curvature in their respective meridian planes; when r becomes equal to R itis evident that a spherical surface will result. N ^<. ^ \ \ / r … Fig. 18 Sectional Views of Toric Lens and Torus In the use of glasses the inconvenience often arising from requiring lensesof different focus for near and distant vision has lead to the introduction of avariety of forms of double focus lenses, now well-known as bifocals, theprinciple of their…
Lenses · Eyeglasses
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