General Books publication date: 2009 Original publication date: 1906 Original Publisher: W.B. Saunders Notes: This is a black and white OCR reprint of the original. It has no illustrations and there may be typos or missing text. When you buy the General Books edition of this book you get free trial access to Million-Books.com where you can select from more than a million books for free. Excerpt: What proportion of the accommodation is available for continuous near work? About two-thirds of the whole. If au effort is made to exert more than this, much of the time, the ciliary muscle and nerves governing it are over-fatigued and symptoms of eye- strain appear. What is presbyopia? The diminution of the power of accommodation by age to such an extent as to interfere with the ordinary use of the eyes for reading, writing, sewing, and similar near work. When does presbyopia usually occur ? Between forty and fifty years of age. Reading, writing, etc. are ordinarily done at a distance of from twelve to eighteen inches, requiring the use of 2 D. or 3 D. of accommodation; and when the total accommodation has so far diminished that this would be more than two-thirds of it, the trouble begins. What are the symptoms of presbyopia ? One of the first is a tendency to hold reading matter further from the eyes than has previously been the custom; things requiring particularly accurate vision, as threading a needle, or reading very fine print, can no longer be done, except in a very good light. After the use of the eyes for close work for a time the thing looked at is apt to become dim, and it is necessary to rest the eyes for a little time. Or there is pain or headache after the use of the eyes for near work, or the eyes become congested, or even inflamed, after such work; such inflammation is often ascribed to cold. What is the remedy for presbyopia ? The use of the proper convex lenses for all near work. The lens will do a part of the work which would otherwise …