A rear-facing pupil diameter sensing system for an ophthalmic lens comprisingan electronic system is described herein. The rear-facing pupil diametersensingsystem is part of an electronic system incorporated into the ophthalmic lens.Theelectronic system includes one or more batteries or other power sources, powermanagement circuitry, one or more sensors, clock generation circuitry, controlalgorithms and circuitry, and lens driver circuitry. The rear-facing pupildiametersensing system is utilized to determine pupil position and use thisinformation to controlvarious aspects of the ophthalmic lens.
