We report a case of severe ocular injury and impaired vision after self-administration of alum. A 56-year-old female administered an alum substance in the left eye and experienced severe corneal thinning, a scar, and decreased vision. The active compounds in the alum substance were analyzed using scanning electron microscopy. When topically administered, alum may cause severe ocular injury. Public awareness, early recognition of the injuries, and timely intervention may prevent permanent ocular damage.