Retinal photography in colour.

HISTORICAL.-Monochrome photography of the human retina has been practised increasingly since the early pioneer work on this subject in the latter half of the 19th century. The instrument in most common use to-day is the Zeiss-Nordenson retinal camera, which first appeared in 1915. Several modifications of the original instrument have since appeared, and over 10 years ago it was reported that about 350 of these cameras had been distributed by the manufacturers (Koch, 1941). The early models employed a carbon arc light source, and later an incandescent lamp was used. The general appearance of the apparatus is shown in Fig. 1. Colour photography of the ocular fundus has been developed relatively recently; early results on Dufaycolor and Agfacolor were hardly satisfactory, but Kodachrome began to be used successfully about 1935. Many collections of Kodachrome transparencies have by now been made, and the Zeiss-Nordenson carbon-arc model has been favoured for this purpose. It is also interesting to note that, after much research, the Bausch and Lomb Co. have reverted to the use of a carbon-arc in their new retinal camera (Med. biol. Illus., 1952, 2, 58). Various workers (Bedell, 1940; Koch,, 1941) have reported that exposure times of -112 sec. are necessary to obtain results with this type of subject and equipment. With exposures such as these, there is a considerable risk of records being marred by movement of the subject, and the unstable nature of an open carbon arc makes serial FIG. 1-General appearance of Zeissrecording unpredictable. These diffiNordenson retinal camera.