Confirming a change in refraction with assistance of a programmable calculator.

A computer program has been developed that allows a refractionist to determine the dioptric difference between the powers of two spherocylinder lenses with an inexpensive programmable calculator. The lens system that has been thus calculated may be placed in front of the patient's present spectacles. This allows rapid comparison between the results of the refractive examination and the patient's present spectacles. In difficult cases, this procedure is a useful adjunct in making a decision as to whether the refractive prescription should be changed.