The disc is called a cephaloscope, and it helps ENTs (or ear, nose, and throat doctors) visualize various body cavities of interest. To use the device, the medical professional swings the mirror down over one eye and peers through the center hole. A light source is then shone on the concave side of the mirror, reflecting and illuminating the black hole in question. Essentially, the cavity can be seen without allowing the light source to block the doctor's view.
It takes practice for a physician to learn how best to position the mirror and his or her head to properly reflect the light and provide the best view. Because they are worn so often, they become an easy way to provide a stereotypical view of the doctor, although wearing one in the center of the forehead - rather than over one eye - is not really accurate.
Many modern doctors have opted for fiber-optic headlamps, which provide illumination that is not so difficult to perfect. Physicians trained in traditional headlamps may decide to stay with it; residency programs still include mirrors. When used properly, it can cast a very bright light.
The mirror was originally designed by a French medical specialist named Levert to examine the larynx, and the technique was later improved by a German doctor who used a candle as a light source.Johann Nepomuk Czermak is credited with inventing the cephalometric mirror as we know it today, and he presented it to the medical community in 1858.
Like many medical tools, the use of the headlamp often depends on the setting. A headlamp may be the best choice for examining a squirming child because it has its own light source and can be maneuvered more easily. However, if you're dressing up as a doctor for Halloween, then a headscope may be your best option.