OPHTHALMOSCOPE from Gk. 600aX4s, ophthal mos, eye ± csoreip, skopein, to view). An instrument invented by Helmholtz in 1551 for the purpose of examining the deep-seated structures of the eye, and for detecting disease in it. It is a concave circular mirror, of about 10 inches focus, having a hole in the centre, and mounted on a handle and accompanied by a set of convex and concave lenses. In the most ap proved forms the mirror is cut in approximately the form of a parallelogram and is so arranged as to he tilted toward either side. The lenses are placed near the circumference of a disk, by pres sure upon the reeded edge of which they are brought successively before the opening in the mirror. Light is reflected into the interior of the eye by the mirror, and a portion returns, through the opening in the mirror and through the lens placed opposite it, to the eye of the observer, OpurruALmoscortc. EXAMINATION. (1) Of t he edia.—]n a darkened room, an Argand burner is placed several inches from either side of the patient, a few inches behind, and on a level with the eyes. Facing the patient, the observer looks through the perforation in the mirror, which is held about 15 inches from the patient's eye and reflects light into it. An orange-red reflex from the fundus is seen in the normal eye. Dark spots show opacities of the media or cornea ; ametropia (see SIGHT, DEFECTS OF) is shown by ability to see the vessels in the flinch's. (2) Indirect Mcthod.—This gives an inverted image of the fundus. For both this and the direct method the pupil should be dilated by some mydriatic. The light is placed as before, and the ophthalmoscope is held at the same distance but with a positive lens of sufficient strength before the opening.
The light is directed by the mirror into the eye through a strong convex lens held at its focal dis tance of about two inches in front of the patient's eye. By varying the distance of the mirror and lens an inverted image of the fundus is obtained. The fundus appears as an orange-red surface, darker in brunettes than in blondes, finely dotted by pigment cells. It is crossed by blood-vessek which radiate from the optic disk, the arteries bright, the veins darker red and more tortuous. The optic disk is usually circular, pinkish, often bordered by a white ring of sclera, and an exter nal dark ring formed by the ehoroid coat. The blood-vessels emerge front a depression at the centre of the disk. The appearance of the normal fundus varies greatly. (3) Direct Method.— This gives an erect image, magnified about 14 times, a smaller field at one time, allows estima tion of errors of refraction by noting the lens which is necessary to give a clear view. and is less difficult. The light is placed on the side of the eye examined; the ophthalmoscope is held about one inch in front of the patient's eye. Dif ferent portions of the fundus are brought into view by movement of the eye of the patient. In this method correction by lenses 'mist be made for errors of refraction of both patient and ob server. practice is required for the skill ful use of the ophthalmoscope, but it is now as essential in the diagnosis of diseases of the eye as the stethoscope is in that of thoracic affec tions. Those of other parts of the body may also be detected or confirmed by its use. For ex ample, inflammation of the optic disk occurs in 90 per cent. of brain tumors.