The Eye and Night Vision
Robert E. Miller II, Col, USAF, (RET) and Thomas J. Tredici, Col, USAF, (RET); USAF Special Report, AL-SR-1992-0002, 'Night Vision Manual for the Flight Surgeon'
The basic structure of the eye is shown in Figure 1. The anterior portion of the eye is essentially a lens system, made up of the cornea and crystalline lens, whose primary purpose is to focus light onto the retina. The retina contains receptor cells, rods and cones, which, when stimulated by light, send signals to the brain. These signals are subsequently interpreted as vision.
Most of the receptors are rods, which are found predominately in the periphery of the retina, whereas the cones are located mostly in the center and near periphery of the retina. Although there are approximately 17 rods for every cone, the cones, concentrated centrally, allow resolution of fine detail and color discrimination. The rods cannot distinguish colors and have poor resolution, but they have a much higher sensitivity to light than the cones.
Web Resource: American Optometric Association
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