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[citation needed]. 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.[7]
[edit] Differential diagnosis
Conjunctivitis is a relatively non-specific symptom.[1] Even after bio microscopy, 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) strongly suggests a cause from fecal matter, unless there is known exposure to toxins. 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 bio microscopy.
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 who have 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.
