Funduscopic systems: magnification in ametropia and aphakia.

The magnification of the fundus image with various forms of funduscopy in ametropia and aphakia is poorly understood. This paper investigates these relationships. Direct and indirect ophthalmoscopy and biomicroscopic funduscopy is included. The Gullstrand Simplified Schematic Eye is modified by changing either the axial length, the power of the cornea, or the index of refraction of the lens to produce ametropia. Aphakia is produced by considering these same eyes with the crystalline lens removed. The magnification of these various eye/funduscope systems is presented, along with general principles illustrated by the figures.