Conjunctivitis differential diagnosis
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Conjunctivitis must be differentiated from keratoconjunctivitis sicca, trachoma, dry eye, glaucoma, uveitis, and keratitis.
Differentiating Conjunctivitis from other Diseases
Conjunctivitis symptoms and signs are relatively non-specific. Even after biomicrosopy, laboratory tests are often necessary to determine the underlying pathophysiology with certainty.
Bacterial Causes
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.
Viral Causes
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.
Trachoma
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.
Dry Eye Variants
Clinical tests for lagophthalmos, dry eye (Schirmer test) and unstable tear film may help distinguish the various types of dry eye.
Serious Illnesses such as Glaucoma, Uveitis, Keratitis and even Meningitis or Caroticocavernous Fistula
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.