Seasonal allergic conjunctivitis differs from vernal keratoconjunctivitis in its immunopathological mechanism in that SAC involves primarily which type of hypersensitivity without a T-cell late-phase component?

• A Type I immediate hypersensitivity with IgE-mast cell degranulation as the sole mechanism ✓
• B Type IV (delayed-type hypersensitivity mediated by sensitized Th1 cells)
• C Type II cytotoxic hypersensitivity targeting conjunctival epithelium
• D Type III immune complex deposition in conjunctival vessels

Explanation

Seasonal allergic conjunctivitis (SAC) and perennial allergic conjunctivitis (PAC) are pure Type I immediate hypersensitivity reactions — allergen crosslinks IgE on mast cells causing rapid histamine and prostaglandin release. The clinical features (itching, chemosis, watery discharge) occur within minutes. Vernal keratoconjunctivitis additionally involves a late-phase reaction with eosinophil and T-cell infiltration (Type IV mechanisms), producing giant papillae, limbal Horner-Trantas dots, and corneal complications. This mechanistic difference explains why topical antihistamines alone control SAC but VKC requires mast cell stabilizers and steroids.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.