What is the Conjunctiva?
The conjunctiva is a thin membrane lining the inside of your eyelids (both upper and lower) and the outer portion of the sclera (white part of the eye). It doesn't cover the cornea, the clear covering on the front of the eye.
The conjunctiva plays a vital role in ocular health. It protects the eye from foreign bodies and infections. The conjunctiva also lubricates the eyes by adding to the tear film.
What is the Difference Between Sclera and Conjunctiva?
It's common to confuse the conjunctiva with the sclera. Both structures play important roles in eye functioning. However, there are some key differences, including:
Conjunctiva vs. Sclera
Description
- Conjunctiva. The clear, thin membrane covering the inner eyelids and sclera.
- Sclera. Thick, opaque connective tissue that forms the white of the eye.
Vascularization
- Conjunctiva. Contains many blood vessels.
- Sclera. Has fewer blood vessels.
Function
- Conjunctiva. Protects the eye and eyelid from infection and foreign objects. Contributes to the tear film.
- Sclera. Maintains the shape and integrity of the eye. Protects the inner components needed for vision.
What is the Conjunctiva’s Function?
The conjunctiva serves many important functions, including:
1. Protection
The conjunctiva protects the eye from contaminants, including:
- Foreign bodies
- Microbes that may cause viral or bacterial infections
2. Nourishment
The conjunctiva is highly vascularized. These blood vessels circulate oxygen and nutrients throughout the eye.
3. Lubrication
Finally, the conjunctiva lubricates the eye’s front surface and the inner eyelids. It contains goblet cells, which secrete mucin. These conjunctival goblet cells help form your tear film.
Your tear film is comprised of three layers:
- Mucin
- Aqueous (water)
- Lipid (oil)
You need all three intact to have a healthy ocular surface. Without proper moisture, you can develop dry eye symptoms. Poor tear quality can lead to friction from blinking, which leads to further irritation.
Can Contacts Get Stuck Behind the Conjunctiva?
If you wear contact lenses, you may wonder if you can get a lens stuck behind the eye. The conjunctiva makes this 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, all tissue underneath is visible.
Anatomy of the Conjunctiva
The conjunctiva consists of the following parts:
- Tenon’s capsule. A sheath that surrounds the eyeball and merges with the conjunctiva. This capsule protects the eye and prevents ocular infections from spreading behind it.
- The limbus. The area where the conjunctiva meets the cornea.
- The palpebral conjunctiva (also called the tarsal conjunctiva). The part lining the inner surface of the eyelids.
- The bulbar conjunctiva. The part covering the sclera.
The bulbar and palpebral conjunctiva comprise one continuous piece of tissue, connecting at the fornix.
What Eye Problems Affect the Conjunctiva?
Many conditions can affect the conjunctiva. Some are common and cause mild symptoms; others are rare and can be vision- or life-threatening.
These conditions include:
Conjunctivitis
Conjunctivitis is inflammation of the conjunctiva. This common condition is sometimes called pink eye.
Types of conjunctivitis include:
- Viral conjunctivitis
- Bacterial conjunctivitis
- Allergic conjunctivitis
Signs and symptoms of conjunctivitis include:
- Redness
- Chemosis (swelling)
- Discharge that may cause the eyes to crust
- Itchy, watery eyes (allergic conjunctivitis)
- Foreign body sensation (viral conjunctivitis)
Thick discharge may cause blurred vision. However, visual acuity returns to normal when the discharge is cleared.
Viral and bacterial conjunctivitis are highly contagious. Allergic conjunctivitis isn't contagious because it's due to an allergic reaction.
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 reduce symptoms.
Pterygium and pinguecula
These are benign growths on the conjunctiva often associated with ultraviolet exposure. They're more common in people who spend a lot of time outdoors.
- Pinguecula are small, yellowish bumps
- 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 sunglasses protection.
If large enough to affect vision or cause a foreign body sensation, pterygia may be surgically removed.
Subconjunctival hemorrhage
A Subconjunctival hemorrhage occurs when a blood vessel in the conjunctiva breaks. This causes blood to leak underneath the tissue. These hemorrhages appear as bright, red spots on the eye. They may look concerning but are typically harmless and usually resolve within a week or two.
Causes of a subconjunctival hemorrhage include:
- Forceful actions like sneezing or heavy lifting
- Trauma, including rubbing your eye too hard or scratching it while removing contacts
- Medical conditions such as diabetes and hypertension
- Certain medications, such as anticoagulants and antiplatelets
Conjunctival cysts
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 cause eye irritation.
Pyogenic granuloma
This 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 due to abnormal wound healing. Steroid eye drops or injections can help, but some pyogenic granulomas must be surgically removed.
Squamous cell papillomas
These are conjunctival growths often associated with human papillomavirus (HPV). These papillomas are not life-threatening. However, they can irritate the eye and obstruct the tear duct. Many people find them aesthetically undesirable.
Papillomas can be surgically removed but may grow back.
Conjunctival nevus
A conjunctival nevus is a benign, pigmented growth on the bulbar conjunctiva. These growths can range from yellow to brown to black.
Some people are born with a nevus, while others develop it later in life. Treatment isn't usually required, though your eye doctor should monitor it to ensure it doesn't become malignant (cancerous).
Conjunctival melanomas
Conjunctival melanomas are rare cancerous growths. They typically appear as raised, pigmented lesions. Approximately 1% to 6% of these melanomas arise from a nevus.
You should see an eye doctor right away if you notice:
- A new growth on your eye after adolescence
- An existing growth that changes in size, shape, or color
Your eye doctor will evaluate the growth and remove it if necessary. Conjunctival melanomas can be life-threatening if the cancer spreads to other body parts via the lymphatic system.
Conjunctival lymphomas
These are fleshy, salmon-pink patches that often form in the fornices or bulbar conjunctiva. They're usually painless and can be hidden by the lower or upper eyelid.
An ophthalmologist will take a biopsy of the growth to look for lymphoma. They'll consult an oncologist to determine whether it's systemic or localized to the eye.
Systemic lymphoma requires treatment with immunotherapy or chemotherapy. Localized growths can be treated with external beam radiation therapy.
In this article
