We published the second edition of Ophthalmology in 2004. Now, only 5 years later, we again find that enormous advances have taken place in ophthalmic technology, genetics, and immunology, along with other areas. We continue to recognize the advantage of a complete textbook of ophthalmology in a single volume, rather than a multivolume textbook. Our major effort has been updating and keeping current the third edition. Towards this end we endeavored to delete old out-of-date material as we added new material. One of the easiest parts of a revision is adding new material; the most difficult part, but essential, is to delete the old, so as to keep the book at approximately the same size. Throughout our revision we have successfully maintained this balancing act, culminating in a finished product that is essentially the same size as the prior edition.