Learning Iridology is relatively easy. There are many courses offered including diplomas. Iridology on its own may not be enough to start a healing practice though. The assessment of the body is best accompanied by an alternate healing therapy like nutrition, herbal medicine, naturopathy etc.
Dr. Pesek runs a corespondance course called "Holistic Iridology". His company is the International Institute of Iridology out of North Carolina. This particular course is available to you if you live outside the U.S. Clayton College runs courses out of the U.S. on Iridology as well as other courses in natural health.
Two organizations to look into are "Bernard Jensen International", and "International Iridology Practitioners Association". Both of these organizations have some of the highest credibility of North America for healing with Iridology.