FORMATION OF KERATIN PATCHES
These patches of thickened keratinocytes develop as superficial keratin layers split apart during their migration to the periphery in a manner reminiscent of the fragmentation of ice floes during spring thaw.
Keratin patches, ink dots, migrate peripherally and fragment as they move toward the annulus. The slow zone has a comparatively thin stratum corneum and contains few patches.
This schematic diagram illustrates the process involved in the formation of keratin patches.
As the stratum corneum of the umbo migrates peripherally, it must spread to cover a much larger area at the annulus.
The superficial keratin layers must therefore split during their movement outward, creating the patches.