While searching about laser surgery for my myopia, I came across different system to measure the quality of individuals' eye sight. When speaking about quality of eyesight, I am referring to the classic test where one has to read smaller and smaller symbols (usually letters or numbers).

I found four different measures:

1. One is a scale from 0 to 1.0+, where the average/normal eyesight is 1.0. People can be above but I don't know how much higher than average.
2. Another scale from 0 to 20+, the average between 20. I guess that this one is proportionally related to the first one.
3. I saw negative integers (like -5,-2) sometimes, but I didn't understand how they work exactly. I guess they measure how bad your eyesight is compare to average.
4. My optometrist used dioptries.

**My question**: what are the (most used) measure of the quality eyesight and how do they relate to each other?