الفهرس 
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Abstract
The eye as an optical apparatus may be well compared with a photographic camera, which consists essentially of a dark box, at one end of which is a strong convex lens and at the other a screen placed so as to receive the image of an object formed by the lens. The eye has two lens systems, the more powerful formed by the cornea and aquous humour and the other by crystalline lens. The retina corresponds to the sensitive plate of the camera; ’
At first sight the matter would seem to be much more difficult, for instead of simple convex lens with the same medium (air) on either side, the system com¬prises a curved optically complex (cornea), the aquous humour, the crystalline lens itself optically complex, and vitreous body the object of this more complicated arrangement is to shorten the focal distance of the system, so the eye may be smaller and more compact fortunately great simplifications can be made. The cornea has almost the same refractive index as the aqueous, which is also equal to that of the vitrous. The anterior surface of the cornea may be regarded as nearly spherical, the radius of curvature being 8mm. The centers of curvature of the cornea and the two surfaces of the lens are all on the same straight line, which is called the