The prospects for perfect vision.

R efractive surgery and other high-tech methods for correcting the optical aberrations of the eye aim to make the eye optically perfect. The notion that perfect vision may be within our grasp is a distinctly 21st century concept which is a quantum leap forward from the foundations of oph-thalmic practice in the 20th century. Throughout history the assumption has been that the chief cause of poor vision is poor optical quality of the retinal image. From this basic principle, the following line of argument leads one to contemplate the prospects for perfect vision through refractive surgery or other means. Refractive errors are common , at least in the developed countries of the world, and these uncorrected refractive errors cause the retinal image to become blurred. This uncor-rected optical blur reduces visual performance on almost every visual task imaginable because it reduces contrast in the retinal image. The successful history of ophthalmic clinical practice in the 20th century is proof that elimination of sphero-cylindrical blur with spectacles, contact lenses, intraocular lenses, and refractive surgery is a miracle cure that literally restores sight to the blind. Therefore, it stands to reason that the 21st century goal of eliminating all traces of optical blur due to higher-order aberrations of the eye, which clinicians sometimes call "irregular astigmatism," suggests the prospect of perfect retinal images producing perfect vision. If the goal is to achieve retinal images of such high quality that they are no longer limited by the optical imperfections of the eye, then the only remaining optical limitation will be the unavoidable effects of diffraction. This is the meaning of the phrase "diffraction-limited retinal images." When contemplating the prospects for achieving diffrac-tion-limited retinal images even under night-time viewing conditions when pupils are dilated, three questions immediately come to mind. 1) Is this quest for diffraction-limited image quality really possible, or is it just wishful thinking? 2) What would be the potential benefits of perfect retinal images, if they can be obtained? 3) What are the potential penalties? In other words, is there a down side to having perfect retinal images? The purpose of this brief article is to frame these questions in terms that are understandable to clini-cians and visual scientists alike, and at the same time to expose some of the complexity of the issues raised. ARE PERFECT RETINAL IMAGES REALLY POSSIBLE? Other papers in this feature issue address the technical issues …