Pellucid Marginal Degeneration

Pellucid marginal degeneration is a progressive form of corneal ectasia that causes your cornea to thin and bulge. Treatments include glasses, contacts and surgery.


What is pellucid marginal degeneration?

Pellucid marginal degeneration (PMD) is a slowly progressive disorder that affects your cornea. It’s a rare form of corneal ectasia (a group of disorders that cause your cornea to grow thin and bulge outward).

A healthy cornea is thick and helps you see clearly. With PMD, a crescent-shaped area of your cornea gradually thins over time. Usually, this happens in the lower part of your cornea. Think of your eye as a round clock. The thinned part of your cornea typically extends from 4:00 to 8:00. Above this thinned area, your cornea bulges outward. These changes to your cornea lead to astigmatism and reduced visual acuity (sharpness of vision) over time.

Usually, PMD affects both eyes. But it can occasionally affect just one eye. PMD doesn’t cause scarring of your eye. Therefore, your cornea remains transparent (“pellucid” means clear).

PMD develops slowly, so you may have no symptoms for a long time. But as the condition progresses, your vision may keep getting worse. This is because your astigmatism increases as your cornea continues to thin and bulge. So, PMD can make it difficult for you to carry out your normal daily tasks.

Who does PMD affect?

PMD affects people of all ethnicities. Some research shows it’s more common among men and people assigned male at birth. Diagnosis usually happens in your 20s, 30s or 40s. Less often, people receive diagnoses in their 50s or even beyond.

How common is PMD?

Researchers don’t know exactly how many people have this condition. However, it’s less common than another form of corneal ectasia called keratoconus. Estimates show anywhere between 1 in 400 and 1 in 2,000 people have keratoconus.


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Symptoms and Causes

What are the symptoms?

The main symptom of pellucid marginal degeneration is vision that gradually gets worse over time. This is due to increasing levels of astigmatism. Most people with PMD don’t experience pain or other symptoms.

Rarely, PMD leads to acute corneal hydrops (sudden swelling of your cornea). This serious complication causes sudden blurred vision and sensitivity to light. Some people also experience intense pain.

What causes pellucid marginal degeneration?

Researchers don’t know what causes PMD or raises your risk of developing it.


Diagnosis and Tests

How is PMD diagnosed?

Eye care specialists diagnose PMD through an eye exam and testing. They’ll ask about your symptoms, including vision that seems to be getting worse over time.

What tests diagnose this condition?

Corneal topography is the gold standard for diagnosing pellucid marginal degeneration. This is a quick and painless test. You sit in front of a device that takes pictures of your eyes and generates color-coded maps. These maps show the landscape of your corneas. An eye care specialist interprets these maps to learn the shape and curvature of your corneas.

With PMD, a map may show a classic “kissing doves” or “crab claw” image. The color red indicates steep curvature in your cornea, meaning your cornea is bulging outward in those spots.

An eye care specialist studies these maps to diagnose you with PMD or, in some cases, another form of corneal ectasia.

Management and Treatment

What are the treatment options for pellucid marginal degeneration?

Treatment depends on the severity of your condition and how far it’s progressed. Early on, you may benefit from glasses or contact lenses to improve your vision. There are many types of contacts available. An eye care specialist will help you choose the best type in your individual situation.

It’s important to keep in mind that contacts will help you see more clearly, but they can’t slow down the progression of PMD. So, down the road, you may need surgery if glasses or contacts don’t improve your vision enough to support your daily tasks. Surgery may involve replacing some or all your cornea with corneal tissue from a donor. There are many different surgical techniques available, and your provider will discuss the pros and cons of each with you.



How can I prevent PMD?

Unfortunately, there’s nothing you can do to prevent PMD. This is because researchers don’t know exactly what causes it.

However, be sure to visit an optometrist or ophthalmologist for yearly eye check-ups. They’ll check the overall health of your eyes and catch any problems early. Early diagnosis of PMD allows your provider to monitor its progression and plan treatment at the appropriate time.

Outlook / Prognosis

What can I expect if I have PMD?

Your provider is the best person to ask about your outlook. Pellucid marginal degeneration doesn’t cause complete blindness. But it can greatly impact your daily routine as your vision gets worse. The pace of progression is different for everyone. You’ll need lifelong follow-ups so your provider can monitor your condition and treatment plan.

Living With

How do I take care of myself?

If you have PMD or another form of corneal ectasia, it’s important to:

  • Avoid rubbing your eyes. This may, rarely, lead to complications like corneal hydrops.
  • Avoid blowing your nose too hard. This can raise your intraocular pressure (pressure inside your eye), leading to corneal hydrops.
  • If you wear contacts, clean them properly according to your provider’s instructions.
  • Practice good eye hygiene. Wash your eye area with mild soap and warm water daily. Gently dry the area with a soft washcloth.

When should I see my provider?

You should see an eye care specialist once a year for a check-up. Your provider may ask you to come in more often for follow-up appointments or testing. Be sure to go to all your appointments.

You should also call your provider if you have new or unexplained symptoms.

When should I go to the ER?

Call 911 or your local emergency number if you experience:

These can be signs of a medical emergency that requires immediate care.

What questions should I ask my doctor?

If you’ve been diagnosed with PMD, you probably have many questions. Share all of your questions and concerns with your provider and make sure you get the answers you need. You may want to ask:

  • How far has my condition progressed?
  • What is the best treatment for me?
  • Will I need surgery?
  • What should I do at home to take care of my eyes?
  • Are there any activities I shouldn’t do?

Additional Common Questions

What is the difference between pellucid marginal degeneration and keratoconus?

Early on, PMD looks a lot like keratoconus (a condition that causes your cornea to bulge outward in a cone-like shape). So, some people with PMD receive a keratoconus diagnosis when, in fact, they have PMD. But there are several important distinctions between these two conditions.

Key Differences
Cornea shape
The thinned part of your cornea doesn’t bulge outward. Instead, the bulging section is above the thinned part (or, rarely, below it).
The thinned part of your cornea bulges outward.
Age of diagnosis
Usually diagnosed in your 20s, 30s or 40s.
Usually diagnosed younger, in your teens or 20s.
Progresses slowly, with subtle vision changes over time.
Progresses more quickly.
Serious and painful complications are less likely than in keratoconus.
Corneal hydrops (sudden swelling of your cornea) affects up to 3% of people with keratoconus.
No known genetic link.
Some research shows keratoconus can run in families.
Less common than keratoconus.
The most common form of corneal ectasia.

It’s important to know that you can have both PMD and keratoconus. In fact, about 1 in 10 people with PMD also have keratoconus.

A note from Cleveland Clinic

Pellucid marginal degeneration can affect your daily life and make you worry about what the future will bring. Take things one day at a time and work closely with a specialist to get the care you need. Most people with PMD don’t have serious complications and can manage their condition with glasses or contacts. In some cases, surgery is a good fit. Talk to your provider to learn more about your available options and what you can expect down the road.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 03/13/2023.

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