| Choroid | |
|---|---|
 Cross-section ofhuman eye, with choroid labeled at top. | |
 Interior of anterior half of bulb of eye. (Choroid labeled at right, second from the bottom.) | |
| Details | |
| Artery | Short posterior ciliary arteries,long posterior ciliary arteries |
| Identifiers | |
| Latin | choroidea |
| MeSH | D002829 |
| TA98 | A15.2.03.002 |
| TA2 | 6774 |
| FMA | 58298 |
| Anatomical terminology | |
Thechoroid, also known as thechoroidea orchoroid coat, is a part of theuvea, thevascular layer of theeye. It containsconnective tissues, and lies between theretina and thesclera. The human choroid is thickest at the far extreme rear of the eye (at 0.2 mm), while in the outlying areas it narrows to 0.1 mm.[1] The choroid providesoxygen and nourishment to the outer layers of theretina. Along with theciliary body andiris, the choroid forms theuveal tract.
The structure of the choroid is generally divided into four layers (classified in order of furthest away from the retina to closest):
The human eye is supplied by two largely distinct vascular systems: theretinal circulation, which nourishes the inner retina, and theuveal circulation (choroidal, ciliary body and iris), which nourishes theuvea and the outer retina (via thechoroid). Both systems arise primarily from theophthalmic artery, a branch of theinternal carotid artery.[2]
The uveal circulation is supplied mainly by theposterior ciliary arteries (short and long), which enter the globe independently of theoptic nerve. These arteries provide the dominant blood supply to the choroid and contribute importantly to perfusion of theoptic nerve head (including the anterior portion of the optic nerve).[3]The retinal circulation derives primarily from thecentral retinal artery, which travels within the optic nerve and enters the eye at theoptic disc. It then branches over the inner retinal surface into arterioles and capillaries supplying the nerve fiber and inner retinal layers.[2]
Retinal arteries behave as functionalend-arteries with limited collateralization; consequently, focal obstruction can produce sectoral retinal ischemia. By contrast, the choroid exhibits asegmental vascular organization, and regional perfusion territories supplied by posterior ciliary arteries are clinically relevant because themacula and the anterior optic nerve (structures critical for central vision) depend strongly on choroidal perfusion.[3]
Structural features of the choroid can be assessed withoptical coherence tomography (OCT), while choroidal vascular contrast is classically obtained withindocyanine green angiography (ICGA), an invasive dye-based method that is relatively robust for deeper choroidal vessels.Optical coherence tomography angiography (OCTA) provides non-invasive motion-contrast maps but can be limited by depth-dependent sensitivity, segmentation/projection artifacts, and reduced sensitivity for very slow flow or deeper large vessels.
Laser-Doppler–based approaches provide an additional, non-invasive route to choroidal flow contrast. In ophthalmology,Laser Doppler holography (LDH) is a full-field, camera-based implementation that usesdigital holography and temporal demodulation of reconstructed optical fluctuations to generate Doppler power maps that highlight blood-flow–related signals in retinal and choroidal vessels.[5]
Signal-processing refinements (e.g., spatio-temporal filtering and decomposition methods) have been reported to improve visualization of slower flow components and enhance choroidal vessel contrast in LDH datasets.[4]
Wide-field extensions of Doppler holography have also been described in conference literature for imaging choroidal blood flow over larger posterior-pole regions, with the aim of visualizing major choroidal arteries/veins and outflow patterns (including drainage towardvortex veins) that may be relevant in conditions such as thepachychoroid disease spectrum.[6]
Teleosts bear a body of capillaries adjacent to the optic nerve called the choroidal gland. Though its function is not known, it is believed to be a supplemental oxygen carrier.[7]
Melanin, a dark colored pigment, helps the choroid limit uncontrolled reflection within the eye that would potentially result in the perception of confusing images.
In humans and most otherprimates, melanin occurs throughout the choroid. Inalbino humans, frequently melanin is absent andvision is low. In many animals, however, the partial absence of melanin contributes to superiornight vision. In these animals, melanin is absent from a section of the choroid and within that section a layer of highly reflective tissue, thetapetum lucidum, helps to collect light by reflecting it in a controlled manner. The uncontrolled reflection of light from dark choroid produces the photographicred-eye effect on photos, whereas the controlled reflection of light from the tapetum lucidum produceseyeshine (seeTapetum lucidum).
The choroid was first described byDemocritus (c. 460 – c. 370BCE) around 400 BCE, calling it the "chitoonmalista somphos" (more spongy tunic [than thesclera]).[8] Democritus likely saw the choroid from dissections of animal eyes.[9]
About 100 years later,Herophilos (c. 335 – 280 BCE) also described the choroid from his dissections on eyes ofcadavers.[10][11]
Choroid is the most common site for metastasis in the eye due to its extensive vascular supply. The origin of the metastases are usually from breast cancer, lung cancer, gastrointestinal cancer, and kidney cancer. Bilateral choroidal metastases are usually due to breast cancer, while unilateral metastasis is due to lung cancer. Choroidal metastases should be differentiated fromuveal melanoma, where the latter is a primary tumour arising from the choroid itself.[12]
| 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 | |||||||
