Condition	Signs	Symptoms	Causes
Conjunctivitis
Viral	Normal vision, normal pupil size and reaction to light, diffuse conjunctival injections (redness), preauricular lymphadenopathy, lymphoid follicle on the undersurface of the eyelid	Mild to no pain, diffuse hyperemia, occasional gritty discomfort with mild itching, watery to serous discharge, photophobia (uncommon), often unilateral at onset with second eye involved within one or two days, severe cases may cause subepithelial corneal opacities and pseudomembranes	Adenovirus (most common), enterovirus, coxsackievirus, VZV, Epstein-Barr virus, HSV, influenza
Herpes zoster ophthalmicus	Vesicular rash, keratitis, uveitis	Pain and tingling sensation precedes rash and conjunctivitis, typically unilateral with dermatomal involvement (periocular vesicles)	Herpes zoster
Bacterial (acute and chronic)	Eyelid edema, preserved visual acuity, conjunctival injection, normal pupil reaction, no corneal involvement	Mild to moderate pain with stinging sensation, red eye with foreign body sensation, mild to moderate purulent discharge, mucopurulent secretions with bilateral glued eyes upon awakening (best predictor)	Common pathogens in children: Streptococcus pneumoniae, nontypeable Haemophilus influenzae
			Common pathogen in adults: Staphylococcus aureus
			Other pathogens: Staphylococcus species, Moraxella species, Neisseria gonorrhoeae, gram-negative organisms (e.g., Escherichia coli), Pseudomonas species
Bacterial (hyperacute)	Chemosis with possible corneal involvement	Severe pain; copious, purulent discharge; diminished vision	N. gonorrhoeae
Chlamydial (inclusion conjunctivitis)	Vision usually preserved, pupils reactive to light, conjunctival injections, no corneal involvement, preauricular lymph node swelling is sometimes present	Red, irritated eye; mucopurulent or purulent discharge; glued eyes upon awakening; blurred vision	Chlamydia trachomatis (serotypes D to K)
Allergic	Visual acuity preserved, pupils reactive to light, conjunctival injection, no corneal involvement, large cobblestone papillae under upper eyelid, chemosis	Bilateral eye involvement; painless tearing; intense itching; diffuse redness; stringy or ropy, watery discharge	Airborne pollens, dust mites, animal dander, feathers, other environmental antigens
Other causes
Dry eye (kerato-conjunctivitis sicca)	Vision usually preserved, pupils reactive to light; hyperemia, no corneal involvement	Bilateral red, itchy eyes with foreign body sensation; mild pain; intermittent excessive watering	Imbalance in any tear component (production, distribution, evaporation, absorption); medications (anticholinergics, antihistamines, oral contraceptive pills); Sjögren syndrome
Blepharitis	Dandruff-like scaling on eyelashes, missing or misdirected eyelashes, swollen eyelids, secondary changes in conjunctiva and cornea leading to conjunctivitis	Red, irritated eye that is worse upon waking; itchy, crusted eyelids	Chronic inflammation of eyelids (base of eyelashes or meibomian glands) by staphylococcal infection
Corneal abrasion and foreign body	Reactive miosis, corneal edema or haze, possible foreign body, normal anterior chamber, visual acuity depends on the position of the abrasion in relation to visual axis	Unilateral or bilateral severe eye pain; red, watery eyes; photophobia; foreign body sensation; blepharospasm	Direct injury from an object (e.g., finger, paper, stick, makeup applicator); metallic foreign body; contact lenses
Subconjunctival hemorrhage	Normal vision; pupils equal and reactive to light; well demarcated, bright red patch on white sclera; no corneal involvement	Mild to no pain, no vision disturbances, no discharge	Spontaneous causes: hypertension, severe coughing, straining, atherosclerotic vessels, bleeding disorders
			Traumatic causes: blunt eye trauma, foreign body, penetrating injury
Episcleritis	Visual acuity preserved, pupils equal and reactive to light, dilated episcleral blood vessels, edema of episclera, tenderness over the area of injection, confined red patch	Mild to no pain; limited, isolated patches of injection; mild watering	Idiopathic (isolated presentation)
Keratitis (corneal inflammation)	Diminished vision, corneal opacities/white spot, fluorescein staining under Wood lamp shows corneal ulcers, eyelid edema, hypopyon	Painful red eye, diminished vision, photophobia, mucopurulent discharge, foreign body sensation	Bacterial (Staphylococcus species, Streptococcus); viral (HSV, VZV, Epstein-Barr virus, cytomegalovirus); abrasion from foreign body; contact lenses
Iritis	Diminished vision; poorly reacting, constricted pupils; ciliary/perilimbal injection	Constant eye pain (radiating into brow/temple) developing over hours, watering red eye, blurred vision, photophobia	Exogenous infection from perforating wound or corneal ulcer, autoimmune conditions
Glaucoma (acute angle-closure)	Marked reduction in visual acuity, dilated pupils react poorly to light, diffuse redness, eyeball is tender and firm to palpation	Acute onset of severe, throbbing pain; watering red eye; halos appear when patient is around lights	Obstruction to outflow of aqueous humor leading to increased intraocular pressure
Chemical burn	Diminished vision, corneal involvement (common)	Severe, painful red eye; photophobia	Common agents include cement, plaster powder, oven cleaner, and drain cleaner
Scleritis	Diffuse redness, diminished vision, tenderness, scleral edema, corneal ulceration	Severe, boring pain radiating to periorbital area; pain increases with eye movements; ocular redness; watery discharge; photophobia; intense nighttime pain; pain upon awakening	Systemic diseases, such as rheumatoid arthritis, Wegener granulomatosis, reactive arthritis, sarcoidosis, inflammatory bowel disease, syphilis, tuberculosis