The human eye is a complicated structure that sends information to the brain and includes such parts as the pupil, cornea, retina, lens and optic nerve. The eye acts as a camera, taking pictures of objects. Light enters the eye after it is reflected off of an object and then passes through the structures in the eye, permitting us to see.
The human eye contains the following structures: pupil, cornea, retina, lens, optic nerve, aqueous humor, sclera, choroid, arteries and veins, vitreous humor and ciliary muscle/body.
Pupil, Iris and Cornea
The pupil is defined as the small, round black center of the iris. The pupil constricts or dilates to allow light into the eye. The iris is what we know as the colored portion of the eye. The cornea is the clear, dome-like structure that acts as a window for the eye.
Aqueous and Vitreous Humor
The aqueous humor is the liquid between the cornea and the lens and keeps a constant pressure in the eye, while the vitreous humor is a transparent, jelly-like substance that is located behind the lens.
Sclera, Retina and Optic Nerve
The sclera is a dense, white membrane that forms the external portion of the eyeball and is known as the “whites of the eyes.” The retina is the inner lining of the back of the eye and has about 137 million specialized cells called photoreceptors, which are rods and cones. They handle how we see in both black and white (rods) and in color (cones) by converting the light that comes into the eye into electro-chemical signals that are sent to the brain. The optic nerve sends the signals to the brain by acting like a specialized cable that connects the eye with the brain.
The human eye's main function is “to work with the brain to provide us with vision. The eye and brain translate light waves into a sensation we call vision,” according to the website Mama's Health. When the eye takes pictures of objects, as a camera does, the light bounces off those objects and passes into the eye through the aqueous humor. According to the website WebMD, “Depending on how much light there is, the iris may contract or dilate, limiting or increasing the amount of light that gets deeper into the eye.” Then the light passes through the lens, which focuses it. Finally, the light reaches the retina, where the photoreceptors take the picture and allow us to see a black and white image or one in color.