Since contact lenses are responsible for producing corneal change it is essential to rigorously examine for variables involved. The need to control corneal change further dictates that fitting procedures or techniques should also be critically evaluated. Given in this first of a two part series is a background discussion of contact lens prescribing characteristics and resultant data collected during an orthokeratology study. Specifically examined were the effects of the base curve-cornea relationship, lens position and temporal factors. Though each was noticed to be involved in the results obtained, their failure to account for all changes observed suggest that other mechanisms need be considered.