| Macular corneal dystrophy |
Macular corneal dystrophy, also known as Fehr corneal dystrophy, is a rare pathological condition affecting the stroma of cornea first described by Arthur Groenouw in 1890.[1] Signs are usually noticed in the first decade of life and progress afterwards, with opacities developing in the cornea and attacks of pain. This gradual opacification leads to visual impairment often requiring keratoplasty in the later decades of life.[2]
While Macular Corneal Dystrophy is found throughout the world, countries with the highest prevalence include Iceland, Saudi Arabia, India, and the United States.[3] [4] [5] In Iceland, MCD accounts for almost one-third of all corneal grafts performed. Estimates from Claims Data in the United States place the prevalence of MCD at 9.7 per million, which represents less than 1% of corneal dystrophies.[6]
Macular Corneal Dystrophy is an autosomal recessive genetic disorder caused by mutations in the carbohydrate sulfotransferase gene (CHST6), resulting in abnormal proteoglycan synthesis. The accumulation of abnormal glycosaminogycans in the corneal epithelium and stroma leads to progressive opacification of the cornea and subsequent loss of visual acuity.[7] [8] There are three variants of MCD characterized by immunophenotype:
These three variants are clinically and histopathologically indistinguishable.
The first signs of MCD are cloudy regions that appear on the cornea during adolescence, although opacification may be noticed as early as the first decade. These minute, gray, punctate opacities will over time merge into larger areas, causing the entire corneal stroma to become opaque. Ultimately this results in severe visual impairment, generally before the 5th decade of life.
While some individuals remain asymptomatic, initial symptoms typically consist of painful attacks with photophobia, foreign body sensations, and recurrent erosions. Corneal sensitivity is also reduced.
Histopathological staining shows characteristic alcian blue-positive deposits. Various imaging modalities, including confocal microscopy and ocular coherence tomography, can provide information about the changes within the cornea and may be suitable replacements for tissue biopsy and excision.
When visual acuity is impacted, various forms of keratoplasty are often indicated. While corneal transplant
Various gene therapies, including enzyme replacement therapy and gene-targeting therapy, remain a potential future treatment modality for MCD.