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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's tears are composed of three layers: oil, water and mucous. The outermost oily layer is produced by the meibomian glands which line the edge of the eyelids. The â¦ watery portion of the tear film is produced by the lacrimal gland. This gland lies underneath the outer orbital rim bone, just below the eyebrow.