ANATOMY OF THE CONJUNCTIVA
The conjunctiva is a thin mucous membrane which lines the posterior surface of lids and covers the anterior surface of the sclera (it does not cover the cornea).
The conjunctiva is formed of 5 parts:
1. Palpebral conjunctiva:
It is the conjunctiva that lines the posterior surface of lid. It starts at lid margin and firmly adherent to the tarsus, being transparent it allows one to see the Meibomian glands. It shows a groove 2 mm from lid margin called "sulcus subtarsalis". It is further subdivided into divided into following zones:
a. Marginal conjunctiva starts at grey line to the sulcus subtarsalis.
b. Tarsal conjunctiva from sulcus subtarsalis to upper border of tarsus.
c. Orbital conjunctiva lies between upper border of the tarsal plate and fornix. It is related to Muller's muscle.
2. Bulbar conjunctive:
It is the conjunctiva that covers the anterior part of the sclera. It is subdivided into sclera and limbal parts. The scleral part is loosely adherent to the sclera, while the limbal part is firmly adherent.
It is the continuous cul-de-sac representing the reflected portion of the conjunctiva between the bulbar and palpebral parts. It is divided for purpose of description into superior, inferior, medial and lateral portions. Through the superior fornix the ducts of main and accessory lacrimal glands open.
It is a crescentic fold of conjunctiva at medial canthus, it represents the third lid in lower animals (nictitating membrane).
It is a vascular fleshy elevation at the medial canthus. It is a piece of modified skin containing hairs and sebaceous glands.
Microscopic anatomy of the conjunctiva:-
It is a non keratinizing epithelium that differs according to its site as following:
- Marginal conjunctiva is lined by stratified squamous non-keratinizing epithelium.
- Tarsal conjunctiva is lined by two layers of epithelial cells; a superficial columnar and deep cubical layers.
- Fornix is lined by three layers of epithelial cells.
- In bulbar conjunctival epithelium the number of layers increase to become again stratified squamous non-keratinizing epithelium to be continuous with corneal epithelium.
N.B.: The conjunctival epithelium contains goblet cells which secrete mucus. They are numerous in the fornices and plica, but absent near the lid margin and limbus.
2. Substantia propria:
It is formed of 2 layers:
a. Superficial adenoid layer consists of loose connective tissue and lymphocytes. It is formed after the age of 3 month. So that, conjunctival follicles never form before this age.
b. Deep fibrous layer.
a. Posterior conjunctival arteries: they are branches of palpebral arcades. They supply the conjunctiva except the circumcorneal 4 mm.
b. Anterior conjunctival arteries: They are branches of anterior ciliary arteries before they pierce the sclera, they supply only an area about 4 mm around the limbus.
They follow the arteries.
a. Posterior conjunctival veins: They drain into veins of lid.
b. Anterior conjunctival veins: They drain to anterior ciliary vein to ophthalmic vein.
Lymph drainage & nerve supply:- As the lids.
Anti-microbial defence of the conjunctiva:
1. The temperature is cool due to tear evaporation.
2. Continuous wash with tears.
3. Healthy and integrated epithelium.
4. Lymphoid tissue subepithelialy.
5. Anti-microbial proteins in tears as lysozyme and IgA.
6. Normal flora (staph albus, diphtheroids and xerobacillus) secrete antibiotics that inhibit pathogenic bacteria.
The major clinical manifestations of conjunctivitis are:-
- Watery in cases of viral and toxic conjunctivitis.
- Ropy mucus discharge in cases of spring catarrhal.
- Mucopurulent in cases of mild bacterial and chlamydial infections.
- Purulent in cases of severe bacterial infections.
- Sanguineous in cases of membranous conjunctivitis.
2. Conjunctival injection due to dilatation of posterior conjunctival vessels. It is fire red, more obvious in the fornices and moves with the movement of conjunctiva.
3. Conjunctival and lid edema.
4. Special reactions:-
A. Papillae: Pink elevations of proliferated conjunctival epithelium with a vascular connective tissue core.
B. Follicles due to aggregation of lymphocytes in the lymphoid layer. They appear as grey pale elevations.
Differential diagnosis of follicular conjunctivitis:
1. Chlamydial infections:
b. Inclusion blanorrhea.
c. Acute trachoma in foreigners: It occurs when a non immunized person (usually a foreigner) is exposed to a heavy dose of infection by chlamydia trachomatis A, B, & C. The clinical picture will be acute. Follicles will be formed in the upper and lower parts of the conjunctiva.
2. Viral conjunctivitis (as adenovirus & herpes simplex and Zoster).
3. Chronic follicular conjunctivitis (see later).
4. Folliculosis: it is a disease of children. There are follicles in the lower fornices and enlargement of adenoids and tonsils.
Diseases of the conjunctiva can be classified into:-
A. Acute infectious diseases:
i. Bacterial infections:
- Catarrhal conjunctivitis.
- Mucopurulent conjunctivitis.
- Purulent conjunctivitis.
- Membranous conjunctivitis.
- Ophthalmia neonatorum.
ii. Chlamydia: Inclusion blanorrhea.
iii. Viral conjunctivitis as adenovirus, HZV, HSV, ... .
B. Chronic infective conjunctivitis:
ii. Angular blepharoconjunctivitis.
iii. Fungal conjunctivitis due to candidiasis.
C. Non infectious:-
i. Allergic diseases:
- Phlyctenular kerato-conjunctivitis.
- Spring catarrhal.
- Chronic follicular conjunctivitis.
ii. Chemical injuries.
iii. Autoimmune diseases.
II. Degenerative diseases: - Pinguicula & pterygium.
III. Miscellaneous subjects:-
- Dry eye syndrome.
- Conjunctival pigmentation.