The ability to see depends on the functions of several structures in and around the eyeball. The illustrations below show the important parts of the eyes.
The conjuctiva is the thin, transparent tissue that covers the outer surface of the eye. It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids. It is nourished by the tiny blood vessels that are nearly invisible to the naked eye.
The vitreous is a thick, transparent substance that fills the center of the eye. It is composed mainly of water and comprises about 2/3 of the eye’s volume, giving it form and shape.
The optic nerve transmits electrical impulses from the retina to the brain. It connects to the back of the eye near the macula. The visible portion of the optic nerve is called the optic disc.
The retina is a very thin layer of tissue that lines the inner part of the eye. It is responsible for capturing the light rays that enter the eye. Much like the film’s role in photography. These light impulses are then sent to the brain for precessing, via the optic nerve.
When you look at the object, light rays are reflected from the object to the cornea, which is where the miracle begins. The light rays are bent, refracted and focused by the cornea, leans and vitreous. The lens’ jobs is to make sure the rays come to a sharp focus on the retina. The resulting image on the retina is upside-down. Here at the retina, the light rays are converted to electrical impulses which are then transmitted through the optic nerve, to the brain, where the image is translated and perceived in an upright position.
The colored part of they eye is called the iris. It controls light levels inside the eye similar to the aperture on a camera. The round opening in the center of the iris is called the pupil. The iris is embedded with tiny muscles that dilate(widen) and constrict (narrow) the pupil size. The muscle in the iris makes the pupil smaller or bigger. When the light is bright the iris closes so the pupil becomes smaller. When the light is dim the iris opens so the pupil becomes bigger.
The pupil is the black, circular opening in the center of the iris. It opens and closes in order to regulate the amount of light entering the eyeball.
The sclera, commonly knows as “the white of the eye” is the tough, opaque tissue that serve as the eye’s protective outer coat.
The cornea is the transparent, dome-shaped window covering the front of the eye. It is a powerful refracting surface, providing 2/3 of the eye’s focusing power. Like the crystal on watch, it gives us a clear window to look through.
The purpose of the lens is to focus light onto the back of the eye. The nucleus, the innermost part of the lens is surrounded by softer material called the cortex. The lens is encased in a capsular-like bag and suspended within the eye by tiny guy wires called zonules.
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