Managing Two Rare Corneal Stromal Dystrophies
By William L. Miller, OD, PHD, FAAO
Treatment strategies are important in managing several corneal dystrophies such as epithelial basement membrane dystrophy and Fuchs' Dystrophy. However, two less frequently encountered corneal dystrophies—central cloudy dystrophy of François (CCDF) and fleck dystrophy— may not require treatment.
Fleck dystrophy is an autosomal dominant entity that involves a mutation in the PIP5K3 gene that controls intracellular lipid production and storage (Aldave and Sonmez, 2007). Gray to white flecks within the corneal stroma represent glycosaminoglycans and lipids within the keratocytes. They may appear as granules, commas, ovals, or circles.
Visual acuity is unaffected in patients who have fleck dystrophy, and rarely do they have any other symptoms. There is one report of reduced corneal sensitivity (Birndorf and Ginsberg, 1972). No treatment is indicated in patients who have fleck dystrophy.
CCDF is another corneal stromal dystrophy that often requires no treatment. As with nearly all corneal dystrophies, it is bilateral and can present in an asymmetric fashion. Its clinical presentation is similar to posterior crocodile shagreen, with the inheritance pattern representing the only differentiating feature. Posterior crocodile shagreen exhibits a sporadic presentation that is age-related compared to the autosomal dominant pattern in CCDF.
Biomicroscopy reveals gray opacities separated by clear lines arranged in a polygonal or mosaic pattern (Figure 1). The opacities are located in the central cornea and are positioned in the posterior corneal stroma, with some extending into the anterior third of the stroma. Although positioned centrally, they rarely affect vision. As with fleck dystrophy, patients have no other symptoms.
Figure 1. Central cloudy dystrophy of François.
The pathophysiology of CCDF is unknown and to date it has not been associated with any particular gene. Transmission electron microscopy and in vivo confocal microscopy have shown fibrogranular vacuoles around and within the keratocytes and a sawtooth-like pattern of collagen lamellae, which might explain the mosaic pattern. Refractile granules not unlike those in long-term contact lens wearers are also present, often referred to as stromal microdots (Kobayashi et al, 2004). In addition, microstriae are also present, which may be a sign of the malpositioning of collagen lamellae.
Confirm Your Diagnosis
It is important to differentially rule out other causes of central corneal clouding that may result in ocular or systemic conditions such as recurrent corneal erosions or kidney, skeletal, and nervous system problems. Other diseases that fall in your differential diagnosis list could include ichthyosis, lecithin cholesterol acetyltransferase deficiency, and systemic mucopolysaccharidosis. A careful review of systems will help you arrive at a diagnosis when any of these entities are suspected. CLS
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|Dr. Miller is an associate professor and chair of the Clinical Sciences Department at the University of Houston College of Optometry. He is a member of the American Academy of Optometry and the AOA where he serves on its Journal Review Board. He is a consultant or advisor to Alcon and Vistakon and has received research funding from Alcon and CooperVision and lecture or authorship honoraria from Alcon and B+L. You can reach him at email@example.com.|