 20/200 visual acuity is considered blind, legally however, they can often see normally by using glasses or contacts or by undergoing LASIK if they qualify.
A typical vision test is performed by using an eye chart most commonly the familiar Snellen eye chart created by Hermann Snellen, a Dutch eye doctor in the 1860's. While today there are many variations, the chart generally has 11 rows with uppercase letters which get smaller in size as they move toward the bottom. The chart begins with the capital letter – ''E'' with the addition of more letters on the lines as they get smaller. During the eye exam, the eye doctor will look for the smallest line of letters you can read. Each line is given a rating, 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 persons, the ''Tumbling E'' chart is employed. Similar to the regular Snellen chart, the ''Tumbling E'' is composed of only the capital letter E in different rotations. The patient uses their hand to point to the right, left, top or bottom to show which direction the E is pointing. Both charts should be positioned 20 feet away from where the patient is viewing it.
Despite common conception, 20/20 eyesight does not mean an individual sees perfectly but rather that they see well at a distance. Total eyesight includes many other important skills such as side or peripheral vision, depth perception, focus for near vision, color vision and coordination between the eyes to name a few.
While an eye exam with a Snellen chart can establish whether you need glasses to see far away it doesn't provide the optometrist a full perception of the complete status of your eyes and vision. It's recommended that you still schedule a yearly comprehensive eye exam which can diagnose vision-threatening conditions. Call our office now to schedule a Costa Mesa, CA eye exam.