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Author: Dr Julie Fraser, Adelaide, Australia. Chief Editor: Dr Amanda Oakley, Dermatologist, Hamilton, New Zealand, December 2015.
Conjunctivitis is inflammation of the conjunctiva of the eye.
The conjunctiva is the semi-transparent membrane that covers the white part of the eye (the sclera) and lines the inside of the eyelids.
When the conjunctiva is inflamed, the white of the eye appears red. Conjunctivitis is the most likely diagnosis when a patient has a red eye and discharge.
Allergic conjunctivitis is a non-infectious form of conjunctivitis and is due to a reaction to an allergen in contact with the surface of the eye.
Allergic conjunctivitis can be caused by an immediate Type 1 hypersensitivity reaction, often to airborne allergen.
The allergen causes the rapid release of chemical mediators including histamine and others, resultin in acute or episodic symptoms within minutes of exposure.
Chronic allergic conjunctivitis is often more correctly called keratoconjunctivitis because it usually involves the cornea as well as the conjunctiva. The most common forms of allergic keratoconjunctivitis are vernal keratoconjunctivitis and atopic keratoconjunctivitis.
Conjunctivitis due to Type III hypersensitivity reaction arises as part of Stevens-Johnson syndrome-toxic epidermal necrolysis (SJS-TEN), a serious systemic reaction to a drug.
Conjunctivitis can also be due to delayed Type IV hypersensitivity reactions to allergens, which includes local reactions to preservatives or medicaments (eg neomycin) in eye drops. It may take some hours or days to start reacting to these.
Conjunctivitis is a diagnosis of exclusion. All forms of conjunctivitis are characterised by:
The following "red flags" point to other more serious diagnoses, such as keratitis (inflammation of the cornea), iritis, or angle closure glaucoma:
Allergic conjunctivitis is distinguished by:
Vernal keratoconjunctivitis is a chronic form of allergic conjunctivitis. Atopic keratoconjunctivitis is characterised by bilateral eyelid dermatitis.
Most forms of allergic conjunctivitis are relatively mild, but in certain cases (eg SJS-TEN), severe complications may occur. Pain, loss of vision or photophobia require immediate referal to an ophthalmologist.
Complications from allergic conjunctivitis include corneal ulceration.
Treatment of allergic conjunctivitis or keratoconjunctivitis includes:
Nonsteroidal anti-inflammatory drugs, such as ketorolac, and steroid eyedrops or systemic glucocorticoids are sometimes used under specialist advice. Warning: glucocorticoids can cause sight-threatening complications, including corneal scarring and perforation, cataracts and glaucoma, when used inappropriately.
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