Differential Diagnosis for Red, Itchy Eye

Given the symptoms of redness, itching, no discharge, no pain, and no swelling in one eye, with recent history of congestion and frequent flying, here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Allergic conjunctivitis: This is likely due to the symptoms of redness and itching without discharge or pain, especially considering the patient has been congested, which could be related to allergies. The recent travel and changes in environment could also expose the patient to new allergens.

• Other Likely Diagnoses

  • Dry eye syndrome: Frequent flying can lead to dry eyes due to the low humidity in airplane cabins. The use of Visine (an over-the-counter eye drop) without relief suggests the condition might not be simply allergic or infectious.
  • Viral conjunctivitis: Although the patient mentions no discharge, early stages of viral conjunctivitis can present with redness and itching before the onset of discharge.
  • Irritant conjunctivitis: Exposure to irritants during travel, such as pollen, dust, or even the air pressure changes during flights, could cause irritation.

• Do Not Miss Diagnoses

  • Acute angle-closure glaucoma: Although the patient reports no severe pain or decreased vision, which are typical symptoms, it's crucial to rule out this condition due to its potential for permanent vision loss if not promptly treated.
  • Corneal ulcer: Especially if the patient has been using contact lenses during travel, a corneal ulcer could present with redness and discomfort, and it requires urgent medical attention.
  • Scleritis or episcleritis: These are inflammatory conditions that can cause redness and discomfort. While less common, they are important to consider due to their potential for complications.

• Rare Diagnoses

  • Phlyctenular keratoconjunctivitis: An allergic type of conjunctivitis that can cause redness and itching, often related to an immune response to antigens like staphylococcal toxins.
  • Conjunctival or corneal foreign body: Although the patient doesn't report any history of trauma, a small foreign body could cause irritation and redness, especially if it's not immediately noticeable.