Defects of sight and hearing : their nature, causes, prevention, and general management / by T. Wharton Jones.

  • Thomas Wharton Jones
Date:
1859
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Licence: Public Domain Mark

Credit: Defects of sight and hearing : their nature, causes, prevention, and general management / by T. Wharton Jones. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    CYLINDRICAL EYE. But as with the loss of the crystalline body, there is loss of the faculty of the eye to adjust itself for different distances, except so far as variations in the size of the pupil contribute to this effect, glasses of different degrees of convexity are required according as the patient wishes to view near or distant objects. Thus, convex lenses of two and a half inches focus are generally required for reading, and lenses of four and a half inches focus for viewing objects around him. [Lenses of three to three and a half inches focus for viewing objects near him, and for distant objects four to four and a half inches.] Of course before fixing on any particular powers, the patient will try which suit him best, and the test which should guide him in his choice is, that when the specta- cles are put on, or, if hand-glasses, when they are held im- mediately before the eyes, he sees objects distinctly at the same distance as he saw them before he became blind. [Hand glasses as a general rule are objectionable, particu- larly for cataract cases such glasses should always be placed before the eyes in spectacle frames.] Kecourse is not to be had to the use of cataract glasses until the eyes have perfectly recovered from the operation, and have been so for some time,—say six months. Cylindrical Eye. Cases are met with in which the rays of light in enter- ing the eye are refracted to a nearer focus in a vertical than in a horizontal plane. This would take place, if the cornea, instead of being a surface of revolution, in which the curvature of all its sections through the axis must be equal, were of some other form, in which the curvature in a vertical plane is greater than in a horizontal. This is,