Iridology is a study of the iris for the purpose of diagnosing ailments. The iridologist evaluates the unique markings and patterns in the colored part of the eye, attempting to determine conditions in the rest of the body and to identify genetic tendencies that could lead to health issues which are physical, mental, and emotional.

Unlike palm reading, which attempts to determine past, present and future trends, the iridologist, cannot make conclusions about specific diseases. It is considered a preventative practise, similar to a doctor's evaluation of a patient's skin condition. In the belief that the eyes are the mirror to the soul, iridology associates the events in the iris to the conditions of the physical body and the mental state.

Iridology was known to the Greeks, but first appeared as a diagnostic tool in 17th century Europe. By the late 19th century, theories by physicians were advanced in which it was proposed that the iris could reveal specific ailments and tendencies. It had been noticed that patients with fractures had black marks in their eyes and that individuals who had suffered ailments when younger experienced a darkening of color in the iris.

Iridology is more prevalent in Europe than anywhere else because of a longer history of research. It first became known in the United States in the 1950's, when an American chiropractor, began giving classes in his own method, which mainly concentrated on iris color, the body's exposure to toxins, and the use of natural foods as detoxifiers.