Conjunctivitis

Conjunctivitis (also called pink eye or madras eye ) refers to inflammation of the conjunctiva (the outermost layer of the eye and the inner surface of the eyelids). It is most commonly due to an infection (usually viral, but sometimes bacterial ) or an allergic reaction.

Classification
Classification can be either by cause or by extent of the inflamed area.

By cause

 * Allergic conjunctivitis
 * Bacterial conjunctivitis
 * Viral conjunctivitis
 * Chemical conjunctivitis
 * Neonatal conjunctivitis is often defined separately due to different organisms

By extent of involvement
Blepharoconjunctivitis is the dual combination of conjunctivitis with blepharitis (inflammation of the eyelids).

Keratoconjunctivitis is the combination of conjunctivitis and keratitis (corneal inflammation).

Episcleritis is an inflammatory condition that produces a similar appearance to conjunctivitis, but without discharge or tearing.

Signs and symptoms
Red eye (hyperaemia), irritation (chemosis) and watering (epiphora) of the eyes are symptoms common to all forms of conjunctivitis. However, the pupils should be normally reactive and the visual acuity normal.

Viral
Viral conjunctivitis is often associated with an infection of the upper respiratory tract, a common cold, and/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 other.

Viral conjunctivitis, commonly known as "pink eye", shows a fine, diffuse pinkness of the conjunctiva, which is easily mistaken for the ciliary injection of iritis, but there are usually corroborative signs on microscopy, particularly numerous lymphoid follicles on the tarsal conjunctiva, and sometimes a punctate keratitis.

Bacterial
Bacterial conjunctivitis due to common pyogenic (pus-producing) bacteria causes marked grittiness/irritation and a stringy, opaque, greyish or yellowish mucopurulent discharge that may cause the lids to stick together, especially after sleep. Another symptom that could be caused by bacterial conjunctivitis is severe crusting of the infected eye and the surrounding skin. However, contrary to popular belief, discharge is not essential to the diagnosis. Bacteria such as Chlamydia trachomatis or Moraxella can cause a non-exudative but persistent conjunctivitis without much redness. The gritty and/or scratchy feeling is sometimes localized 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. Corynebacterium diphtheriae causes membrane formation in conjunctiva of non immunized children.

Chemical
Chemical eye injury is due to either an acidic or alkali substance getting in the eye. Alkalis are typically worse than acidic burns. Mild burns will produce conjunctivitis while more severe burns may cause the cornea to turn white. Litmus paper is an easy way to rule out the diagnosis by verifying that the pH is within the normal range of 7.0—7.2. Large volumes of irrigation is the treatment of choice and should continue until the pH is 6—8. Local anaesthetic eye drops can be used to decrease the pain.

Irritant or toxic conjunctivitis show primarily marked redness. If due to splash injury, it is often present only in the lower conjunctival sac. With some chemicals, above all with caustic alkalis such as sodium hydroxide, there may be necrosis of the conjunctiva with a deceptively white eye due to vascular closure, followed by sloughing of the dead epithelium. This is likely to be associated with slit-lamp evidence of anterior uveitis.

Other
Inclusion conjunctivitis of the newborn (ICN) is a conjunctivitis that may be caused by the bacteria Chlamydia trachomatis, and may lead to acute, purulent conjunctivitis. However, it is usually self-healing.

Conjunctivitis is identified by irritation and redness of the conjunctiva. Except in obvious pyogenic or toxic/chemical conjunctivitis, a slit lamp (biomicroscope) is needed to have any confidence in the diagnosis. Examination of the tarsal conjunctiva is usually more diagnostic than the bulbar conjunctiva.

Causes
Conjunctivitis is most commonly caused by viral infection, but bacterial infections, allergies, other irritants and dryness are also common etiologies for its occurrence. Both bacterial and viral infections are contagious. Commonly, conjunctival infections are passed from person-to-person, but can also spread through contaminated objects or water.

The most common cause of viral conjunctivitis is adenoviruses. Herpetic keratoconjunctivitis (caused by herpes simplex viruses) can be serious and requires treatment with acyclovir. Acute hemorrhagic conjunctivitis is a highly contagious disease caused by one of two enteroviruses, Enterovirus 70 and Coxsackievirus A24. These were first identified in an outbreak in Ghana in 1969, and have spread worldwide since then, causing several epidemics.

Diagnosis
Cultures are done infrequently because most cases of conjunctivitis are treated empirically and (eventually) successfully, but often only after running the gamut of the common possibilities.

Swabs for bacterial culture are necessary if the history and signs suggest bacterial conjunctivitis, but there is no response to topical antibiotics. Research studies indicate many bacteria implicated in low-grade conjunctivitis are not detected by the usual culture methods of medical microbiology labs, so false negative results are common. Viral culture may be appropriate in epidemic case clusters. Conjunctival scrapes for cytology can be useful in detecting chlamydial and fungal infections, allergy and dysplasia, but are rarely done because of the cost and the general lack of laboratory staff experienced in handling ocular specimens. Conjunctival incisional biopsy is occasionally done when granulomatous diseases (e.g., sarcoidosis) or dysplasia are suspected.

Differential diagnosis
Conjunctivitis is a relatively nonspecific symptom. Even after biomicroscopy, laboratory tests are often necessary if proof of etiology is needed.

A purulent discharge (a whitish-yellow, yellow or yellow-brown substance, more commonly known as pus) suggests a bacterial infection. It can also be caused by bacteria from feces, pet hair, or by smoke or other fumes. Infection with Neisseria gonorrhoeae should be suspected if the discharge is particularly thick and copious.

Itching (rubbing eyes) is the hallmark symptom of allergic conjunctivitis. Other symptoms include past history of eczema, or asthma.

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 conjunctivitis.

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.

Many people with conjunctivitis have trouble opening their eyes in the morning because of the dried mucus on their eyelids. There is often excess mucus over the eye after sleeping for an extended period.

Management
Conjunctivitis resolves in 65% of cases without treatment, within two to five days. The prescribing of antibiotics to most cases is not necessary.

Allergic
For the allergic type, cool water poured over the face with the head inclined downward constricts capillaries, and artificial tears sometimes relieve discomfort in mild cases. In more severe cases, nonsteroidal anti-inflammatory medications and antihistamines may be prescribed. Persistent allergic conjunctivitis may also require topical steroid drops.

Bacterial
Bacterial conjunctivitis usually resolves without treatment. Antibiotics, eye drops, or ointment are thus only needed if no improvement is observed after three days. In patients receiving no antibiotics, recovery was in 4.8 days, with immediate antibiotics it was 3.3 days, and with delayed antibiotics 3.9 days. No serious effects were noted either with or without treatment.

Viral
Although there is no specific treatment for viral conjunctivitis, symptomatic relief may be achieved with cold compresses and artificial tears. People are often advised to avoid touching their eyes or sharing towels and washcloths. Due to the contagious nature of pink eye travel is banned to some countries notably Argentina and Vanuatu.

Chemical
Conjunctivitis due to chemicals is treated via irrigation with Ringer's lactate or saline solution. Chemical injuries (particularly alkali burns) are medical emergencies, as they can lead to severe scarring, and intraocular damage. People with chemically-induced conjunctivitis should not touch their eyes, regardless of whether or not their hands are clean, as they run the risk of spreading the condition to another eye.

Prevention
The best effective prevention is hygiene and not rubbing the eyes by infected hands. Vaccination against adenovirus and haemophilus influenzae is also effective.