| Pellucid marginal degeneration | |
|---|---|
| Classification and external resources | |
Pellucid corneal degeneration with hydrops and detachment of Descemet's membrane |
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| ICD-10 | H18.74 |
| eMedicine | article/1196382 |
Pellucid Marginal Degeneration (PMD; keratotorus), is a degenerative corneal condition, often confused with keratoconus. It is typically characterized by a bilateral thinning (ectasia) in the periphery of the cornea, that is non-inflammatory, although unilateral cases have been reported.[1] The term was first coined in 1957 by the ophthalmologist Schalaeppi.[2]
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Incidence of PMD is rare, but it is unknown how many cases occur each year, due in part to the confusion of the condition with keratoconus.
Unlike keratoconus, pain is not normally present, and aside from the visual deterioration, no symptoms accompany the condition. Normally, PMD does not present with vascularization of the cornea, scarring, or any deposits of lipid.[1]
Upon examination by an optometrist or ophthalmologist, the patient exhibits normal corneal thickness in the center, with an intact central epithelium, but the inferior cornea exhibits a peripheral band of thinning.In pmd we can see high against the rule astigmatism along with horizontal bow ties and inferior peripheral thinning seen in between 7 and 4 o'clock meridian.
Although there has been only one reported association of PMD and scleroderma,[3] no other identifiable factors have been found to link to race, sex, or age, although most cases present early in life, in the age group of 20-40.[4] No known cause for the disease has been found.[2]
Visual function declines as a result of the irregular corneal shape, resulting in astigmatism, and causing a distortion in vision. Deterioration can become severe over time.
Like keratoconus, PMD rules a patient out for refractive surgery. Due to the thinning of the cornea, procedures such as LASIK and PRK would make the patient a poor candidate.[4]
Visual acuity can not usually be corrected with the use of corrected lenses, but success has been shown with the use of rigid contact lenses combined with over-refraction. Patients wearing contacts 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.
However new studies show that the use of a "GP" or Scleral contact lens has shown promise for most patients that exhibit Pellucid Marginal Degeneration. Most of these lenses are in the range of 15.5mm to 18.0mm in diameter. Regardless of the lens size, it is thought that the larger the GP lens, regardless of the fact that it is a rigid lens, will in most cases be more comfortable then standard rigid corneal lenses, and at times more comfortable than soft lenses. 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.
The use of intacs implants has been tested as a treatment for PMD, with slight improvement in visual acuity noted after eleven months,[5] and intacs have been used with keratoconus with success.[6]