Is a prescription for contact lenses different than for glasses?
This is a very common clinic question and the answer is YES... but why?
When you have your eyes tested, the prescription that you are given is for glasses because this is how the prescription was derived... through ophthalmic lenses. A contact lens prescription is different for several reasons
 the actual powers may need to be adjusted because the lenses now sit on the eye vs. in-front of the eye.
 contact lenses do not come in every possible power like spectacle lenses and the power may need to be modified
 because the contact lens is a medical device sitting directly on the eye, the material of the lens has to be carefully considered and there has to be a plan to monitor ocular health
 there are different type/designs of contact lens that address different eye problems
 a contact lens has a shape factor that needs to be assessed on-the-eye to avoid problems
 some contact lenses need not to rotate and this needs to be assessed on the eye.
Hope that helps! Dr.j