This is a matter of your wise, educated choice. I "draw a line" for myself - on whether I need "medical advice", or when I can obtain my own lenses (plus or minus) to use with intelligence on myself.
If you are wise enough to have a Snellen on the wall (highly recommended), and are reading 1/2 the letters on the 20/60 line, then these remarks will apply to you.
http://frauenfeldclinic.com/optic-shop-require-prescriptions/Find an OD who understands what you need - and his goal and your goal. Then work with him.
