Tests for Sensory Defects

Where large numbers of people are employed, it is comparatively easyto use tests for discovering defects of sight or hearing by simpleapparatus without requiring the services of a high priced expert. Byadopting these test methods any manager of a large industrialestablishment can satisfy himself whether his employees are up tocertain normal standards. He can even apply the tests to himself.

Optical tests can be conducted by securing an ordinary letter chartsuch as is used by oculists and opticians. Seat the subject twentyfeet away. If he can read all the lines of letters from the largestdown to the smallest his eyesight is practically perfect. In a largepercentage of cases the smaller lines of type are blurred andinvisible. To detect the cause and degree of defects of the eyes it isnecessary to try out the eyes by using a trial spectacle frame andinserting detached lenses before the right eye and the left eyealternately. One of the most common forms of defective vision isastigmatism. A chart has been designed with a series of circles andstraight lines radiating from the center. If the subject is astigmatiche will see some of the straight lines distinctly while others will beblurred. For instance, one or two of the vertical lines may appearvery black and strong while all others will look like a hazy network.This defect, due to unevenness of the spherical surface of theeyeball, is easily corrected with properly ground glasses.

Defects in hearing can be easily determined by means of a "acoumeter." This little instrument measures the acuteness of thehearing very accurately by means of shot dropped from varying heightsupon strips of glass, copper and cardboard. Tests with this deviceindicate whether the subject's hearing is above or below normal.
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