Defective eyesight : the principles of its relief by glasses / by D.B. St. John Roosa.

  • Daniel Bennett St. John Roosa
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Defective eyesight : the principles of its relief by glasses / by D.B. St. John Roosa. Source: Wellcome Collection.

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    tably proven before Helmholtz showed how this was accomplished. His theory is that the con- traction of the ciliary muscle causes the zone of Zinn to advance, and thus to diminish the trac- tion exerted by it upon the crystalline lens. The lens then becomes more convex, especially on its anterior surface, by means of its own elasticity. Fig. 8. — The Helmholtz Theory of Accommodation, after Arlt When the ciliary muscle becomes relaxed from a cessation of the innervation for accommodation for near objects, the ciliary process becomes tense, and stretches the zonula, which now flattens the lens by exerting traction upon it in the direction of the equator. Tscherning^ is the chief opponent of Helmholtz's 1 Transactions, International Congress of Ophthalmology, Edin- burgh, 1894,