Single most likely diagnosis
- Viral conjunctivitis: The symptoms of increasing tearing, itchiness, and discharge over the first 24 hours are consistent with a viral conjunctivitis, which is a common and highly contagious condition.
Other Likely diagnoses
- Allergic conjunctivitis: The itchy and teary eye could also suggest an allergic reaction, especially if the patient has a history of allergies.
- Bacterial conjunctivitis: Although less likely given the gradual onset, bacterial conjunctivitis could still be a consideration, especially if the discharge becomes more purulent.
Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Acute angle-closure glaucoma: Although the pain level is not extremely high, any condition that causes severe eye pain and vision changes should prompt consideration of acute angle-closure glaucoma, which is an emergency.
- Corneal ulcer: A corneal ulcer could present with pain, discharge, and tearing, and if left untreated, could lead to serious complications, including vision loss.
Rare diagnoses
- Ocular herpes simplex: This condition can cause a range of symptoms including pain, discharge, and tearing, but is less common than viral conjunctivitis.
- Episcleritis or scleritis: These are inflammatory conditions of the eye that can cause pain, redness, and discharge, but are less common and might not fit perfectly with the described symptoms.