The Cure of Imperfect Sight by Treatment
Without Glasses - online book

The Original Bates Method, for correcting vision defects

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190 Adverse Conditions a Benefit to the Eyes
and thus shut out the light entirely. The universal fear of reading or doing fine work in a dim light is, however, unfounded. So long as the light is sufficient so that one can see without discomfort, this practice is not only harmless, but may be beneficial.
Sudden contrasts of light are supposed to be particu larly harmful to the eye. The theory on which this idea is based is summed up as follows by Fletcher B. Dress-lar, specialist in school hygiene and sanitation of the United States Bureau of Education:
"The muscles of the iris are automatic in their move ments, but rather slow. Sudden contrasts of strong light and weak illumination are painful and likewise harmful to the retina. For example, if the eye, adjusted to a dim light, is suddenly turned toward a brilliantly lighted ob ject, the retina will receive too much light and will be shocked before the muscles controlling the iris can react to shut out the superabundance of light. If contrasts are not strong, but frequently made, that is, if the eye is called upon to function where frequent adjustments in this way are necessary, the muscles controlling the iris become fatigued, respond more slowly and less perfectly. As a result, eyestrain in the ciliary muscles is produced and the retina is over-stimulated. This is one cause of headaches and tired eyes."1
There is no evidence whatever to support these state ments. Sudden fluctuations of light undoubtedly cause discomfort to many persons, but, far from being in jurious, I have found them, in all cases observed, to be actually beneficial. The pupil of the normal eye, when it has normal sight, does not change appreciably under
Hygiene, Brief Course Series in Education, edited by M