images of pellucid marginal degeneration

8, 9 Densitometric evaluation provides quantitative data of the transparency of the cornea at different depths and in different zones. The assessment of corneal densitometry in patients with different corneal pathologies has recently attracted increasing attention. 5, 7 Therefore, analyzing only the anterior corneal surface without additional information is not sufficient in the differential diagnosis of inferior keratoconus and PMD. In inferior keratoconus, the sagittal curvature map does not display the true corneal shape, and it exaggerates the presumed location of the cone. These eyes do not show the classic band-like inferior thinning that is best demonstrated by a full-coverage (12 mm) corneal thickness map. 6Ī significant number of PMD cases reported in the literature actually have corneal topographies compatible with inferior keratoconus. 4, 5 However, both prognosis and management of PMD and keratoconus are different, and PMD should be distinguished from keratoconus. 3 Inferior keratoconus, in which the cone is localized away from the corneal center and a crab claw pattern is seen on the sagittal topographic map, is often confused with PMD. 2 In keratoconus, corneal thinning usually occurs in the paracentral region, and corneal topography shows central or inferior steepening and asymmetric bowtie patterns. 1 Crab claw or butterfly patterns on the sagittal topographic map of anterior corneal curvature reveal steepening of the inferior corneal periphery and flattening of the cornea along the vertical meridian. In PMD, the thinning extends 1–2 mm away from the inferior limbus, and the corneal protrusion occurs above the area of thinning. Keratoconus and pellucid marginal degeneration (PMD) are bilateral, progressive, ectatic corneal disorders characterized by thinning of the cornea. Tomographic and densitometric evaluations may facilitate the differential diagnosis. Therefore, analyzing only the anterior corneal surface is not sufficient in differential diagnosis. There is a higher probability of a patient with crab claw pattern on the topography of having inferior keratoconus than having PMD. The densitometry values of PMD were significantly higher than those of the controls in all zones and layers ( P<0.01) and significantly higher than the densitometry values of inferior keratoconus in the 6–10 and 10–12 mm zones ( P<0.05). In the PMD, all deviation indices were higher than the controls ( P<0.01), whereas the deviation indices, except Dt ( P=0.960), were lower than the inferior keratoconus ( P<0.01).

The thinnest corneal point and maximum anterior and posterior elevation points were located lower in the PMD than in the inferior keratoconus ( P<0.01). The control group consisted of 40 patients (33.1±4.6 years). PMD was detected in 11 eyes of eight patients (mean age 50.2☑1.1 years), and inferior keratoconus was detected in 36 eyes of 24 patients (mean age 34.7☑0.1 years). The topographic, tomographic, and densitometric measurements were analyzed. They were divided into two groups, inferior keratoconus and PMD, based on clinical findings. Forty-seven eyes of 32 patients with crab claw patterns were identified from 2751 patients with corneal ectasia. To evaluate the topographic, tomographic, and densitometric properties of patients with pellucid marginal degeneration (PMD) and inferior keratoconus.

Images of pellucid marginal degeneration