Sunday, September 3, 2017

Eye as a Camera

Light is excluded or permitted to enter by the eyelids. The equivalent of the camera shutter. Once admitted, the amount of light is further regulated by a variable opening, the pupil, which is like the aperture of a camera. The diameter of the pupil is controlled by the expansion and contraction of muscles in the iris. If a bright light is shone into the eye, the pupil immediately constricts. This is the light reflex, the purpose of which is to protect the retina from too intense illumination. As time passes, the retina adapts to the new level of light and the pupil returns to its original size.

Light ray are focused by a lens system composed of the cornea and crystalline lens, and an inverted image in projected in the retina. To prevent the blurring of images by internal reflection, the inner walls of the camera, the choroid layer, are painted black. The process by which the lens focuses on external objects is called accommodation. When a distant object is viewed, the lens is fairly flat. As the object moves nearer, the lens increasingly thickness, or curves outward. Lens shape is controlled by the ciliary body. A blurred image elicits reflected impulses to the ciliary body that promote contraction or relaxation until the image is sharp.

The description of how eye work as camera that cornea is the transparent, curved front layer of the eye. The pupil, behind the cornea, is a hole in the colored membrane called the iris. Tiny muscles in the iris change the size of the pupil – like the aperture of a camera – to control the amount of light getting into the eye. There is a small, powerful lens behind the pupil which changes shape based on the pull of muscles in the eye. Like a camera lens, the lens in the eye focuses incoming images from the outside world (incidentally, cataract surgery removes this lens and replaces it with a clear artificial one).

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