Choroid

What is the choroid?

The choroid is a part of the uvea, the middle layer of your eyeball’s outer wall. It’s a key supplier of blood to some of your eyes’ most critical structures. The choroid (pronounced “KOR-oid”) also plays a role in how light acts inside your eye, making it a crucial part of how you see the world around you.

What does the choroid do?

The choroid has two main jobs: blood supply and light absorption.

Blood supply

Blood supply is the choroid’s main job. In particular, it supports the retina and optic nerve. Those structures are constantly sending signals to your brain, so they have an unusually high demand for blood and nutrients compared to other eye tissues. The choroid contains layers upon layers of blood vessels, allowing it to supply the needed blood.

Light absorption

The choroid’s other job, light absorption, isn’t as obvious, but it’s no less important.

The choroid contains larger amounts of melanin than most other tissues in your eyes. Your body uses melanin in your skin to absorb the sun’s ultraviolet rays. That absorption limits the damage that UV rays can do to the DNA in your skin (damage that can add up and cause skin cancer). Melanin absorbs larger amounts of all visible light, too, not just UV rays.

Melanin inside your eyes works similarly to acoustic foam insulation. That foam dampens and absorbs sound waves, keeping them from bouncing and echoing. Recording studios use it to keep unwanted outside noise out and keep desirable sounds inside from being overwhelming. Likewise, melanin inside your eyes stops light from scattering so it doesn’t overload and confuse the light-sensitive photoreceptor cells in your retinas.

Where is the choroid?

The choroid surrounds the rear two-thirds of your eyeball, sitting just underneath the eye’s white outer wall (the sclera) and just above the retina, the light-detecting layer that lines the inside rear areas of your eye. The choroid ranges from 0.1 millimeters (mm) thick — about the same thickness as standard, letter-size printer paper — to 0.22 mm thick.

What does the choroid look like?

The choroid is densely packed with blood vessels. It’s also darker-colored because of the melanin in it. And you can have birthmarks or freckles (nevi) on your choroid, too. These are invisible, and the only way most people learn they have them is when an eye care specialist or other provider sees these coloration differences or markings during an eye exam.

What conditions and disorders can affect the choroid?

Many diseases can affect the choroid. They range from circulatory conditions to inflammatory diseases and more. They include:

• Albinism, since a lack of melanin can cause vision problems and light sensitivity
• Congenital (present at birth) conditions like choroideremia that damage your retina
• Diabetes-related retinopathy
• Choroidal neovascularization and macular degeneration (especially the wet form)
• Eye cancers (especially intraocular melanoma)
• Eye ischemia (lack of blood flow) like from an eye stroke
• Glaucoma-related damage to the optic nerve and retina
• Injuries
• Inflammatory diseases like uveitis or chorioretinitis

What are some possible symptoms of choroid-related conditions?

Symptoms of choroid-related conditions may include:

• Blind spots (scotomas) or visual field defects
• Blurred vision
• Double vision (diplopia)
• Eye pain
• Headaches
• Light sensitivity (photophobia)
• Low vision

There are also several symptoms that can indicate a more serious or emergency issue. These include:

• Nausea and vomiting that happen with eye pain/pressure
• Rainbow-colored halos around lights
• Sudden vision loss of any kind
• Suddenly seeing flashing lights (photopsias) in your vision

What are some tests for choroid-related issues and conditions?

An eye care specialist doing a routine eye exam can see changes in the choroid through the thin layers of the retina or through changes in the retina itself. There are also several tests that can help check the choroid or diagnose conditions affecting it. They include:

• Visual acuity test.
• Visual field and depth perception tests.
• Slit lamp exam.

Retinal imaging tests can also be helpful for checking the choroid because of the circulatory connection between the choroid and retina. Examples of tests like this include fluorescein angiography, indocyanine green angiography and optical coherence tomography.

What are some common treatments for conditions that affect the choroid?

Most of the treatments that affect the choroid only work indirectly. That means treating the underlying condition affecting the choroid. And those treatments can vary widely depending on the underlying cause. Some examples include:

• Albinism treatments. Albinism is a genetic disease, so there’s no way to treat it directly. The treatments revolve around reducing the symptoms
• Anti-glaucoma medications. These reduce pressure near the front of your eye, preventing or stopping damage to structures atop and around the choroid
• Anti-inflammatory drugs. These drugs reduce inflammation, and they can either be systemwide (throughout your body) or specific to your eyes
• Anti-vascular endothelial growth factor (VEGF) drugs. Anti-VEGF drugs block the formation of new blood vessels
• Cancer treatments. Like many other types of cancers, eye cancers may need treatments like surgery, chemotherapy, radiation therapy and others
• Drugs that assist/improve blood flow. These include blood thinners (anticoagulants), blood pressure medications and many more
• Eye surgeries. Some conditions that affect your choroid need surgery to repair them

Depending on the underlying condition you have, other treatments may be likely. Your eye care specialist or another healthcare provider can tell you more about these treatments and help guide you in choosing one that works best for you.

What can I do to maintain and improve the health of my choroid?

There are several things you can do to maintain and improve your eye health, including the health of your choroid. The most important thing you can do for your choroid is to get regular eye exams. That goes for everyone, not just people who wear glasses or contacts.

Other steps you can take include:

• Wear eye protection. Always wear safety glasses or goggles made specifically to protect you from whatever you’re handling
• Avoid nicotine use. Smoking, vaping and smokeless tobacco products (like chewing tobacco or snuff) can all affect your circulatory system
• Manage chronic conditions. If you have a condition that can affect your eyes and/or circulatory system, managing this condition can help you avoid or delay eye-related changes and damage
• Take care of your health overall. Reaching and maintaining a weight that’s healthy for you and getting proper nutrition are both key to having the best possible eye health