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Parts of the EyeBy: Jakob Palmer

Friday, February 1, 2013

The Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because light rays entering the pupil are either absorbed by the tissues inside the eye directly, or absorbed after diffuse reflections within the eye that mostly miss exiting the narrow pupil.

In humans the pupil is round, but other species, such as some cats, have vertical slit pupils, goats have horizontally oriented pupils, and some catfish have annular types.


The Iristhe Iris is a thin, circular structure in the eye, responsible for controlling the size of the pupils and the the amount of light reaching the retina.

Eye color is the color of the iris, which in humans can be green, blue, brown, and in rarer cases, hazel, grey, violet, or even pink. In response to the amount of light entering the eye, muscles attached to the iris expand or contract the aperture at the center of the iris, known as the pupil. The larger the pupil, the more light can enter.


The EyelidAn eyelid is a thin fold of skin that covers and protects the eye. It has the thinnest skin of the whole body. The eyelid opens when you want it to. You can do this if you want or not. The human eyelid has a row of eyelashes which serve to protect the eye from dust and other debris.

Its key function is to regularly spread the tears and other liquids on the eye surface to keep it moist, since the cornea must always be moist. They keep the eyes from drying out when asleep.


The ScleraThe sclera also known as the white of the eye, is the opaque, fibrous, protective, outer layer of the eye. In humans the whole sclera is white, with the colored iris, but in other mammals the visible part of the sclera matches the color of the iris.

In children, it is thinner and shows some of the underlying appearing slightly blue. In the elderly, fatty deposits on the sclera can make it appear slightly yellow.


The CorneaThe cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber.

The cornea, with the anterior chamber and lens, refracts light, with the cornea accounting for approximately two thirds of the eye's total optical power. While the cornea contributes most of the eye's focusing power, its focus is fixed.

The curvature of the lens, on the other hand, can be adjusted to tune the focus depending upon the object's distance.


The LensThe crystalline lens is a transparent structure in the eye that, along with the cornea, helps to refract light to be focused on the retina.

The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at different distances, then allowing a sharp real image of the object of interest to be formed on the retina. The lens is more flat on its anterior side than on its posterior side.


The RetinaThe Retina

The retina is a light sensitive layer at the back of the eye that covers about 65 percent of its interior surface. Photosensitive cells called rods and cones in the retina convert incident light energy into signals that are carried to the brain by the optic nerve. It is the center of the eye's sharpest vision and the location of most color perception.


The Optic NerveThe optic nerve is the second of twelve paired cranial nerves but is considered to be part of the central nerves of the eye. As a consequence, the fibers are covered with myelin produced by some part of the eye rather than Schwann cells, which are found in the peripheral nervous system, and are encased within the meninges.


The Vitreous Humor

The vitreous humor or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates.


eye parts 1

Documents

eye color

eye surface

light rays

colored iris

narrow pupil

light sensitive layer

crystalline lens

cornea accounting