In this interview from AAO 2016, Dr. C. Stephen Foster discusses the rare presentations of red eye. The diseases that are often misdiagnosed are

• herpes simplex virus conjunctivitis
• episcleritis or scleritis
• atopic conjunctivitis mimicking ocular cicatricial pemphigoid
• sebaceous carcinoma mimicking chalazion
• scleritis as first manifestation of systemic vasculitis
• infectious uveitis

To safeguard against misdiagnosis, he recommends the following protocol:

• Take extreme care in history taking, especially review of systems.
• Inspect face, skin, ears, and hands – don't forget to turn the lights on!
• Perform a thorough eye examination.
• Select laboratory tests.
• Biopsy anything that can be biopsied, and plan ahead with pathology.