Vision is very important to us. Everyone desires 20/20 vision. Some patients say that they don't want 20/15 vision but prefer 20/20. This statement will appear hilarious when you have read and understood this article.

We all want great vision. Why? So that we can have a competitive advantage. In prehistoric times it gave us the edge to see the wild animals earlier. As society became more organized a method of comparing vision was needed. The credit for the most commonly used method goes to Snellen. Hence the chart which displays the letters or numbers bears his name. It compares a person's vision to the that of the average for the population. 20/20 means that the person whose vision is being tested is normal. If the vision is 20/40 it means that a normal person can see the object at 40 feet away whereas the patient being tested has to go much closer than this to 20 feet before he can see as well. That implies that the test subject has poorer vision. If it is 20/200 than the vision is even worse. Conversely 20/15 means that the test subject can see an object from even further than a normal person. He can see at 20 feet what a normal would see at only 15 feet. 20/10 vision is even better.

A little bit of history.The early work was done in Europe. The measurement was done in meters. As most of the doctors had small rooms, Snellen came up with the average vision of 4/4. It got refined to 6/6 to decrease the source of error. When the science crossed the Atlantic, we converted meters to feet and 20/20 gained its popularity.

This method of testing has some drawbacks, it tests in semi darkened room. It does not take into account contrast sensitivity, the field of vision or vision in bright light. It does not also reflect driving vision very accurately.

Newer advances include auto-projectors, video monitors and measurement in log units.Currently DMV is working with vision scientists to develop a more comprehensive vision testing system. Till than enjoy your 20/20 vision.



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