The Anatomy of the Ciliary Body

Helps focus the lens of the eye

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The ciliary body is a structure that greatly affects the ability to view the world around you. By circling the iris (colored area) and lens of the eyeball, the ciliary body muscles help focus the eye on objects that are close up. This process is called accommodation. Without it, it would be nearly impossible to read or see what’s right in front of you.

The ciliary body also produces a clear fluid called aqueous humor, which flows between the lens and cornea, providing nutrients and contributing to the fullness and shape of the eye. Here’s what you should know about this small but mighty eye muscle that our eyes rely on every day.

Eye doctor looking at patient’s eyes
Geber86 / E+ / Getty Images

Anatomy

The ciliary body is part of the uvea of the eye, which also includes the iris and choroid.

Structure

The ciliary body is a disk-shaped tissue entirely hidden behind the iris. The inner part is the ciliary muscle, made of smooth muscle. Smooth muscles contract and relax automatically, so you don’t have conscious control over them. Instead, the ciliary body functions in response to natural reflexes based on environmental stimuli.

Groups of small blood vessels and capillaries toward the eye’s surface make up another section of the ciliary body. The capillaries are responsible for exchanging fluids and other materials between the tissue and the blood cells.

This part of the eye is also called the ciliary process. Its numerous folds increase the ciliary body’s surface area to allow for greater secretion of the aqueous humor fluids.

Location

The ciliary body is located in the middle of the eye, meaning it can be found on the eye’s inner wall, behind the iris. The ciliary body also forms a ring around the lens, helping the lens hold shape and adjust focus. Behind the ciliary body is the vitreous humor, a fluid made up of mostly water, which helps the eye retain its fullness.

Anatomical Variations

Anterior segment dysgenesis (ASD) is a congenital (present at birth) condition that impacts the ciliary body. Because ASD affects the development of the front of the eye, it can alter the ciliary body and the cornea, iris, and lens.

Issues may include displacement of the lens or a lens that’s missing altogether. Impaired vision or damage to the outer layer of the eye are possible side effects of ASD.

To test for ASD, doctors review your medical history and perform a physical exam. Sometimes, laboratory testing and a glimpse at the Genetic Testing Registry can also help to identify the condition. 

Function

One function of the ciliary body is to control the lens of the eye. The ciliary body’s smooth muscles contract and relax to focus on near or far away objects. Muscle contractions are partly responsible for the round shape of the eye’s lenses since fine ligaments directly attach the lens to the ciliary body.

The ciliary body’s capillaries secrete aqueous humor, a liquid in the front of the eye that’s responsible for keeping the eye healthy and inflated. Aqueous humor also controls the eye’s pressure and supplies vital nutrients to the lens and cornea.

Associated Conditions

The ciliary body can be affected by conditions including traumatic injury or melanoma.

Trauma to the Ciliary Body

Blunt trauma, such as an automobile airbag deploying or a hard hit to the head, or small projectiles getting lodged in the eye may damage the ciliary body. This can result in inflammation of the iris and changes in eye pressure (high or low).

In severe trauma cases, the ciliary body can separate from the circular fibers of the ciliary muscles. This is a condition called cyclodialysis. If this happens, a pool of blood may develop between the cornea and iris (hyphema), the choroidal from the back wall of the eye may detach, and the eye can become inflamed.

Ciliary Body Melanoma

Another issue that can affect the ciliary body is ciliary body melanoma. This melanoma is a smaller branch of a larger melanoma or intraocular melanoma. Intraocular melanoma is when cancer cells begin forming in the eye tissue.

Although intraocular melanoma is the most frequent form of eye cancer in adults, it’s rare overall. It grows in the eye’s pigmented cells (melanocytes) and can affect the iris, ciliary body, and choroid.

Intraocular melanoma has four stages. Stage 2B is when it’s found in the ciliary body and is likely to have already spread to other areas. Symptoms may include blurred vision, dark spots on the iris, spots in your vision, and size or shape changes of the pupil. Older adults and people with fair skin and blue or green eyes tend to be at greater risk.

The prognosis for intraocular melanoma depends on several factors, such as whether the cancer cells have spread, whether you’ve had cancer before, which part of the eye the cancer is located in, and the size or thickness of the tumor (small, medium, or large).

Treatment of ciliary body melanoma includes surgery (resection or enucleation), charged particle external beam, and plaque radiation therapy.

Tests

Common tests to assess the ciliary body’s function and check for damage (including the presence of melanoma tumors) include:

  • Dilated pupil eye exam: A special solution dilates the eyes so they can be evaluated closely.
  • Fluorescein angiography: Dye is injected into blood vessels, where it travels to the retina, and specialized cameras look for blockages or leaks.
  • High-resolution ultrasound biomicroscopy: This supplies high-resolution imagery of areas in the eye not visible otherwise.
  • Ultrasound exam of the eye: Ultrasound technology provides a deeper view into the eye structure.
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Article Sources
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