Defined 

Pellucid Marginal Degeneration (PMD)  -  is a condition whereby the lower cornea becomes thinner and the optic surface of the cornea becomes irregular and the vision becomes blurry. The resulting shape of the cornea is similar to a pregnant belly whereby the lower portion of the cornea protruding forward.  PMD  is the leading cause of high astigmatism and irregular astigmatism. PMD is similar to Keratoconus, although , the resulting cornea shape can be quite different. PMD often has cornea sizes similar to that of a regular eye but a very steep curve in the bottom of the cornea. PMD has been observed in families giving it an inherited genetic trait and on occasion it has been observed unilaterally in one eye only. Typically it is bilateral affecting both eyes. Proper diagnosis of PMD can be accomplished with the use of cornea topography (cornea surface shape) and cornea pachymetry (cornea thickness) mapping. We use an Orbscan II Z to render these mappings. See Lens Fittings for more info.

Onset

Onset of the disease is seen usually in early adulthood. Many mild cases of PMD go undiagnosed in the early stages and are many times detected while consulting for Refractive Laser surgery. Eyeglasses  can correct early stages of PMD. In later stages of the disease, Vision can become blurred within a few years whereby driving vision can not be attained without treatment with specialized contact lenses. 

Progression of PMD

Progression of PMD is quite slow and often can stabilize. Use of contact lenses can correct this condition to near normal levels of vision.

Treatment of PMD with contact lenses

Fitting contact lenses on an eye with PMD requires a different approach than that of Keratoconus making diagnosis very important. Lesser degrees of PMD can utilize eyeglasses with fair vision resulting. Soft Toric contact lenses will fit many PMD eyes provided that they accommodate for the astigmatism resulting from PMD. More severe cases can be fit with a modified gas permeable Keratoconus or our special Bi-Toric lens to accommodate for the steepness of curves with an added cylindrical surface cut into the back surface of the contact lens.

PMD Causes Irregular and Oblique Astigmatism - The trademark shape of the cornea is the pregnant belly making the cornea asymmetrical causing irregular astigmatism.

PMD Cornea Map &Topography   Enlarge Photo 

Above is an Orbscan® IIz cornea map of an eye with Pellucid Marginal Degeneration. In the lower right of the photo, you can see where the cornea has an elongated thin zone extending to the edge of the cornea. In the lower left of the photo, you can see where the thinning of the cornea has induced an irregular astigmatism.

Wearing eyeglasses on an eye like this typically does not result in very clear vision. Correction with a special fit lens can correct many of these type of eyes to 20/30 or better.

Laser corrective surgery is not indicated for individuals with PMD. Laser surgery may thin the cornea even worse than it already is causing greater distortion.

Prognosis 

Prognosis of PMD is quite good. Vision restoration with our special contact lenses results in normal vision allowing legal driving with minimal visual distortions. Many eyes can be be restored to normal vision even in severe cases. After ten years from initial onset, PMD has been known to stabilize and progression can be very little through decades of life.