Health Conditions Discover Plan Connect. Read this next. Sclera Medically reviewed by the Healthline Medical Network. Superior oblique Medically reviewed by the Healthline Medical Network. Ophthalmic artery Medically reviewed by the Healthline Medical Network.
Medial rectus Medically reviewed by the Healthline Medical Network. Optic chiasma Medically reviewed by the Healthline Medical Network. Optic nerve Medically reviewed by the Healthline Medical Network. Orbicularis oculi Medically reviewed by the Healthline Medical Network. Jejunum Overview. What is the Vagus Nerve? Medically reviewed by Seunggu Han, M. One muscle within the iris constricts the pupil in bright light full sunlight, for example , and another iris muscle dilates enlarges the pupil in dim lighting and in the dark.
Ciliary body: The ciliary body holds the lens of the eye in place. It is connected to the lens with a network of many tiny ligaments called ciliary zonules or zonules of Zinn that suspend the lens in place behind the pupil.
The ciliary body also secretes the clear aqueous fluid that fills the space in the anterior segment of the eye between the cornea and the iris and lens, and it contains the muscle that controls accommodation of the eye. Choroid: The posterior portion of the uvea — the choroid — contains many tiny blood vessels and has the vital role of nourishing the retina. A number of things can go wrong with the uvea.
Some uvea problems are genetic, while others are age-related conditions or are associated with other health problems. Uveitis: This is inflammation of the uvea. When confined to the iris, it's called iritis.
If the inflammation affects the iris and the ciliary body, it's called anterior uveitis or iridocyclitis. There are many potential causes of uveitis, but often the cause cannot be determined.
Symptoms include a painful red eye , sensitivity to light and decreased visual acuity. Synechia: Pronounced "si-NECK-ee-ah," this is when parts of the iris adhere to the back surface of the cornea or the front of the lens. Synechiae plural; pronounced "si-NECK-ee-ee" can occur because of trauma to the eye, iritis or other causes. Synechiae are dangerous because they can lead to certain types of glaucoma. Develop and improve products. List of Partners vendors. The iris is the colored part of the eye that controls the amount of light that enters into the eye.
It is the most visible part of the eye. The iris lies in front of the crystalline lens and separates the anterior chamber form the posterior chamber. The iris in part of the uveal tract which includes the ciliary body that also lies behind the iris. The iris tissue makes up the pupil.
The pupil is the hole in the iris in which light passes through to the back of the eye. The iris controls the pupil size.
The size of the pupil is controlled by two muscles in the iris. The sphincter pupillae surrounds the border of the pupil and when it contracts, the pupil decreases in size. This is called miosis. The second muscle that controls pupil size is the dilator pupillae.
This muscle contains fibers that are arranged in a radial pattern in the iris. When it contracts, the pupil dilates or increases in size. This is called mydriasis. The parasympathetic system controls the sphincter pupillae and the sympathetic system controls the dilator pupillae.
There is a connection between these muscles in that that the dilator muscle must relax to allow the sphincter to constrict the pupil. Normal pupil size ranges from 2 to 4 mm in diameter in the light to 4 to 8 mm in the dark. Iris color depends on the amount of melanin pigment in the iris. A person with brown eyes has the same color of melanin pigment that a person with a blue eye has.
However, the blue-eyed person has much less pigment. The back of the iris is usually heavily pigmented to prevent light from shining through the iris. The inheritance patterns of iris color is a heavily studied area.
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