. A treatise on the diseases of the eye. accurate description of the variouskinds of ophthalmoscope whichhave been invented, I must referthe reader to Mr. Carters trans-lation of Zander. Ophthalmoacopes may be di-vided into four different classes: 1. The portable or hand oph-thalmoscopes. Of these I shallnotice those of Liebreich, Coccius,and Zeheuder [and Loring.—H.],[and Knapp.—B.]. 2. The fixed or stand ophthal-moscopes, such as Liebreichs, andits excellent modification by Smithand Beck. 3. The binocular ophthalmo-scopes of Giraud-Teulon, and ofLaurence and 4. The aut-ophthalmoscop
. A treatise on the diseases of the eye. accurate description of the variouskinds of ophthalmoscope whichhave been invented, I must referthe reader to Mr. Carters trans-lation of Zander. Ophthalmoacopes may be di-vided into four different classes: 1. The portable or hand oph-thalmoscopes. Of these I shallnotice those of Liebreich, Coccius,and Zeheuder [and Loring.—H.],[and Knapp.—B.]. 2. The fixed or stand ophthal-moscopes, such as Liebreichs, andits excellent modification by Smithand Beck. 3. The binocular ophthalmo-scopes of Giraud-Teulon, and ofLaurence and 4. The aut-ophthalmoscope. All ophthalmoscopes may alsobe divided into two principalclasses, the homo-centric and thehetero-centric. In the Jiomo-centric the mirror is concave, and its focus, cal-culated from its surface, is fixed and definite ; whereas in the hetero-centricthe mirror is plane or convex, and the focus is negative, situated behind themirror, and can be altered according to the strength of the biconvex lenswhich is fixed beside the THE POKTABLE OR HAND OPHTHALMOSCOPES. 733 Fie. 230. 1.—THE POKTABLE OE HAND OPHTHALMOSCOPES. (1) The Ophthalmoscope of Liebreich. As has been already mentioned above, Ruete was the first to employa concave perforated mirror (which was, however, fixed) as a substitute forthe slips of glass of Helmholtz, and thisprinciple has formed the base for the nu-merous modifications at present in all the different forms of concavemirror, I think Liebreichs (Fig. 230) themost handy and useful. It consists of aconcave metal mirror, about one and one-fourth inches in diameter, and eightinches focal length. Its centre is perfoi-ated by a small aperture, about one linein diameter, the edges of which are ex-ceedingly thin. The bronze back of thespeculum around this opening is bevelledoff towards the edge, so that the lattermay be as thin as possible, in order thatthe peripheral rays of the cone of light,which passes through the aperture, maynot be interce
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