In a method for visualizing an object under conditions of low ambient light, the object to be visualized is exposed to incident electromagnetic radiation having a wavelength greater than what can normally be seen by the naked eye. Light reflected from the object is then perceived with an enhanced eye. The enhanced eye contains an up-conversion material optically coupled to the photoreceptors. Up-conversion materials absorb in the infrared and luminesce in the visible. Particles containing such materials are delivered to the eye where they are optically coupled to the retina or photoreceptor cells and nearby tissues. There they provide in-situ up-conversion of infrared frequencies (from about 700 to about 11,000 nm) to the otherwise unaided eye.