Updated classification gives order to corneal dystrophy

Reviewed by Jayne S. Weiss, MD

New Orleans-What’s in a name? Would Schnyder corneal dystrophy (SCD) by any other name cause as much vision loss? Perhaps, said Jayne S. Weiss, MD, but it might not be properly diagnosed. 

Too often the condition has been referred to as Schnyder crystalline corneal dystrophy, leading clinicians to misdiagnose patients who had no crystals in their corneas, said Dr. Weiss, chairman, Department of Ophthalmology, Louisiana State University, New Orleans.

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And that’s only one example of many confusing and misleading names of dystrophies, she said. Dr. Weiss has led an effort to properly differentiate and name corneal dystrophies.

“If we don’t even know what we’re looking at, how in the world will we ever make any headway into scientific investigation for a better treatment or prevention?” she asked. “That ultimately, as a clinician scientist, was my goal for this.”

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In 2005, she organized the International Committee for the Classification of Corneal Dystrophies (IC3D), whose results were first published in 2008. Between 2008 and 2012, new information about the dystrophies became available so Dr. Weiss then led the update effort of the IC3D and presented the new document at the American Society of Cataract and Refractive Surgery annual meeting.

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The updated classification appears in Cornea under the title “IC3D classification of corneal dystrophies-edition 2,” and is most easily accessed by selecting the publisher’s button in its Pubmed listing. 

Most important changes

The most important changes in the update:

·      A new anatomic category for dystrophies that map to the TGFBI gene.

·      Expansion of the epithelial recurrent erosion dystrophy (ERED) category. “This is a dystrophy that I think most people are not taught about,” says Dr. Weiss. “It’s not in all the books.” Recent research has uncovered more subtypes of ERED, which often causes recurrent unexplained corneal erosions in children and can lead to multiple opacities in adults. The condition is autosomal dominant disease.

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·      Eliminated a chromosome 10 dystrophy from the Thiel-Behnke category. Earlier reports of a Thiel-Behnke dystrophy on chromosome 10 were not substantiated by further research, which confirmed that all Thiel-Behnke dystrophies are on the TGFBI gene on chromosome 5. The dystrophy reported on chromosome 10 that resembles Thiel-Behnke, may belong in the ERED category.

·      Eliminated congenital hereditary endothelial dystrophy 1 (CHED 1). The autosomal dominant condition that was being called CHED 1 was actually a different dystrophy called posterior polymorphous corneal dystrophy. “Sometimes these dystrophies with new names turn out to be old ones,” said Dr. Weiss. Consequently, autosomal dominant CHED 1 has been eliminated and the autosomal recessive corneal dystrophy previously called CHED 2 is now named CHED.

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In addition, the authors have added histopathologic descriptions with photos.

The new document builds on the work in the original document, which replaced categories based on anatomy with categories based on genes.

“Two things that look the same if they have a different genetic origin are probably not the same,” Dr. Weiss said. “And we may have some diseases on the same gene that may look very different, but if they’re on the same gene, maybe with different mutations, there could be more similarity to those diseases than you might guess at first glance.”

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In the process of that work, the researchers found exceptions to the commonly used definition of corneal dystrophy -an inherited, bilateral, slowly progressing corneal disease without systemic associations. Not all are inherited, bilateral or slowly progressing, and some have systemic associations, Dr. Weiss explained.

Helping patients plan for the future

The document offers one-page descriptions of each dystrophy, how it is inherited, genetic information, the age of onset, signs and symptoms, how rapidly it progresses, and clinical photos.

“There are levels of detail in the article that are certainly relevant to many doctors in terms of assisting them to make the diagnosis, helping inform the patient what the prognosis is, and the possibility of passing the disease on to their progeny,” Dr. Weiss said.

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Some corneal dystrophies cause few symptoms. Others can lead to opacification, but corneal transplants can usually restore good vision in these patients, she noted.

“One of my goals is for us to get to the next level that we have gotten to in many other diseases, where we can intervene to prevent disease progression and avoid visual loss,” she said.

In the meantime, better diagnosis can help patients plan for the future, Dr. Weiss said.

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“When we see a patient, they want to know what do they have and what can they expect as their life goes on,” she said. “Are they going to need surgery? Is their vision going to be impaired? What are the chances of them giving this to their progeny? And unless we really understand what we’re looking at, we can’t give the disease the correct name and most importantly we can’t really give the patient an accurate idea about what they may face in the future.”

Dr. Weiss, an authority on Schnyder corneal dystrophy, gives the example of a young patient with this dystrophy who wanted to be a pilot. She was able to show the patient a chart indicating how the patient’s vision was likely to be affected at each age. The patient decided to become a pilot with the understanding that this career might not last past the age of 30 or 40 years.

“Many times when I’m in a room with patients I’ll open the IC3D article and show them where they are,” Dr. Weiss said. “I find that my patients are always appreciative of information because knowledge is power.”

In another case, she saw a Schnyder patient referred by another ophthalmologist who was considering laser treatment for corneal crystals. She pointed out that the treatment would not entirely restore the patient’s vision because of coexistent corneal haze underneath the crystals.

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A correct diagnosis might help uncover systemic conditions as well. Since families with Schnyder often have elevated cholesterol levels whether or not the eye is affected, clinicians should advise these patients to have their systemic cholesterol levels checked, Dr. Weiss noted.

“No one wants a disease, but the unknown is often more frightening than the known,” she said.

Jayne S. Weiss, MD

E: jweiss@lsuhsc.edu 

This article was adapted from Dr. Weiss’ delivery of the Richard L. Lindstrom, MD, Lecture during the 2016 meeting of the American Society of Cataract and Refractive Surgery. She did not indicate any proprietary interest in the subject matter.