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January 1950


Arch Ophthalmol. 1950;43(1):142-143. doi:10.1001/archopht.1950.00910010147009

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To the Editor:  —The purpose of this communication is to clarify a minor but significant point in the physiology of vision. The subject is not clearly presented in some of the most widely used textbooks on ophthalmology, as evidenced by inquiries which I have received. A typical inquiry is this: "Which author is correct—Duke-Elder, who states in his `Text-Book of Ophthalmology,' volume 1, page 755, that the retinal image is increased during accommodation, or Cowan, who says in `Refraction of the Eye,' page 147, that the retinal image is decreased during accommodation?"An examination of the material referred to shows that in a sense both authors are correct, but what they wanted to explain has not been fully and adequately presented. Dr. Cowan states, page 147:In accommodation the dioptric power is increased and the principal focal distances are shortened. The retinal image, therefore, is decreased in size during accommodation.

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