Now where i work the snellen chart's best friend is dust nobody uses it and i never bothered asking. In what situations does an Optician use the snellen chart??? How can you overrefract or underrefract using a snellen chart. I don't know anything about the snellen chart except that your suppose to stand 20 feet away to read above the red line which is 20/20, so please bare with me.

If someone can refer me to a website that shows you how to use a snellen chart that would be great :D