Have you ever wondered why 20/20 is the standard for ''perfect'' vision and what it truly represents? The phrase 20/20 eyesight describes a normal level of sharpness of eyesight also known as visual acuity measured from 20 feet away from the object. In other words an individual with 20/20 vision will be able to see an object clearly at a distance of 20 feet that most individuals should be able to see from such a distance.
For those who cannot see at 20 feet away, their visual acuity score is assigned according to the distance at which they are able to see sharply, compared to what is normally expected. For example, 20/100 vision indicates that you must be as close as 20 feet to see what someone with normal eyesight can see at a distance of 100 feet.
Someone whose vision is 20/200 or below is considered legally blind but can often see normally with the use of eyeglasses or contacts or by undergoing laser eye surgery if they qualify.
A typical vision screening is performed with the use of an eye chart such as the classic Snellen eye chart developed by Hermann Snellen, a Dutch eye doctor in the mid-1800's. While today there are many variations, the chart usually has 11 rows of capital letters which get progressively smaller as one looks downward. The chart begins with the uppercase letter - ''E'' with the addition of more letters on the lines as they get smaller. During the vision screening, the optometrist will look for the line with the smallest lettering you can make out. Your score is determined since each line is given a rating, with the 20/20 row typically being assigned the eighth row. For young children, illiterate or handicapped persons who are not able to read or vocalize letters, a variation of the chart is used called the ''Tumbling E''. Similar to the regular Snellen chart, the ''Tumbling E'' is composed of only the uppercase E in different rotations. The optometrist asks the patient to point to the right, left, top or bottom according to the direction the E is pointing. Either chart needs to be positioned at a distance of 20 feet from where the patient is viewing it.
Despite what many think, 20/20 eyesight does not show a person sees perfectly but only that their distance vision is normal. There are many other essential elements that contribute to your overall vision such as peripheral sight, perception of depth, color vision, near vision and focusing and coordination between the eyes to name a few.
While a vision screening using a Snellen chart will establish if you require eyeglasses to see far away it doesn't provide the eye doctor a complete perception of your complete eye health. It's recommended that you still schedule a comprehensive eye exam annually or bi-annually, depending on your optometrist's recommendation, to screen for any more serious conditions. Call our office now to schedule an eye exam in Squamish or Vancouver, BC.