The highlight to the scleral design and the correction of eye disorders such as pellucid marginal degeneration is that vision with these types of lenses is exceptional when fit correctly. Regardless of the lens size, it is thought that the larger the RGP lens will in most cases be more comfortable then standard rigid corneal lenses, and at times more comfortable than soft lenses, regardless of the fact that it is a rigid lens. Most of these lenses are in the range of 15.5mm to 18.0mm in diameter. New studies found that the use of Scleral contact lens, a type of rigid gas permeable (RGP) lens, may be a good option for most people with PMD. People wearing contacts don't report increased problems with glare and contrast sensitivity, but it is not clear if this is due to the corneal disease, or the contact lenses themselves. Success has been shown with the use of rigid gas permeable contact lenses combined with over- refraction. The early stages of pellucid marginal degeneration may also be managed with soft contact lenses.
Most people can be treated non-surgically with eyeglasses, or contact lenses. Thus, if corneal topography is used for diagnosis, it should be in conjunction with clinical findings of peripheral, inferior corneal thinning. Corneal topography may show a "crab claw-like" appearance, a finding that is seen in both keratoconus and in pellucid marginal degeneration. However, it may not be as specific as corneal pachymetry, because corneal topography only evaluates the degree and distribution of surface irregularities on the cornea, not the thickness of the cornea. The gold standard diagnostic test for PMD is corneal topography. PMD lacks apical corneal scarring, Rizutti's phenomenon, Munson's sign, and the central corneal thickness is usually normal. The inferior peripheral thinning is seen between the 4 o'clock and 8 o'clock positions. In PMD we can see high against the rule astigmatism along with horizontal bow ties. The portion of the cornea that is immediately adjacent to the limbus is spared, usually a strip of about 1–2 mm. 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 Bowman's layer of the cornea may be absent, irregular, or have ruptured areas. There may be an increase in the number of mucopolysaccharides in the corneal stroma. The thinning of the corneas may approach 20% of normal thickness. PMD is an idiopathic, non-inflammatory condition. Normally, PMD does not present with vascularization of the cornea, scarring, or any deposits of lipid. This is described as a "beer belly" appearance since the greatest protrusion occurs below the horizontal midline (unlike keratoconus). The cornea just above the region of thinning is of normal thickness, and may protrude anteriorly, which creates an irregular astigmatism. The distribution of the degeneration is crescent or arcuate shaped. PMD is characterized by bilateral thinning ( ectasia) in the inferior and peripheral region of the cornea. While PMD usually affects both eyes, some unilateral cases have been reported. 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. Pain is not typically present in pellucid marginal degeneration, and aside from vision loss, no symptoms accompany the condition. The condition is rare, though the exact prevalence and incidence are unknown. The word "pellucid" means clear, indicating that the corneas retain clarity in pellucid marginal degeneration. The term "pellucid marginal degeneration" was first coined in 1957 by the ophthalmologist Schalaeppi.
Surgery is reserved for individuals who do not tolerate contact lenses. Intacs implants, corneal collagen cross-linking, and corneal transplant surgery are additional options. Treatment usually consists of vision correction with eyeglasses or contact lenses. Corneal pachymetry may be useful in confirming the diagnosis. Pellucid marginal degeneration is diagnosed by corneal topography. The cause of the disease remains unclear. 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. Rarely, it may cause acute vision loss with severe pain due to perforation of the cornea. It typically presents with painless vision loss affecting both eyes. Pellucid marginal degeneration ( PMD) is a degenerative corneal condition, often confused with keratoconus. Vision correction ( eyeglasses or contact lenses) Pellucid corneal degeneration with hydrops and detachment of Descemet's membrane Medical condition Pellucid marginal degeneration
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