Pellucid marginal degeneration, or PMD, is a lesser-known cousin of keratoconus — and one that can be especially frustrating to correct with glasses or ordinary contacts. Scleral lenses are often the most effective solution.
What PMD is
PMD is a corneal thinning disorder, like keratoconus, but the thinning occurs in a band along the lower edge of the cornea. This produces a distinctive "against-the-rule" irregular astigmatism that warps vision in ways standard corrections can't handle. Patients often cycle through prescription after prescription with disappointing results.
Why PMD resists glasses and soft lenses
The peripheral, asymmetric nature of PMD's distortion means the focusing surface of the eye is uneven in a complex pattern. Glasses correct only regular curves. Soft lenses drape over the irregularity and reproduce it. Even standard RGP lenses can struggle to stay centered on a cornea that bulges low.
How scleral lenses succeed
A scleral lens vaults over the entire cornea — including that troublesome lower band — and rests on the sclera. It creates a smooth optical surface independent of the underlying distortion, and its large diameter keeps it stable and well-centered despite the irregular shape below. For PMD patients, this often means the clearest, most consistent vision they've had in years.
The comfort bonus
Because the lens never presses on the thinned, sensitive corneal tissue, and because the fluid reservoir keeps everything hydrated, comfort is usually excellent even for these challenging eyes.
Expert fitting is essential
PMD's off-center distortion makes lens design and positioning critical. Dr. Salley uses detailed corneal mapping to build a lens that clears the thinned zone and centers reliably — and for the most difficult cases, impression-based EyePrintPRO® lenses can capture the eye's exact contours.
If PMD has made clear vision feel impossible, scleral lenses may change that. Book a PMD lens consultation at CFE Memphis.