Konjungtivitis Alergi

01Pathophysiology

Allergic conjunctivitis is driven by a Type I hypersensitivity reaction. Upon initial exposure to an allergen (pollen, dust mite proteins, animal dander), antigen-presenting cells in the conjunctival mucosa process the allergen and stimulate B cells to produce allergen-directed IgE antibodies. These IgE molecules bind to high-affinity FcεRI receptors on mast cells residing in the conjunctival substantia propria, completing the sensitization phase.

On re-exposure, the allergen cross-links adjacent surface-bound IgE molecules on mast cells, triggering degranulation. This releases preformed mediators, most importantly histamine, along with tryptase, prostaglandins, and leukotrienes. Histamine acts on H1 receptors on sensory nerve endings (producing the intense pruritus that defines this condition), on conjunctival blood vessels (producing vasodilation and the characteristic injection and chemosis), and on goblet cells (stimulating the watery-to-mucoid discharge).

The early phase reaction occurs within minutes and is predominantly histamine-driven. A late phase reaction follows 4 to 24 hours later, mediated by recruited eosinophils, basophils, and T-helper type 2 (Th2) lymphocytes releasing cytokines such as IL-4, IL-5, and IL-13. This late phase is responsible for prolonged inflammation and, in chronic forms, structural remodeling of the conjunctiva (giant papillae formation). The reason these patients almost always have bilateral involvement is that airborne allergens contact both eyes simultaneously, unlike infectious causes which often begin unilaterally.

02Classification and Clinical Manifestation

The distinction between the simple forms (SAC/PAC) and the severe forms (VKC/AKC) is high-yield. SAC and PAC are self-limited nuisances, while VKC and AKC carry the risk of corneal complications and permanent vision loss, changing the management approach entirely.

03Diagnostic Workup

Allergic conjunctivitis is overwhelmingly a clinical diagnosis. The combination of bilateral pruritus, watery or stringy discharge, and a personal or family history of atopy is usually sufficient. Vignettes will often embed seasonal variation or known triggers to reinforce this.

When the presentation is ambiguous or severe, conjunctival scraping is the next step. Finding eosinophils confirms an allergic etiology and effectively excludes bacterial (neutrophil-predominant) and viral (lymphocyte-predominant) conjunctivitis. This is a commonly tested discriminator.

Skin prick testing or serum-based allergen panels are not used to diagnose conjunctivitis itself but rather to identify the offending allergen for avoidance counseling or immunotherapy planning. In the context of VKC or AKC, a slit-lamp exam with fluorescein staining becomes mandatory to detect corneal complications such as shield ulcers or neovascularization, which alter management urgency.

04Management and Treatment

Acute stabilization centers on removing the allergen and providing symptomatic relief. Cold compresses and artificial tears provide immediate comfort by diluting allergens in the tear film and physically reducing edema. Pharmacologically, the dual-action topical agents (olopatadine, ketotifen) are first-line because they simultaneously block H1 receptors (immediate relief) and stabilize mast cells (prevent further degranulation). Pure mast cell stabilizers like cromolyn sodium take 1 to 2 weeks to reach full efficacy, making them better suited for prophylactic use before allergy season rather than acute symptom control.

Topical corticosteroids should be reserved for moderate-to-severe flares unresponsive to first-line therapy and must always be prescribed in short, tapering courses under ophthalmologic supervision. The key contraindication to remember is that prolonged topical steroid use causes steroid-induced glaucoma (open-angle, from increased aqueous outflow resistance in the trabecular meshwork) and posterior subcapsular cataracts. This is a frequent test point.

For chronic severe disease (VKC, AKC), topical calcineurin inhibitors (cyclosporine, tacrolimus) serve as steroid-sparing agents. They suppress Th2 lymphocyte activation and reduce eosinophilic infiltration without the intraocular pressure and cataract risks of corticosteroids. An important clinical pearl: topical steroids should never be applied to eyelid skin in AKC because periocular skin is extremely thin and susceptible to atrophy and glaucoma from dermal absorption. Instead, tacrolimus ointment is used for lid eczema.

05Differential Diagnosis and Distractors

The single most reliable discriminator in any conjunctivitis vignette is the quality of the primary symptom. Allergic conjunctivitis presents with itching as the dominant complaint. Bacterial conjunctivitis leads with purulent discharge. Viral conjunctivitis presents with watery discharge and irritation but not true pruritus. Anterior uveitis and angle-closure glaucoma present with pain and photophobia, not itching. If the stem says "itchy eyes," think allergic until proven otherwise.

06Traps and High-Yield Pearls

The most common way students miss questions on allergic conjunctivitis is by confusing discharge types and failing to anchor on the chief complaint. The vignette will describe a patient with bilateral red eyes, and the student must immediately classify the discharge (watery/stringy versus purulent) and the primary symptom (itching versus burning versus pain). Picking bacterial conjunctivitis for a patient whose chief complaint is itching with watery discharge and a history of seasonal allergies is a classic error.

A second trap involves VKC and AKC being mistaken for simple SAC. If the vignette describes a young boy in a warm climate with giant cobblestone papillae, ropy discharge, and corneal findings, this is VKC, not seasonal allergies. The management escalates to topical steroids and calcineurin inhibitors, and the question may test whether you recognize the risk of corneal scarring.

Third, students sometimes choose topical corticosteroids as first-line therapy. Topical steroids are never first-line for routine allergic conjunctivitis. The correct first-line answer is a dual-action topical antihistamine/mast cell stabilizer. The question may then test knowledge of steroid complications (glaucoma, cataracts, superinfection) as reasons for this sequencing.

Finally, remember the cytology pearl: eosinophils on conjunctival scraping confirm allergic etiology. Neutrophils point to bacterial, lymphocytes to viral, and basophils with granular debris to atopic or vernal keratoconjunctivitis. This cell-type correlation is a reliable way the exam tests whether you understand the underlying immunology.

The core competency being assessed is pattern recognition of allergic eye disease within the broader "red eye" differential, correct sequencing of therapy (avoidance and topical antihistamine/mast cell stabilizer before steroids), and recognition of sight-threatening complications in the chronic severe subtypes.