A "red eye" can be caused by many conditions. Some causes are common and readily identified while others may be subtle. It is important to distinguish those conditions that can have serious consequences to the patient from those that are more mundane.


Differential diagnosis of red eye:

(1) bacterial infection

(2) viral infection

(3) other infection (fungal, parasitic)

(4) uveitis

(5) iritis

(6) keratitis

(7) acute glaucoma

(8) allergic conjunctivitis

(9) dry eye

(10) blepharitis

(11) scleritis

(12) episcleritis

(13) topical drug or chemical reaction

(14) foreign body

(15) contact lens use

(16) occult conjunctival injury

(17) factitious injury

(18) entropion

(19) lagophthalmos

(20) trichiasis (ingrowth of the eyelashes)

(21) blepharitis (inflammation of the eyelids)

(22) cellulitis in orbital soft tissues

(23) ocular pseudotumor

(24) ocular neoplasm


The initial assessment should include an evaluation for:

(1) ocular pain

(2) blurred vision

(3) photophobia

(4) itching of the eyes

(5) type of discharge (none, watery or purulent)

(6) examination for foreign bodies or focal lesions

Common Findings


purulent discharge

bacterial conjunctivitis

watery discharge AND no itching

viral conjunctivitis

watery discharge AND itching

allergic conjunctivitis

no pain AND no vision blurring AND no discharge AND itching

dry eye, allergic conjunctivitis, blepharitis


A patient should be referred to an ophthalmologist if the patient has:

(1) ocular pain

(2) blurred vision with photophobia

(3) suspicion that the patient has uveitis, iritis, keratitis, acute glaucoma, intra-ocular foreign body, tumor, chemical exposure or any significant ocular pathology


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