The determination of the necessity for wearing glasses / by D.B. St. John Roosa.

  • Roosa D. B. St. John (Daniel Bennett St. John), 1838-1908.
Date:
1887
Catalogue details

Licence: Public Domain Mark

Credit: The determination of the necessity for wearing glasses / by D.B. St. John Roosa. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    CHAPTER II. PRESBYOPIA. Glasses have been used for its correction ever since they were invented to assist vision.—Accommodation j how it is accomplished.—Helmholtz s theory the accepted one.—Recession of the near point, the essential mark of presbyopia.—Method of adjusting glasses for presbyopia.—Astigmatism in conjunction with pres- byopia to be corrected.—Second sight.—Illustrative examples of correction of presbyopia. Ever since glasses were invented by Salvinus Amatus or Friar Bacon, in the thirteenth century, they have been used for presbyopia, or the sight of old age. Convex glasses are used for the correction both of hypermetropia and presbyopia, but the two condi- tions should not be confounded. Presbyopia is a failure of the accommodative power of the eye, while hypermetropia depends upon an insufficient refractive power, usually due to a shortening of the antero- posterior diameter of the eye-ball, although in some instances it may depend upon insufficient refractive power of the lens alone. The ciliary muscle acting upon the crystalline lens is the agent of accommodation. The accepted theory of accomodation, although it has some oppon- ents, is, that in vision for near objects; the lens be-