Pellucid marginal degeneration (PMD) is a rare, slowly progressive eye disorder that affects the cornea, causing it to thin and bulge. It's a type of corneal ectasia.
Understanding Pellucid Marginal Degeneration (PMD)
PMD is characterized by thinning of the cornea, typically in a clear band about 1-2 millimeters wide, near the bottom edge of the cornea. Unlike other corneal ectasias like keratoconus, the thinning in PMD doesn't usually involve inflammation or scarring. The cornea takes on a characteristic "beer belly" or "sagging" appearance.
Key Features of PMD
- Corneal Thinning: The most significant feature is the thinning of the cornea in the peripheral region.
- Progressive Condition: PMD typically progresses over time, potentially leading to increased astigmatism and decreased vision.
- Absence of Inflammation: Unlike some other corneal conditions, PMD usually doesn't involve inflammation or scarring of the cornea.
- Astigmatism: Irregular astigmatism is a common symptom as the cornea's shape becomes distorted.
- Visual Distortion: Blurry or distorted vision is a common complaint as PMD progresses.
How PMD Affects Vision
The thinning and bulging of the cornea in PMD lead to irregular astigmatism. This means the cornea is not perfectly spherical, causing light to focus unevenly on the retina. This results in:
- Blurred vision
- Distorted images
- Difficulty with night vision
Diagnosis
An eye doctor diagnoses PMD through a comprehensive eye exam, including:
- Slit-lamp examination: Allows the doctor to examine the cornea closely.
- Corneal topography: Maps the surface of the cornea to identify areas of thinning and irregularity.
- Pachymetry: Measures the thickness of the cornea.
Treatment Options
Treatment for PMD aims to improve vision and prevent further progression of the condition. Options include:
- Eyeglasses or contact lenses: Can correct mild astigmatism in the early stages. Rigid gas permeable (RGP) contact lenses are often more effective as the condition progresses.
- Corneal cross-linking (CXL): A procedure that strengthens the cornea to slow or halt the progression of PMD.
- Surgical options: In more severe cases, surgical options like corneal transplantation or lamellar keratoplasty (partial thickness corneal transplant) may be considered.
PMD is a corneal disorder characterized by progressive peripheral corneal thinning, leading to irregular astigmatism and visual distortion. Early diagnosis and management are crucial for preserving vision.
