Answer:

Based on the prescription you enter during checkout, our lens recognition system will suggest the most suitable lens, which will have an average thickness that matches your prescription. When a lens is not suitable for your prescription (e.g. because it is too thick), our system automatically disables this option.  Depending on your personal preference, you may choose to upgrade to a thinner lens.

If you cannot escape thick lenses, try selecting a frame with a full rim rather than semi-rimless or rimless. Full rim frames can help hide the thickness of lens edges, especially with thick plastic frames. Additionally, the lenses for full rim frames may be manufactured with a wider range of thickness, while semi-rimless and rimless glasses have a minimum thickness requirement. 

Another tip would be to try to pick out a frame as small as possible, especially if your prescription is a high minus (For example, like a -7.00 sphere and up).