Differences in the Long-term Progression Course of Two Cases of Pellucid-like Keratoconus: Are they the Same Condition with Different Phenotypic Presentation?

We report the long-term follow-up of two cases of untreated corneal ectasia presenting a crab claw-like sagittal and tangential topographic pattern at baseline, but without peripheral thinning. Currently, according to clinical examination, these two cases are diagnosed as pellucidlike keratoconus (PLK). The first case was a 58-year-old male who developed a true pellucid marginal degeneration (PMD) in one eye and with a nonprogressive PLK in the other eye. The second case presented was a 19-year-old male without clinical signs of ectasia at baseline that progressed to PLK with evident changes in topographic and pachymetric maps but maintaining the point of minimum corneal thickness (MCT) in the central area. The presence of two different conditions in the same patient (case 1) and the progression from inferosuperior asymmetry to the development of a crab claw-pattern (case 2) suggest that PMD, PLK, and keratoconus may be different phenotypic presentations of the same pathophysiological condition.