Corpus: Conjunctiva

The conjunctiva is a mucosa-like layer of tissue that connects the eyeball (bulbus oculi) to the eyelids (palpebrae).

The conjunctiva, also called tunica conjunctiva, consists of 2 parts:

• Conjunctiva bulbi or Tunica conjunctiva bulbi: It covers the bulbus oculi on the ventral surface and lies there displaceably against the sclera and Tenon's capsule. The conjunctiva bulbi runs from the limbus corneae to the upper and lower conjunctival folds (fornix conjunctivae).
• Conjunctiva tarsi or Tunica conjunctiva palpebrarum: It covers the posterior aspect of the eyelids and merges into the conjunctiva bulbi at the conjunctival fornix.

Together, these two parts of the conjunctiva form the conjunctival sac (saccus conjunctivalis). It consists of two conjunctival sacs, which are formed by the conjunctiva's envelope at the superior and inferior conjunctival fornix.

Alternatively, the fornical parts of the conjunctiva can be defined as a separate section and the conjunctiva can be divided into three regions:

• Bulbar conjunctiva (Conjunctiva bulbi)
• Fornical conjunctiva (Fornix conjunctivae)
• Tarsal conjunctiva (conjunctiva tarsi)

At the nasal corner of the eye, the conjunctiva forms an additional fold known as the plica semilunaris conjunctivae ("nictitating membrane"). It is only very slightly pronounced in humans.

The conjunctiva bulbi has a multi-layered, non-keratinising squamous epithelium, in which isolated goblet cells are embedded. Its secretion serves to moisten the eye and is an important component of the precorneal tear film. Beneath this - separated by a basement membrane - is a layer of loose connective tissue (lamina propria or subconjunctiva). It is permeated by many small blood vessels, which are normally not visible but become visible as a so-called conjunctival injection when the eye is irritated due to hyperaemia.

The conjunctiva tarsi consists of a multi-layered, highly prismatic epithelium (cylindrical epithelium) with numerous goblet cells and an underlying layer of connective tissue. It is loose in the area of the fornices and taut at the eyelid cartilages. Accumulations of lymphocytes and plasma cells are interspersed in the submucosa - especially at the fornices - which perform tasks in the local immune defence and can be interpreted as part of the MALT.

See also: Conjunctival epithelium

The most important conjunctival vessels are the anterior and posterior conjunctival arteries. They are supplied by the muscular rami, the anterior ciliary arteries and the lateral and medial palpebral arteries from the ophthalmic artery.

Venous drainage takes place via the conjunctival veins, which in turn drain into the superior and inferior ophthalmic veins.

The conjunctiva is a sensitive tissue with extensive sensitive innervation from branches of the trigeminal nerve. Branches from the conjunctiva include:

• Frontal nerve
• lacrimal nerve
• Nasociliary nerve

The conjunctiva is transparent, smooth, moist and well supplied with blood. It is firmly fused to the eyelids and is only loosely attached to the bulb. It covers the ventral part of the bulb up to the corneal edge (limbus corneae) and thus completely covers the visible part of the sclera. The conjunctival sac is heavily folded and thus serves as a tissue reserve for eye movements.

7.1. Diagnostics

The conjunctiva can be viewed by turning over the upper and lower eyelids, which is called ectropionisation. Ectropionation of the lower eyelid is part of the physical examination and provides visual diagnostic evidence of anaemia (pale conjunctiva) or icterus (yellowish discoloured conjunctiva). Furthermore, ectropionisation of the conjunctiva enables the detection of foreign bodies and irrigation of the conjunctival sac.

7.2. Disease symptoms

The conjunctiva can become inflamed for various reasons (viruses, bacteria, allergy, mechanical irritation) - this is referred to as conjunctivitis. Examples are allergic rhinoconjunctivitis or keratoconjunctivitis epidemica.

A haemorrhage under the conjunctiva is called a hyposphagma.

7.3. Application of eye drops

Like all mucous membranes, the conjunctiva has good absorption properties and is therefore used as an application route for many eye medications. The medication is instilled into the conjunctival sac.

The occurrence of systemic effects cannot be ruled out even with local application of medication into the conjunctival sac (e.g. beta blockers).