In the study of small areas of the fundus as the disc and macula, depth relationships may be of considerable importance. A binocular direct ophthalmoscope has been designed to accomplish such observation with greater simplicity than other techniques. The instrument produces a magnification of 15 times, an excellent stereoscopic effect, and is hand held.
Donaldson DD. Binocular Direct Ophthalmoscope. Arch Ophthalmol. 1969;82(6):781-783. doi:10.1001/archopht.1969.00990020773010