How can I differentiate between allergic conjunctivitis and bacterial conjunctivitis in a primary care setting?

To differentiate allergic conjunctivitis from bacterial conjunctivitis in a primary care setting, focus on the clinical presentation and symptom characteristics.

• Allergic conjunctivitis typically presents with bilateral eye redness, intense itching, watery discharge, and associated allergic symptoms such as sneezing or nasal congestion. The conjunctiva often appears swollen and pale or boggy due to inflammation, and symptoms tend to be seasonal or related to allergen exposure.
• In contrast, bacterial conjunctivitis usually presents with unilateral or bilateral redness accompanied by purulent, sticky discharge that may cause the eyelids to stick together, especially after sleep. It is often associated with a gritty or foreign body sensation rather than itching.
• Systemic symptoms are generally absent in both, but allergic conjunctivitis is more likely to have a history of atopy or other allergic conditions.
• Visual acuity is typically unaffected in both conditions, but bacterial conjunctivitis may sometimes cause mild discomfort or photophobia.
• In primary care, the presence of itching and watery discharge strongly suggests allergic conjunctivitis, whereas purulent discharge and eyelid matting point towards bacterial conjunctivitis.

These distinctions are supported by UK clinical guidelines which emphasize symptom pattern and discharge type for diagnosis, and are corroborated by recent literature highlighting the importance of history and clinical signs in differentiating these conditions without immediate need for laboratory tests.

¹: CG183 - Drug allergy: diagnosis and management; (Alfonso et al., 2015); (Mahoney et al., 2023); (Winters et al., 2024)