Pomerantzeff O, Pankratov M M, Wang G J, Schepens C L
Ophthalmology. 1984 Feb;91(2):197-203. doi: 10.1016/s0161-6420(84)34310-x.
An indirect ophthalmoscope that could provide higher magnification (up to 15X) would offer definite advantages in fundus diagnosis. If it could also supply an erect fundus image, it could advantageously replace the surgical microscope in vitrectomy operations. The surgical microscope requires the use of a contact lens, which restricts the surgical techniques and may damage the corneal epithelium, and it reduces image brightness when the magnification is increased. In contrast, an indirect ophthalmoscope does not require a contact lens and keeps the image brightness constant regardless of magnification. Increased magnification can be obtained in an indirect ophthalmoscope by incorporating telescopes in the ophthalmoscope oculars. The possible use of two telescopic systems, Keplerian and Galilean, and the problems of stereopsis and image inversion are discussed. A new, optimized ophthalmoscope is described, with Keplerian telescopes, that provides a range of magnifications from 2X to 15X as well as options for an erect or inverted fundus image.
