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Corneal Dystrophy, Granular
The corneal opacities in this disorder are usually located in the anterior stroma of the central cornea, and consist of discrete grayish-white, irregular granules with sharp margins. The peripheral cornea and areas between the opacities remain clear. The opacities may be apparent in the first decade but vision remains good throughout childhood. The epithelial surface is usually smooth in children but adults can develop irregularities. As the opacities enlarge and grow in number the cornea becomes increasingly opaque and older patients experience considerable loss of vision. There is some variation in the number of opacities among individuals and considerable clinical heterogeneity occurs both within and between families. The histologic appearance of the corneal deposits are said to be characteristic with eosinophilic deposits in the anterior stroma secondary to accumulations of mutant transforming growth factor beta induced protein.
The number and morphology of the granular deposits change throughout life, influenced to some extent by episodes of recurrent corneal erosions and age of patients. Deposits become more annular and lattice-like in morphology, especially in the third decade and become more discoid by the fifth decade.
It has been reported that the morphology and function of the meibomian glands are altered in this disease as well.
No associated systemic disease has been described.
This is another autosomal dominant corneal dystrophy resulting from mutations in the TGFBI gene (5q31) (others being Reis-Bucklers, Thiel-Behnke, lattice types I and IIIA, epithelial basement membrane disease, and Avellino). These are therefore allelic disorders of the same mutant gene.
Penetrating keratoplasty can be temporarily helpful in restoring vision but recurrence is common. Various forms of laser refractive surgery are probably contraindicated as some patients with initially clear corneas have developed typical granular opacities.