Marginal Degeneration (PMD) - Correction and Treatment
with Contact Lenses
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.
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 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
shape of the cornea is the pregnant belly making the cornea asymmetrical
causing irregular astigmatism.
PMD Cornea Map
Above is an OrbscanŽ
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.
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.
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.