Pellucid marginal degeneration
| Pellucid marginal degeneration | |
|---|---|
 |
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| Pellucid corneal degeneration with hydrops and detachment of Descemet's membrane | |
| Classification and external resources | |
| Specialty | ophthalmology |
| ICD-10 | H18.7 |
| ICD-9-CM | 371.48 |
| DiseasesDB | 33144 |
| eMedicine | article/1196382 |
Pellucid marginal degeneration (PMD), is a degenerative corneal condition, often confused with . It is typically characterized by a clear, bilateral thinning (ectasia) in the inferior and peripheral region of the cornea, although some cases affect only one eye. The cause of the disease remains unclear.
The term "pellucid marginal degeneration" was first coined in 1957 by the ophthalmologist Schalaeppi. The word "pellucid" means clear, indicating that the corneas retain clarity in pellucid marginal degeneration.
Pain is not typically present in pellucid marginal degeneration, and aside from vision loss, no symptoms accompany the condition. However, in rare cases, PMD may present with sudden onset vision loss and excruciating eye pain, which occurs if the thinning of the cornea leads to perforation. While PMD usually affects both eyes, some unilateral cases have been reported.
PMD is characterized by bilateral thinning (ectasia) in the inferior and peripheral region of the cornea. The distribution of the degeneration is crescent or arcuate shaped. The cornea just above the region of thinning is of normal thickness, and may protrude anteriorly, which creates an irregular astigmatism. This is described as a "beer belly" appearance since the greatest protrusion occurs below the horizontal midline (unlike keratoconus). Normally, PMD does not present with vascularization of the cornea, scarring, or any deposits of lipid.
PMD is an idiopathic, non-inflammatory condition. The thinning of the corneas may approach 20% of normal thickness. There may be an increase in the number of mucopolysaccharides in the corneal stroma. The Bowman's layer of the cornea may be absent, irregular, or have ruptured areas.
The center of the cornea shows normal thickness, with an intact central epithelium, but the inferior cornea exhibits a peripheral band of thinning, to about 1–2 mm. The portion of the cornea that is immediately adjacent to the limbus is spared, usually a strip of about 1–2 mm. In PMD we can see high against the rule astigmatism along with horizontal bow ties. The inferior peripheral thinning is seen between the 4 o'clock and 8 o'clock positions.
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