Macular corneal dystrophy is a progressive, bilateral disorder with increasing corneal cloudiness throughout life. The onset of corneal haze is variable. It can be seen in infancy but usually becomes apparent in the second or later decades of life. Visual impairment can be severe, especially by mid-life. The stroma, Descemet membrane, and endothelium are involved as keratocytes and endothelial cells accumulate intracytoplasmic vacuoles of glycosaminoglycans. Corneal thickness is reduced, presumably due to abnormally dense packing of collagen fibrils in the stroma. The epithelium does not seem to be involved.
Based on immunohistochemical profiles of inclusions, as well as phenotypic differences, attempts have been made to distinguish at least three types of macular dystrophy, I, IA, and II. This may not be justified as the same gene is involved, and especially since several types have been described within the same inbred family. Most likely these are variations in the phenotypic expression of the same gene, a feature of many genetic disorders.
