Iridology is the science that focuses on the study of the eye's iris, which is the colored part of the eye surrounding the pupil.  Iridology reveals abnormalities within the body, the location and stage of development.  It shows at a cellular level, the physical condition, weakness and any other changes in a person's biological system.  Through iridology, the constitutional strength of an organism is detected as well as its ability to react to different diseases.  It also reveals what kind of health problems a specific organism will face in the future.  Iridology detects the weaker organs as well as regions of the body which have accumulated excessive amounts of toxins.

So, to sum it up, iridology detects the cellular level at which the body is degenerating.