Allergic Conjunctivitis

Background

• 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)

History

• 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.

Management

• 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