Outline four differential diagnosis of a watering eye?

1. Conjunctivitis: This is the inflammation of the conjunctiva, which is the thin, transparent layer that covers the white part of the eye and the inner surface of the eyelids. Conjunctivitis can cause excessive tearing or watering of the eye, along with redness, itching, and discharge.

2. Blocked tear duct: A blocked tear duct occurs when the tear drainage system is obstructed, preventing tears from draining properly. This can lead to a watery eye, as tears are unable to flow normally. Other symptoms may include recurrent eye infections, discharge, and crusting of the eyelids.

3. Dry eye syndrome: Contrary to its name, dry eye syndrome can also cause excessive tearing. When the eyes are not producing enough tears or the tears evaporate too quickly, the body compensates by producing more tears, resulting in a watery eye. Other symptoms may include a gritty or burning sensation, redness, and blurred vision.

4. Allergies: Allergic reactions to substances such as pollen, dust mites, pet dander, or certain medications can cause the eyes to water excessively. This is often accompanied by itching, redness, swelling, and a runny or stuffy nose. Allergic conjunctivitis is a common cause of watering eyes in individuals with allergies.