Spectacles, and How to Choose Them; An Elementary Monograph (Paperback)

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. 1881. Excerpt: ... CHAPTER XL TIIE ADJUSTMENT OF GLASSES FOR PRESBYOPIA; CHANGES IN TlIB EYE DUE TO AGE; RECESSION OF THE NEAR POINT; THE CALCULATIONS REQUIRED; PRESBYOPBS SHOULD HAVE ABUNDANT AID; GENERAL PRINCIPLES FOR THE TREATMENT; DANGERS OF ERROR. The nearest point of distinct vision begins to recede at a very early period of life. A child, at the age ot ten years, can usually thread a small-eyed needle held at a distance of two and three-quarters inches from the eve; at the age of fifteen years, the near point has receded to about three and a quarter inches; at twenty, it has gone to about three and three-quarters inches; at thirty, to about four and a half inches; at forty, to about nine inches; at forty-five, to about twelve inches; at fifty to about eighteen inches; at fifty-five, to about twenty-two inches; at sixty, from thirty to thirty-six. inches; at eighty, there is no distinct vision without glasses. As a rule, a young person who sees as well, or better, with his mother's or grandmother's glasses, is hypermetropic. Other changes also take place in the eye as age comes on. There is a loss of the transparency of the media, FiQ. XXXII. Coin silver frames with "Split lenses," or "Franklin glasses." It is a matter of taste, generally, as to whether the different powers shall be ground on a single piece of glass, or two half-lenses be placed together. Sometimes they are ground on one piece in more fanciful shapes, as the upper half with a shorter radius than the lower half, etc., presenting a very genteel appearance. which though gradual, is yet so steadily progressive that oculists are able to closely estimate the age of a person by this change alone. The entire construction of the eye also undergoes changes not necessary to enumerate in this connection. The pra...