Ever ask what 20/20 vision truly stands for? The term 20/20 vision expresses a normal level of sharpness of eyesight or visual acuity determined from 20 feet away from the object. That is to say that an individual with 20/20 eyesight can clearly see an object at a distance of 20 feet which is deemed the norm to see from that distance.
For those who don't have 20/20 visual acuity, the number is determined according to the distance at which they are able to see clearly, in comparison to what is normally expected. As an example, if your acuity is 20/100 that indicates that at a distance of 20 feet you can only see an object that a person with normal vision can see at 100 feet .
A person whose vision is 20/200 or worse is considered legally blind however, they can often see normally by using glasses or contact lenses or by having LASIK if they are eligible.
A typical eye screening is done by using an eye chart such as the familiar Snellen eye chart invented by Hermann Snellen, a Dutch eye doctor in the 1860's. While today there are quite a few variations, the chart usually has eleven lines of capital letters which get progressively smaller as one looks downward. The top of the chart usually shows the uppercase letter – ''E'' with the addition of more letters on the lines as they get smaller. During the vision test, the eye doctor will examine which is the line with the smallest lettering you can read. Your score is determined since each row is assigned a distance, with the 20/20 row typically being assigned the eighth row. In cases where the patient can't read, such as young children or handicapped individuals, the ''Tumbling E'' chart is used. Similar to the regular Snellen chart, this variation portrays only the uppercase E in different rotations. The optometrist tells the person being tested to indicate the rotational direction the ''fingers'' of the E are facing.. Both charts should be placed at a distance of 20 feet from the patient's eyes.
Despite common perception, 20/20 visual acuity does not indicate a person sees perfectly but merely that they see as expected at a distance. There are many other essential abilities needed to make perfect vision such as peripheral sight, perception of depth, color vision, near vision and focusing and eye coordination to name a few.
It's important to remember that even though a vision screening using an eye chart will often establish if you need eyeglasses to improve distance vision it doesn't provide the optometrist a comprehensive understanding of your complete eye health. You should still schedule a yearly comprehensive eye exam to screen for vision-threatening diseases. Contact our office now to book an eye exam in Manhattan, NY.