Differential Diagnosis for Photophobia, Redness, and Tearing in the Left Eye

Single Most Likely Diagnosis

• Acute Conjunctivitis: This is the most likely diagnosis given the symptoms of conjunctival erythema, photophobia, redness, and tearing. The condition is common and can be caused by viral or bacterial infections, which align with the acute onset described.

Other Likely Diagnoses

• Acute Angle-Closure Glaucoma: Although less common, this condition can present with severe eye pain, redness, photophobia, and tearing, along with nausea and vomiting. The pain radiating to the nose could be indicative of this condition due to the involvement of the trigeminal nerve.
• Corneal Abrasion or Ulcer: These conditions can cause significant pain, photophobia, and tearing. The presence of my orbital tenderness could suggest an issue with the cornea, especially if there's a history of trauma or contact lens use.
• Iritis (Anterior Uveitis): This inflammation of the iris can cause eye pain, photophobia, and tearing. It might also present with orbital tenderness and could be a consideration, especially if there's an underlying inflammatory condition.

Do Not Miss Diagnoses

• Endophthalmitis: A severe, vision-threatening infection within the eye that requires immediate treatment. Although it's less likely without a history of recent surgery or trauma, it's crucial to consider due to its potential for severe consequences.
• Orbital Cellulitis: An infection of the tissues surrounding the eye, which can cause pain, redness, swelling, and potentially severe complications if not promptly treated.
• Meningitis: In rare cases, photophobia can be a symptom of meningitis, especially if accompanied by fever, headache, and stiff neck. Although the other symptoms don't perfectly align, meningitis is a condition that must not be missed due to its high mortality rate if untreated.

Rare Diagnoses

• Scleritis: Inflammation of the sclera, which can cause severe eye pain, redness, and photophobia. It's less common than other conditions listed but should be considered, especially if there's an underlying autoimmune condition.
• Keratitis: Inflammation of the cornea, which can be caused by infection or injury. While not as rare as some other conditions, it's less likely than conjunctivitis or acute angle-closure glaucoma but still important to consider, especially with symptoms of photophobia and tearing.