The ciliary body is a part of the
eye that includes the
ciliary muscle
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea (vascular layer). It controls accommodation for viewing ...
, which controls the shape of the lens, and the ciliary epithelium, which produces the
aqueous humor
The aqueous humour is a transparent water-like fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens of the eyeball. It fills both the anterior and the posteri ...
. The
aqueous humor is produced in the non-pigmented portion of the ciliary body. The ciliary body is part of the
uvea
The uvea (; Lat. ''uva'', "grape"), also called the ''uveal layer'', ''uveal coat'', ''uveal tract'', ''vascular tunic'' or ''vascular layer'' is the pigmented middle of the three concentric layers that make up an eye.
History and etymolog ...
, the layer of tissue that delivers
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and nutrients to the eye tissues. The ciliary body joins the
ora serrata
The ora serrata is the serrated junction between the choroid and the ciliary body. This junction marks the transition from the simple, non-photosensitive area of the ciliary body to the complex, multi-layered, photosensitive region of the retina ...
of the choroid to the root of the
iris
Iris most often refers to:
*Iris (anatomy), part of the eye
*Iris (mythology), a Greek goddess
* ''Iris'' (plant), a genus of flowering plants
* Iris (color), an ambiguous color term
Iris or IRIS may also refer to:
Arts and media
Fictional ent ...
.
[Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company, 1990.]
Structure
The ciliary body is a ring-shaped thickening of tissue inside the
eye that divides the
posterior chamber
The posterior chamber is a narrow space behind the peripheral part of the iris, and in front of the suspensory ligament of the lens and the ciliary processes. The posterior chamber consists of small space directly posterior to the iris but anterio ...
from the
vitreous body
The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous hu ...
. It contains the
ciliary muscle
The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea (vascular layer). It controls accommodation for viewing ...
, vessels, and fibrous connective tissue. Folds on the inner ciliary epithelium are called
ciliary processes
The ciliary processes are formed by the inward folding of the various layers of the choroid, viz. the choroid proper and the lamina basalis, and are received between corresponding foldings of the suspensory ligament of the lens.
Anatomy
They ...
, and these secrete aqueous humor into the posterior chamber. The aqueous humor then flows through the pupil into the anterior chamber.
The ciliary body is attached to the lens by
connective tissue called the
zonular fibers (fibers of Zinn). Relaxation of the ciliary muscle puts tension on these fibers and changes the shape of the lens in order to
focus
Focus, or its plural form foci may refer to:
Arts
* Focus or Focus Festival, former name of the Adelaide Fringe arts festival in South Australia Film
*''Focus'', a 1962 TV film starring James Whitmore
* ''Focus'' (2001 film), a 2001 film based ...
light
Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 te ...
on the retina.
The inner layer is transparent and covers the
vitreous body
The vitreous body (''vitreous'' meaning "glass-like"; , ) is the clear gel that fills the space between the lens and the retina of the eyeball (the vitreous chamber) in humans and other vertebrates. It is often referred to as the vitreous hu ...
, and is continuous from the neural tissue of the
retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
. The outer layer is highly pigmented, continuous with the
retinal pigment epithelium
The pigmented layer of retina or retinal pigment epithelium (RPE) is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells, and is firmly attached to the underlying choroid and overlying retinal visual ce ...
, and constitutes the cells of the
dilator 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 the
iris
Iris most often refers to:
*Iris (anatomy), part of the eye
*Iris (mythology), a Greek goddess
* ''Iris'' (plant), a genus of flowering plants
* Iris (color), an ambiguous color term
Iris or IRIS may also refer to:
Arts and media
Fictional ent ...
, where it takes on pigment. The retina ends at the
ora serrata
The ora serrata is the serrated junction between the choroid and the ciliary body. This junction marks the transition from the simple, non-photosensitive area of the ciliary body to the complex, multi-layered, photosensitive region of the retina ...
.
Nerve supply
![Ciliary ganglion pathways](https://upload.wikimedia.org/wikipedia/commons/c/cb/Ciliary_ganglion_pathways.png)
The parasympathetic innervation of the ciliary body is the most clearly understood. Presynaptic parasympathetic signals that originate in the
Edinger-Westphal nucleus are carried by cranial nerve III (the
oculomotor nerve) and travel through the
ciliary ganglion
The ciliary ganglion is a bundle of nerve parasympathetic ganglion located just behind the eye in the posterior orbit. It is 1–2 mm in diameter and in humans contains approximately 2,500 neurons. The ganglion contains postganglionic parasympath ...
. Postsynaptic fibers from the ciliary ganglion form the short ciliary nerves.
Parasympathetic activation of the M3
muscarinic receptors
Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-rec ...
causes ciliary muscle contraction, the effect of contraction is to decrease the diameter of the ring of ciliary muscle. The parasympathetic tone is dominant when a higher degree of accommodation of the lens is required, such as reading a book.
The ciliary body is also known to receive sympathetic innervation via long ciliary nerves. When test subjects are startled, their eyes automatically adjust for distance vision.
Function
The ciliary body has three functions:
accommodation,
aqueous humor
The aqueous humour is a transparent water-like fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens of the eyeball. It fills both the anterior and the posteri ...
production and
resorption
Resorption is the absorption of cells or tissue into the circulatory system, usually by osteoclasts.
Types of resorption include:
* Bone resorption
* Herniated Disc Resorption
* Tooth resorption
* Fetal resorption
* Blood resorption
See also ...
, and maintenance of the lens zonules for the purpose of anchoring the lens in place.
Accommodation
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.
Aqueous humor
The ciliary epithelium of the ciliary processes produces
aqueous humor
The aqueous humour is a transparent water-like fluid similar to plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens of the eyeball. It fills both the anterior and the posteri ...
, which is responsible for providing oxygen, nutrients, and metabolic waste removal to the lens and the
cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Along with the anterior chamber and lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power ...
, which do not have their own blood supply. Eighty percent 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
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk of glaucoma. Most tonometers are calibrated t ...
affects the rate of ultrafiltration, but not secretion.
Lens zonules
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.
Clinical significance
Glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
is a group of ocular disorders characterized by high
intraocular pressure
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk of glaucoma. Most tonometers are calibrated t ...
-associated neuropathies. 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 against
glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
. Its inhibition leads to the lowering of aqueous humor production and causes a subsequent drop in the
intraocular pressure
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk of glaucoma. Most tonometers are calibrated t ...
. There 3 main types of medication affecting the ciliary body:
*
Beta blockers
Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack ( secondary prevention). They are ...
, the second most common treatment method for glaucoma, reduce the production of aqueous humor. They are relatively inexpensive and are available in generic form.
Timolol
Timolol is a beta blocker medication used either by mouth or as eye drops. As eye drops it is used to treat increased pressure inside the eye such as in ocular hypertension and glaucoma. By mouth it is used for high blood pressure, chest pa ...
,
Levobunolol
Levobunolol (trade names AKBeta, Betagan, Vistagan, among others) is a non-selective beta blocker. It is used topically in the form of eye drops to manage ocular hypertension (high pressure in the eye) and open-angle glaucoma.
Contraindications
...
, and
Betaxolol are common beta blockers prescribed to treat glaucoma.
*
Alpha-adrenergic agonists work by decreasing production of fluid and increasing drainage.
Brimonidine and
Apraclonidine
Apraclonidine ( INN), also known under the brand name Iopidine, is a sympathomimetic used in glaucoma therapy. It is an α2 adrenergic receptor agonist and a weak α1 adrenergic receptor agonist.
Topical apraclonidine is administered at a conc ...
are two commonly prescribes alpha agonists for glaucoma treatment. Alphagan P uses a purite preservative, which is better tolerated those who have allergic reactions than the older BAK preservative in other eye drops.
Furthermore, less selective alpha agonists such as
pinephrinemay decrease the production of aqueous humor through vasoconstriction of the ciliary body (only for open-angle glaucoma).
*
Carbonic anhydrase inhibitors
Carbonic anhydrase inhibitors are a class of pharmaceuticals that suppress the activity of carbonic anhydrase. Their clinical use has been established as anti-glaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, ...
also decrease fluid production. They are available as eye drops (
Trusopt and
Azopt) and pills (
Diamox
Acetazolamide, sold under the trade name Diamox among others, is a medication used to treat glaucoma, epilepsy, altitude sickness, periodic paralysis, idiopathic intracranial hypertension (raised brain pressure of unclear cause), urine alkali ...
and
Neptazane). This may be helpful if using more than one type of eye medication.
See also
*
Intraocular pressure
Intraocular pressure (IOP) is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk of glaucoma. Most tonometers are calibrated t ...
*
Iridodialysis
*
Glaucoma
Glaucoma is a group of eye diseases that result in damage to the optic nerve (or retina) and cause vision loss. The most common type is open-angle (wide angle, chronic simple) glaucoma, in which the drainage angle for fluid within the eye rem ...
*
Cyclodestruction
Cyclodestruction or cycloablation is a surgical procedure done in management of glaucoma. Cyclodestruction reduce intraocular pressure (IOP) of the eye by decreasing production of aqueous humor by the destruction of ciliary body. Until the developm ...
References
External links
*
* - "Sagittal Section Through the Eyeball"
{{Authority control
Human eye anatomy