Editing Conjunctivitis (section)

=== Differential diagnosis ===

Some more serious conditions can present with a red eye, such as infectious keratitis, angle-closure glaucoma, or iritis. These conditions require the urgent attention of an ophthalmologist. Signs of such conditions include decreased vision, significantly increased sensitivity to light, inability to keep the eye open, a pupil that does not respond to light, or a severe headache with nausea.<ref name="McGra-Hill">{{Cite book |title=Harrison's Principles of Internal Medicine |vauthors=Longo DL |date=2012 |publisher=McGra-Hill |chapter=Disorders of the Eye(Horton JC)}}</ref> Fluctuating blurring is common, due to tearing and mucoid discharge.  Mild photophobia is common. However, if any of these symptoms is prominent, considering other diseases such as [[glaucoma]], [[uveitis]], [[keratitis]], and even [[meningitis]] or [[caroticocavernous fistula|carotico-cavernous fistula]] is important.{{citation needed|date=September 2022}}

A more comprehensive differential diagnosis for the red or painful eye includes:<ref name="McGra-Hill" />
* [[Corneal abrasion]]
* [[Subconjunctival hemorrhage]]
* [[Pinguecula]]
* [[Blepharitis]]
* [[Dacryocystitis]]
* [[Keratoconjunctivitis sicca]] (dry eye)
* [[Keratitis]]
* [[Herpes simplex]]
* [[Herpes zoster]]
* [[Episcleritis]] – an [[Inflammation|inflammatory]] condition that produces a similar appearance to conjunctivitis, but without discharge or tearing
* [[Uveitis]]
* [[Acute angle-closure glaucoma]]
* [[Endophthalmitis]]
* [[Orbital cellulitis]]