Peripheral crescentic ulceration with an epithelial defect, thinning and stromal infiltration at the limbus (Fig. 3.1). It begins as a crescent-shaped gray-white infiltrate in the peripheral cornea later followed by epithelial defect and stromal thinning. The ulcer typically involves the superficial one-third of the stroma initially. The ulcer is concentric to the limbus; the leading edges are undermined, infiltrated, and de-epithelialized. The spread is circumferential and occasionally central with variable epithelial loss and stromal thinning. As it progresses, it creates an overhanging edge at its central border. An undermined and infiltrated leading edge is characteristic. Probing of this edge may reveal a greater degree of stromal destruction in contrast to what it appears clinically [1–3]. In the severe cases stromal thinning may progress to corneal perforation. The perforated area is often plugged by the iris (Fig. 3.2) sealing the gap.

Several distinct foci may be present and subsequently coalesce.

Limbitis may be present.

Scleritis, when present aids in distinguishing from systemic disease-associated PUK.

Vascularization involving the bed of the ulcer up to its leading edge but not beyond.

As the disease progresses, behind the advancing edge of the ulcer, healing may take place. The healing stage is characterized by thinning, vascularization, and scarring (Fig. 3.1). The healed area remains clouded.

In an advanced case of Mooren’s ulcer most of the cornea is lost, leaving behind a central island surrounded by area of grossly thinned, scarred, and vascularized tissue.

Iritis and anterior chamber cells, flares are not uncommon.

The adjacent conjunctiva and sclera are usually inflamed and hyperemic.

PUK associated with systemic autoimmune disease presents with certain specific features that are often helpful in differentiating from Mooren’s ulcer [3–5].