PATHOGENESIS

By definition, Mooren ulcer is of unknown cause. PUK due to known local (eg, rosacea) or systemic (eg, rheumatoid arthritis) diseases should not be called Mooren ulcer. Evidence is mounting that autoimmunity plays a key role in the pathogenesis of Mooren ulcer, as the following have been found in patients with this condition:

• abnormal function of T-suppressor cells

• increased level of IgA

• increased concentration of plasma cells and lymphocytes in the conjunctiva adjacent to the ulcerated areas

• increased CD4⁺-to-CD8⁺ and B7-2⁺-to-APC ratios as well as increased vascular cell adhesion molecule 1, very late antigen 4, and intercellular adhesion molecule 1 in the vascular endothelium of conjunctival vessels

• tissue-fixed immunoglobulins and complement in the conjunctival epithelium and peripheral cornea

A significant number of resident cells in Mooren ulcer specimens express MHC class II antigens, a reflection of the degree of immune-mediated inflammation in the tissue. It has been suggested that autoreactivity to a cornea-specific antigen may play a role in the pathogenesis of this disorder, and humoral and cell-mediated immune mechanisms may be involved in the initiation and perpetuation of corneal destruction. The proximity of the ulcerative lesion to the limbus probably has pathophysiologic importance (as discussed earlier, in the section on PUK), because resection or recession of the limbal conjunctiva can often have a beneficial therapeutic effect.

Although the cause of Mooren ulcer is unknown, precipitating factors include accidental trauma, surgery, or exposure to parasitic infection. The latter is of considerable importance, as the incidence of Mooren ulcer is particularly high in areas where parasitic (eg, helminthic) infections are endemic. The principal hypotheses are that inflammation associated with previous injury or infection may alter the expression of corneal or conjunctival antigens (to which autoantibodies are then produced) or that cross-reactivity occurs between the immune effectors generated in response to infection and corneal autoantigens. The simultaneous presence of multiple types of inflammatory cells, adhesion molecules, and costimulatory molecules in Mooren ulcer conjunctiva suggests that their interaction may contribute to a sustained immune activation as at least part of the pathogenic mechanism of this disorder.

Kafkala C, Choi J, Zafirakis P, et al. Mooren ulcer: an immunopathologic study. Cornea. 2006; 25(6):667–673.

CLINICAL PRESENTATION

Mooren ulcer is a chronic, painful, progressive ulceration of the peripheral corneal stroma and epithelium. Typically, the ulcer starts in the periphery of the cornea and spreads circumferentially and then centripetally, with a leading undermined edge of deepithelialized tissue (Fig 11-18). Slower ulceration proceeds toward the sclera. The eye is inflamed and pain can be intense, with photophobia and tearing. Perforation may occur with minor trauma or during secondary infection. Extensive vascularization and fibrosis of the cornea may occur.

In some patients, it may be very difficult to differentiate Mooren ulcer from idiopathic PUK. An important distinguishing feature is the purely corneal involvement of Mooren ulcer; in PUK, the sclera is often involved.

Figure 11-18 Mooren ulcer.

(Courtesy of Vincent P. deLuise, MD.)

Two clinical types of Mooren ulcer have been described. Unilateral Mooren ulcer typically occurs in an older patient population. Sex distribution is equal in this form, which is slowly progressive. A second type of Mooren ulcer is more common in Africa. This form is usually bilateral, rapidly progressive, and poorly responsive to medical or surgical intervention. Corneal ulceration (Fig 11-19) and perforation are frequent. Many patients with this form of Mooren ulcer also have coexisting parasitemia. It is possible that in this subgroup of West African males, Mooren ulcer may be triggered by antigen–antibody reaction to helminthic toxins or antigens deposited in the limbal cornea during the blood-borne phase of parasitic infection. Hepatitis C should be considered in patients who present with Mooren ulcer–like findings.

MANAGEMENT

The multitude of therapeutic strategies used against Mooren ulcer under-scores the relative lack of effective treatment. Topical corticosteroids (including difluprednate), contact lenses, acetylcysteine 10% and L-cysteine (0.2 molar), topical cyclosporine, limbal conjunctival excision, and lamellar keratoplasty have all reportedly been used with variable success. Topical interferon-α2a (IFN-α2a) and topical cyclosporine 2%, as well as infliximab, have been reported as effective alternatives. Systemic immunosuppressive treatment of Mooren ulcer with agents such as oral corticosteroids, cyclophosphamide, methotrexate, cyclosporine, and TNF-α inhibitors has been described. Hepatitis C–associated cases of Mooren ulcer–type PUK have responded to interferon therapy.

Figure 11-19 Mooren ulcer with severe limbal ulceration and thinning.

Alhassan MB, Rabiu M, Agbabiaka IO. Interventions for Mooren’s ulcer. Cochrane Database Syst Rev. 2014;(1):CD006131.

Cordero-Coma M, Benito MF, Fuertes CL, Antolín SC, García Ruíz JM. Adalimumab for Mooren’s ulcer. Ophthalmology. 2009;116(8):1589, 1589.e1.

Garg P, Reddy JC, Sangwan VS. Mooren ulcer. In: Mannis MJ, Holland EJ, eds. Cornea. Vol 1. 4th ed. Philadelphia: Elsevier; 2017:1082–1087.

Wilson SE, Lee WM, Murakami C, Weng J, Moninger GA. Mooren-type hepatitis C virus-associated corneal ulceration. Ophthalmology. 1994;101(4):736–745.

Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.