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'Conjunctivitis' is an inflammation of the conjunctiva (the outermost layer of the eye and the inner surface of the eyelids), most commonly due to an allergic reaction or an infection (usually bacterial or viral.
Other causes of conjunctivitis include thermal and ultraviolet burns, chemicals, toxins, overuse of contact lenses, foreign bodies, vitamin deficiency, dry eye, dryness due to inadequate lid closure, exposure to chickens infected with Newcastle disease, epithelial dysplasia (pre-cancerous changes), and some conditions of unknown cause such as sarcoidosis.

Contents

Epidemiology

Diagnosis

Symptoms

Signs

Differential diagnosis

Epidemiology

There are three common varieties of conjunctivitis: viral, allergic, and bacterial].
;Bacterial conjunctivitis:is most often caused by [[pyogenic bacteria such as ''Staphylococcus'' or ''Streptococcus'' from the patient's own skin or respiratory flora. Others are due to infection from the environment (e.g. insect-borne), from other people (usually by touch—especially in children), but occasionally via eye makeup or facial lotion.
;Viral conjunctivitis: So-called "pink eye" is spread by aerosol or contact with viruses, particularly those that cause the common cold (adenovirus), so that it is often associated with upper respiratory tract symptoms (pharyngoconjunctival fever). Because of the contagious nature of these infections, viral conjunctivitis often affects multiple contacts (at work, home or school settings). Clusters of cases have been attributed to inadequately-sterilised ophthalmic instruments contacting the ocular surface in medical settings.
;Allergic conjunctivitis: occurs more frequently among those with allergic conditions, with the symptoms having a seasonal correlation. It can also be caused by allergies to substances such as cosmetics, perfume, protein deposits on contact lenses, or drugs. It usually affects both eyes, and is accompanied by swollen eyelids.

Diagnosis

Symptoms

Redness, irritation and watering of the eyes are symptoms common to all forms of conjunctivitis. Itch and the closing of the throat is variable.
Acute ''allergic conjunctivitis'' is typically itchy. Sometimes distressingly so, and the patient often complains of some lid swelling. Chronic allergy often causes just itch or irritation, and often much frustration because the absence of redness.
''Viral conjunctivitis'' is often associated with an infection of the upper respiratory tract, a common cold, or a sore throat. Its symptoms include watery discharge and variable itch. The infection usually begins with one eye, but may spread easily to the fellow eye.
''Bacterial conjunctivitis'' due to the common pyogenic (pus-producing) bacteria causes marked grittiness/irritation and a stringy, opaque, grey or yellowish mucopurulent discharge (''gowl'', ''goop'', ''sleep'', or other regional names) that may cause the lids to stick together (''matting''), especially after sleeping. Another symptom that could be caused by Bacterial Conjunctivitis is severe crusting of the infected eye and the surrounding skin. However discharge is not essential to the diagnosis, contrary to popular belief. Many other bacteria (e.g., ''Chlamydia'', ''Moraxella'') can cause a non-exudative but very persistent conjunctivitis without much redness. The gritty and/or scratchy feeling is sometimes localised enough for patients to insist they must have a foreign body in the eye. The more acute pyogenic infections can be painful. Like viral conjunctivitis, it usually affects only one eye but may spread easily to the other eye.
''Irritant'' or ''toxic conjunctivitis'' is irritable or painful when the infected eye is pointed far down or far up. Discharge and itch are usually absent. This is the only group in which severe pain may occur.

Signs

''Allergic conjunctivitis'' shows pale watery swelling or edema of the conjunctiva and sometimes the whole eyelid, often with a ropy, ''non-purulent'' mucoid discharge. There is variable redness.
''Viral conjunctivitis'', commonly known as "pink eye", shows a fine diffuse pinkness of the conjunctiva which is easily mistaken for the 'ciliary infection' of iritis, but there are usually corroborative signs on biomicroscopy, particularly numerous lymphoid follicles on the tarsal conjunctiva, and sometimes a punctate keratitis.
Pyogenic ''bacterial conjunctivitis'' shows an opaque purulent discharge, a very red eye, and on biomicroscopy there are numerous white cells and desquamated epithelial cells seen in the 'tear gutter' along the lid margin. The tarsal conjunctiva is a velvety red and not particularly follicular. Non-pyogenic infections can show just mild injection and be difficult to diagnose. Scarring of the tarsal conjunctiva is occasionally seen in chronic infections, especially in trachoma.

Differential diagnosis

Conjunctivitis symptoms and signs are relatively non-specific.
A purulent discharge strongly suggests bacterial cause, unless there is known exposure to toxins. Infection with ''Neisseria gonorrhoeae'' should be suspected if the discharge is particularly thick and copious.
A diffuse, less "injected" conjunctivitis (looking pink rather than red) suggests a viral cause, especially if numerous follicles are present on the lower tarsal conjunctiva on biomicroscopy.
Scarring of the tarsal conjunctiva suggests trachoma, especially if seen in endemic areas, if the scarring is linear (von Arlt's line), or if there is also corneal vascularisation.
Clinical tests for lagophthalmos, dry eye (Schirmer test) and unstable tear film may help distinguish the various types of dry eye.
Other symptoms including pain, blurring of vision and photophobia should not be prominent in conjunctivitis. Fluctuating blurring is common, due to tearing and mucoid discharge. Mild photophobia is common. However, if any of these symptoms are prominent, it is important to exclude other diseases such as glaucoma, uveitis, keratitis and even meningitis or caroticocavernous fistula.