Differential Diagnosis for Left Eye Pain and Discharge

The patient's symptoms of left eye pain, burning, redness, and discharge, along with a history of a similar episode in the right eye that resolved with antibiotic eye drops, suggest an infectious or inflammatory cause. Here is a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Bacterial Conjunctivitis: Given the patient's symptoms of eye pain, burning, redness, and discharge, and a history of a similar episode that resolved with antibiotic eye drops, bacterial conjunctivitis is the most likely diagnosis. The recurrence in the other eye suggests a possible infectious etiology that is responsive to antibiotics.

• Other Likely Diagnoses

  • Viral Conjunctivitis: This could also present with similar symptoms, although it typically does not respond to antibiotics. The history of a similar episode could suggest a viral etiology, but the resolution with antibiotics in the past makes this less likely.
  • Allergic Conjunctivitis: This condition can cause eye redness, itching, and discharge, but it is usually bilateral and associated with other allergic symptoms. The patient's history does not strongly suggest an allergic cause, but it cannot be ruled out without further questioning.
  • Blepharitis: Inflammation of the eyelids can cause eye redness, burning, and discharge. It is a chronic condition and could be a contributing factor to the patient's symptoms.

• Do Not Miss Diagnoses

  • Endophthalmitis: Although less likely given the patient's history and the fact that vision is 20/200 (which, while reduced, does not indicate severe vision loss typically seen in endophthalmitis), this is a serious infection within the eye that requires prompt treatment to prevent vision loss. It is more commonly associated with recent eye surgery or trauma.
  • Acute Angle-Closure Glaucoma: This is an emergency that presents with severe eye pain, redness, decreased vision, and possibly nausea and vomiting. The patient's symptoms do not fully align with this condition, but any suspicion of glaucoma warrants immediate ophthalmologic evaluation.
  • Herpes Simplex Keratitis: This condition can cause eye pain, redness, and discharge, and can lead to serious complications if not treated properly. A history of similar episodes could suggest a recurrent herpes simplex infection.

• Rare Diagnoses

  • Fungal Keratitis: More common in contact lens wearers or after trauma to the cornea, this condition can cause eye pain, redness, and discharge. It is less likely given the patient's presentation but should be considered, especially if there is a history of risk factors.
  • Parasitic Infections: Such as acanthamoebiasis, which can cause keratitis, especially in contact lens wearers. This would be an uncommon diagnosis but should be considered if other causes are ruled out and there is a relevant exposure history.