Choroid Anatomy

A set of 69 question-and-answer flashcards covering choroid anatomy, layers, blood supply, innervation, and related ocular pathologies.

What is the choroid?

The posterior portion of the uvea located between the retina and sclera, extending from the ora serrata to the optic nerve.

What are the major functions of the choroid?

Provides nourishment to the outer retina, supplies oxygen to the retinal pigment epithelium and photoreceptors, absorbs stray light, regulates retinal temperature, and serves as a vascular reservoir.

What is the appearance of the choroid?

A thin, highly vascular, darkly pigmented tissue.

Why does the choroid appear dark?

Due to the presence of large amounts of melanin within melanocytes.

What structures does the choroid lie between?

The sclera externally and the retina internally.

What is the approximate thickness of the choroid?

Approximately $0.1-0.4\,\text{mm}$ depending on location and age.

Where is the choroid thickest?

Near the posterior pole beneath the macula.

Where is the choroid thinnest?

Near the ora serrata and with increasing age.

What is the suprachoroidal space?

A potential space between the sclera and choroid.

What structures are found within the suprachoroidal space?

Collagen fibers, melanocytes, fibroblasts, nerves, and blood vessels.

What are the four major layers of the choroid from outermost to innermost?

Suprachoroid, Haller's layer, Sattler's layer, and choriocapillaris.

What is Haller's layer?

The outer vascular layer of the choroid containing the largest blood vessels.

What vessels are found in Haller's layer?

Large arteries and veins.

What is Sattler's layer?

The middle vascular layer of the choroid containing medium-sized blood vessels.

What vessels are found in Sattler's layer?

Medium-sized arteries and veins.

What is the choriocapillaris?

The innermost vascular layer of the choroid composed of a dense capillary network.

What is the primary function of the choriocapillaris?

Supply oxygen and nutrients to the retinal pigment epithelium and outer retina.

Where is the choriocapillaris located?

Directly adjacent to Bruch's membrane and the retinal pigment epithelium.

What type of capillaries make up the choriocapillaris?

Fenestrated capillaries.

Why are choriocapillaris capillaries fenestrated?

To facilitate rapid transport of nutrients and metabolic waste.

What is Bruch's membrane?

A thin multilayered extracellular matrix located between the retinal pigment epithelium and choriocapillaris.

What structures does Bruch's membrane separate?

The retinal pigment epithelium and choroid.

What are the major functions of Bruch's membrane?

Structural support and movement of nutrients and waste products between the retina and choroid.

What are the five layers of Bruch's membrane?

Basement membrane of the retinal pigment epithelium, inner collagenous layer, elastic layer, outer collagenous layer, and basement membrane of the choriocapillaris.

What is the retinal pigment epithelium (RPE)?

A monolayer of pigmented epithelial cells located between the neural retina and choroid.

How does the choroid support photoreceptors?

By delivering oxygen and nutrients through the choriocapillaris and Bruch's membrane.

Which portion of the retina receives its blood supply from the choroid?

The outer retina, including photoreceptors.

What percentage of ocular blood flow goes through the choroid?

The majority of total ocular blood flow.

Why does the choroid have one of the highest blood flow rates in the body?

To meet the high metabolic demands of photoreceptors and regulate retinal temperature.

Why is high oxygen delivery important for photoreceptors?

Photoreceptors have extremely high metabolic activity and oxygen consumption.

What role does melanin play in the choroid?

Absorbs stray light and reduces intraocular light scatter.

Why is absorption of stray light important?

It improves image quality and visual acuity.

What cells are commonly found in the choroid?

Melanocytes, fibroblasts, macrophages, mast cells, vascular endothelial cells, and smooth muscle cells.

What are melanocytes?

Pigment-containing cells that produce melanin.

What is the primary pigment produced by melanocytes?

Melanin.

What is the vascular stroma of the choroid?

Connective tissue that supports blood vessels, nerves, and melanocytes.

What connective tissue components are present in the choroid?

Collagen fibers, elastin fibers, proteoglycans, and extracellular matrix.

What is the blood supply to the choroid?

Primarily the short posterior ciliary arteries.

What arteries contribute to choroidal circulation?

Short posterior ciliary arteries and long posterior ciliary arteries.

Where do the short posterior ciliary arteries enter the eye?

Around the optic nerve through the posterior sclera.

What structure do short posterior ciliary arteries supply?

The choroid and portions of the optic nerve head.

How does venous blood leave the choroid?

Through the vortex veins.

How many vortex veins are typically present?

Four major vortex veins.

Where do vortex veins drain?

Into the ophthalmic venous circulation.

What is the sensory innervation of the choroid?

Long and short ciliary nerves.

What autonomic innervation does the choroid receive?

Sympathetic and parasympathetic innervation.

What effect does sympathetic stimulation have on choroidal blood vessels?

Vasoconstriction.

What effect does parasympathetic stimulation have on choroidal blood vessels?

Vasodilation.

What is choroidal circulation responsible for removing?

Metabolic waste products produced by the outer retina.

Why is the choroid considered highly vascular?

Because it contains extensive arterial, venous, and capillary networks.

What is the ora serrata?

The anterior termination of the neural retina and anterior border of the choroid.

From where to where does the choroid extend?

From the ora serrata to the optic nerve.

What is age-related macular degeneration (AMD)?

A degenerative disease involving the macula, retinal pigment epithelium, Bruch's membrane, and choroid.

What are drusen?

Deposits of extracellular material that accumulate within or beneath Bruch's membrane.

Why are drusen clinically important?

They are a hallmark finding of age-related macular degeneration.

How can thickening of Bruch's membrane affect vision?

It impairs nutrient and waste transport between the retina and choroid.

What is choroiditis?

Inflammation of the choroid.

What symptoms may occur with choroiditis?

Blurred vision, floaters, decreased vision, and visual field abnormalities.

What is choroidal neovascularization?

Growth of abnormal blood vessels originating from the choroid.

Why is choroidal neovascularization dangerous?

The vessels may leak blood and fluid, damaging retinal tissues.

What disease commonly involves choroidal neovascularization?

Wet (neovascular) age-related macular degeneration.

What is a choroidal melanoma?

A malignant tumor arising from choroidal melanocytes.

What is the most common primary intraocular malignancy in adults?

Choroidal melanoma.

Why can a choroidal melanoma be difficult to detect early?

It develops beneath the retina within the posterior segment of the eye.

What retinal structures depend most heavily on choroidal circulation?

The retinal pigment epithelium and photoreceptors.

Why can interruption of choroidal blood flow rapidly affect vision?

The outer retina has very high metabolic demands and depends heavily on the choroidal circulation.

What is the relationship between the choroid and the retinal pigment epithelium?

The choroid supplies nutrients and oxygen to the RPE through Bruch's membrane.

What is the relationship between the choroid and sclera?

The choroid lies internal to the sclera and is separated from it by the suprachoroidal space.

What is the relationship between the choroid and retina?

The choroid lies external to the retina and supplies the outer retinal layers.