The ocular surface may exhibit a wide variety of immunologic responses resulting in inflammation of the conjunctiva and cornea. In the Gell and Coombs classification system for various immunologic hypersensitivity reactions, 5 types of reactions are recognized. The major type I hypersensitivity reactions involving the conjunctiva are commonly referred to as allergic conjunctivitis.
Diagnosis of allergic conjunctivitis is generally made by thorough history and careful clinical observation (see Clinical). The presence of an antigen starts the allergic cascade, and, thus, avoidance of the offending antigen is the primary behavioral modification for all types of allergic conjunctivitis. In other respects, management of allergic conjunctivitis varies somewhat according to the specific subtype. Allergic conjunctivitis can be treated with a variety of drugs, including topical antihistamines, mast cell stabilizers, nonsteroidal anti-inflammatory drugs, and corticosteroids (see Treatment).
See the following for more information:
- Acute Hemorrhagic Conjunctivitis
- Atopic Keratoconjunctivitis
- Bacterial Conjunctivitis
- Emergent Treatment of Acute Conjunctivitis
- Epidemic Keratoconjunctivitis
- Giant Papillary Conjunctivitis
- Keratoconjunctivitis Sicca
- Neonatal Conjunctivitis
- Superior Limbic Keratoconjunctivitis
- Viral Conjunctivitis
Immunologic reactions of conjunctiva and cornea
Type I (immediate) hypersensitivity reactions occur when a sensitized individual comes in contact with a specific antigen. Immunoglobulin E (IgE) has a strong affinity for mast cells, and the cross-linking of 2 adjacent IgE molecules by the antigen triggers mast cell degranulation.
The mast cell’s degranulation releases various preformed and newly formed mediators of the inflammatory cascade. Most notable of these inflammatory mediators are histamine, tryptase, chymase, heparin, chondroitin sulfate, prostaglandins, thromboxanes, and leukotrienes. These various inflammatory mediators, together with various chemotactic factors, result in an increase in vascular permeability and migration of eosinophils and neutrophils. This type I hypersensitivity reaction is the most common allergic response of the eye. These immune-derived reactions may be the underlying cause of various ocular conditions, such as cicatricial pemphigoid and Mooren ulcer.
Type III hypersensitivity reactions result in antigen-antibody immune complexes, which deposit in tissues and cause inflammation. A classic systemic type III reaction is the Arthus reaction, and ocular type III hypersensitivity reactions include Stevens-Johnson syndrome and marginal infiltrates of the cornea. These type III reactions can often induce a corneal immune (Wesley) ring that dissolves when the inflammatory reaction subsides.
Type IV hypersensitivity reactions, also known as cell-mediated immunity, are interceded by T lymphocytes. This inflammatory cell-driven reaction is also referred to as delayed-type hypersensitivity, since its onset is generally after 48 hours, in contrast to the type I reaction, which is an immediate hypersensitivity.
Type IV hypersensitivity reactions imply immunocompetence on the part of the individual since an intact immune system is required to mount the cell-mediated response. Ocular examples of type IV hypersensitivity include phlyctenular keratoconjunctivitis, corneal allograft rejection, contact dermatitis, and drug allergies.
Allergic conjunctivitis subtypes
Allergic conjunctivitis may be divided into 5 major subcategories.
Seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC) are commonly grouped together.
Early diagnosis and treatment will help prevent the rare complications that can occur with this disease.
Since allergic conjunctivitis generally clears up readily, the prognosis is favorable. Complications are very rare, with corneal ulcers or keratoconus occurring rarely. Although allergic conjunctivitis may commonly reoccur, it rarely causes any visual loss.
Patients should make every attempt to identify the allergen causing the problem and to avoid the offending antigen. For patient education information, see the Eye and Vision Center, as well as Pinkeye, Eye Allergies, and How to Instill Your Eyedrops.