The optics of fundus examination.

It has been 140 years since the invention of the ophthalmoscope in 1851 by Herman von Helmholtz. Since then, a considerable amount of time and effort has been devoted to improving the clinician's view of the fundus both for diagnostic and therapeutic reasons. Recently, there have been some notable advances in this respect, such as the 90 diopter lens, the "2.2 pan retinal" lens, and numerous "wide angle" fundus-viewing contact lenses to which the Volk Quadraspheric fundus lens has been the most recent addition. This paper is a review of the optical principles underlying the methods of fundus examination currently available.