• Home
• About

The standard eyeglass prescription’s aim is to give a person 20/20 vision. This formula is based on an arbitrary measurement developed by Hermann Snellen in 1862 and is much too strong. Except for students looking at the blackboard, when was the last time you needed to see ¼ inch letters 20 feet away? For daily living and most tasks 20/30 to 20/50 is sufficient. Automobile driver’s licenses legally require only 20/40. Only airline pilots require 20/20.

What is 20/20 vision? If you have 20/20 vision, it means that when you stand 20 feet away from the Snellen eye chart you can read the letters on the 20/20 line and your vision is considered normal. If you have 20/30 vision, it means that when you stand 20 feet away from the eye chart you can see what a person with 20/20 vision can see at 30 feet. If you have 20/40 vision, it means that when you stand 20 feet away from the eye chart you can see what a person with 20/20 can see at 40 feet.

The first number is always 20, the distance to the eye chart, and the second number is the distance at which a person with 20/20 could read the line. The smallest line that you can read on the eye chart is your visual acuity. The larger the second number the worse your vision.

The Snellen eye chart is the standard against which most eyeglass prescriptions are based and is considered scientific and infallible. However, in 1862 Hermann Snellen simply based his 20/20 vision measurement on the vision of an assistant whom he felt had good eyesight. Not very scientific is it.

The fact that all readings of the Snellen eye chart are done at 20 feet, means that nearsighted eyeglass prescriptions are focused and prescribed for 20 feet. They are distance vision eyeglasses suited for looking 20 feet and farther because eyes do not have to focus at this distance. However, these distance vision eyeglasses are unsuited for looking closer than 20 feet because the eyes must focus to see objects closer than 20 feet.

By wearing 20/20 vision distance eyeglasses, the nearsighted eyes must adjust focus to see objects closer than 20 feet and must further adjust focus to overcome the eyeglasses prescribed for 20 feet. The eyes unnaturally doubly strain to adjust focus and this results in more nearsightedness that eventually requires bifocal eyeglasses.

The Snellen eye chart, upon which most eyeglass prescriptions are based, really measures one visual skill - our distance vision. This is only one small part of our vision. There is much more to our vision: near vision, peripheral vision, eye coordination, color perception, light sensitivity, endurance, etc. Basing our eyeglass prescriptions on 20/20 vision is unnecessary and ultimately harms our eyes.

Comments

No comments yet.

Leave a comment