On Defects of Vision Which Are Remediable by Optical Appliances

On Defects of Vision Which Are Remediable by Optical Appliances

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1877 edition. Excerpt: ...peculiarities of formation are often hereditary, and are often shared by other members of the family. The popular belief about squint arising from imitation seems to have no better foundation than its frequent occurance, as a result of similar physical formation, in several brothers and sisters. Not long ago, I operated for squint, at St. George's Hospital, upon six sisters and their mother; and it is the exception, rather than the rule, for only one child in a family to be affected. The conditions of vision depend entirely upon the degree of the hypermetropia, checked by the power of accommodation. If the hypermetropia is of small degree, as of one dioptric, and the range of accommodation normal, no inconvenience will be experienced until the accommodation is curtailed by the advance of years, and then the only symptom will be the early on-coming of presbyopia. Such a patient will require reading-spectacles by the age of forty, and always thereafter will require for all purposes glasses a dioptric stronger than his period of life would indicate. When his power of accommodation is lost, he will require glasses of one dioptric for clear distant vision. When the hypermetropia is originally of such a degree as to consume for its correction nearly half the power of accommodation, so that the use of the eyes upon near objects can only be accomplished by means of the remaining half, or whenever this state of things is brought about later in life by decline of the accommodation, any attempt at sustained effort of the eyes is soon rendered impossible by muscular fatigue. The symptoms of this fatigue have been known for many years as constituting one of the forms of the malady called asthenopia; but it was reserved for Donders to trace this form of...show more

Product details

  • Paperback | 52 pages
  • 189 x 246 x 3mm | 109g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236635450
  • 9781236635457