What is allergic conjunctivitis?

Allergic Conjunctivitis: Definition and Introduction

Allergic conjunctivitis (AC) is an inflammatory disease of the conjunctiva primarily caused by an IgE-mediated mechanism, representing the most common form of ocular allergy. 1 Despite being considered the most benign form of conjunctivitis, it significantly impacts patients' quality of life, reduces work productivity, and increases healthcare costs.

Classification of Allergic Conjunctivitis

Allergic conjunctivitis can be categorized into several distinct clinical entities:

Acute Forms:

• Seasonal Allergic Conjunctivitis (SAC): The most common ocular allergy, representing the ocular component of hay fever 2
• Perennial Allergic Conjunctivitis (PAC): Often caused by house dust mites, with symptoms present year-round 2, 3
• Acute Allergic Conjunctivitis (AAC): Occurs when a large quantity of allergen inoculates the eye, usually self-limiting 2

Chronic Forms:

• Vernal Keratoconjunctivitis (VKC): Affects primarily boys under 10 years of age, potentially sight-threatening due to corneal involvement 2
• Atopic Keratoconjunctivitis (AKC): Occurs in atopic adults, can affect the cornea 2
• Giant Papillary Conjunctivitis (GPC): Results from repeated contact with foreign surfaces, such as contact lenses 2

Pathophysiology

The pathogenesis of allergic conjunctivitis involves:

• Acute phase: Primarily mast cell-driven inflammation resulting in:

  • Itching
  • Tearing
  • Lid and conjunctival edema and redness
  • Photophobia 4

• Late-phase response: Occurs in a subset of individuals with:

  • Eosinophilia
  • Neutrophilia 4

• Chronic disease: Can develop with remodeling of ocular surface tissues in severe cases 4

The immunological mechanism centers around IgE-mediated mast cell degranulation and release of multiple preformed and newly formed inflammatory mediators 5.

Clinical Presentation

The primary symptoms of allergic conjunctivitis include:

• Itching (cardinal symptom)
• Redness of the mucosa
• Swelling of the eyelids
• Tearing 3

In SAC and PAC, which are the most common forms, the allergic response is mediated predominantly by mast cells. The more severe conditions (VKC, AKC, and GPC) are associated with a preponderance of T cells 2.

Diagnosis

Diagnosis of allergic conjunctivitis is typically clinical, based on:

• Thorough history
• Careful examination
• Confirmation through:
  • Skin-prick tests
  • Presence of eosinophils in conjunctival smear
  • Elevated tear or serum total IgE 2, 3

Clinical Significance

Despite being considered benign, allergic conjunctivitis has significant impacts:

• Considerable effect on quality of life
• Reduced work productivity
• Increased healthcare costs 1

In severe cases, particularly with VKC and AKC, patients may experience extreme discomfort and sustain damage to the ocular surface, potentially threatening vision 4.

Common Pitfalls in Diagnosis

• Mistaking non-allergic irritation for allergic conjunctivitis
• Failing to recognize that astigmatism, heterophoria, and photosensitization may trigger symptoms of allergic conjunctivitis in atopic patients 3
• Overlooking the possibility of unilateral forms of chronic allergic conjunctivitis 3
• Not considering the frequent association of allergic conjunctivitis with other forms of chronic conjunctivitis 3