What is the main component of the lens of the eye?

In a previous example, you saw that when reading a book, your lens is rounder or more convex, but when you look up to see a student entering the library, your lens becomes flatter or less convex. What muscle action results in the lens becoming less convex?

Your friend tells you that she has just been diagnosed with myopia, and she wonders if staring at her computer screen too much might have caused her problem. What do you tell her?