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Conjunctivitis - allergic - Making a diagnosis
How do I know my patient has allergic conjunctivitis?
Allergic conjunctivitis is one cause of a red eye. When assessing a person with a red eye, it is essential to first exclude the serious causes. Allergic conjunctivitis is diagnosed by identifying its characteristic features and excluding irritant and infective conjunctivitis.
- Exclude the serious causes of a red eye — acute glaucoma, keratitis, and iritis. If any of the following features are present, perform a full examination (including fluorescein staining), and refer the person for same-day assessment:
- Moderate to severe eye pain or photophobia.
- Marked redness of the eye: the greater the redness, the more likely that the cause is serious. Ciliary injection is indicated by redness and dilated blood vessels seen between the white of the eye and the coloured part (iris) of the eye. It occurs with inflammation of deeper structures but it is not always obvious.
- Reduced visual acuity: any loss of visual acuity, as measured with a Snellen chart.
- Exclude irritant conjunctivitis. Irritant conjunctivitis is likely when a mechanical or chemical cause is identified:
- Common mechanical causes include eyelashes rubbing against the surface of the eye or a foreign body lodged beneath the upper eyelid.
- Chemical causes, such as getting shampoo in the eye or chlorine in a swimming pool, are usually obvious.
- Exclude infective conjunctivitis. An infective cause of conjunctivitis is likely when:
- There is a history of close contact with another affected person.
- Symptoms of upper respiratory tract infection are present.
- The eyes are glued together by discharge after sleep, or mucopurulent discharge is seen on examination.
- An enlarged lymph node in front of the ear is identified.
- Identify the characteristic features of allergic conjunctivitis:
- Itching is the main symptom, but a burning sensation or minimal photophobia may occur.
- On examination, the person has a red eye, which may be associated with oedema of the conjunctival sac and lid swelling.
[American Academy of Ophthalmology, 2003; Yanoff and Duker, 2004]
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