Conjunctiva

The connective membrane of the eye, or conjunctiva (tunica conjunctiva), is a mucous membrane of pale pink color that lines the eyelids from the back side and passes to the eyeball until the cornea and, thus, connects the eyelid with the eyeball. When the eye gap is closed, the connective shell forms a closed cavity - a conjunctival sac, which is a narrow slit-shaped space between the eyelids and the eyeball.

The mucous membrane covering the posterior surface of the eyelids is called the conjunctiva of the eyelids (tunica conjunctiva palpebrarum), and the covering sclera is conjunctiva of the eyeball (tunica conjunctiva bulbaris) or sclera. Part of the conjunctiva of the eyelids, which, forming the vaults, passes to the sclera, is called the conjunctiva of the transitional folds or the vault. Accordingly, the upper and lower conjunctival vaults (fornix conjunctiva superior et inferior) are distinguished. At the inner corner of the eye, in the area of rudiment of the third century, the conjunctiva forms a vertical semilunar fold and teardrop.

All the space lying in front of the eyeball, limited by conjunctiva, is called the conjunctival sac (saccus conjunctivalis) which closes when the eyelid closes. The lateral angle of the eye (angulus oculi lateralis) is more acute, the medial (angulus oculi medialis) is rounded and from the medial side restricts the deepening - the lacrimal lake (lacus lacrimalis). Here, at the medial angle of the eye, there is a slight elevation - the teardrop (caruncula lacrimalis), and lateral from it - the semilunar fold of the conjunctiva (plica semilunaris conjunctivae) - the remainder of the blinking (third) century of the lower vertebrates.On the free edge of the upper and lower eyelids, near the medial angle of the eye, outside of the lacrimal lake, there is a noticeable elevation - the papilla lacrimalis .At the top of the papilla there is a hole - a lacrimal point (punctum lacrimale), which is the beginning of the tear duct.

In the conjunctiva, two layers are distinguished: epithelial and subepithelial. The conjunctiva of the eyelids are tightly fused to the cartilaginous plate. Epithelium of conjunctiva is multilayered, cylindrical with a lot of goblet cells. The conjunctiva of the eyelids are smooth, shiny, pale pink, through which the yellowish columns of meibomian glands appear through the cartilage. Even in the normal state of the mucosa at the outer and inner corners of the eyelids, the conjunctiva covering them looks slightly hyperemic and velvety due to the presence of small papillae.

Allocate:

• The conjunctival epithelium has a thickness of 2 to 5 layers of cells. Basal cubic cells transform into plane polyhedral cells reaching the surface. With chronic exposure and drying, the epithelium can be keratinized.
• The stroma (substantia propria) consists of a richly vascularized connective tissue, separated from the epithelium by the main membrane. The adenoid surface layer does not develop until about 3 months after birth. This is associated with the absence of a newborn follicular conjunctival reaction. A deep, thicker fibrous layer is associated with the tarsal plates and represents a subconjunctival tissue, and not actually a conjunctiva.

Conjunctival glands

Cells secreting mucin

• goblet cells are located within the epithelium, with the greatest density in the lower-nasal region;
• Henle crypts are located in the upper third of the upper and lower third of the lower tarsal conjunctiva;
• The glands of Manz surround the limb.

NB: Destructive processes in the conjunctiva (for example, a scarring pemphigoid) usually cause mucin secretion disorders, whereas chronic inflammations are associated with an increase in the number of goblet cells.

Additional lacrimal glands Krause and Wolfring are located deep within their own plate. 

The conjunctiva of the transitional folds is connected to the underlying tissue loosely and forms folds, allowing the eyeball to move freely. The conjunctiva of the arches is covered with multilayered flat epithelium with a small number of goblet cells. The subepithelial layer is a loose connective tissue with inclusions of adenoid elements and accumulations of lymphoid cells in the form of follicles. In the conjunctiva there is a large number of additional lacrimal glands of Krause.

The conjunctiva of the sclera is tender, loosely connected with the episcleral tissue. Multilayered flat epithelium of the conjunctiva of the sclera smoothly passes to the cornea.

The conjunctiva borders on the skin on the edges of the eyelids, and on the other hand on the corneal epithelium. Diseases of the skin and the cornea may extend to the conjunctiva, and conjunctival diseases - to the skin of the eyelids (blepharoconjunctivitis) and the cornea (keratoconjunctivitis). Through the lacrimal point and the tear duct of the conjunctiva is also associated with the mucous membrane of the lacrimal sac and nose.

The conjunctiva is abundantly supplied with blood from the arterial branches of the eyelids, as well as from the anterior ciliary vessels. Any inflammation and irritation of the mucous membrane is accompanied by a bright hyperemia of the vessels of the conjunctiva of the eyelids and arches, the intensity of which decreases towards the limbus.

Due to a dense network of nerve endings of the first and second branches of the trigeminal nerve, the conjunctiva acts as a cover sensitive epithelium.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

Functions

The main physiological function of the conjunctiva is the protection of the eye: when a foreign body enters the room, eye irritation occurs, the secretion of the tear fluid increases, and blinking movements increase, as a result of which the foreign body is mechanically removed from the conjunctival cavity. The secret of the conjunctival sac constantly moistens the surface of the eyeball, reduces friction during its movements, helps maintain the transparency of the moistened cornea. This secret is rich in protective elements: immunoglobulins, lysozyme, lactoferrin. The protective role of the conjunctiva is also ensured by the abundance of lymphocytes, plasma cells, neutrophils, mast cells and the presence of immunoglobulins of all five classes.

Clinical features that are characteristic for the diagnosis of conjunctival diseases are: complaints, detachable, conjunctival reaction, films, lymphadenopathy.

Symptoms of conjunctival diseases

Nonspecific symptoms: lacrimation, irritation, pain, burning sensation and photophobia.

1. Pain and sensation of the foreign body involve the involvement of the cornea in the process.
2. Itching is a sign of allergic conjunctivitis, although it can be with blepharitis and dry keratoconjunctivitis.

Detachable

It consists of exudate, which is filtered through the conjunctival epithelium from the enlarged blood vessels. On the surface of the conjunctiva, the products of decay of epithelial cells, mucus and tears are found. The discharge can vary from watery, mucopurulent to pronounced purulent.

1. The watery discharge consists of serous exudate and an excess of reflexively secreted tears. It is typical for acute viral and allergic inflammation.
2. Mucous discharge is typical for spring conjunctivitis and dry keratoconjunctivitis.
3. Purulent discharge can occur in severe acute bacterial infections.
4. Muco-purulent discharge is found in both mild bacterial and chlamydial infections.

[11], [12], [13], [14], [15]

Conjunctival reaction

• Conjunctival injection is most pronounced in arches. The velvety, bright red conjunctiva indicates a bacterial etiology.
• Podkonyunktivalnye hemorrhages usually occur in viral infections, although they can be with bacterial infections caused by Strep. Pneumoniae and N. Aegypticus.
• Edema (chemosis) occurs in acute inflammation of the conjunctiva. Transparent swelling occurs due to exudation of protein-rich fluid through the walls of inflamed blood vessels. In the arch, large excess folds can be formed and in severe cases the edematous conjunctiva can go beyond the closed eyelids.
• Scarring can occur with trachoma, ocular form of cicatricial pemphigus, atopic conjunctivitis, or with prolonged use of topical medications.

[16], [17], [18]

Follicular conjunctival response

Composition

• Follicles - subepithelial foci of hyperplastic lymphoid tissue within the stroma with additional vascularization;

Symptoms

• Numerous, separate, slightly elevated formations resembling small grains of rice, most dominant in the vaults.
• Each follicle is surrounded by a tiny blood vessel. The size of each formation can be from 0.5 to 5 mm, which indicates the severity and duration of the inflammation.
• The follicles increase in size, so the accompanying vessel moves to the periphery, resulting in a vascular capsule forming the base of the follicle.

Causes

• The causes may be viral and chlamydial infections, Parinaud syndrome and hypersensitivity to local treatment.

[19], [20]

Papillary conjunctival reaction

The papillary conjunctival reaction is non-specific and therefore is of less diagnostic value than the follicular reaction.

Composition

• Hyperplastic conjunctival epithelium located in numerous folds or protrusions with the central vessel, diffuse infiltrate of inflammatory cells, including lymphocytes, plasma cells and eosinophils.
• Papillae can form only in palpebral and bulbar conjunctiva in the limb region, where the conjunctival epithelium is connected by fibrous septa with the underlying structures.

Symptoms

• Papillae are the most frequent finding on the conjunctiva of the upper eyelid in the form of an elegant mosaic-like structure with towering polygonal hyperspace areas separated by pale furrows.
• The central fibrovascular nucleus of the papilla secretes a secret on its surface.
• With prolonged inflammation, the fibrous septa, which attach the papillae to the underlying tissues, can rupture and cause them to merge and increase in size.
• Recent changes include superficial stromal hyalinization and the formation of crypts containing goblet cells between the papillae;

At the normal upper edge of the tarsal plate (when the inferior is inverted), the papilla can mimic the follicles, which can not be considered a clinical sign.

Causes

Chronic blepharitis, allergic and bacterial conjunctivitis, the wearing of contact lenses, upper limbal keratoconjunctivitis and the syndrome of the "sleeping" century.

Films

1. Pseudomembranes consist of a coagulated exudate attached to the inflamed conjunctival epithelium. They are easily removed, leaving the epithelium intact (a characteristic feature). The causes may be severe adenovirus and gonococcal infections, fibrous conjunctivitis and Stevens-Johnson syndrome.
2. The true membranes impregnate the superficial layers of the conjunctival epithelium. Attempts to remove the membrane can be accompanied by a detachment of the epithelium and bleeding. The main causes are infections caused by Strep, pyogenes, and diphtheria.

[21], [22], [23], [24], [25], [26], [27], [28]

Lymphadenopathy

Drainage of lymph from the conjunctiva goes to the parotid and submandibular nodes (as well as lymph drainage from the eyelids). The main causes of lymphadenopathy are viral, chlamydial, gonococcal infections and Parinaud syndrome.