point on an object must meet again in a common point upon the retina, their conjugate focus. In the normal eye all the rays from an object are focused on the retina and form upon it an image of the object which, as in the camera, is inverted, because of the crossing of the rays behind the cornea. Once focused on the retina the light traverses the various layers to the layer of rods and cones, where chemical action takes place and affects the little filaments of the optic nerve, by which the message is carried to the brain.
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Fig. 26.—Diagram showing the difference between (A) emmetropic, (B) myopic and (C) hypermetropic eyes. (American Text-book of Physiology.)
When the eye is at rest the pupil and lens are in their normal condition and at such times the eye sees only
