Light microscopy of living tissue: the state and future of the art.

Since its introduction over a decade ago, confocal microscopy has found wide applicability in the microscopy of thick specimens and living tissue because of its ability to obtain images from deep inside the sample without interference from scattered or out-of-focus light. Three new instruments that are capable of imaging optically dense specimens such as the skin are considered here: a modified tandem-scanning confocal, the video-rate laser-scanning confocal microscope (both of which were developed specifically to examine skin in vivo), and the two-photon laser-scanning microscope, a design which is "inherently confocal." The tandem-scanning and video-rate confocals use visible and infra-red light, respectively, to acquire reflection images, whereas the two-photon scanner is a fluorescence microscope. The advantages and drawbacks of each of these instruments is considered.