A system and method for identifying a custom contact lens for a patient. The method includes receiving as input results from a bare eye examination of a patient including at least a measured sphere power; receiving as input a target or actual measured sphere power of a selected fitting lens; receiving as input results of an over-refraction examination of a patient wearing the fitting lens, wherein the results of the over-refraction examination include at least a measured sphere power; calculating the power delivered by the fitting lens on the patient's eye based on input received from the bare eye examination and over-refraction examinations; calculating an Effectiveness Ratio using the calculated power delivered by the fitting lens and the target or actual measured sphere power of the fitting lens; and calculating a custom lens power for the patient using the Effectiveness Ratio and measured sphere power from the bare eye examination.