What are the other Names for this Condition? (Also known as/Synonyms)

• Irregular Astigmatism
• PMD (Pellucid Marginal Degeneration)

What is Pellucid Marginal Degeneration? (Definition/Background Information)

• Pellucid Marginal Degeneration (PMD) is an eye condition in which the bottom and outer part of the cornea, which is the clear, dome-like, front part of the eye, experiences thinning, usually in both eyes
• Pellucid Marginal Degeneration is a rare type of corneal ectasia, meaning the condition causes certain areas of the cornea to get thinner and stretch outwards, changing the normal shape of the cornea. This results in blurry and distorted vision
• The condition may be treated using glasses or contact lenses. In some cases, the cornea may be severely damaged that a corneal transplant surgery may be needed. The prognosis is generally good with adequate treatment

Who gets Pellucid Marginal Degeneration? (Age and Sex Distribution)

• Pellucid Marginal Degeneration most commonly presents in early to mid-adulthood, between the ages of 20 and 50
• Both male and female genders are affected, and no preference is noted
• Worldwide, no racial and ethnic group predilection is also noted

What are the Risk Factors for Pellucid Marginal Degeneration? (Predisposing Factors)

• Pellucid Marginal Degeneration (PMD) has no known risk factors, as the etiology (cause) is unclear. However, PMD appears to have an association with keratoconus, a condition in which the cornea transforms into a cone-shaped dome
• In general, the risk factors for keratoconus include the following:
  • Chronic eye rubbing, as this may cause the cornea to stretch and change shape over time
  • Eye allergies, which increases the likelihood of chronic eye rubbing
• PMD has not been proven to be a hereditary condition, meaning no family history of the condition is yet noted

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Pellucid Marginal Degeneration? (Etiology)

The exact cause of Pellucid Marginal Degeneration (PMD) is presently unknown.

• PMD appears to result in the displacement of collagen, connective tissue proteins in the cornea, which causes the cornea to stretch and change shape, similar to keratoconus
• As the cornea thins, the pressure from inside the eye causes the thinned parts of the cornea to protrude outward (bulge), changing its shape
• The corneal thinning occurs slowly over time, while the center part of the cornea maintains its normal thickness

The cornea is the first structure of the eye to bend light rays towards the retina, present in the back of the eye. When the cornea forms an irregular shape, light cannot get focused properly onto the retina, causing blurry and distorted vision.

What are the Signs and Symptoms of Pellucid Marginal Degeneration?

The signs and symptoms of Pellucid Marginal Degeneration may include:

• Increased astigmatism due to the change in corneal shape
• Slowly and progressively deteriorating vision
• Thinning and stretching of the bottom-part and outer-part of the cornea over time (typically in both the eyes)
• Abnormal reflex of light noted in the back of the eye
• Typically, no pain is involved unless the corneal stretching causes the fourth layer of the cornea to rupture, leading to corneal swelling
• Glare
• Double vision
• Corneal swelling (rarely noted)

How is Pellucid Marginal Degeneration Diagnosed?

The following tests and exams may be used in diagnosing Pellucid Marginal Degeneration:

• Complete physical exam and evaluation of medical history
• Eye exam and assessment of the presenting signs and symptoms
• Onset of high against-the-rule astigmatism (football-shaped cornea steeper horizontally than vertically)
• Poor, decreased vision with glasses or contact lenses 
• Slit lamp exam:
• Observation of thinned corneas from 4 o’clock to 8 o’clock (bottom-part and outer-part of the corneas), as seen with a slit lamp (instrument that provides a magnified view of the corneas) in both eyes
• Observation of small vertical stretch marks within the cornea during slit-lamp examination
• Corneal topographer, an instrument that shows a map of the surface of the cornea, reveals a “kissing doves” or “crab-claws” image, depicting the thinned areas of the cornea
• Pachymeter, an instrument that measures the thickness of the cornea, reveals thinned corneas near the bottom

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Pellucid Marginal Degeneration?

Complications due to Pellucid Marginal Degeneration could include:

• Poor and/or decreased vision with glasses or soft contact lenses
• Distorted vision
• Rare onset of hydrops (corneal swelling that causes pain)
• Corneal scarring (that may be noted rarely)
• Spontaneous corneal perforation (tiny holes created in the cornea due to thinning and stretching of the cornea)

How is Pellucid Marginal Degeneration Treated?

The treatment measures for Pellucid Marginal Degeneration (PMD) include:

• Use of glasses and/or soft contact lenses, although these lens options typically do not result in the best possible vision
• Specialty hard or rigid gas permeable contact lenses can provide better vision for patients with PMD than glasses or soft contact lenses
• Scleral contact lenses, for more advanced cases, similar to rigid gas permeable contact lenses, but are much larger and fit on the white part of the eye and vault the entire cornea, again mimicking a more spherical refractive surface at the front of the eye. These types of contact lenses can provide a more stable fit on the eyes, since it does not sit exactly on the irregular surface of the cornea
• Keratoplasty: Many different types of corneal transplants can replace the irregular part of the cornea with healthy, donor corneal tissue

How can Pellucid Marginal Degeneration be Prevented?

• No known preventive methods for Pellucid Marginal Degeneration (PMD) are currently available
• However, an avoidance of chronic eye rubbing may help minimize the risk for keratoconus, which is associated with PMD

What is the Prognosis of Pellucid Marginal Degeneration? (Outcomes/Resolutions)

• Pellucid Marginal Degeneration causes deteriorating vision slowly over time, mostly during the third to fifth decades
• The condition is rare and not many studies have followed the course of the condition with a large sample size
• Vision can usually be maintained at a satisfactory level with specialty contact lenses and/or surgery

Additional and Relevant Useful Information for Pellucid Marginal Degeneration:

• Pellucid Marginal Degeneration (PMD) is often misdiagnosed as keratoconus. The two conditions are very similar, and it has been questioned whether they are two different types of the same condition. Both conditions are considered corneal ectasias. PMD is much rarer than keratoconus
• Individuals affected by PMD are not good candidates for refractive surgery such as LASIK
• Hard contact lenses create a pool of tears between the back of the contact lens and the irregular cornea, mimicking a more spherical refractive surface at the front of the eye. However, because the surface of the cornea is irregular in those with PMD, these types of contact lenses do not always stay properly on the cornea