- Soft contact lens users must have removed their lenses at least 1 week before baseline measurements. Hard contact lens users (PMMA or rigid gas permeable lenses must have removed their lenses at least 4 weeks prior to baseline measurements, and have 2 central keratometry readings and 2 manifest refractions taken at least 1 week apart that do not differ by more than 0.50D in either meridian; mires shall be regular.