I guess it really doesn't make sense because how can you truly wear them to test them if you can't see well with them? There will be so many other difficulties that not seeing well can cause even like headaches......& how can you tell whether it's the bad prescription or the lenses that aren't fitting well & causing problems......that was where I was coming from. One may not be able to tell whether it's the wrong prescription or the difference in contact lens that is causing the discomfort unless there is a specific discomfort from the lens & that you will know almost immediately & not have to give it days.