Iridology (also known as iridodiagnosis or iridiagnosis) is an alternative medicine technique whose proponents claim that patterns, colors, and other characteristics of the iris can be examined to determine information about a patient's systemic health. Practitioners match their observations to iris charts, which divide the iris into zones that correspond to specific parts of the human body. Iridologists see the eyes as "windows" into the body's state of health.

Iridologists claim they can use the charts to distinguish between healthy systems and organs in the body and those that are overactive, inflamed, or distressed. Iridologists claim this information demonstrates a patient's susceptibility towards certain illnesses, reflects past medical problems, or predicts later health problems.

As opposed to evidence-based medicine, iridology is not supported by quality research studies and is considered pseudoscience. The features of the iris are one of the most stable features on the human body throughout life. The stability of iris structures is the foundation of the biometric technology which uses iris recognition for identification purposes.

In 1979, Bernard Jensen, a leading American iridologist, and two other iridology proponents failed to establish the basis of their practice when they examined photographs of the eyes of 143 patients in an attempt to determine which ones had kidney impairments. Of the patients, 48 had been diagnosed with kidney disease, and the rest had normal kidney function. Based on their analysis of the patients' irises, the three iridologists could not detect which patients had kidney disease and which did not.