OPHTHALMOSCOPE, THE, is an instrument recently invented for the purpose of examining the deep-seated structures of the eye, and for detecting disease in them. In its simplest form, it is merely a concave circular mirror, of about 10 in. focus, made of silvered glass or polished steel, and having a hole in the center; and with it there is sup plied, as a separate piece of apparatus, a Convex lens an inch and a half in diameter, with a focal length of about two and a half inches, set in a common eye-glass frame, with a handle 3 in. long. The patient (his pupil having been previously dilated by the application of a drop of solution of atropine) is made to sit by a table in a dark room, with a sliding argand lamp placed by the side of his head, with the flame on a level with the eye, from which it is screened by a little flat plate of metal attached to the burner. The following description of the mode of using the instrument, and of the parts brought into view by it, is borrowed from the article on this subject contributed by Mr. Haynes Walton to the last edition of Druit's Surgeon's Vade Mecum: "The operator sits directly in front, and holding the instrument close to his eye, and a little obliquely to catch the light from the lamp, he commences. at the distance of about 18 in. from the patient, to
direct the reflection on the eye. When this is got, the convex lens must be held at a distance of two and a half inches from the eye, and the focusing commenced by moving it slowly- backwards and forwards. When the light fairly enters the eye a reddish glare appears; and as it is focusraLan orange-red or orange-yellow is seen; then the blood-vessels of the retina come into view. The retina itself presents a whitish aspect, through which the choroid is more or less discernible. The entrance of the rtie nerve should now be sought. The way to discern it is to make the patient look inward. It appears as a white circular spot, in the center of which are the central vein and artery of the retina, giving off six or eight branches." This optic disc is the most important part to ha observed; but a thorough ophthalmoscopic examination will reveal structural differences, not only in it, but in the retina, ehoroid, and vitreous humor, and will reveal cataract in its early stage. In short, the ophthalmoscope is now as essential in the diagnosis of diseases of the deep-seated parts of the eye as the stethoscope is in the diagnosis of thoracic diseases.