Lens thickness refers to your prescription, frame choices, and lens choices. 
*Click here to check how to pick out the best lens due to prescription.
We all know that there are several numbers on the prescription if you have one. The numbers are appearing with a negative or positive sigh. The negative numbers and positive numbers on the sphere section determine what type of eyesight issue you have.
Negative sphere numbers indicate that you are near-sighted (can see well up-close but have trouble focusing into the distance). Positive numbers are for far-sighted (can see well into the distance but need help focusing up-close).