I thank Drs Belin, Khachikian, and Ambrosio for their interest in our article. They have reflected concern about topographical diagnosis of pellucid marginal corneal degeneration (PMCD) in our case series. PMCD is a rare, bilateral, noninflammatory, peripheral thinning disorder of the inferior cornea. It is characterized by high degrees of central against-the-rule astigmatism and with-the-rule astigmatism in the area of thinning. Although it is often misdiagnosed as keratoconus, PMCD has been distinguished from this more common condition on the basis of slit-lamp findings and corneal topographical examination.
In our article, we clearly described this in the inclusion criteria: “The diagnosis of PMCD was based on slit-lamp findings, including inferior corneal thinning and ectasia above the area of maximum thinning. The diagnosis was verified by corneal topography, which demonstrated a steep contour in the inferior peripheral cornea with high keratometric powers radiating from the inferior oblique meridians toward the center.” Our diagnosis was not based merely on the corneal topography. We have accepted the classical definition of pellucid marginal degeneration diagnosis as a combination of slit-lamp and corneal topography findings. Dr Belin and colleagues are basing their criticism in the pachymetric Orbscan map (Bausch & Lomb, Rochester, New York, USA), which does not show a typical inferior thinning, and this is probably because the device is unable to detect peripheral thinning in some cases, as that case showed. We insist on this, because the concern is that the pachymetric map of the Orbscan does not show peripheral thinnings. Probably this is an innate limitation of the Orbscan system. In previous publications about intracorneal ring segments in PMCD, the same trend was observed in the cases shown (no inferior flattening in the Orbscan pachymetric maps). Therefore, we emphasize that we agree in that the Pentacam (Oculus Optikgeräte, Wetzlar, Germany) has the best ability to reveal peripheral corneal thinnings.