Iridology's central claim, that trained practitioners can detect known medical conditions by examining the iris, is unusually well suited to direct, blinded testing, since it can be checked by giving iridologists iris photographs from patients whose actual diagnoses are already independently known and confirmed, without telling the iridologists which photograph belongs to which diagnosis. The most cited such study, published in JAMA in 1979 by Simon, Worthen, and Mitas, photographed the irises of 143 patients, 95 with healthy kidneys and 48 with kidney disease severe enough to produce clearly abnormal blood chemistry, and had iridologists assess the photographs blind to the patients' actual status; the iridologists' assessments showed no significant ability to distinguish the two groups, performing at a level consistent with chance. Subsequent controlled, masked studies testing iridology against other confirmed conditions have reached the same conclusion, finding no diagnostic validity beyond chance.
Because iridology involves no needles, substances, or physical intervention, it carries essentially no direct physical risk of its own. The documented harm associated with it is indirect, arising when an iris reading leads a patient to believe they have, or do not have, a condition that has not actually been medically confirmed, potentially delaying appropriate diagnosis and treatment. Iridology continues to be offered within some naturopathic and alternative practices despite this consistent negative trial record, generally framed as a screening or wellness tool rather than a stand-alone diagnostic method.