Items related to Vision; its optical defects. and the adaptation of...
Vision; its optical defects. and the adaptation of spectacles, embracing first, physical optics second, physiological optics third, errors of ... accommodation, or optical defects of the eye - Softcover
Synopsis
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. 1875 Excerpt: ...me that much close work does not essentially injure the eyes, at least those that are emmetropic, and that the range of accommodation diminishes scarcely, if at all, more rapidly under such circumstances, than it does in agriculturists, sailors, and others who for the most part look to distant objects." (Danders.) In the adaptation of spectacles to presbyopic eyes, the rules given under the head of spectacles should be strictly followed, particularly for the stronger numbers; and, as in presbyopia glasses are required for near vision when there is a convergence of the visual axes, the mutual distance of the glasses should be less than those worn for distant vision. In all theoretical calculations, the eye is considered simply as a dioptrical apparatus; to render these results practical, the associations existing between the ciliary and internal recti muscles must be taken into consideration. Glasses which would, theoretically, neutralize the errors of refraction, are usually too strong; "they compel the muscle of accommodation to a relaxation greater than corresponds to the developed circumstances of association." A person in making trials for the selection of proper spectacles, without the assistance of the ophthalmic surgeon, should always begin with those which are a little too weak, and increase the numbers until he finds a pair that makes the letters at 10", or 12", look clear, distinct, sharply defined, and of the natural size--as near as possible as they looked before his eyes were presbyopic. If he makes trial at first of those that magnify too much, it interferes with his judgment; the objects look unnaturally large, bright, and distinct; when the really suitable glasses are found, he compares the impression they produce wi...
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- PublisherRareBooksClub.com
- Publication date2012
- ISBN 10 1154115798
- ISBN 13 9781154115796
- BindingPaperback
- LanguageEnglish
- Number of pages102
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