Arlt's line is seen in-
Vernal keratoconjunctivitis
Pterygium
Ocular pemphigoid
Trachoma
Arlt's line is seen in trachoma due to conjuctival scrarring,which may be irregular,star shaped or linear. this linear scar present in the sulcus subtarsalis is called Al's line Ref ; A K KHURANA Comorehensive Ophtalmology edition 4,page-69 ref img
Conjunctiva