A Pair of Anterior Corneal Dystrophies
BY WILLIAM L. MILLER, OD, PHD, FAAO
We will continue our series on corneal dystrophies by addressing the less commonly encountered Reis Buckler's (RB) and Thiel-Behnke (T-B) anterior corneal dystrophies. They are sometimes referred to as CDB (Corneal Dystrophy of Bowman's) I and CDB II, respectively, and are part of a group of dystrophies known as transforming growth factor, beta-induced corneal dystrophies.
Both dystrophies affect the anterior limiting lamina (Bowman's membrane) and, similar to anterior basement membrane dystrophy (ABMD), can cause recurrent corneal erosions (RCEs).
Making the Diagnosis
These two dystrophies are often confused and clinically are virtually impossible to distinguish from each other; however, biomicroscopy may show bilateral subepithelial opacities, with RB having generally rod-like granules while T-B demonstrates honey-comb-like opacities typically in the central and midperipheral cornea. Microscopically they both exhibit missing areas of anterior limiting lamina, subepithelial fibrocellular tissue and aberrant collagen fibers. They are definitively distinguishable from each other using light and electron microscopy. Recently, in vivo confocal microscopy has been used to differentiate between the two dystrophies with each showing qualitative reflectivity differences (Kobayashi and Sugiyama, 2007).
Each dystrophy is autosomal dominant and causes corneal opacities; both RB and T-B have been mapped to Chromosome 5q31. It's believed that RB is actually an anterior variant of granular stromal dystrophy.
Patients who have RB and T-B may complain of distorted vision, photophobia, tearing and perhaps eyelid edema. Symptoms as well as the corneal opacification are typically not as severe in cases of T-B. RCEs with RB occur in the first and second decade with moderate to severe vision loss. A similar timeframe exists for RCEs occurring with T-B, except the visual loss typically happens later than what occurs in RB.
As with ABMD, your first treatment goal is to prevent RCEs by providing lubrication to the ocular surface. A slightly more viscous solution for daytime use can help along with an ointment or gel for nighttime use, both of which should preferably be preservative-free. Some of the more commonly used daytime tear supplements would include Systane PF (Alcon), GenTeal Mild (Novartis Ophthalmics), Thera Tears Liquid Gel (Advanced Vision Research), Bion Tears (Alcon) and OcuCoat PF (Bausch & Lomb) whereas patients can use GenTeal and Refresh PM (Allergan) atbedtime. Some practitioners also favor a hyperosmotic agent not only in post-RCE management, but also as a prophylactic agent.
A bandage contact lens may help prevent RCEs when used with suitable rewetting drops to prevent lens desiccation and promote movement with the blink. In cases when irregular astigmatism accompanies the dystrophy, a large intralimbal or mini-scleral GP lens would correct the astigmatism and provide a post-lens tear film reservoir to hydrate the surface and minimize RCEs.
As with ABMD, in severe cases corneal surgery such as anterior lamellar keratoplasty or PTK can remove the dystrophic cornea and create a new corneal surface. PTK has also been coupled with Mitomycin C post-operatively to prevent RCEs (Miller et al, 2006). Recurrences appear to happen earlier and are more severe in RB cases. CLS
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Dr. Miller is the Director, Cornea and Contact Lens Service at the University of Houston College of Optometry. He is a member of the American Optometric Association and serves on its Journal Review Board. You can reach him at firstname.lastname@example.org.