Measuring Refractive Error Change of the Contact Lens Wearer

The total effective spherical power before the eye while a contact lens is worn is composed of the lacrimal lens, the contact lens power in air and a refractive addition, lens in situ. Comparing the original fitting day's results to a late result is the true measure of refractive error change for the contact lens wearer. A second measure of change is to compare the equivalent sphere of the pre‐fitting subjective refraction to that of the late refraction, contact lens immediately removed. Comparing these two changes and resultant visual acuities evaluates the change and reveals other clinically useful data.