Eyeball
Eyeball
The eyeball (/ˈaɪˌbɔːl/), also known as the globe, is the spherical structure within the human eye that allows for vision.
Etymology
The term "eyeball" originates from the Old English words "ēage" (eye) and "bēall" (ball), literally translating to "eye ball".
Anatomy
The eyeball is composed of three layers: the sclera, the choroid, and the retina. The sclera, the outermost layer, is a tough white fibrous tissue that covers about five-sixths of the eyeball. The choroid, the middle layer, is a thin, pigmented layer that supplies the outer retina with blood. The retina, the innermost layer, contains the light-sensitive cells that convert light into electrical signals.
The front part of the eyeball is the cornea, a transparent dome that helps to focus light onto the retina. Behind the cornea is the iris, the colored part of the eye, which controls the amount of light that enters the eye by adjusting the size of the pupil. Behind the iris is the lens, which further focuses light onto the retina.
The interior of the eyeball is filled with two types of fluid: the aqueous humor in the front part of the eye, and the vitreous humor in the back part of the eye. These fluids help to maintain the shape of the eyeball and transmit light to the retina.
Related Terms
- Optic nerve: The nerve that transmits electrical signals from the retina to the brain.
- Macula: The part of the retina responsible for central vision.
- Fovea: The center of the macula, where visual acuity is highest.
- Conjunctiva: The thin, transparent tissue that covers the front of the eyeball and lines the inside of the eyelids.
External links
- Medical encyclopedia article on Eyeball
- Wikipedia's article - Eyeball
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