A contribution to ophthalmoscopy / by W. Laidlaw Purves.

  • Purves, William Laidlaw, -1917.
Date:
1873
Catalogue details

Licence: Public Domain Mark

Credit: A contribution to ophthalmoscopy / by W. Laidlaw Purves. 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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    A CONTRIBUTION TO OPHTHALMOSCOPY. Instead of tlie present slow and tedious method of determining the refraction of the eye by the Ophthal- moscope, I ha\e to propose that a modified Stokes lens be employed in place of the cumbersome and trouble- some number of spherical glasses generally used. The instrument which I believe Avill answer the pur- pose best, is that made by Cretes, of Paris, a short description of the modifications of which, from the usuall} arranged Stokes, I have given in a paper on the use of the Stokes lens as a determiner of the re- fraction. I would, however, modify the instrument of Cretes by using still stronger cylindrical lenses, so as to include a greater number of lenses in its action ;* making the diameter of the lenses half the size, or there- abouts, so that the observer has no difficulty in ap- proaching close up to the patient’s eye, a great advantage when he will observe the peripheral portion of the retina in the erect image; and arranging at the other end of the handle that the scale giving the equivalent lens for the different rotations is well extended, in order to have the action of each definitely marked. By moving the whole lens through the quarter of the circle, or having the axes of the lenses marked, and the rim of the box in which they are placed graduated, the two lenses together *For the method of calculating the power given to each lens according to the rotation—vide Bonders, &c.