Have you ever wondered why 20/20 is the standard for ''perfect'' vision and what it truly stands for? The term 20/20 vision expresses normal visual acuity or sharpness of vision. That is to say that someone with 20/20 vision can clearly see an object at a distance of 20 feet that most individuals should be able to see from that distance.
For those who cannot see at 20 feet away, their visual acuity score is determined according to the distance at which they are able to see clearly, in relation to what is normally expected. As an example, if your vision is 20/100 that indicates that you have to be as close as 20 feet to see clearly what a person with normal vision can see at 100 feet away.
It's also possible to have better than 20/20 vision. For instance someone that has 20/10 eyesight can see clearly at 20 feet what most can only see at 10 feet distance. Certain animals have been known to have incredibly acute vision in comparison to humans. For example, hawks have been known to have 20/2 eyesight, enabling them to spot prey from great heights.
Most eye doctors use a form of the Snellen eye chart, which was developed by Hermann Snellen, a Dutch eye doctor in the 1860's, to conduct an eye test. While today there are a number of variations, the chart usually shows 11 rows with uppercase letters which get progressively smaller as they move toward the bottom. The top of the chart usually shows one uppercase letter - ''E'' and gradually includes more letters on the lines as they get smaller. During the vision test, the optometrist will look for the smallest line of letters you can see clearly. Every row is assigned a rating, with the 20/20 row usually being assigned forth from the bottom. In cases where the patient can't read, such as young children or disabled individuals, an alternate version of the chart is used called the ''Tumbling E''. At the same scale as the traditional Snellen chart, this version portrays only the uppercase letter E in different directions. The patient uses their hand to point to the right, left, top or bottom based on the direction the E is facing. Either chart must be positioned 20 feet away from the patient's eyes.
While 20/20 visual acuity does indicate that the person's sight for distances is good, this metric alone doesn't mean that the individual has perfect vision. Total eyesight includes a number of other necessary competencies such as side or peripheral vision, depth perception, color vision, near vision and focusing and coordination between the eyes to name a few.
Although a vision screening using a Snellen chart can conclude whether you require a visual aid to see clearly at a distance, it doesn't give the optometrist a complete picture of the complete status of your eyes and vision. It's recommended that you still book an annual comprehensive eye exam which can identify potential diseases. Contact our office today to book an eye exam in North Vancouver, BC.