Ever wonder why 20/20 is the benchmark for ''perfect'' vision and what it truly stands for? 20/20 vision is a phrase used to describe a normal level of sharpness of eyesight (visual acuity) calculated from 20 feet away from the object. In other words an individual with 20/20 vision can see an object clearly from 20 feet away that the majority of individuals should be able to see from that distance.
In cases of individuals that cannot see an object clearly at 20 feet away, their visual acuity score is assigned according to where they begin to see clearly in relation to the norm. As an example, if your acuity is 20/100 that means that you must be at a distance of 20 feet to see what someone with normal eyesight can see at 100 feet away.
An individual can also have vision that is above the norm. For example someone that has 20/10 vision can see clearly at 20 feet an object that most can see only at 10 feet. Members of the animal kingdom have more acute vision compared to man. A hawk for instance can have 20/2 vision, designed for spotting prey from high in the air.
Most eye doctors utilize a version of the Snellen eye chart, which was invented by Dutch eye doctor, Herman Snellen in the mid-1800's, to conduct a vision exam. While there are now many versions, the chart typically shows 11 lines of capital letters which get smaller in size as one looks toward the bottom. The chart begins with the capital letter – ''E'' with letters being added gradually as you look down the chart. During the eye exam, the eye doctor will look for the smallest line of letters you can see clearly. Your score is determined since each row is given a rating, with the 20/20 row usually being ascribed the eighth row. For young children, illiterate or disabled persons who can not read or vocalize letters, the ''Tumbling E'' chart is used. Similar to the traditional Snellen chart, this variation shows only the capital E in different directions. The patient uses their hand to indicate which rotational direction the arms of the E are pointing.. In order for the results to be accurate the chart should be placed at a distance of 20 feet from where the patient is viewing it.
While 20/20 visual acuity does indicate that the person's sight for distances is normal, this measure alone doesn't suggest that a person has flawless eyesight. ''Perfect'' eyesight includes many other important skills such as peripheral vision, perception of depth, color vision, near vision and focusing and eye coordination to name a few.
While a vision screening with a Snellen chart can conclude whether you require a visual aid to see far away it will not provide the eye doctor a complete picture of your complete eye and vision health. Make sure you still book a yearly comprehensive eye exam which can diagnose vision-threatening diseases. Call us now to book an eye exam in New York, NY.