This type of anterior corneal dystrophy is genetically heterogeneous (caused by mutations in more than one locus). Recurrent corneal erosions are the main clinical feature and can begin in the first and second decades. The epithelium is irregularly thickened while the Bowman layer and basal lamina of the basement membrane have degenerative changes which lead to the clinically evident honeycomb pattern of opacities. Advanced changes in these tissues eventually leads to some vision loss.
The honeycomb pattern of degenerative changes in the corneal epithelium and Bowman membrane helps to distinguish this disorder from other anterior corneal dystrophies. These are more prominent centrally with relative sparring of the juxtalimbal areas. The epithelial basement membrane may be missing in some areas. Histology is required for a definitive diagnosis with electron microscopy revealing characteristic 'curly' collagen fibrils in the subepithelial and anterior stromal tissues. These degenerative changes tend to recur even after ablative procedures.
There is a great deal of clinical heterogeneity and the diagnosis is often unclear especially in younger individuals. No doubt much of this is due to the fact that mutations in the major gene (TGFBI) responsible are also responsible for at least 5 other heritable corneal dystrophies and the argument can be made that all are variants of the same condition (vida infra).