Differential diagnosis
The differential diagnosis of a red eye includes:
- Conjunctivitis
- Uveitis
- Acute glaucoma
- Corneal disease or foreign body trauma
- Scleritis and episcleritis.1
For this patient, conjunctivitis is the most likely diagnosis. The absence of eye pain or loss of vision makes uveitis, acute glaucoma, or corneal disease (including foreign-body trauma) less likely. The round shape of the pupil and the absence of the limbal blush also make uveitis less likely. The pattern of injection does not match the wedge-shaped inflammation of episcleritis or the depth of scleritis.
Diagnosis: viral conjunctivitis
This patient has viral conjunctivitis. Conjunctivitis can be infectious, allergic, chemical/irritative, or autoimmune in origin. The most common infectious agents are viral—specifically, the adenoviruses. Other infectious agents include bacteria (Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria gonorrhoeae), chlamydia, and herpes simplex virus.
Both infectious and allergic conjunctivitis are common. In this patient, the presence of nasal discharge, preauricular lymphadenopathy, and the lack of pruritus make viral infection more likely than allergic. Conjunctivitis that is bilateral without purulent discharge is more likely to be viral than bacterial.
What about the brown macule?
This patient also had a brown macule on her conjunctiva. The differential diagnosis of pigmented areas on the conjunctiva includes nevus, racial melanosis, primary acquired melanosis, secondary pigmentary deposition, and ocular melanoma.2 These conditions (besides ocular melanoma) are benign.