11, 12 Therefore, the corneal densitometric values increase. 10 In ectatic diseases, serious structural changes occur in the corneal stroma, and both the structure and the sequence of collagen fibrils are disrupted. For corneal transparency, collagen fibrils should be arranged orthogonally and regularly with a small diameter, and keratocyte distribution must be compatible with it. 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.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |