Definition
Allergies of the eye, like all allergies, are overreactions of the immune system to foreign substances, which might otherwise be harmless. In people without allergies, the immune response that occurs following exposure to an allergen is controlled, and produces few if any symptoms. In people with allergies, activation of the immune response results in the release of inappropriate, high quantities of chemical mediators -- the most common is histamine. These mediators are responsible for the symptoms of allergic reactions. The different types of allergies affecting the eye - atopic (vernal keratoconjunctivitis, atopic keratoconjunctivitis, and hayfever conjunctivitis), medication reactions, toxic papillary reactions, and contact lens-related allergies are covered below.
Different Types of Allergies

Atopic
  • Vernal keratoconjunctivitis: a seasonally recurring conjunctivitis which can also affect the peripheral cornea, generally occurring in children and young adults.
  • Atopic keratoconjunctivitis: a similar entity to vernal keratoconjunctivitis, but occurs mainly in older patients who have had a history of atopic eczematoid dermatitis, is not seasonal, and can cause more extensive corneal and conjunctival scarring if untreated.
  • Hayfever conjunctivitis: a sudden intense response to an (usually) airborne allergen, this type tends to be short-lived and episodic. Also known as "seasonal allergic conjunctivitis."
Adverse or Allergic Reactions to Medications
IgE mediated (anaphylactoid): a sudden, intense reaction which often includes chemosis (conjunctival swelling) and an urticarial response (intense itching). Common offenders include topical penicillin, bacitracin, sulfacetamide, and anesthetics.
Toxic (irritative) papillary reactions: very common and result in a chronic red eye. Can occur anytime after one week of medication use, and are due to some antibiotic and antiviral drops, as well as certain preservatives.
Allergic contact reactions are slower and more gradual in onset than the above two, caused by many topical medications, and easily treated by discontinuing the offending agent.
Contact Lens Related Allergy

Contact allergic conjunctivitis occurs when the contact lenses themselves or the proteins in tear film that bind to the surface of the lens can cause an irritative response of the conjunctiva, resulting in redness, itching, mucous discharge, and lens discomfort. A more severe form, known as giant papillary conjunctivitis, has been recognized, typified by large swellings of the mucous membranes of the upper lid and may result ultimately in the inability to wear lenses. Symptoms
  • Swelling or puffiness of the eyes
  • Redness
  • Itching
  • Tearing
  • Mucous discharge
  • Contact lens discomfort
  • Foreign body sensation
The symptoms described above may not necessarily mean that you have allergies of the eye. However, if you experience one or more of these symptoms, contact your eye doctor for a complete exam.
Treatment
Atopic Allergies
Cool compresses and artificial tears are often helpful; topical vasoconstrictors and antihistamines are useful to counteract the histamine-induced leakiness and dilation of blood vessels. Many of these are now available as over-the-counter preparations. Topical steroids may be used in severe cases. Mast cell stabilizers (cromolyn sodium, lodoxamide) can be used in seasonal cases and are most effective if instituted before or soon after the onset of symptoms. These agents limit the body's sensitivity to an allergen, resulting in less of an immune response.

Medication Allergies
Discontinue the offending agent; topical vasoconstrictors and antihistamines provide relief, and artificial tears may help remove any remaining medication and lubricate the corneal surface if irritated. Contact Lens Allergy
Decreasing lens wear time, insuring proper cleaning of lenses, and perhaps changing the cleaning regimen may improve this condition. In addition, recognition of early symptoms is essential in limiting this problem, e.g., if eight hours of wear feels fine, but then the eyes get red and irritated, it is wise to remove the lenses then, and not to continue to wear them for hours more. If these measures are not helpful or if there is already moderate to severe disease, one may add mast cell stabilizers and a short course of mild steroids to help "put out the fire" and limit the body's response. If still not helpful, consider changing the lens type. A period of weeks to months without any lens wear is often helpful in controlling this entity.