Macular corneal dystrophy: A review

Macular corneal dystrophy is a corneal stromal dystrophy which leads to progressive vision loss. Macular corneal dystrophy is an autosomal recessive condition in which there is abnormality of proteoglycan synthesis. Mutations in the carbohydrate sulfotransferase gene prevent normal sulfation of corneal keratan. Different immunophenotypes have been described depending on the presence of keratan sulfate in cornea and/or serum. The deposition of abnormal proteoglycans leads to loss of corneal transparency and decreased vision. Imaging techniques such as in vivo confocal microscopy and anterior segment ocular coherence tomography have helped enhance our understanding of the corneal ultrastructural changes in this condition. These imaging modalities provide additional information without the need for a tissue biopsy or excision. Traditionally, full-thickness penetrating keratoplasty to replace the opacified cornea has remained the standard of treatment to improve vision. However, newer surgical interventions such as deep anterior lamellar keratoplasty and phototherapeutic keratectomy have also been shown to play a role in the treatment. Disease recurrence remains a challenge and the reason for poor visual prognosis. Newer techniques such as gene-targeting therapies and enzyme replacement therapies are being studied for a potential permanent solution in macular corneal dystrophy. Recent research is directed toward development of genetically modified products to integrate into host corneal DNA and block the mutant genes and hence overcome the underlying pathophysiology. Enzyme replacement therapy is another intervention with potential to treat macular corneal dystrophy. Animal studies show clearance of accumulated keratan sulfate from the body tissues in the treatment of systemic mucopolysaccharidosis by long-term enzyme replacement therapy. Future research should be directed toward elucidation of the relationship between the mutated carbohydrate sulfotransferase gene, the mechanism of deposit formation, and the development of pharmaceutical agents based on gene therapy.