Causes of Defective Vision in Normal Eyes 79
Noise is also a frequent cause of defective vision in the normal eye. All persons see imperfectly when they hear an unexpected loud noise. Familiar sounds do not lower the vision, but unfamiliar ones always do. Country chil dren from quiet schools may suffer from defective vision for a long time after moving to a noisy city. In school they cannot do well with their work, because their sight is impaired. It is, of course, a gross injustice for teachers and others to scold, punish, or humiliate such children.
Under conditions of mental or physical discomfort, such as pain, cough, fever, discomfort from heat or cold, depression, anger, or anxiety, errors of refraction are always produced in the normal eye, or increased in the eye in which they already exist.
The variability of the refraction of the eye is respon sible for many otherwise unaccountable accidents. When people are struck down in the street by automobiles, or trolley cars, it is often due to the fact that they were suffering from temporary loss of sight. Collisions on railroads or at sea, disasters in military operations, avia tion accidents, etc., often occur because some responsible person suffered temporary loss of sight.
To this cause must also be ascribed, in a large degree, the confusion which every student of the subject has noted in the statistics which have been collected regard ing the occurrence of errors of refraction. So far as I am aware it has never been taken into account by any investigator of the subject; yet the result in any such investigation must be largely determined by the condi tions under which it is made. It is possible to take the best eyes in the world and test them so that the subject will not be able to get into the Army. Again, the test