Corpus: Conjunctiva

The conjunctiva is a mucosa-like layer of tissue that connects the eyeball to the eyelids.

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

• Bulbar conjunctiva: It covers the eyeball on the ventral surface and lies there displaceably against the sclera and Tenon's capsule. The bulbar conjunctiva runs from the corneal limbus to the upper and lower conjunctival fornix.
• Palpebral conjunctiva: It covers the posterior aspect of the eyelids and merges into the bulbar conjunctiva at the conjunctival fornix.

Together, these two parts of the conjunctiva form the conjunctival sac (saccus conjunctivalis). It consists of two conjunctival pockets, which are formed by the conjunctival fold 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
• Fornical conjunctiva
• Tarsal conjunctiva

At the nasal corner of the eye, the conjunctiva forms an additional fold known as the semilunar fold of conjunctiva. It is only slightly pronounced in humans.

The bulbar conjunctiva is made up of a non-keratinized stratified squamous epithelium that contains scattered goblet cells. These goblet cells secrete mucus, which helps to moisten the eye and contributes to the precorneal tear film. Beneath the epithelium, separated by a basement membrane, is a layer of loose connective tissue called the lamina propria or subconjunctiva. This layer is rich in small blood vessels, which are not visible under normal conditions. However, when the eye is irritated, these blood vessels become engorged (a condition known as hyperemia), resulting in visible redness referred to as conjunctival injection.

The tarsal conjunctiva is composed of a multilayered columnar epithelium that contains numerous goblet cells, supported by an underlying layer of connective tissue. In the area of the fornices, this connective tissue is loose, while at the level of the eyelid cartilages, it is more tense. The submucosa, particularly in the fornices, contains clusters of lymphocytes and plasma cells. These immune cells play a role in local immune defense and are part of the mucosa-associated lymphoid tissue (MALT).

The most important conjunctival vessels are the anterior and posterior conjunctival arteries. These arteries are branches of the muscular branches, the anterior ciliary arteries, and the lateral and medial palpebral arteries, all of which originate from the ophthalmic artery.

Venous drainage of the conjunctiva is handled by the conjunctival veins. These veins ultimately drain into the superior and inferior ophthalmic veins.

The conjunctiva is a sensitive tissue with extensive sensory innervation provided by branches of the trigeminal nerve (cranial nerve V). The following branches contribute to its innervation:

• Frontal nerve
• Lacrimal nerve
• Nasociliary nerve

The conjunctiva is a transparent, smooth, and moist membrane that is richly supplied with blood. It is firmly attached to the eyelids, but only loosely connected to the eyeball. The conjunctiva extends over the front part of the eyeball up to the edge of the cornea (limbus corneae), fully covering the visible portion of the sclera. The conjunctival sac is highly folded, providing a reserve of tissue that accommodates eye movements.

7.1. Diagnostics

The conjunctiva can be examined by everting the upper and lower eyelids, a procedure known as ectropionization. Eversion of the lower eyelid is a standard part of the physical examination and can provide visual diagnostic evidence of anemia (pale conjunctiva) or jaundice (yellow discoloration of the conjunctiva). Additionally, ectropionization allows for the detection of foreign bodies and facilitates irrigation of the conjunctival sac.

7.2. Disease symptoms

The conjunctiva can become inflamed due to various causes, such as viruses, bacteria, allergies, or mechanical irritation. This condition is known as conjunctivitis. Examples include allergic rhinoconjunctivitis and epidemic keratoconjunctivitis.

A hemorrhage beneath the conjunctiva is referred to as a subconjunctival hemorrhage or hyposphagma.

7.3. Application of eye drops

Like all mucous membranes, the conjunctiva has excellent absorption properties and is therefore commonly used as a route for administering eye medications. These medications are instilled into the conjunctival sac.

However, even with the local application of medications into the conjunctival sac (e.g., beta-blockers), systemic effects cannot be completely ruled out.