Histologic phenomenon with columnar narrow cone of parakeratosis extending through the orthokeratotic horny material. The epithelium at these sites is slightly sunken, focally lacking the stratum corneum.
Keratinocytes below the corneal lamella are vacuolated, isolated single cell necroses are found; the corneal lamella is characteristic for diseases of the porokeratosis group and was primarily described by the Italian dermatologist Vittorio Mibelli.