The optics of the ophthalmoscope and related instruments

The history of practical methods for examining the internal structures of the eye spans 130 years, with the greatest advances occurring since the end of the second world war. The present review examines the optics of direct and indirect ophthalmoscopes and the extension of these principles to fundus photography, angiography, laser delivery and intraocular microsurgery. Problems of measurement and the possible future role of holography are given passing mention. The fundamental principles behind most ophthalmoscopic instruments are not complex by modern optical standards; indeed, the early workers Helmholtz, Gullstrand and Thorner had virtually solved not only the problem of how to see into an eye but also the difficulty of overcoming unwanted reflexes from the various refractive surfaces in the system, and the challenge of obtaining a three-dimensional view of the fundus oculi. Progress in instrument development and design has been closely linked to the new understanding of light energy, photographic processes, improved lens design and the emergence of the recent discipline of microsurgery. Thus, new technology has found a ready application in ophthalmoscopy and medical ingenuity has provided the element of urgency so vital to fresh initiatives in instrument design. With the hindsight provided by the late complications from uncontrolled use of X-rays, it is perhaps surprising that the damaging effects of light on the retina have only recently begun to attract attention. These findings will have a strong influence on future research and development of ophthalmoscopic instruments.