
The structure and function of the eye are complex. Each eye focuses on both near and far objects, constantly adjusting the amount of light it lets in, producing a continuous image that is instantly transmitted to the brain. , a cavity in bone that contains nerves, blood vessels, and structures that produce and drain tears. Each orbit is a pear-shaped structure formed by multiple bones.
look in the eye
look in the eye
The outer covering of the eyeball consists of a relatively hard white layer called the sclera (or the white of the eye).
Near the front of the eye, in the area protected by the eyelids, the sclera is covered by a thin transparent membrane (conjunctiva) that extends to the rim of the cornea. The conjunctiva also covers the eyelids and the moist back of the eyeball.
Light enters the eye through the cornea, the transparent curved layer in front of the iris and pupil. The cornea acts as a protective covering for the front of the eye and also helps focus light onto the retina at the back of the eye. ).
The iris — the circular colored area surrounding the pupil — controls the amount of light entering the eye. The iris lets in more light (enlarges or dilates the pupil) when the environment is dark and reduces light (contracts or narrows the pupil) when the environment is bright. Similar to the aperture of a camera lens, the pupil expands and contracts in response to changes in ambient light. Pupil size is controlled by the sphincter pupillae and the dilator muscle. The
lens is behind the iris. The crystalline lens focuses light onto the retina by changing its shape. A small muscle (called the ciliary muscle) causes the lens to thicken to focus on near objects and thin to focus on distant objects.
The retina contains light-sensitive cells (photoreceptors) and the blood vessels that nourish them. The most sensitive part of the retina is a small area called the macula, which contains millions of closely packed photoreceptors (called cones). Just as high-definition digital cameras have more megapixels, a higher cone density in the macula results in more detailed visual images.
Eye Overview
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