Several devices for determining a distance of an object a user of an electro-active lens is looking at are presented. Once the distance is determined, the devices may alter the optical power of the electro-active lens to ensure that the object is correctly focused. Optical range finding is a possible means for carrying out this task. An active rangefinder may emit optical radiation from a transmitter directed at the object. The optical radiation may then be reflected off the object. The reflected optical radiation may then be received with an appropriate receiver. The received optical radiation may then be processed by appropriate circuitry to determine a distance to the object. A passive rangefinder works without a transmitter. Instead, an appropriate receiver receives ambient sources of light from the object. The received light may then be processed by appropriate circuitry to determine a distance to the object.