Definition and epidemiology
Conjunctivitis is inflammation of the conjunctiva from infectious, allergic, or irritant causes. It is extremely common, accounting for a large share of outpatient and emergency eye complaints worldwide.
- Viral conjunctivitis is the most common overall cause, typically from adenovirus; it is highly contagious and often occurs in outbreaks (schools, workplaces, swimming pools).
- Bacterial conjunctivitis is more common in young children and is often caused by Streptococcus pneumoniae, Haemophilus influenzae (children), or Staphylococcus aureus (adults).
- Allergic conjunctivitis is common in patients with atopy (allergic rhinitis, asthma, eczema) and is often seasonal or perennial.
- Neonatal conjunctivitis (ophthalmia neonatorum) has distinct causes (chemical, gonococcal, chlamydial) and timing, and is a separate high-yield topic.
Most cases of acute conjunctivitis in adults are viral and self-limited; bacterial causes are overdiagnosed and overtreated in practice.
- Viral conjunctivitis (adenovirus) is the most common cause of acute conjunctivitis overall.
- Preauricular lymphadenopathy strongly suggests viral, not bacterial, conjunctivitis.
- Purulent discharge with lids stuck shut in the morning favors bacterial conjunctivitis.
- Itching plus bilateral involvement and atopic history points to allergic conjunctivitis.
- Hyperacute, copious purulent discharge suggests gonococcal infection — treat as an emergency.
- Avoid topical corticosteroids until HSV keratitis is ruled out by fluorescein staining.
- Vision loss, severe pain, or photophobia out of proportion means it is not simple conjunctivitis.
- Chlamydial and gonococcal conjunctivitis in adults indicate concurrent STI screening is needed.
Etiology and risk factors
Infectious
- Viral: adenovirus (most common), herpes simplex virus, varicella-zoster virus, enterovirus.
- Bacterial: S. pneumoniae, H. influenzae, S. aureus; Neisseria gonorrhoeae and Chlamydia trachomatis in sexually active adults or neonates (hyperacute or chronic course).
Noninfectious
- Allergic: IgE-mediated reaction to environmental allergens (pollen, dust, pet dander); often bilateral with itching.
- Irritant/toxic: chemicals, chlorine, smoke, contact lens solutions, prolonged contact lens wear.
- Giant papillary conjunctivitis: chronic contact lens use or ocular prosthesis.
Risk factors
- Close contact with infected individuals, poor hand hygiene, contact lens wear, atopic history, crowded settings (schools, daycare), and sexual contact (for gonococcal/chlamydial forms).
Pathophysiology
The conjunctiva is a vascularized mucous membrane rich in lymphoid tissue, making it reactive to pathogens and allergens.
- Viral: direct viral invasion of conjunctival epithelium triggers a lymphocytic inflammatory response, producing watery discharge and follicular reaction (lymphoid follicles on the tarsal conjunctiva).
- Bacterial: bacterial colonization and neutrophilic infiltration cause purulent exudate and papillary (not follicular) reaction.
- Allergic: allergen cross-links IgE on conjunctival mast cells, triggering histamine release, vasodilation, and itching; a type I hypersensitivity reaction.
- Gonococcal: N. gonorrhoeae can directly invade intact corneal epithelium, explaining its rapid, severe, hyperacute course and risk of corneal perforation if untreated.
Clinical features
| Feature | Viral | Bacterial | Allergic |
|---|---|---|---|
| Discharge | Watery/mucoid | Purulent, eyelids stuck shut | Watery, stringy mucus |
| Laterality | Starts unilateral, spreads bilateral | Unilateral or bilateral | Bilateral |
| Itching | Mild | Minimal | Prominent |
| Lymph nodes | Preauricular adenopathy common | Absent | Absent |
| Associated symptoms | URI symptoms, pharyngitis | None typically | Allergic rhinitis, atopy |
- Common to all: conjunctival injection (redness), foreign body sensation, mild photophobia.
- Vision is typically preserved; significant vision loss or severe pain suggests an alternative diagnosis (keratitis, uveitis, acute angle-closure glaucoma, scleritis).
- Hyperacute, copious purulent discharge with rapid progression suggests gonococcal infection and is an emergency due to corneal perforation risk.
Diagnosis
Diagnosis is primarily clinical, based on history and slit-lamp or penlight examination.
- History: onset, discharge character, unilateral vs bilateral, contact history, contact lens use, sexual history, atopy.
- Examination: visual acuity (should be normal or only mildly reduced), pattern of injection, discharge type, presence of follicles vs papillae, preauricular lymph nodes, corneal clarity, pupil reactivity.
- Fluorescein staining: to rule out corneal involvement (dendritic lesions suggest HSV keratitis; this changes management significantly).
- Laboratory testing is not routine but is indicated for:
- Suspected gonococcal or chlamydial infection (Gram stain, culture, PCR)
- Neonatal conjunctivitis
- Severe, recurrent, or treatment-refractory cases
- Immunocompromised patients
- Red flags warranting referral: reduced vision, severe pain, photophobia out of proportion, corneal involvement, contact lens wearers with pain (risk of microbial keratitis), neonates.
Differential diagnosis
- Keratitis (especially contact lens-related microbial keratitis) - pain, photophobia, corneal infiltrate.
- Acute angle-closure glaucoma - severe pain, nausea, fixed mid-dilated pupil, high intraocular pressure.
- Anterior uveitis/iritis - photophobia, ciliary flush, cells in anterior chamber.
- Episcleritis/scleritis - localized or diffuse redness, scleritis is painful and tender to palpation.
- Subconjunctival hemorrhage - painless, sharply demarcated blood, no discharge.
- Dry eye disease - chronic irritation, normal discharge pattern, often bilateral.
- Blepharitis - eyelid margin inflammation that can cause secondary conjunctival irritation.
Management
Management depends on the underlying cause; most acute conjunctivitis is self-limited.
Viral conjunctivitis
- Primarily supportive: artificial tears, cold compresses, antihistamine drops for symptomatic relief.
- No antibiotics needed; emphasize hand hygiene and avoiding contact lens use and sharing towels/pillows due to high contagiousness.
- Typically resolves in 1-2 weeks; adenoviral keratoconjunctivitis can occasionally cause subepithelial infiltrates requiring topical corticosteroids under ophthalmology guidance.
- HSV conjunctivitis/keratitis requires topical or oral antivirals; topical corticosteroids are contraindicated until HSV keratitis is excluded.
Bacterial conjunctivitis
- Often self-limited within 1-2 weeks even without treatment; topical antibiotics (e.g., erythromycin, trimethoprim-polymyxin B, fluoroquinolones) can shorten duration and are commonly used, especially in contact lens wearers or when symptoms are more severe.
- Guideline consensus varies: some advocate watchful waiting for mild cases, others favor early topical antibiotics to reduce transmission (e.g., school/daycare return policies).
- Gonococcal conjunctivitis: ophthalmologic emergency; requires systemic antibiotics (e.g., ceftriaxone) plus ocular lavage, with concurrent treatment for possible chlamydial coinfection (e.g., azithromycin or doxycycline), since ceftriaxone does not cover Chlamydia.
- Chlamydial conjunctivitis: systemic antibiotics (e.g., azithromycin or doxycycline), as it reflects a sexually transmitted infection requiring partner treatment.
Allergic conjunctivitis
- Allergen avoidance, cool compresses, topical antihistamine/mast cell stabilizers (e.g., olopatadine, ketotifen) as first-line.
- Oral antihistamines for associated allergic rhinitis.
- Topical corticosteroids reserved for severe, refractory cases under ophthalmology supervision due to glaucoma and cataract risk with prolonged use.
General principles
- Avoid topical corticosteroids unless HSV keratitis has been excluded.
- Discontinue contact lens use until symptoms resolve.
- Educate on hygiene to prevent spread (frequent handwashing, avoid touching eyes, separate towels).
Complications and prognosis
- Most cases of viral and bacterial conjunctivitis resolve without sequelae within 1-3 weeks.
- Corneal involvement (keratoconjunctivitis) can cause photophobia and, rarely, scarring or visual impairment, particularly with adenovirus or HSV.
- Gonococcal conjunctivitis can rapidly progress to corneal ulceration and perforation if untreated, making prompt recognition critical.
- Chlamydial conjunctivitis, if untreated, can become chronic and is associated with trachoma in endemic regions, a leading infectious cause of blindness worldwide.
- Neonatal conjunctivitis from gonococcal or chlamydial infection can cause severe ocular damage and systemic infection if not treated promptly.
- Overall prognosis for typical acute conjunctivitis in immunocompetent patients is excellent with appropriate care and hygiene.
Red eye RULE-OUTS before calling it conjunctivitis: 'VPC-GA' — Vision loss, Pain (severe), Ciliary flush, Grossly abnormal pupil, Acute IOP rise — if any present, think beyond conjunctivitis.
Practice questions
1. A 24-year-old man presents with a 2-day history of red, watery eyes, starting in the left eye and now also affecting the right. He reports a recent upper respiratory infection and tender preauricular lymph nodes. Visual acuity is normal. Which of the following is the most likely diagnosis?
2. A 3-day-old neonate develops bilateral purulent eye discharge with marked eyelid swelling. The mother received no prenatal care. Gram stain of the discharge shows gram-negative diplococci. Which of the following is the most appropriate immediate management?
3. A 19-year-old woman with a history of seasonal allergic rhinitis presents with bilateral itchy, watery eyes and mild lid swelling that worsens during spring. Examination shows conjunctival injection without discharge crusting. Which of the following is the most appropriate first-line treatment?
Frequently asked questions
What causes conjunctivitis?
Conjunctivitis is most often caused by viruses (especially adenovirus), followed by bacteria, allergens, or irritants. Viral and bacterial forms are contagious and spread through contact with infected secretions or contaminated surfaces. Allergic conjunctivitis results from an immune reaction to environmental allergens like pollen or pet dander rather than infection. Identifying the discharge type and associated symptoms helps distinguish the likely cause.
What are the first symptoms of conjunctivitis?
The earliest symptoms are usually eye redness, a gritty or foreign-body sensation, and some form of discharge, which may be watery, mucoid, or purulent depending on the cause. Many people also notice mild itching, tearing, or crusting of the eyelids, especially after sleep. Vision typically stays normal in the early stages, which helps differentiate it from more serious eye conditions.
How is conjunctivitis diagnosed?
Conjunctivitis is diagnosed clinically through history and eye examination, looking at the pattern of redness, type of discharge, and whether one or both eyes are affected. Fluorescein staining is often used to check the cornea and exclude more serious conditions like herpes keratitis. Laboratory testing (culture, PCR) is reserved for suspected gonococcal or chlamydial infection, neonates, or cases that do not improve with standard care.
Is conjunctivitis curable?
Yes, most cases of conjunctivitis resolve completely, often without specific treatment. Viral conjunctivitis typically clears within one to two weeks as the immune system fights off the infection, while bacterial conjunctivitis often improves with or without topical antibiotics within a similar timeframe. Allergic conjunctivitis is a chronic or recurrent condition that is well controlled, though not permanently cured, with allergen avoidance and antihistamine therapy.
Viral vs bacterial conjunctivitis — what is the difference?
Viral conjunctivitis typically produces watery discharge, often starts in one eye and spreads to the other, and is commonly accompanied by preauricular lymph node swelling and upper respiratory symptoms. Bacterial conjunctivitis tends to cause thicker, purulent discharge with eyelids crusted shut in the morning, and lacks the lymph node involvement seen with viral infection. Viral cases are more common overall and do not require antibiotics, while bacterial cases may benefit from topical antibiotic treatment.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: H10
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.