Step 1: Vernal keratoconjunctivitis (spring catarrh) is a recurrent, bilateral, allergic (type I and type IV) inflammation of the conjunctiva seen mainly in young males in warm, dry climates.
Step 2: A shield ulcer is a characteristic corneal feature: a shallow, oval, sterile epithelial ulcer in the upper part of the cornea caused by toxic mediators from the inflamed conjunctiva. So option a is a true feature.
Step 3: Horner-Trantas spots are small, white, gelatinous, raised dots made of degenerated eosinophils and epithelial debris found at the limbus, again typical of vernal disease. So option b is true.
Step 4: The palpebral form shows large, flat-topped cobblestone papillae, that is papillary hypertrophy of the upper tarsal conjunctiva, so option c is true as well. Since all three are recognized features, the correct answer is All of the above.