Refractive error
The maximum refractive error is measured starting with uncorrected vision.
When you use contactlenses you shouldn't wear them for 48 hours.
Your refractive error is the strenght of correction in diopters you need to get 20/20 vision.
It's just a very simple eye test wich every doctor or optometrist does.
Any form of influencing you're uncorrected vision will leed to failure.
So don't use OK lenses or refractive surgery, without telling. Because they will find out, and lying is considered a serious offense.