Macular corneal dystrophy (MCD), an IC3D category 1 dystrophy, is an autosomal-recessive condition. It is the least common of the 3 major stromal corneal dystrophies but the most severe. It is characterized by multiple irregular gray-white opacities in the corneal stroma that extend out into the peripheral cornea.
Unlike granular corneal dystrophy, there are no clear areas between opacities.  Opacities usually first appear in adolescence but may become apparent anytime from early infancy to the sixth decade of life. Affected individuals usually experience severe visual impairment before the fifth decade of life once opacities have coalesced and the entire stroma becomes cloudy.  Examples of macular dystrophy are shown in the images below.
The cornea is the clear outer coat of the front of the eye. A dystrophy of the cornea is defined as a bilateral noninflammatory clouding of the cornea. Corneal dystrophies can be placed into 3 categories based on their location within the cornea: (1) Anterior corneal dystrophies affect the corneal epithelium and may involve the Bowman layer, (2) stromal corneal dystrophies affect the central layer of the cornea (the stroma), and (3) posterior corneal dystrophies involve the Descemet membrane and the endothelium.  Macular corneal dystrophy is a stromal corneal dystrophy, but, in advanced disease, corneal endothelium and the Descemet membrane may be affected. 
The age of onset for most corneal dystrophies is less than 20 years (exceptions include map-dot-fingerprint dystrophy and Fuchs corneal dystrophy). Most corneal dystrophies are inherited in a dominant pattern. Exceptions include macular corneal dystrophy, type 3 lattice dystrophy, and the autosomal-recessive form of congenital hereditary endothelial dystrophy.
Subgroups of macular dystrophy can be identified by immunohistochemical methods. Keratan sulfate was not detected in the serum of patients with histopathologically confirmed macular corneal dystrophy. Because keratan sulfate in the serum appears to be predominantly derived from the normal turnover of cartilage,  these studies strongly suggest that the defect in keratan sulfate synthesis in macular corneal dystrophy is not restricted to corneal cells and that this condition is one manifestation of a systemic disorder of keratan sulfate.
Macular corneal dystrophy is uncommon, but areas with the highest prevalence include parts of the United States.
Although relatively uncommon, macular corneal dystrophy is most prevalent in India, Saudi Arabia, Iceland, and parts of the United States. 
Corneal changes become visible in the first decade of life. A significant reduction in vision usually occurs by age 20-40 years. Eye pain from recurrent corneal erosions can occur but is much less common than in patients with lattice or granular corneal dystrophies.
No sexual predilection has been reported.
Corneal changes become visible in the first decade of life; vision may be significantly reduced by age 20-40 years.
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