Pellucid Marginal Degeneration vs. Keratoconus: Understanding the Similarities and Differences

When it comes to corneal conditions, two often misunderstood and misdiagnosed disorders are Pellucid Marginal Degeneration (PMD) and Keratoconus (KC). Although they share some similarities in their symptoms and treatment approaches, it is important to distinguish between the two for accurate diagnosis and appropriate management. In this blog post, we will explore the similarities and differences between PMD and KC, shedding light on their causes, symptoms, and treatment options.

 1. Understanding Pellucid Marginal Degeneration (PMD):

Pellucid Marginal Degeneration is a rare, non-inflammatory corneal disorder characterized by a thinning and protrusion of the lower portion of the cornea. This condition primarily affects the peripheral cornea, leading to a gradual change in the corneal shape. PMD typically starts in the late teens or early adulthood and tends to progress slowly over time. While the exact cause of PMD remains unknown, it is believed to have a genetic component.

2. Understanding Keratoconus (KC):

Keratoconus is a progressive eye condition characterized by the thinning and bulging of the central cornea, resulting in a cone-like shape. This irregular corneal shape causes visual abnormalities, such as distorted and blurred vision. While the exact cause of KC remains uncertain, genetic and environmental factors, including eye rubbing and collagen abnormalities, are believed to play a role.

3. Treatments for Pellucid Marginal Degeneration

Corneal collagen cross-linking – this procedure involves soaking your cornea in vitamin B2 and then applying ultraviolet light to the area.  This strengthens your cornea to try and halt the progression of your PMD. Supplemental oxygen may be applied to your corneal to enhance the effect of the treatment.   

Corneal Allogenic Intrastromal Ring Segments (CAIRS) – CAIRS is like a “mini” corneal transplant for Pellucid Marginal Degeneration.  CAIRS has mostly superseded the older style Keraring™ and Intac™ procedures due to the number of advantages it has over the older plastic corneal inserts.

Other treatments for PMD include topography guided laser resurfacing of your cornea (t-PTK), Deep Anterior Lamellar Keratoplasty (DALK) and Penetrating Keratoplasty (PK).  With the advent of corneal collagen cross linking and CAIRS for Pellucid Marginal Degeneration the other procedures are now performed less frequently. 

Conclusion:

While Pellucid Marginal Degeneration (PMD) and Keratoconus (KC) share some similarities, such as corneal thinning and progressive vision changes, they differ in terms of the location and pattern of corneal thinning, symptom onset, association with eye rubbing, and potential corneal scarring. Accurate diagnosis by an eye care professional is crucial to ensure appropriate management and treatment. Whilst the treatments for both conditions have similarities, there are subtle differences in the approach your corneal specialist will adopt.