Changes and suggestions for Chapter 7   Eyes and Ears

This table lists changes in blue and suggestions in green. The location of  each change and suggestion is specified by book page number, text column, and paragraph () in the column. The first line of text in a column begins the first paragraph in that column even if the first line begins in the middle of a sentence.

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CHAPTER 7 Eyes and Ears

 

 

 

 

 

 

 

 

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These problems can be largely overcome by using eyeglasses with bifocal or trifocal lenses, which have regions with two or three different refractive powers, respectively. Eyeglasses with progressive lenses provide multiple refractive powers with smooth transitions between them.  Thus, one set of glasses can be used over a wide range of distances simply by looking through the appropriate region of the multipowered lenses. Unfortunately, each region of the lens has a limited field of view, and such lenses are sometimes considered to have undesirable cosmetic effects. They are also expensive.

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In many people, one or more diseases compound the adverse effects of aging of the eyes. The incidence of such diseases increases with age, so that the risk for those over age 75 is 2.5 times greater than the risk for those between ages 50 and 65. Some of these diseases are little more than a nuisance, while others drastically reduce the quality of vision and in severe cases cause blindness. To see the effects of the more serious diseases on vision, go to http://www.nei.nih.gov/photo/sims/sims.htm .

162 2 2 For Internet images of normal eye structures or eye diseases, search the Images section of http://www.google.com/ for specific items (e.g., cataract). For diseases, I highly recommend searching WebPath: The Internet Pathology Laboratory , the excellent complete version of which can be purchased on a CD.
 

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The sticky cerumen and the hairs trap small particulate matter and insects, preventing such items from reaching the eardrum and injuring it or interfering with its vibrations. The cerumen also keeps the eardrum pliable so that it can vibrate without cracking, and cerumen inhibits the growth of microbes. Cerumen slowly moves to the outer opening of the ear canal, where it is easily removed by wiping or washing.

 

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When gravity pulls on the otoliths, it causes them and the gel to so which the otoliths and gel are attached. Speeding up or slowing down of the head also causes a shifting of the otoliths and gel, resulting in bending of the neurons. Changes in speed produce this effect because the otoliths tend to keep moving at the same speed because of inertia. Thus, a neuron with otoliths attached moves like a flexible car antenna with a ball or other weight  attached to its tip.

 

 

 

 

 

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Copyright 2006 - Augustine G. DiGiovanna - All rights reserved.
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