Iridology is a fairly old concept that doesn't get much recognition. This book basically introduces the reader to the basic priciples of iridology. In it, the authors describe the different marks that one can find on the iris and describes the associations each area has with the body.
The ability to self-diagnose with the use of this text is limited. The eye charts, although interesting, are so specific that without the use of digital imaging, the best one could do is generalize.
The largest problem with the text is the lack of research provided. There are a few studies mentioned without the supporting data, but nothing substantiating the claims. Of course, the whole area of iridology is basically still in its infancy, from a purely research oriented perspective.
With that said, the whole idea is pretty interesting, and if you know nothing of the science, this book will do nicely as an intro.