THE NORMAL EYE

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The eye is like a camera with a lens system up front and a film in the back. The curvature of the cornea and the length of the eye are coordinated by special feedback control mechanisms so that a distant image is maintained in focus of the retina.

The lens system up front is composed of two lenses. The first lens is called the cornea. It accounts for two thirds of the power of the lens system-40 diopters. This is the first lens that light rays encounter when traveling to the retina of the eye.

The second lens is officially called the lens. It changes focus so we can see distant and near objects. It accounts for one-third of the focusing power of the lens system-20 diopters. When the feedback control mechanism fails, it results in one of the focusing problems of the eye (myopia, hyperopia, or astigmatism).