a method of manufacturing a prescription lens , for eyeglasses on site by compression molding , in a pair of upper and lower molds having a mold surfaces from a thermoplastic preformed lens blank having opposite surfaces and a periphery , comprising the steps of : preheating a preform blank at a first temperature and preheating the upper and lower molds to a second higher temperature ; positioning the preheated preform between the upper and lower preheated molds such that the preform makes a single point or line contact with each of the mold surfaces ; initially compressing the preformed at a first fixed rate of speed regardless of pressure exerted on the preform , with the preform being compressed to about 4 mm of a predetermined lens thickness desired for the prescription lens ; finally compressing the preform to a substantially finished prescription lens at a second fixed rate of speed substantially higher than the first fixed rate of speed regardless of pressure exerted on the preform while substantially maintaining the predetermined temperature , and shutting off the heating to the molds , and stopping travel of the molds with respect to each other upon reaching the predetermined lens thickness ; and cooling the molds to another , but lower predetermined temperature ; and thereafter opening the molds so as to remove the finished prescription lens .