Conjunctivitis, which is often termed “pink eye”, is one of the most frequent causes of red eye presentations within primary care and the emergency department. In most cases, the condition is self-limiting. However, recognising the type of conjunctivitis – viral, bacterial, or allergic – is essential to managing it appropriately. Furthermore, it aids the prevention of unnecessary antibiotic use or missed complications.
This article aims to give medical students and resident doctors a foundational summary of the different causes of conjunctivitis, and an approach to recognising and differentiating the major types of conjunctivitis.
What is Conjunctivitis?
Conjunctivitis is inflammation of the conjunctiva, which is the transparent mucous membrane covering the sclera and inner eyelids (1). It presents with red eyes, discomfort, and discharge. The cause determines specific clinical features and treatment.
https://www.eyeqindia.com/allergic-conjunctivitis-everything-you-need-to-know/ – An example of allergic conjunctivitis. Last accessed 02/06/25
Clinical Comparison of different causes of conjunctivitis
The table below provides a comparison between viral, bacterial and allergic conjunctivitis (1, 2, 3).
| Feature | Viral Conjunctivitis | Bacterial Conjunctivitis | Allergic Conjunctivitis |
| Onset | Acute | Acute | Acute or seasonal |
| Laterality | Often starts unilateral, becomes bilateral | Often unilateral, may spread | Bilateral |
| Discharge | Watery or mucoid | Purulent, yellow/green | Watery, stringy |
| Itching | Mild or absent | Rare | Prominent |
| Associated features | Preauricular lymphadenopathy, upper respiratory infection | Eyelid crusting, sticky lashes | Sneezing, allergic rhinitis, atopy |
| Visual acuity | Usually normal | Usually normal | Normal |
| Contagious? | Yes | Yes | No |
| Typical duration | 1-2 weeks | 7-10 days | Persistent/recurrent during allergen exposure |
Management Overview
The management of the different types of conjunctivitis is summarised below (1,2,3).
| Type | Management |
| Viral | Supportive care (lubricants, cold compress). Avoid antibiotics. Highly contagious. |
| Bacterial | Topical antibiotics (e.g., chloramphenicol) if moderate to severe or high-risk patient group. Self-limiting in most cases. |
| Allergic | Antihistamine drops, mast-cell stabilisers, allergen avoidance. |
Red Flags – When to Refer
Regardless of the underlying type, there are certain features which require an urgent ophthalmology referral (2):
- Reduced visual acuity
- Severe pain or photophobia
- Corneal involvement (e.g., keratitis)
- Contact lens use with bacterial features (risk of Pseudomonas keratitis)
- No improvement after 1 week of treatment
- Suspected herpes simplex virus (dendritic lesions)
- Neonatal conjunctivitis (within first 6 weeks of life) – previously known as ophthalmia neonatorum. This can be due to maternally transmitted chlamydia/gonorrhoea.
- Chlamydia/gonococcal conjunctivitis – this can also affect adults. Both require systemic treatment and contact tracing. Management is usually led by the GUM clinics.
What You Can Do as a Resident
- Take a focused history:
- Ask about the duration, discharge type, associated symptoms (itching, upper respiratory tract infection, exposure)
- Allergies and medication history
- Examine the eye:
- Check the visual acuity
- Inspect the conjunctiva and cornea with fluorescein if available
- Palpate for preauricular nodes
- Investigations:
- Bacterial/viral swabs of the conjunctiva if the diagnosis is in doubt (allergic vs. infective). This is usually done by Ophthalmology.
- Management:
- Oral antihistamines for allergic conjunctivitis
- Topical chloramphenicol is the antibiotic of choice for bacterial conjunctivitis if necessary.
- Educate the patient:
- Viral and bacterial types are contagious – it is important to emphasise the role of hygiene to minimise spreading it.
- Allergic conjunctivitis is not contagious but often chronic.
Take-Home Points
- Most conjunctivitis is viral and self-limiting.
- Purulent discharge suggests bacterial; intense itching suggests allergic.
- Know the red flags for when to escalate care.
- Avoid antibiotics unless clearly indicated – overuse of antibiotics promotes resistance.
References
- Azari AA, Arabi A. Conjunctivitis: A Systematic Review. J Ophthalmic Vis Res. 2020;15(3):372-395. Published 2020 Aug 6. doi:10.18502/jovr.v15i3.7456
- The Royal College of Ophthalmologists. Emergency Eye Care Guidelines. Updated July 2021. Available: https://rcophth.ac.uk
- Centers for Disease Control and Prevention (CDC). Conjunctivitis (Pink Eye). Updated January 2023. Available: https://www.cdc.gov/conjunctivitis
Written by Dr Michael Milad (FY1) & reviewed by Mr Matthew George (Post-CCT fellow)
