What is Conjunctivitis?
Conjunctivitis is an inflammation of the conjunctiva — the thin, transparent mucous membrane that lines the inner surface of the eyelids and covers the white part (sclera) of the eye. It is one of the most common eye conditions, affecting people of all ages. The condition can be classified into three main categories: infectious (viral or bacterial), allergic, and irritant/toxic conjunctivitis. Viral conjunctivitis, most frequently caused by adenoviruses, is highly contagious and often occurs in epidemic outbreaks. Bacterial conjunctivitis is caused by organisms such as Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae. Allergic conjunctivitis is triggered by allergens such as pollen, dust mites, or animal dander and is frequently associated with other atopic conditions like asthma and allergic rhinitis. While most cases are self-limiting, proper diagnosis is important to distinguish conjunctivitis from more serious conditions requiring urgent treatment.
Symptoms
- Redness (hyperemia) of the eye — the hallmark sign
- Watery or mucous discharge (viral) or thick, yellow-green purulent discharge (bacterial)
- Itching, especially prominent in allergic conjunctivitis
- Burning or gritty sensation
- Tearing (epiphora)
- Swollen eyelids
- Crusting of the eyelids, particularly upon waking
- Sensitivity to light (photophobia) in some cases
- Swollen preauricular lymph nodes (viral)
Causes and Risk Factors
The causes of conjunctivitis vary depending on the type. Viral conjunctivitis is most commonly caused by adenoviruses and is highly contagious through direct contact, respiratory droplets, or contaminated surfaces. Bacterial conjunctivitis results from direct inoculation of bacteria into the eye. Allergic conjunctivitis is an IgE-mediated hypersensitivity reaction to environmental allergens. Risk factors include:
- Close contact with an infected individual
- Poor hand hygiene
- Sharing towels, pillows, or cosmetics
- Contact lens wear, especially extended-wear lenses
- Seasonal allergies or a history of atopy
- Exposure to chemical irritants, smoke, or chlorinated water
- Immunocompromised state
Diagnosis
Conjunctivitis is typically diagnosed clinically based on history and slit-lamp examination. The ophthalmologist evaluates the pattern of redness, type of discharge, presence of follicles or papillae on the tarsal conjunctiva, and any corneal involvement. In severe, recurrent, or treatment-resistant cases, conjunctival swabs may be taken for bacterial culture and sensitivity testing or viral PCR (polymerase chain reaction). It is essential to rule out other causes of a red eye, including keratitis, uveitis, acute glaucoma, and foreign bodies, which may present with similar symptoms but require different management.
Treatment
Treatment depends on the underlying cause:
- Viral conjunctivitis — usually self-limiting within 7 to 14 days; supportive care includes cold compresses and artificial tears; in severe adenoviral cases with corneal subepithelial infiltrates, topical corticosteroids may be considered under specialist supervision
- Bacterial conjunctivitis — topical antibiotic eye drops or ointment (e.g., fluoroquinolones, aminoglycosides, or chloramphenicol); most cases resolve within 5 to 7 days of treatment
- Allergic conjunctivitis — avoidance of known allergens, topical antihistamines, mast cell stabilizers (e.g., olopatadine, ketotifen), cold compresses, and artificial tears; oral antihistamines for systemic relief
- Irritant conjunctivitis — removal of the offending agent and copious irrigation with saline or clean water
Prevention and Recommendations
- Wash hands frequently and avoid touching or rubbing your eyes
- Do not share towels, pillowcases, or eye cosmetics
- Replace eye makeup regularly and never share it
- Clean and store contact lenses properly; follow recommended replacement schedules
- Stay home from school or work if you have infectious conjunctivitis until you are no longer contagious
- Use protective eyewear when swimming in chlorinated pools
- If you have seasonal allergies, start prophylactic antihistamine drops before allergy season begins