Have you ever wondered why 20/20 is the standard for ''perfect'' vision and what it really represents? 20/20 vision is a term to express normal visual acuity or sharpness of vision. In other words an individual with 20/20 eyesight will be able to see an object clearly at a distance of 20 feet that the majority of people should be able to see from such a distance.
For those who don't have 20/20 visual acuity, the number is determined based on the first point at which they are able to see sharply, in relation to what is normally expected. As an example, 20/100 vision means that you have to be at a distance of 20 feet to see what a person with normal eyesight would see at 100 feet away.
A person whose eyesight is 20/200 or below is considered legally blind however, they can often see normally with the use of prescription glasses or contact lenses or by undergoing laser eye surgery if they are eligible.
An average vision test is done with the use of a vision chart usually the classic Snellen eye chart invented by Hermann Snellen, a Dutch eye doctor in the 1860's. While there are now many variations, the chart typically shows eleven rows of uppercase letters which get progressively smaller as one looks downward. The chart begins with one capital letter – ''E'' with letters being added subsequently as you look down the chart. During the vision screening, the optometrist will look for the line with the smallest lettering you can make out. Every row is given a rating, with the 20/20 row usually being ascribed forth from the bottom. For small children, illiterate or disabled persons who can not read or vocalize letters, a different version of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, the ''Tumbling E'' shows only the uppercase E in different spatial orientations. The optometrist tells the person being tested to point to the right, left, top or bottom according to the direction the E is pointing. 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.
While 20/20 vision does indicate that an individual is able to see at the norm from a distance this metric alone does not suggest that a person has flawless vision. There are a number of other essential abilities needed to make perfect vision such as peripheral vision, depth perception, color vision, near vision and focusing and eye coordination amongst others.
While a vision screening with an eye chart will often conclude if you need a visual aid to see far away it doesn't give the eye doctor a complete picture of your overall eye health. You should still book an annual comprehensive eye exam which can diagnose potential conditions. Contact us today to schedule a Salmon Arm, BC eye test.