What is the conjunctiva?
The conjunctiva is a mucosa-like layer of tissue that connects the eyeball (bulbus oculi) to the eyelids. It is well supplied with blood, transparent, moist, smooth and shiny. In the area of the eyelid, the conjunctiva is firmly fused. At the eyeball it lies somewhat looser. The conjunctiva covers the sclera up to the edge of the cornea. There is no conjunctiva in the area of the cornea covering the iris and pupil, otherwise the cornea would be cloudy.
The conjunctiva is very sensitive to external stimuli.
The three sections of the conjunctiva
The conjunctiva consists of three sections:
- Eyelid conjunctiva: It covers the inside of the eyelids. Medical term: conjunctiva tarsi or tunica conjunctiva palpebrarum.
- Conjunctiva: It covers the front, visible part of the eyeball. Medical term: Conjunctiva bulbi or Tunica conjunctiva bulbi.
- Upper and lower conjunctival sac: These two folds form the transition between the eyelid and the conjunctiva. The medical term for conjunctival sac is saccus conjunctivalis.
The conjunctiva consists of several cell layers. Occasional mucus-forming goblet cells and additional lacrimal glands are embedded in this non-keratinized squamous epithelium. The secretion of the conjunctiva serves to moisten the eye and is an important component of the tear film.
Beneath it – separated by a basement membrane – is a layer of loose connective tissue (lamina propria; subconjunctiva). It is permeated by many fine blood vessels.
The blood vessels of the conjunctiva are normally invisible. If the eye is irritated, they are increasingly filled with blood (conjunctival injection) – the eye becomes red.
The conjunctiva is firmly and immovably attached to the eyelid cartilage (tarsus palpebrae), a crescent-shaped flexible connective tissue plate in the upper and lower eyelids that provides some firmness to the eyelids.
In the area of the inner corner of the eye, a small curved mucosal fold (plica semilunaris conjunctivae). This is a rudimentary remnant, of the well-mobile nictitating membrane still preserved in animals, which is also called the “third eyelid”.
On the dorsal surface of the eyelids, the conjunctiva has follicles containing plasma cells and lymphocytes, which provide a barrier to pathogens and are involved in the immune response.
Sensitive and absorbent
Because the conjunctiva is heavily permeated by sensitive nerves, it is correspondingly sensitive to stimuli, foreign bodies or the like. It is also highly absorbent, which is why many medications for the eyes are dripped into the conjunctival sac.
What problems can the conjunctiva cause?
Various complaints and diseases can occur in the conjunctiva.
Chemical burns
Accidents involving strong acids, alkalis or other chemicals can cause chemical burns to the conjunctiva and cornea. In the worst case, the affected eye loses its vision.
In case of eye burns, quick action is necessary! Always alert the emergency services in case of accidents with chemicals.
Inflammation of the conjunctiva
Conjunctivitis (inflammation of the conjunctiva) can be recognized by a “red” eye, a foreign body sensation in the eye and a watery, mucous or even purulent secretion. The possible triggers of the inflammation are manifold:
In other cases, the inflammation is the result of an allergy: For example, a so-called rhinoconjunctivitis can develop in the context of house dust allergy, animal hair allergy or hay fever. This is a combination of inflammation of the nasal mucosa (with a runny or blocked nose) and inflammation of the conjunctiva.
Very often, however, conjunctivitis is also triggered by non-specific stimuli. These include:
- Smoke
- Dust
- heat
- Cold
- Wind
- UV light
- Overexertion of the eyes, e.g. due to long work at the PC, exhaustion, lack of sleep or incorrectly correcting glasses
- Misalignment of the eyelids: ectropion (outward turning of an eyelid) and entropion (inward turning of an eyelid)
- Trichiasis: inward turning of the eyelashes without entropion – the eyelashes rub on the conjunctiva, which can cause it to become inflamed
