Choroid

The choroid is a vital layer of blood vessels in the eye. It sits between the retina and sclera. This part of the uveal tract is essential for good vision and helps the retina work right.

The choroid’s blood supply is rich. It feeds the retinal pigment epithelium and outer retinal layers. This ensures they get the nutrients and oxygen they need.

If the choroid doesn’t work right, the eye’s balance can be upset. This could lead to vision issues. Knowing about the choroid’s structure and role in the eye is important for eye health. We’ll explore more about it in the next sections.

Anatomy and Location of the Choroid

The choroid is a key part of the eye, found between the retina and sclera. It’s a vascular layer that nourishes the retina and keeps the eye temperature right. Its location helps it deliver oxygen and nutrients to the retina, keeping vision sharp.

Being part of the uveal tract, the choroid works with the ciliary body and iris to keep the eye healthy. The uveal tract is a continuous layer of tissue inside the eye. It supports the eye and supplies blood. Here’s a table showing the uveal tract’s parts and what they do:

The choroid is close to the retina and sclera, making it effective. The retina needs the choroid for its metabolic needs. The sclera protects and supports the eye, and the choroid supplies it with blood.

Positioned Between the Retina and Sclera

The choroid’s spot between the retina and sclera is key for eye health. It acts as a buffer, protecting the retina from stress. It also keeps the retina cool when exposed to bright light.

Part of the Uveal Tract

The choroid is part of the uveal tract, working with the ciliary body and iris. The uveal tract is a continuous layer of tissue inside the eye. It delivers nutrients, produces aqueous humor, and controls light. Together, these structures keep the eye working well and vision clear.

Layers of the Choroid

The choroid has four layers, each with special features. These layers are Bruch’s membrane, the choriocapillaris, the stroma, and the suprachoroidea. They work together to keep the eye healthy.

Bruch’s Membrane

Bruch’s membrane is a thin, elastic layer. It acts as a barrier between the retinal pigment epithelium and the choriocapillaris. It controls the flow of nutrients and waste between these two areas.

Bruch’s membrane has five sublayers:

Choriocapillaris

The choriocapillaris is a dense network of capillaries next to Bruch’s membrane. It has many fenestrations for quick exchange of nutrients and oxygen. This is key for the outer retina’s health.

Stroma

The stroma is a layer of connective tissue. It has blood vessels, collagen fibers, and melanocytes. Melanocytes produce melanin, which absorbs light and improves vision.

The stroma’s blood vessels are larger than those in the choriocapillaris. They supply blood to the outer choroid layers.

Suprachoroidea

The suprachoroidea is the outermost layer. It’s between the stroma and the sclera. It has collagen fibers, melanocytes, and lymphatic vessels.

These lymphatic vessels help drain excess fluid. They keep the eye’s pressure right.

Blood Supply and Drainage

The choroid gets its blood mainly from the ophthalmic artery, a branch of the internal carotid artery. This blood supply is key for delivering oxygen and nutrients to the outer retina. The outer retina needs a lot of these to function well.

The ophthalmic artery splits into smaller arteries that feed different parts of the choroid:

These arteries create a network of capillaries in the choroid called the choriocapillaris. The choriocapillaris is very good at letting nutrients and waste pass through. It helps the choroid and retina exchange these important substances.

Vortex Veins

The vortex veins help drain the choroid. There are usually four of them, one in each eye quadrant. They collect blood from the choroidal veins and leave the eye through the sclera.

Then, they drain into the ophthalmic vein and the cavernous sinus. This system is vital for the retina’s health and function. Any problems can cause choroidal disorders and affect vision.

Functions of the Choroid

The choroid is vital for eye health. It delivers nutrients to the outer retina, providing oxygen and essential nutrients. This ensures the retina works well.

The choroid also removes waste from the retina. It has a vast network of blood vessels. This helps clear waste, keeping the retina healthy.

It helps control temperature in the eye too. The blood flow in the choroid vessels cools the eye. This is key to prevent damage and keep vision stable.

In early development, the choroid is key for eye growth. It helps the eye grow and shape correctly. Without it, eyes might not develop properly, leading to vision problems.

Choroidal Thickness and Variations

Choroidal thickness is key to eye health. Many things can change its measurements. Knowing these changes helps doctors diagnose and track eye problems.

Factors Influencing Thickness

Age affects choroidal thickness, with it getting thinner as we get older. Myopic eyes have thinner choroids than hyperopic ones. Choroidal thickness also changes throughout the day, being thickest in the morning and thinnest at night.

Other things can also change choroidal thickness, such as:

• Axial length of the eye
• Systemic blood pressure
• Medications (e.g., corticosteroids)
• Ocular diseases (e.g., age-related macular degeneration, central serous chorioretinopathy)

Measurement Techniques

Optical coherence tomography (OCT) is the best way to measure choroidal thickness in vivo. It’s a non-invasive method that uses light to create detailed images of the retina and choroid. Enhanced depth imaging (EDI) OCT and swept-source OCT have made it even better.

The table below shows how different OCT techniques compare for measuring choroidal thickness:

Understanding what affects choroidal thickness and using advanced tools like OCT helps doctors. They can then better check and keep track of this important eye part.

Choroid and Retinal Pigment Epithelium Interaction

The choroid and retinal pigment epithelium work together to keep the retina healthy. The choroid brings nutrients to the retinal pigment epithelium through its choroidal circulation. The retinal pigment epithelium then removes waste from the retina.

A healthy choroidal blood supply is key for the retinal pigment epithelium to work right. The choriocapillaris, the innermost layer of the choroid, is packed with capillaries close to the retinal pigment epithelium. This setup helps deliver nutrients and remove waste efficiently.

The retinal pigment epithelium also helps keep the choroid healthy. It makes growth factors and signaling molecules that control blood flow in the choroid. If the retinal pigment epithelium doesn’t work well, it can cause problems in the choroid and lead to retinal diseases.

It’s important to understand how the choroid and retinal pigment epithelium interact to find new treatments for retinal diseases. Researchers are looking into ways to improve choroidal circulation and support the retinal pigment epithelium. Their goal is to save vision and stop retinal degeneration.

Role in Visual Adaptation

The choroid is key in visual adaptation, helping our eyes adjust to different light levels. It’s involved in both dark adaptation and light adaptation. These processes are vital for our eyes to work well.

In dark adaptation, the choroid helps the eye get better at seeing in the dark. It does this by supporting the eye’s ability to detect low light. The choroid gives the retina the nutrients and oxygen it needs to see better at night.

For light adaptation, the choroid adjusts how much light the retina gets. It controls blood flow and makes pigments to block too much light. This keeps the photoreceptors from getting too much stimulation and helps us see clearly in bright light.

The table below summarizes the key aspects of the choroid’s role in visual adaptation:

The choroid is vital for our eyes to adjust to different light levels. It helps the eye regenerate rhodopsin and controls light exposure. This lets our eyes smoothly switch between dark and light environments.

Choroidal Disorders and Diseases

The choroid is a key part of the eye. But, it can get sick and cause vision loss. Common problems include age-related macular degeneration, central serous chorioretinopathy, and choroidal melanoma.

Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a disease that affects the macula. It’s a big reason for vision loss in older people. AMD can be dry or wet. Dry AMD gets worse slowly, while wet AMD can cause quick vision loss because of blood vessel growth.

Central Serous Chorioretinopathy

Central serous chorioretinopathy (CSC) is when fluid builds up under the retina. It causes blurry vision and blind spots. It usually happens in one eye and is more common in middle-aged men. Stress, steroids, and sleep problems might increase the risk. Most cases get better on their own, but repeated episodes can cause permanent vision loss.

Choroidal Melanoma

Choroidal melanoma is a rare but serious eye cancer. It grows in the choroid’s pigmented cells. It can lead to vision loss and spread if not treated quickly. Symptoms include blurred vision, flashes, and blind spots. Treatment depends on the tumor’s size and location and might include radiation, laser, or surgery.

The following table summarizes the key features of these choroidal disorders:

Diagnostic Imaging of the Choroid

The choroid is key to eye health. To check its health, doctors use special imaging. These tools help see how thick the choroid is, its blood flow, and any problems. Optical coherence tomography, fluorescein angiography, and indocyanine green angiography are top choices for looking at the choroid.

Optical Coherence Tomography

Optical coherence tomography (OCT) is a safe way to see inside the eye. It uses light to make detailed pictures of the choroid and retina. OCT can measure how thick the choroid is and spot changes. It’s great for watching over eye problems like age-related macular degeneration and central serous chorioretinopathy.

Fluorescein Angiography

Fluorescein angiography is a more invasive test. It involves putting a dye into the blood. Then, photos are taken as the dye moves through the choroid’s blood vessels. This method can show issues with blood flow and where dye leaks, helping spot choroidal problems.

Indocyanine Green Angiography

Indocyanine green angiography is another invasive test. It uses a dye that shows up better in the choroid’s blood vessels. This helps doctors see the choroid’s blood vessels more clearly. It’s good for finding choroidal neovascularization, polypoidal choroidal vasculopathy, and other issues not seen with fluorescein angiography.