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What Is the Conjunctiva?
The conjunctiva is a thin membrane that lines the inside of your eyelids (both upper and lower) and covers the outer portion of the sclera (white part of the eye). It does not cover the cornea, which is the clear covering on the front of the eye. The area where the conjunctiva meets the cornea is called the limbus.
Tenon’s capsule is a sheath that surrounds the eyeball and merges with the conjunctiva in the limbal area. This capsule protects the eye and prevents ocular infections from spreading behind the eye.
The part lining the inner surface of the eyelids is called the palpebral or tarsal conjunctiva. The part covering the sclera is called the bulbar conjunctiva. The bulbar and palpebral conjunctiva comprise one continuous piece of tissue, connecting at the fornix.
What Is the Function of the Conjunctiva?
The conjunctiva protects the eye from foreign objects such as dust and dirt, as well as from bacteria and other microbes that can cause infections. Your conjunctiva also contains many blood vessels, which circulate oxygen and nutrients throughout the eye.
Another function is to provide lubrication to the front surface of the eye and the inner eyelids. The conjunctiva contains goblet cells, which secrete mucin. Your tear film is comprised of three layers:
- Mucin
- Aqueous (water)
- Lipid (oil)
You need all three layers intact to have a healthy ocular surface. Without proper moisture, you can develop dry eye symptoms. Additionally, blinking your eyelids would cause friction that causes further irritation.
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If you wear contact lenses, you may wonder if you can get a lens stuck behind the eye. Because of the conjunctiva, it is physically impossible. Although the lens can get stuck underneath the eyelid, it cannot go behind the eye.
What Color Is the Conjunctiva?
The conjunctiva is very thin and practically transparent (except for the blood vessels) so that any tissue underneath the conjunctiva is visible.
What Is The Difference Between Sclera and Conjunctiva?
Some people confuse the conjunctiva for the white part of the eye, which is the sclera. The sclera is a tough, opaque, fibrous tissue. This connective tissue helps to maintain the shape of your eyeball, while the conjunctiva is a mucous membrane covering the outer part of your sclera.
Problems Associated with the Conjunctiva & Treatment Options
Many conditions can affect the conjunctiva. Some are common and cause mild symptoms, while others are rare and can be vision-threatening or even life-threatening. Several of these conditions include:
- Conjunctivitis is an inflammation of the conjunctiva, sometimes called pink eye. This condition causes redness, chemosis (swelling), tearing, and discomfort. Conjunctivitis can be related to infection (from bacteria or viruses) or allergic reactions. Viral conjunctivitis often goes away on its own, while bacterial infections may require treatment with antibiotic eye drops. People with allergic conjunctivitis may take antihistamine drops or pills to alleviate symptoms.
- Pterygium and pinguecula are benign growths on the conjunctiva often associated with ultraviolet exposure. These findings are more common in people who spend a lot of time outdoors. Pinguecula are small, yellowish bumps, while pterygia look like wedge-shaped growths that extend from the conjunctiva to the cornea. Most of these growths can be managed with lubricating drops and the use of sunglasses protection. If large enough to affect vision or cause a foreign body sensation, pterygia may be surgically removed.
- Subconjunctival hemorrhage occurs when a blood vessel in the conjunctiva breaks, leaking blood underneath the tissue. These hemorrhages appear as bright, red spots on the eye that may look concerning but are typically harmless and resolve within a week or two. Forceful actions such as sneezing, straining, or heavy lifting can cause conjunctival hemorrhages. Trauma (even from rubbing your eyes too hard or scratching your eye while removing contacts) is another frequent cause. Less common etiologies include diabetes, hypertension, and the use of anticoagulant and antiplatelet medications.
- Conjunctival cysts are clear, blister-like bumps filled with fluid. Injury, infection, or inflammation can cause them to form. These cysts may go away on their own but can be drained or cauterized if they irritate the eye.
- Pyogenic granuloma is a benign growth shaped like a lobe and filled with blood vessels. They can occur on either the palpebral or bulbar conjunctiva. Pyogenic granulomas often develop after trauma or surgery as a result of abnormal wound healing. Steroid eye drops or injections can help, but some pyogenic granulomas need to be surgically removed.
- Squamous cell papillomas are conjunctival growths often associated with human papillomavirus. These papillomas are not life threatening. However, they are not desirable cosmetically, can irritate the eye, and even obstruct the tear duct. Papillomas can be surgically removed but may grow back.
- Conjunctival nevus is a benign, pigmented growth on the bulbar conjunctiva. They can range from yellow to brown to black. Some people are born with a nevus, while others develop them later on in life. These growths do not require treatment. Your eye doctor should monitor a nevus to ensure it does not become malignant (cancerous), although the overall risk is low.
- Conjunctival melanomas are rare but cancerous growths. They typically appear as raised, pigmented lesions. Approximately 1% to 6% of conjunctival melanomas arise from a nevus. You should be suspicious if you notice a new growth on your eye after adolescence or if an existing growth changes in color, size, or shape. These growths should be evaluated promptly by an ophthalmologist for removal.
Conjunctival melanomas can be life-threatening if the cancer spreads to other parts of the body via the lymphatic system.
- Conjunctival lymphomas are fleshy, salmon-pink patches that often form in the fornices or bulbar conjunctiva. They are usually painless and can be hidden by the lower or upper eyelid. The ophthalmologist will take a biopsy of the growth and consult an oncologist to determine whether systemic lymphoma is present or if the lymphoma is localized to the eye. Systemic lymphoma requires treatment with immunotherapy or chemotherapy, while localized growths can be treated with external beam radiation therapy.
