Allergic Conjunctivitis


  • Common (4-5/1000/year)- mostly contact; then allergic (seasonal)
  • Inflammation of the conjunctiva due to a hypersensitivity reaction after exposure to an allergen.
    • Two main types of hypersensitivity involved
      • Type I (immediate, IgE mediated; associated with atopy; causes release of histamine causing itch, red eye, oedema but rarely corneal inflammation)
      • Type IV (delayed- cell mediated; inflammation of the cornea can occur)
  • Four main types of AC
    • Seasonal (type I- pollens/grasses)
    • Perennial (type I- house dust mites/animal dander)
    • Giant papillary (mixed type I and IV- contact lenses, sutures, prosthetics)
    • Contact (type IV- eye drops, cosmetics, chemicals)


  • Itchy eyes are the predominant feature although there may also be symptoms like foreign body sensation, gritty eyes, blepharospasm etc.
  • Watery discharge may be present.
  • Ask about timing, onset etc (seasonal variation?)
  • Exclude irritant causes (cosmetics, lenses, chlorine, eye drops etc) and infective causes (contact history; purulent/sticky discharge; URTI)
  • On examination
    • The conjunctivae are diffusely injected and can be oedematous (this is known as chemosis).
    • Discharge is usually clear and ‘stringy’.  The fibrous septa that tether the eyelid (tarsal) conjunctivae, in the presence of oedema, causes a classical ‘cobblestone’ appearance.


  • Allergic (seasonal/perennial)
    • Immediate
      • Topical antihistamines and/or vasoconstrictor drops e.g. emedastine/azelastine.
    • Long-term
      • Oral antihistamine (cetirizine, loratedine, fexofenadine)
      • Topical mast cell stabiliser e.g. lodoxamide
  • In other situations, avoid the underlying cause where possible
    • For giant papillary conjunctivitis, topical steroids may be helpful initially where there are severe symptoms

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