This is an important differential diagnosis to make. Viral conjunctivitis is highly contagious so a patient with this condition needs to be advised of this in order to protect other family members and acquaintances. Also, a practitioner examining a patient with viral conjunctivitis needs to take precautions in order not to become infected themselves or spread the infection to other patients.

Typical signs and symptoms of allergic conjunctivitis (see figure) include:

• Redness in both eyes.
• Itching and burning of both the eye and surrounding tissues.
• Watery discharge, often accompanied by acute discomfort in bright sunlight light (photophobia).
• The conjunctiva itself may become very swollen and look light purple, and this may interfere with clarity of vision.
• Eyelids may be affected by an allergic reaction, causing the lids to become swollen with drooping of the eyelid.

Typical signs and symptoms of viral conjunctivitis (see figure) include:

• Redness in one eye quickly spreading to the other.
• Watery discharge.
• Ocular irritation.
• Symptoms and signs usually begin in one eye and spread rapidly to the other.
• Follicles may be present on the palpebral conjunctiva.
• A preauricular lymph node is often enlarged and painful.
• In severe cases photophobia and foreign body sensation.

It is important to note that blurred vision or corneal haze requires urgent referral to an ophthalmologist for both conditions.

The key difference is the itch in allergic conjunctivitis.