A manual of ophthalmic practice / by Charles Higgens.

  • Higgens, C. (Charles), 1846-1920.
Date:
1903
Catalogue details

Licence: Public Domain Mark

Credit: A manual of ophthalmic practice / by Charles Higgens. Source: Wellcome Collection.

    47/408 page 35
    II]. EXAMINATION BY THE OPHTHALMOSCOPE. Description of the instrument.—The ophthal- moscope consists essentially of a mirror of silvered glass or polished metal, having a central opening, with certain accessory portions in the shape of convex lenses of different foci, used as objective lenses. The ophthal- moscope since its introduction has undergone innumer- able modifications, both in principle and detail; the number of different instruments being nearly, or quite, as great as that of ophthalmic surgeons. The most convenient form of ophthalmoscope is Morton’s modification of Couper’s instrument (vide fig. 23). This has two concave mirrors, a large one for indirect examination, and a small one set obliquely for direct examination. The advantage of the oblique mirror is, that the observer can hold the instrument perfectly straight and has not to tilt the mirror in order to direct the light on to the pupillary area, and he obtains a much brighter and more concentrated light. The two mirrors are set in a frame which re- volves around a pivot at its centre. In the case form- ing the body of the instrument is an endless chain of small rings, into, which are fitted lenses of strengths ranging from +°*5 to +12 and from —*5 to —20. The chain is moved around by means of a toothed wheel worked by the index finger of the observer and this simple arrangement augmented by another disc placed at the top of the instrument gives a range of lenses from +°'5 to +32 and from —*5 to —50. Another advantage of this instrument is its length, the handle being sufficiently long and far from the sight hole to D2
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