Charles A. Perera, May's Manuel of the Diseases of the Eye, Williams & Wilkins Co., 1943

THE MEDIA AS SEEN WITH OBLIQUE ILLUMINATION AND THE OPHTHALMOSCOPE AT A DISTANCE. PUPIL DILATED.

The Electric Ophthalmoscope.— A small electric lamp enclosed in the handle furnishes the light; its rays are concentrated and then thrown into the patient's eye by a reflector. The lens-disc with its battery of lenses is attached behind the reflecting surface. The lighting current is either derived from a dry-cell battery in the handle or is conducted by cords connected with the house current through a rheostat. For bedside fundus examinations the battery-in-the-handle instrument is necessary.