Managing Anterior Basement Membrane Dystrophy
BY WILLIAM L. MILLER, OD, PHD, FAAO
Anterior basement membrane dystrophy (ABMD, aka epithelial basement dystrophy, map-dot-fingerprint dystrophy and Cogan's microcystic dystrophy) is the most common corneal dystrophy with a prevalence that ranges between 2 percent and 43 percent. The map form appears to be the most commonly observed pattern (Figure 1).
Histological analysis reveals a thickened epithelial basement membrane that produces finger-like projections into the epithelial cell layer. The aberrant basement membrane interferes with normal cellular attachments such as hemidesmosomes and anchoring collagen plaques, ultimately leading to recurrent corneal erosions (RCEs) in some patients.
Although no direct genetic link has been found, heredity does occasionally play an autosomal dominant part with incomplete penetrance in its effect.
Many patients with ABMD are asymptomatic, but when symptoms do occur they manifest as dry eye (burning and grittiness) complaints, progressing to variable vision and/or ghosting. Later, pain may occur in up to 10 percent of patients, usually in the morning as a result of an RCE.
Early stages of ABMD may be difficult to detect; a carefully performed biomicroscopic exam with a heavy reliance on retroillumination through a dilated pupil may provide clues. In addition, look for subtle negative staining after instilling fluorescein. Keratometry and corneal topography can also demonstrate irregular astigmatism due to the disruption of epithelial surface integrity.
Figure 1. The map-like form of ABMD.
Most treatment options are directed at preventing an RCE. Ocular lubrication, especially at night, can be beneficial for patients who are prone to RCEs to minimize the mechanical effects of the lids against the corneal epithelium. A classic osmotic agent (Muro 128, Bausch & Lomb) or more recent oncotic agents such as Freshkote (Focus Laboratories) or Dwelle and Dakrina (The Dry Eye Company) may help the corneal epithelium lay down firm epithelial attachments to circumvent RCE formation.
Other forms of therapy may include soft or GP lenses to either protect the ocular surface or, in the latter case, to minimize irregular astigmatic effects and to subjectively improve vision. Anterior stromal puncture using a needle has also been promoted to create tiny areas of adhesive scars. This procedure works better in peripherally placed areas of the dystrophy. PTK can help create a new anterior surface and aid in epithelial attachment.
LASIK and LASEK are generally contraindicated because the procedures may result in epithelial sloughing or epithelial in-growth in those patients. In fact, at least one study (Perez-Santonja 2005) indicated that epithelial sloughing at the time of LASIK may be a provocative sign that the patient had undiagnosed ABMD.
Other non-surgical procedures that have been advocated include superficial debridement followed by polishing of the anterior limiting lamina with a diamond-dusted burr. Sridhar et al (2003) have shown that this is at least as effective as PTK. CLS
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Dr. Miller is the Chair of the Clinical Sciences Department at the University Of Houston College Of Optometry. You can reach him at firstname.lastname@example.org