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The retina. Fromer explained that the retina is the innermost of three tissue layers that make up the eye. The outermost layer, called the sclera, is what gives most of the eyeball its white color. The cornea is also a part of the outer layer.The middle layer between the retina and sclera is called the choroid. The 7 Biggest Mysteries of the Human Body ]. Behind the cornea is a colored, ring-shaped membrane called the iris. The iris has an adjustable circular opening called the pupil, which can expand or contract to control the amount of light entering the eye, Fromer said. Ciliary muscles surround the lens.
The eye. The eye is a sense organ that responds to light. Structure of the human eye. Light enters through the pupil, and is focused by the cornea and the lens onto the retina. The shape of the lens can be changed by the ciliary muscles so that the image always comes to a sharp focus at the retina.