The iris of the eye is an exact representation of the organs in the body. Marking in the eyes are related to a chart of Iridology in order to understanding which organ is inherently weak. Studies have revealed organic disease in these organs that showed degeneration through Iridology.
The current iris chart is a vast evolution from its first. It is detailed to inlcude every organ and gland, every tissue structure etc. The left eye represents the left side of the body and vise versa. This is similar to a reflexology chart in that an organ on the left side would appear in the left foot. Organs like the large and small intestines that cross the body appear in both eyes.
The center of the eye represents digestion where the stomach and gastric glands are at the pupil border. The large and small intestines are just outside that. The digestive system is encircled by the collerette or autonomic nerve wreath, blood and lymphatic circulation. At this central ring, there is a division between the digestive organs and all the other ones. It is on this ring that the endocrine organs appear. The outer portion of the iris is more blood and lymphatics as well as skin at the outermost portion.
Here is Dr. David Pesek's Holistic Iridology Chart created in 1999.