Abstract
Purpose: To study the tomographic features of pellucid-like keratoconus (PLK), and to report a new sign on the pachymetry map (PM) in pellucid marginal degeneration (PMD). Patients and methods: A retrospective descriptive case series was performed in Damascus University in 2011. Clinical and tomographic findings of 15 eyes (9 patients) that had the claw pattern of the anterior sagital map (ASM) were reviewed. Patients were distributed into two groups: (1) 4 eyes were considered PMD since they had inferior corneal thinning on both slitlamp biomicroscopy and PM; (2) 11 eyes were considered as PLK since they did not show inferior corneal thinning. Patients were studied using slitlamp biomicroscopy and Scheimpflug-based tomography (Pentacam HR). The ASM, anterior elevation map (AEM) and PM were analyzed and compared to study the “kissing birds” sign, the “bell” sign, and cone location. Results: Patients’ average age was 25.93±8.05 (16–44 years). In total, 60% of patients were male. In group 1, the AEM in the best fit sphere (BFS) mode revealed no kissing birds sign, and the cone was central in 1 eye (25%) and paracentral in 3 eyes (75%). PM showed the bell sign in 4 eyes (100%). In group 2, the AEM in the BFS mode revealed the kissing birds sign in 2 eyes (18.2%), and the cone was central in 1 eye (9.1%), paracentral in 8 eyes (72.7%) and peripheral in 2 eyes (18.2%). PM didn’t show the bell sign in any eye. Conclusion: The claw pattern on the ASM is not a hallmark of PMD; it can be seen in PLK. Cone location does not relate to diagnosis. The “bell” sign on the PM is a deferential diagnostic sign in PMD.
Highlights
Pellucid marginal degeneration (PMD) is an idiopathic, progressive, non-inflammatory, ectatic corneal disorder characterized by a peripheral inferior band of corneal thinning in a crescent-shaped pattern[1], PMD cases with areas of superior thinning have been reported[2]. corneal tomography is an important tool for the diagnosis of this corneal pathology, it should not be used as the only diagnostic criterion because it has been shown that this pattern is not always associated with the diagnosis of PMD; it might be seen with some other corneal ectatic disorders[4]
Corneal tomography is an important tool for the diagnosis of this corneal pathology, it should not be used as the only diagnostic criterion because it has been shown that this pattern is not always associated with the diagnosis of PMD; it might be seen with some other corneal ectatic disorders[4]
Careful studying of corneal tomography with the main three maps is mandatory for diagnosing PMD and differentiating it from other ectatic corneal disorders
Summary
Pellucid marginal degeneration (PMD) is an idiopathic, progressive, non-inflammatory, ectatic corneal disorder characterized by a peripheral inferior band of corneal thinning in a crescent-shaped pattern[1], PMD cases with areas of superior thinning have been reported[2]. Corneal tomography is an important tool for the diagnosis of this corneal pathology, it should not be used as the only diagnostic criterion because it has been shown that this pattern is not always associated with the diagnosis of PMD; it might be seen with some other corneal ectatic disorders[4]. When intracorneal rings (ICRs) implantation is indicated in the management of PMD, caution should be paid to the location of the inferior segment, since it passes through the inferior thinned area. The need to calculate the depth of implantation depending on the thinnest point on the resumed passage, rather than on the thickness of the site of incision, in order to avoid deep corneal penetration
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