Have you ever wondered why 20/20 is the benchmark for ''perfect'' vision and what it actually stands for? The term 20/20 vision represents a normal level of clarity of vision (visual acuity) assessed from 20 feet away from the object. In other words an individual with such eyesight can see an object clearly from 20 feet away which is considered normal to see clearly at that distance.
For those who don't have 20/20 vision, their visual acuity score is assigned based on the first point at which they are able to see sharply, in relation to what is normally expected. As an example, if your acuity is 20/100 that means that you have to be at a distance of 20 feet to see what a person with normal vision would be able to see at a distance of 100 feet.
A person who is assessed with 20/200 visual acuity is considered legally blind but can often see normally by wearing eyeglasses or contacts or by undergoing laser eye surgery if they qualify.
Most eye doctors utilize a form of the Snellen eye chart, created by Dutch eye doctor, Herman Snellen in the 1860's, to perform a vision screening. While today there are a number of variations, the chart typically has 11 lines of capital letters which get smaller in size as one looks toward the bottom. The top of the chart usually shows the capital letter - ''E'' with letters being added gradually as you look down the chart. During the vision screening, the eye doctor will look for the smallest line of letters you can make out. Each line is given a rating, with the 20/20 line typically being ascribed the eighth row. In instances in which the patient can't read, such as small children or handicapped persons, the ''Tumbling E'' chart is employed. At the same scale as the traditional Snellen chart, this variation portrays only the capital letter E in different rotations. The eye doctor tells the person being tested to mimic which rotational direction the ''fingers'' of the E are pointing.. Both charts must be placed 20 feet away from where the patient is viewing it.
Although 20/20 eyesight does mean that the person is able to see at the norm from a distance this measure alone does not imply that a person has flawless eyesight. There are a number of other necessary abilities needed to make perfect vision such as side or peripheral sight, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.
While a vision screening using an eye chart can establish whether you require glasses for better distance vision it will not give the eye doctor a complete perception of the complete status of your eyes and vision. You should still go in for an annual comprehensive eye exam which can identify potential conditions. Contact our office today to schedule an eye exam in Frisco, TX.