Learn about The Eye in this educational video from dizzo95.
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Male Speaker: The eye is like a camera. It has an envelope that holds a lens and instead of film or retina that receives the image. The envelope of the eye is composed of three membrane layers; the outer light layer the sclera helps the eye keep its spherical shape. The transparent part of the sclera is the cornea, a kind of window to the eye and is protected by the conjunctiva. The middle layer or choroid layer supplies the eye with blood. The inner layer or retina receives the light image converting it into impulses that are sent through the optic nerve to the brain. The lens of the eye is elastic and its curvature can be changed by the ciliary body to focus on a particular object. To focus on a far object, the ciliary body relaxes and pulls the lens flat. To focus on a near object the ciliary body contracts and the lens becomes more curved. In each case the images are focused against the retina but are upside-down. It is the brain that automatically reverses the image so that we perceive the correct visual image.
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