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# Choroid

The choroid is a layer rich in blood vessels between the retina and the white of the eye; it feeds the outer retina.

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## What it is

A layer full of blood vessels between the retina and the sclera.

## What it does

Feeds the outer retina; inflamed in posterior uveitis.

## Key points

- One of the most richly perfused tissues in the body; its choriocapillaris feeds the photoreceptors and is the only supply of the fovea
- Bruch membrane, its innermost layer, is where drusen build up and where new vessels break through in wet age-related macular degeneration
- Choroidal (uveal) melanoma is the most common primary intraocular cancer in adults; a flat choroidal naevus is a common benign look-alike

## Key facts

**Where**
Between the retina and the sclera (posterior uvea)

**Blood supply**
Short posterior ciliary arteries

**Function**
Nourishes the outer retina (photoreceptors)

## Relations

**In front**
Continuous with the [ciliary body](https://durgical.com/en/anatomy/ciliary-body/) at the ora serrata

**Behind**
Ends at the [optic disc](https://durgical.com/en/anatomy/optic-disc/), where the [optic nerve](https://durgical.com/en/anatomy/optic-nerve/) leaves the eye

**Superficial**
[Sclera](https://durgical.com/en/anatomy/sclera/), across the potential suprachoroidal space, where fluid or blood can collect (choroidal detachment)

**Deep**
Bruch membrane, the retinal pigment epithelium and the outer [retina](https://durgical.com/en/anatomy/retina/) (photoreceptors), which it nourishes

**Contents**
From outside in: layers of large (Haller) and medium (Sattler) vessels, the choriocapillaris and Bruch membrane; blood leaves through the vortex veins, usually four, one per quadrant

## How to find it

On fundoscopy it gives the orange-red background of the fundus; in thin or myopic fundi its large vessels show through as a striped (tigroid) pattern. Its full thickness is seen only on OCT or ultrasound.

## On imaging

Indocyanine green angiography shows the choroidal circulation best; enhanced-depth OCT measures its thickness; B-scan ultrasound shows a melanoma as a dome- or mushroom-shaped mass with low internal reflectivity.

## Clinical notes

- Posterior uveitis (choroiditis) from toxoplasmosis, tuberculosis or syphilis; toxoplasma retinochoroiditis is a frequent infectious cause, with a white active focus beside an old pigmented scar
- Choroidal tubercles on fundoscopy support the diagnosis of miliary tuberculosis
- Choroidal rupture after blunt trauma appears as a curved yellow-white streak concentric to the optic disc
- Choroidal detachment can follow eye surgery when the eye pressure falls too low

## Development

Forms from neural crest mesenchyme around the optic cup; incomplete closure of the optic (choroidal) fissure leaves a coloboma, typically inferonasal.

## Related conditions

- [Age-related macular degeneration](https://durgical.com/en/conditions/age-related-macular-degeneration/)
- [Uveitis](https://durgical.com/en/conditions/uveitis/)
- [Ocular toxoplasmosis (retinochoroiditis)](https://durgical.com/en/conditions/ocular-toxoplasmosis/)

## Test yourself

Think of the answer, then tap the question to see it.

## What is the blood supply of the fovea?

Only the choriocapillaris of the choroid: the fovea has no retinal vessels.

## Which layer of the choroid is involved in age-related macular degeneration, and how?

Bruch membrane: drusen build up there, and in the wet form new vessels break through it.

## What is the most common primary intraocular cancer in adults, and what is its common benign look-alike?

Choroidal (uveal) melanoma; a flat choroidal naevus is the common benign look-alike.

## What do choroidal tubercles on fundoscopy support?

The diagnosis of miliary tuberculosis.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
chorioidea TA2 6774

**Official Spanish (DeCS)**
Coroides

**English (TA2)**
Choroid

**Also called**
chorioides

## Related

- [Retina](https://durgical.com/en/anatomy/retina/)
- [Sclera](https://durgical.com/en/anatomy/sclera/)

Sources: Terminologia Anatomica (TA2); [Uveitis](https://www.ncbi.nlm.nih.gov/books/NBK540993/); [Anatomy, Head and Neck, Eye](https://www.ncbi.nlm.nih.gov/books/NBK482428/).

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