Looking at cells under a microscope does not always present a true picture of what is going on in real life. One immediate problem is that three-dimensional objects such as cells will appear out of focus for anything that is not resting in the focal plane of the microscope’s lens. A key feature of confocal microscopes is to produce blur-free images of thick specimens at various depths, which is particularly valuable with the dendritic cells of the immune system which have convoluted membranes and “dendritic” extensions that increase their surface contact with the outside environment.
The principle of confocal microscopy was patented in 1957 by Marvin Minsky, who later went on to become a pioneer in the field of computer artificial intelligence. As a young research scientist he saw the limitations of wide-field, conventional fluorescence microscopes which flooded the entire specimen evenly with light from a light source. This produced unfocussed light in the background, which was not only not useful but a positive distraction.
In contrast, he had the idea of a confocal microscope that used point illumination of particular spots on the specimen and a pin-hole to eliminate out-of-focus signals – the “confocal” name derives from this configuration. The image’s optical resolution was much improved over the conventional system.
Then, in 1969, David Egger and Paul Davidovits of Yale University combined confocal microscopy with lasers to increase the resolution still further. Now, laser confocal microscopy, combined with computers, can produce exquisite three-dimensional images of complex biological material, including the highly amorphous structure of dendritic cells.