Confocal microscopy is an optical imaging technique for increasing optical resolution and contrast by means of adding a spatial pinhole placed at the confocal plane of the lens to eliminate out-of-focus light. It provides the capacity for direct, noninvasive, serial optical sectioning of intact, thick, living specimens with a minimum of sample preparation as well as a marginal improvement in lateral resolution.
Biological samples are often treated with antibodies conjugated with fluorescent dyes to make selected molecules visible. Also, transgenic techniques can create organisms that produce their own fluorescent chimeric molecules (such as a fusion of GFP, green fluorescent protein with the protein of interest).
Three-dimensional studies are also done with this technique.