Iridology is the observation of bodily function through the iris. The iris reflects organ physiology and structure. You cannot necessarily diagnose disease via the iris but rather use it as a valuable guide to show the functioning of different organs and systems in the body.
Iridology works well as a tool for preventative medicine, and therefore is an effective tool in naturopathy as a means for preventing disease. Iridology can assess, for example, the constitution of a person, this is the constitution they were born with. It is noted by the weave of the iris, a fine density of fibres, like silk, shows good vitality and a strong constitution, this person may have a good vital response and recover well from illness. An open weave iris will have a weaker constitution and lower vital response and may be prone to illness more often.