Have you ever asked yourself why 20/20 is the standard for ''perfect'' eyesight and what it actually stands for? 20/20 vision is a phrase to express normal visual acuity or clarity of vision. In other words an individual with such visual acuity will be able to see an object clearly from 20 feet away that most individuals should be able to see from that distance.
For those who cannot see at 20/20, the number is assigned based on where they begin to see clearly compared to the norm. For example, 20/100 acuity means that at 20 feet you can only see what the standard would see from 100 feet .
You can also have better than 20/20 vision. For instance a person with 20/10 vision can see clearly at 20 feet what most can only see at 10 feet distance. Members of the animal kingdom particularly birds of prey have more acute vision in comparison to the human species. A hawk for instance can have 20/2 eyesight, designed for spotting prey from great heights.
Most optometrists employ a version of the Snellen eye chart, invented by Dutch eye doctor, Herman Snellen in the mid-1800's, to perform an eye screening. While there are now quite a few variations, the chart usually has eleven lines of uppercase letters which get progressively smaller as they move downward. The top of the chart usually shows the capital letter – ''E'' with letters being added subsequently as you move down the chart. During the eye exam, the eye doctor will examine which is the line with the smallest lettering you can make out. Every row is assigned a rating, with the 20/20 line usually being assigned forth from the bottom. For young children, illiterate or disabled persons who can not read or vocalize letters, the ''Tumbling E'' chart is used. Similar to the standard Snellen chart, this variation is composed of only the uppercase E in different spatial orientations. The person being tested uses their hand to mimic the direction the arms of the E are facing.. Both charts should be placed 20 feet away from the patient's eyes.
Even though 20/20 eyesight does indicate that the person's sight for distances is good, this measure on its own does not show that the individual has perfect eyesight. ''Perfect'' vision involves many other necessary abilities such as peripheral vision, depth perception, color vision, near vision and focusing and eye coordination amongst others.
Although a vision screening using a Snellen chart will determine whether you require eyeglasses to see clearly at a distance it will not provide the optometrist a full understanding of the complete status of your eyes and vision. Make sure you still book an annual comprehensive eye exam to screen for vision-threatening conditions. Call us today to book an eye exam in Bloomington, IL.