| Ciliary body | |
|---|---|
 Anterior part of thehuman eye, with ciliary body near bottom. | |
| Details | |
| Part of | Eye |
| System | Visual system |
| Artery | long and short posterior ciliary arteries |
| Identifiers | |
| Latin | corpus ciliare |
| MeSH | D002924 |
| TA98 | A15.2.03.009 |
| TA2 | 6765 |
| FMA | 58295 |
| Anatomical terminology | |
Theciliary body is a part of theeye that includes theciliary muscle, which controls the shape of the lens, and the ciliary epithelium, which produces theaqueous humor. The aqueous humor is produced in the non-pigmented portion of the ciliary body.[1] The ciliary body is part of theuvea, the layer of tissue that deliversoxygen and nutrients to the eye tissues. The ciliary body joins theora serrata of thechoroid to the root of theiris.[2]
The ciliary body is a ring-shaped thickening of tissue inside theeye that divides theposterior chamber from thevitreous body. It contains theciliary muscle, vessels, and fibrous connective tissue. Folds on the inner ciliary epithelium are calledciliary processes, and these secrete aqueous humor into the posterior chamber. The aqueous humor then flows through the iris into the anterior chamber.[3]
The ciliary body is attached to the lens byconnective tissue called theZonule of Zinn (fibers of Zinn). Relaxation of the ciliary muscle puts tension on these fibers and changes the shape of the lens in order tofocuslight on the retina.
The inner layer is transparent and covers thevitreous body, and is continuous from the neural tissue of theretina. The outer layer is highly pigmented, continuous with theretinal pigment epithelium, and constitutes the cells of thedilator muscle. This double membrane is often considered continuous with the retina and a rudiment of the embryological correspondent to the retina. The inner layer is unpigmented until it reaches theiris, where it takes on pigment. The retina ends at theora serrata.
The space between the ciliary body and the base of the iris is the ciliarysulcus.[4]
The parasympathetic innervation of the ciliary body is the most clearly understood. Presynaptic parasympathetic signals that originate in theEdinger-Westphal nucleus are carried by cranial nerve III (theoculomotor nerve) and travel through theciliary ganglion. Postsynaptic fibers from the ciliary ganglion form the short ciliary nerves.Parasympathetic activation of the M3muscarinic receptors causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle.[5] The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.[6]
The ciliary body is also known to receive sympathetic innervation via long ciliary nerves.[7] When test subjects are startled, their eyes automatically adjust for distance vision.[8]
The ciliary body has three functions:accommodation,aqueous humor production, andresorption, and maintenance of the lens zonules for the purpose of anchoring the lens in place.
Accommodation essentially means that when the ciliary muscle contracts, the lens becomes more convex, generally improving the focus for closer objects. When it relaxes, it flattens the lens, generally improving the focus for farther objects.
The ciliary epithelium of the ciliary processes producesaqueous humor, which is responsible for providing oxygen, nutrients, and metabolic waste removal to the lens and thecornea, which do not have their own blood supply. Approximately 80% of aqueous humor production is carried out through active secretion mechanisms (the Na+K+ATPase enzyme creating an osmotic gradient for the passage of water into the posterior chamber) and twenty percent is produced through the ultrafiltration of plasma.Intraocular pressure affects the rate of ultrafiltration, but not secretion.[9]
The zonular fibers collectively make up the suspensory ligament of the lens. These provide strong attachments between the ciliary muscle and the capsule of the lens.
Glaucoma is a group of ocular disorders characterized by highintraocular pressure-associated neuropathies.[10] Intraocular pressure depends on the levels of production and resorption of aqueous humor. Because the ciliary body produces aqueous humor, it is the main target of many medications againstglaucoma. Its inhibition leads to the lowering of aqueous humor production and causes a subsequent drop in theintraocular pressure. There 3 main types of medication affecting the ciliary body:[11][12]
{{cite news}}: CS1 maint: multiple names: authors list (link)| Fibrous tunic (outer) |
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| Uvea / vascular tunic (middle) |
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| Retina (inner) |
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| Anatomical regions of the eye |
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| Other | |||||||
