What Is the Conjunctiva?

The conjunctiva is a thin layer of clear tissue that lines the inside of the eyelid and covers the white of the eye (sclera). This mucous membrane secretes fluids to keep the eye moist and protect it from foreign bodies and infections. It's also involved in tear production.

This article describes the conjunctiva anatomy as well as diseases and conditions that can adversely affect the white of the eye and inner eyelid.

Conjunctiva Anatomy

The conjunctiva is made up of cells and tissues that serve specific functions. These include goblet cells that secrete mucus and a layer of cells called the stratified squamous epithelium that provide structural stability.

The conjunctiva itself is divided into three segments:

• The bulbar conjunctiva is the segment that covers the sclera but not the cornea (the clear dome in front of the eye).
• The palpebral conjunctiva is the segment that covers the inner surface of the upper and lower eyelids.
• The fornix conjunctiva is a flexible segment between the bulbar and palpebral conjunctivas that allow the eyelid and eyeball to move freely.

These segments form a continuous "closed" structure that prevents objects, like contact lenses, from slipping behind the eyeball.

Function of the Conjunctiva

The primary function of the conjunctiva is to lubricate the eye by producing mucus and tears. Together, these fluids form a layer, called the tear film, which consists of the innermost mucus layer, the middle watery layer, and the outer oily layer.

The tear film serves several important functions:

• Barrier protection: The tear film creates a barrier against harmful microorganisms like bacteria or viruses. It also protects the cornea from grit and things that can cause scratches.
• Lubrication: The tear film allows the eyelid to open and shut smoothly without irritation. The outermost oily layer also prevents the evaporation of fluids, ensuring consistent levels of moisture between blinks.
• Visual acuity: Together, the layers of fluids create a smooth optical surface that you need for good, non-distorted vision.
• Eye health: The tear film contains substances that promote wound healing, suppress inflammation, neutralize free radicals, and create a hostile environment for bacteria and other disease-causing organisms.

While the lacrimal glands are tasked with producing the watery portion of tears, the conjunctiva can also produce these fluids, albeit in smaller quantities.

Associated Conditions

Several conditions can affect the normal functioning of the conjunctiva. Because the surface of the eye is exposed, it is susceptible to many problems including infection, trauma, allergic reactions, and dryness.

Here are some of the most common conjunctival disorders.

Conjunctivitis

Conjunctivitis, also known as pink eye, is inflammation or infection of the conjunctiva. Some bacterial or viral forms of conjunctivitis are highly contagious. Other forms may be triggered by an allergy or exposure to harsh chemicals.

Symptoms of conjunctivitis include:

• Pink or red discoloration of one or both eyes
• A gritty sensation in the eye
• A crusty eye discharge
• Itchy or burning eyes 
• Excessive tearing
• Swollen eyelids
• Blurred vision
• Increased sensitivity to light

Injected Conjunctiva

Injected conjunctiva is a term used to describe bloodshot eyes. The eyes appear red because of the dilation (widening) of blood vessels in the conjunctiva.

Bloodshot eyes can be caused by dry air, sun exposure, dust, foreign body, allergies, infection, or trauma.

Symptoms of injected conjunctiva include:

• Eye redness
• Eye pain or burning
• Eye itchiness
• Swollen eyes
• Eye tearing
  

Conjunctival Hemorrhage

A subconjunctival hemorrhage is bleeding of the eye caused by the rupture of a blood vessel under the conjunctiva. This can lead to a tiny speck of redness on the white of your eye.

If the rupture is larger, the bleeding can spread beneath the conjunctiva, creating a large irregular patch of bright red blood. In rare cases, the bleeding can make the entire white of the eye turn red.

There are many things that can cause a subconjunctival hemorrhage, including:

• Straining while coughing, sneezing, vomiting, or using the toilet
• An eye injury
• Eye infections
• Rubbing the eye too hard
• Wearing contact lenses.
• Taking Coumadin (warfarin) or other blood thinners

A subconjunctival hemorrhage is usually harmless and will resolve on its own without treatment within a couple of weeks.

Conjunctival Lymphoma

Conjunctival lymphoma is a rare type of eye cancer that usually appears as a painless, pink patch on the eye. The tumor is typically painless and usually hidden behind the eyelids. This disease is often discovered during a routine eye exam.

Symptoms of conjunctival lymphoma include:

• Blurred vision
• Seeing spots or floaters
• A fleshy bump on the eye
• Eye redness
• Dry eyes
• Eye irritation
• Light sensitivity
• Yellowish eye discoloration
• A swollen eyelid

Conjunctival Hemangioma

A conjunctival hemangioma is a congenital condition that causes blood vessels to clump on the white part of the eye. It can sometimes cause a visible bump that looks like a tiny blood blister.

Symptoms of a conjunctival hemangioma include:

• A clump of blood vessels that form a bright red bump
• Eye irritation, particularly when blinking
• Spontaneous eye bleeding if vessels are ruptured

A conjunctival hemangioma is usually harmful but should be examined regularly for any changes or signs of progression. It can be surgically removed for cosmetic reasons or if it causes eye irritation.

Conjunctivochalasis

Conjunctivochalasis is a common, aging-related disorder of the conjunctiva. It is characterized by the presence of folds in the conjunctiva that typically develops between the eyeball and eyelids.

The folds, usually found along the lower lid margin, interfere with the normal distribution of tears. This can lead to dry eye disease.

Symptoms of conjunctivochalasis include:

• A gritty sensation in the eye
• Dry, burning eyes
• Eye redness
• Stringy mucus in or around your eyes
• Light sensitivity
• Difficulty driving at night
• Difficulty wearing contact lenses

Chemosis

Chemosis is the irritation of the conjunctiva that can cause it to swell and become inflamed. In some cases, the swelling can look like a blister as it bulges around the edges of the cornea.

Symptoms of chemosis include:

• Eye redness
• Swelling of the conjunctiva
• Itchy eyes
• Blurred vision
• Difficulty focusing
• Eye tearing

Most cases are caused by allergies, eye infections, or simply rubbing the eye too aggressively. Other possible causes include eye infections, eye surgery, and hyperthyroidism (overactive thyroid gland).

Unlike conjunctivitis, chemosis is not contagious.