OPHTHALMOSCOPE

n. O3f-tha2l'mo-skop. From 6 0oVds, the eye, and (ricoire'iv, to examine. Fr., o. Ger., Augenspiegel, Ophthalmoskop. An instrument invented by Helmhqltz in 1851 for examining the media and fundus of the eye by illuminating the interior of the organ with light from a lamp placed at one side and a little behind the patient, and reflected from a plane or concave mirror directly through the pupil. The rays are reflected from the pigment-cell layer of the retina through the pupil and strike the mirror of the o. The centre of this mirror is perforated, or has a small circular space at its c ntre left unsilvered, and through this hole or clear portion of gla the rays com ing from the patient's eye pa into the eye of the observer placed immediately behind it. [F.] lieale's demonstrating o. An o. in which the reflector and lens are inclosed in a tube, to the side of which is adapted a small lamp with a large plano-convex lens. The lens is inclined a little so as to remove out of the field of vision the reflections upon the retina. [F.] Burke's o. An o. consisting of two concave mirrors, one for illumination and the other for uniting the rays from the patient's eye into a real inverted image. [Graefe and Saemisch (F).] Carter's o. An o. consisting of a chin-rest, a perforated concave mirror of large aperture and long focus, and a similar convex gla so arranged that they cast an inverted image of the fundus of the patient's eye. [F.] Coccius's o. An o. consisting of a plane metallic mirror combined with a convex illuminating lens, placed obliquely to the mirror. The mirror is perforated at the centre and mounted on a handle. On the latter is also a transverse arm, in which runs a movable bar or rod. on the upper end of which is the lens. The light is distant from the lens a few inches more than twice its focal distance. A later modification of the instrument has the convex lens fastened by a hinge to a metallic blackened frame. The latter has a large circular opening and two curved borders, so that it can be shoved up over the mirror, and the reflecting surface thus be limited to the opening of the frame. [Graefe and Saemisch (F).] Coccius's prismatic o. An o. which consists of a rectangular prism with unequal sides, in which one of the lateral surfaces is used for reflection, the hypothenuse surface being turned toward the light. [Graefe and Saemisch (F).] Cohn's o. A modification of Loring's o. in which the centre of the disc is not to one side of the mirror, but over it, so that it embraces a greater circumference without coming in collision with the nose of the observer. ["Klin. Mntsbl. f. Augenheilk." (F).] Desmarre's o. An o. in which the concave mirror and handle are constructed of one piece of metal. There is no central opening, but there are two eccentric ones, for use by the two eyes. [Graefe and Saemisch (F).] De Wecker's and Roger's o. for two observers. An o. in which a combination of two prisms of 48 and 42, with their hypothenuse surfaces together, is placed in front of the inverted image cast by a convex lens. A part of the rays coming from the inverted image pa es straight through and enters the eye of one observer, while another part, reflected from the hypothenuse surface, enters the eye of the other observer. [Graefe and Saemisch (F).] De Wecker's o. A modification of Loring's o. in which, as in Cohn's o., a disc with 24 gla es or lenses of very small dimensions is so inserted that it can easily be rotated by means of a toothed wheel. [F.] EpkensDonders o. An o. consisting of a cubical box containing a plane mirror perforated at the centre and movable round its vertical too; Ua, blue; U3, lull; U, full; U, urn; U, like ii (German). [s. 157]