How are they trained their eyes?

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The eyes are the organs of vision, one man's senses that allow communication with the outside world. Each eye is made of the eyeball and the adjoining organs. The first is attached to the eye socket adipose tissue and bone by six muscles. It consists of three membranes: the sclera, choroid and retina. The eyeball is occupied by the vitreous humor, a gelatinous substance. The sclera has fibrous consistency, on the inside is transparent and forms the cornea. The choroid is dark, this highly vascularized, and the front forms the iris, which is located behind the cornea and whose color varies according to heredity. In the center of the iris is a hole, the pupil, which may decrease or increase its diameter as a function of light intensity due to the smooth muscle of the iris. Behind is a small convex lens, the lens. Between the cornea and lens is the aqueous humor, a liquid lubricant. The innermost membrane, the retina is a tissue composed of two types of light-sensitive cells: rods (light receiving) and cones (which distinguish colors) binds to the brain via the optic nerve. Annexes bodies protect the eyeball are the eyelids, eyebrows, eyelashes, lacrimal apparatus and conjunctiva.

What can be vision problems?

Among the defects of vision are farsightedness, nearsightedness and astigmatism (refractive errors), and cataracts (opacities that usually develop as a result of advanced age). Amblyopia is a vision deficiency of which causes are excessive use of snuff, alcohol or drugs.

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