The Choroid: Layers and Board Facts

Master choroid anatomy for boards: layers, blood supply, and the classic outer retina trap tested on NBEO and FRCOphth exams.

Reviewed for accuracyJuly 27, 20263 min read

Cross-section diagram of the choroid showing, from innermost to outermost: retina, RPE, Bruch's membrane, choriocapillaris with small fenestrated vessels, Sattler's layer with medium vessels, Haller's layer with large vessels, the suprachoroidal space, and the sclera

Warm-up

Which ocular layer is highly vascular and lies between the sclera and retina?

Lesson

The Choroid in 30 Seconds

The choroid is the posterior vascular part of the uvea, lying between the sclera and the retina, with Bruch's membrane forming its inner boundary. It provides the principal blood supply to the outer retina, particularly the photoreceptors and RPE. Its layered structure and fenestrated capillaries are central to AMD, choroidal neovascularization, and trauma exam questions.

The Layers (Inner to Outer)

Bruch's membrane: five-layer extracellular matrix separating the RPE from the choriocapillaris. Site of drusen formation and AMD pathology.
Choriocapillaris: single layer of fenestrated capillaries directly beneath Bruch's membrane. Fenestrations face the RPE, allowing metabolic exchange. This is the layer that nourishes the outer retina.
Sattler's layer: medium sized vessels sitting just outer to the choriocapillaris. Contains medium-caliber vessels that supply the choriocapillaris.
Haller's layer: large vessels forming the outermost vascular layer, closest to the sclera. Largest caliber vessels visible on EDI OCT.
Suprachoroid: the outer transition zone between the choroid and sclera. Clinically, a potential suprachoroidal space here is where choroidal detachments and hemorrhages localize.

Note: histologically the choroidal stroma corresponds to Sattler's (medium vessels) and Haller's (large vessels) layers used in modern OCT literature.

4 Facts Exams Always Ask

The choroid is the principal blood supply to the outer retina, including photoreceptors and the RPE, while the central retinal artery supplies the inner retina.
The choriocapillaris is fenestrated on its RPE facing surface, permitting nutrient and oxygen exchange with the outer retina.
Bruch's membrane lies between the RPE and choriocapillaris and is the anatomic site of drusen deposition in AMD.
The choroid has one of the highest blood flow rates per unit tissue in the body, reflecting the metabolic demand of photoreceptors.
The choroid is supplied primarily by the short posterior ciliary arteries, branches of the ophthalmic artery.
The choroid is heavily pigmented, which reduces light scatter and internal reflection within the eye.

The Classic Trap

The most common mistake is assigning outer retinal supply to the central retinal artery. Candidates default to the central retinal artery because it is the more familiar vessel taught with the retina. The correct answer is that the central retinal artery supplies only the inner retinal layers, while the choroid, via the choriocapillaris, supplies the outer retina and photoreceptors.

Clinical Pearl

The choroid's role explains the classic cherry-red spot in central retinal artery occlusion. When the central retinal artery is blocked, the inner retina becomes pale and swollen, but the fovea keeps its normal red-orange color because the underlying choroid still perfuses it. That preserved foveal color against a pale background is the cherry-red spot. This same fenestrated, high-flow vascular bed is also where central serous retinopathy originates, when choroidal hyperpermeability overwhelms the RPE and pushes fluid under the macula.

Check yourself

Checkpoint 1

Which vascular layer primarily nourishes the outer retina?

Checkpoint 2

Bruch membrane lies between the:

Clinical case

A 68 year old presents with metamorphopsia. OCT shows drusen at the level of Bruch's membrane with overlying RPE disruption. The choriocapillaris beneath the affected area appears attenuated. Visual acuity is reduced but the inner retinal layers appear structurally intact on OCT.

The choriocapillaris is located:

Explanation

The choriocapillaris is the innermost vascular layer of the choroid and lies directly adjacent to Bruch membrane. It supplies the outer retina, including the photoreceptor layer.

Case discussion

The findings localize disease to Bruch's membrane and the choriocapillaris, the layers responsible for outer retinal nutrition. Because the choriocapillaris nourishes the photoreceptors and RPE, its attenuation explains the reduced acuity despite normal inner retina, consistent with AMD pathology centered on the Bruch's membrane and choriocapillaris complex.

Sources & Reviewer Info

Reviewed by Vasilis Inglezis: Optometrist and Ocular Oncology Imaging Specialist, Ocular Oncology Center, Athens, Greece. Last updated July 27, 2026.

Diagram created with AI image generation, clinically reviewed for accuracy.

References

American Academy of Ophthalmology, Basic and Clinical Science Course, Section 2: Fundamentals and Principles of Ophthalmology (Ocular Anatomy)
Snell RS, Lemp MA. Clinical Anatomy of the Eye
Schmidt-Erfurth U, Kohnen T, eds. Encyclopedia of Ophthalmology
American Academy of Ophthalmology, EyeWiki: Choroid

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