The inverted image in indirect ophthalmoscopy was turned upright by Donaldson's method1 using pentagonally roofed prisms in front of the observer's eye. The particular difficulty was an inversion of the examiner's field except for the image of the fundus. The main purpose of the present project was to provide an upright image with the indirect method of ophthalmoscopy without this drawback. The principle of a single lens reflex camera's view finder was employed.
In the beginning the problems of image formation were particularly considered apart from illumination. A separation of these problems was conveniently provided by diffuse transscleral illumination of the fundus.
A 5 mm diameter fiber optic cable transmits light from a power unit to the sclera at the lateral horizontal meridian close to the equator (Fig 1). The luminous intensity is of such magnitude that diffuse illumination of the vitreous cavity and retina is possible despite
SCHIRMER KE. The Upright Fundus Image in Indirect Ophthalmoscopy. Arch Ophthalmol. 1967;77(1):67-70. doi:10.1001/archopht.1967.00980020069014