Keratoconus and Pellucid Marginal Degeneration (PMD) are both considered to be cornea ectatic disorders or corneal thinning disorders. While they may have similar topographic features, they have slightly different cornea abnormalities. They can often be misdiagnosed. It is possible for a person to have both eye conditions but this is quite rare.
There is some discussion of whether PMD is a form of keratoconus or its own eye disease entirely. Treating and managing these eye disorders is different so it is important to have a keratoconus or PMD specialist working with you to get the proper diagnosis.
Cornea Abnormalities
PMD shows severe inferior crescent-shaped thinning of the cornea. This shows as the thinning of the corneal band with the cornea protruding above the thinning. It is sometimes referred to as a “beer belly” configuration when you view it from the side. The cornea of a patient with keratoconus is cone-shaped rather than the dome shape of a healthy eye.
In PMD, cornea thinning extends 1–2 mm away from the inferior limbus while in keratoconus, the thinning usually occurs in the paracentral region. If the cone shape is away from the cornea, a patient with keratoconus can often be confused to have PMD.
Hereditary
There is no known hereditary link for those with PMD. It is a bit more complicated with Keratoconus. There is often no hereditary link, but if you have a first-degree relative with keratoconus, you are at higher risk than the general population of developing this eye disease.
Keratoconus is quite a rare disorder and PMD is an even more rare eye disorder. About 3% of cases with corneal ectasia resulted in a PMD diagnosis with the other 97% having keratoconus.
Keratoconus is more likely to occur in men. Some studies have found that PMD might be more apparent in women.
Many patients will have had a history of allergies, hayfever, asthma, or eczema, possibly due to excessive rubbing of the eyes.
Age of Diagnosis
Symptoms of Keratoconus are often diagnosed in the teenage years. PMD symptoms will typically start to show after age 30. Keratoconus will start to plateau after around age 40 but PMD will continue to progress.
Patients with keratoconus are often diagnosed sooner as vision starts to deteriorate earlier. The first signs are often a minor blurring of their vision.
Symptoms of Keratoconus and Pellucid Marginal Degeneration
With both diseases, eyesight deterioration progresses. Both may have astigmatism (eyesight problem of blurriness) present with keratoconus patients also sometimes experiencing myopia. Keratoconus causes astigmatism reducing visual acuity.
Neither eye condition usually causes pain. Keratoconus will typically show scarring while with PMD typically there is usually no scarring present.
Treatments for Keratoconus and Pellucid Marginal Degeneration
Corneal Cross-linking
Corneal cross-linking is a treatment that can halt the progression of both keratoconus and PMD. It is a minimally invasive procedure that uses special eyedrops of Riboflavin (Vitamin B12) and a UV light.
Rigid Gas Permeable Contact Lenses and Custom Scleral Contact Lenses
Rigid Gas Permeable (RGP) contact lenses are often used to treat both eye diseases. Custom scleral contact lenses may feel the most comfortable for those with keratoconus as they are wider and a scleral lens can vault over the dome of the eye.
Glasses or Soft Contact Lenses
Often this is the first treatment for mild cases. Lenses can be custom fit so the patient has a more comfortable experience.
Surgery or Cornea Transplant
In a small number of cases, a patient may need to have surgery or a corneal transplant.
How We Can Help
Having an eye doctor near you that understands the differences between diagnosing and treating keratoconus and pellucid marginal corneal degeneration is essential. Visit our comfortable office in Albuquerque to speak with our eye doctors that have experience treating these eye disorders.