A new model of a small ophthalmoscope / by Walter L. Pyle.

  • Pyle, Walter L. (Walter Lytle), 1871-1921.
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: A new model of a small ophthalmoscope / by Walter L. Pyle. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    The aperture of this inner disc is always rotated back to the sight-hole after use, and is kept in that position to avoid interfering with the movements of the commonly used low- power lenses on the inner disc. 4. By the foregoing arrangement of lenses on the two discs, single lenses, both convex and concave, varying in strength from 1 D. to 24 D., can be rotated continuously and succes- sively before the eye. By means of combinations, which, however, interfere with correct registration and were not anticipated in the construction of the instrument, the range can be increased to 30 D. 5. The registration-marks on (he outer disc are arranged similarly to the lenses, so that when it is rotated just past 6 D., either concave or convex, the red zero-mark is brought before the registration-aperture on the case of the instru- ment. The registration-marks on the inner disc are also arranged similarly to the lenses with the exception of the zero-mark, in the place of which is an aperture cut in the disc allowing the figures on the outer disc to show through. Thus, when the inner disc containing the high-power lenses is not in use it is set at the aperture (zero) and the mark- ings and lenses on the outer disc are unobstructed. In this manner there is obtained continuous and successive registra- tion through a single aperture in the outside case. 6. The mirror is unperforated, the sight-hole being scraped through the silvered back; it is 2 mm. in diameter. The mirror-support is a section of a hollow metal cylinder ob- liquely cut at one end, extending from the back of the mir- ror to the outer disc, completely shutting out all direct or reflected light. These details in construction render the fundus-reflex and retinal image so much more distinct than with the ordinary mirrors that the difference is at once noticed. My experience with such a mirror on the Morton ophthalmoscope led me to adopt it. 7. There is no intricate or expensive mechanism. The apparatus consists of two discs with 25 lenses, and a small driving-wheel. I am indebted to Messrs. Wall and Ochs, of Philadelphia, for the skilful manner in which they have followed my plans and models in the manufacture of the present perfected instrument.