The ophthalmoscope : a manual for students / by Gustavus Hartridge.

  • Gustavus Hartridge
Date:
1907
Catalogue details

Licence: In copyright

Credit: The ophthalmoscope : a manual for students / by Gustavus Hartridge. Source: Wellcome Collection.

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    concave series — •5 D., — 1 D., increasing by one dioptre up to — 12 D., and then hy two dioptres up to — 20 D. Sometimes a higher glass may be re- quired ; these may be supplied on a separate disc; the lenses in this disc may, by combination with the other lenses, form a very large series. The lenses should not be less than 6 mm. in diameter, otherwise they are difficult to centre pro- perly, and cannot be easily cleaned—a point of some importance; they may occasionally be used for the subjective test of estimating the visual acuteness, should the box of trial lenses not be at hand. It will be sufficient here to describe and to figure one of the ophthalmoscopes in general use, though numerous other good instruments will be found in this country and abroad. Morton’s ophthalmoscope, shown in Fig. 29, is a modification of an instrument introduced by Mr. Couper; it contains a series of twenty-nine lenses in metal rings, and one metal ring without a glass; these run round a continuous channel, and are so arranged that each can be brought successively in front of the sight-hole by means of a driving wheel. When no lens is required, then the empty ring occupies the sight-hole; these lenses touch each other sideways, but are not fixed in any way; on the spindle that carries the driving wheel is another wheel with teeth, which propel the lenses round the instrument; a spring and notch attached to the driving wheel centres each lens as it arrives at the