Although the diagnosis may be difficult when a patient first presents with Mooren's ulceration, the clinical appearances are characteristic and should not be confused with other conditions which cause corneal ulceration. Based on the clinical presentation and the low-dose anterior segment fluorescein angiographic findings, there seem to be three distinct varieties of Mooren's ulceration: (1) Unilateral Mooren's ulceration (UM), characterised by an excessively painful progressive corneal ulceration in one eye in elderly patients, associated with non-perfusion of the superficial vascular plexus of the anterior segment. (2) Bilateral aggressive Mooren's ulceration (BAM), which occurs in young patients, progresses circumferentially and, only later, centrally in the cornea. Angiography shows vascular leakage and new vessel formation which extends into the base of the ulcer. (3) Bilateral indolent Mooren's ulceration (BIM), which usually occurs in middle-aged patients presenting with progressive peripheral corneal guttering in both eyes, with little inflammatory response. There is no change from the normal vascular architecture on angiography except an extension of new vessels into the ulcer. The management differs in each of these varieties.