An implant capable of forming a differential image in an eye is shown. The implant comprises an elongated member having a pair of spaced ends wherein one of the pair of ends includes a distal section that extends in a direction substantially parallel to the central axis. The elongated member and the distal section are formed of a dimension to be inserted into and/or passed through a punctum opening of an eye and into the canaliculus. The implant incorporates into at least one of the elongated member and the distal section an energy obstructing material responsive to the application of an energy wave, such as an energy wave in the form of sound waves vibrating at frequencies greater than 20,000 cycles per second or electromagnetic radiation, which upon everting of an eyelid of an eye and exposing the implant to an appropriate energy wave, forms a differential image pattern showing the location of the implant in the eye. Methods for treating an external eye condition due to a deficiency of tears and for locating an implant in the canaliculus of an eye using the implant capable of forming a differential image is also shown.