April 2019

CORNEA

Research highlight
DMEK after radial keratotomy


by Maxine Lipner EyeWorld Senior Contributing Writer


An eye with RK immediately after DMEK
Source: Jack Parker, MD, PhD

 

Despite the small amount of cornea being replaced in Descemet’s membrane endothelial keratoplasty (DMEK), the procedure can offer surprisingly positive outcomes for Fuchs’ dystrophy patients who previously underwent radial keratotomy, according to Jack Parker, MD, PhD. Even for patients who had extremely irregularly shaped corneas, as in a study1 published in Cornea, DMEK alone was able to normalize the shape and offer excellent acuity, Dr. Parker said.
Included in the study were five eyes of three Fuchs’ dystrophy patients who had undergone previous radial keratotomy (RK). Since then, the center has performed DMEK on five additional RK eyes with Fuchs’ dystrophy. One of the issues with eyes that have undergone RK is that they have notoriously unstable corneas, Dr. Parker explained, adding that because these incisions are made in the cornea and often extend out to the limbus, they can be difficult to get around. In addition, they’re frequently quite numerous and can present a problem for any kind of surgical manipulation the surgeon is going to do in the eye.

Double trouble

With this in mind, practitioners are often leery of eyes that have had prior RK. “Having a cornea that is beset by RK doesn’t mean you can’t have additional problems and that includes endothelial decompensation,” Dr. Parker said. The endothelium may go bad as a result of RK incisions that were too deep or if too many incisions were used, but sometimes the decompensation is from an entirely different issue like Fuchs’ dystrophy. “Sometimes patients are doubly unlucky and they have RK and Fuchs’ dystrophy,” Dr. Parker said. The issue becomes what to do for these individuals to preserve their vision. “You would like to be as minimally invasive as possible and you would like to try to restore the anatomy of the cornea back to as normal as possible without doing anything extra,” he said.
Investigators found themselves with such a population in the clinic; patients had issues from previous RK as well as Fuchs’ dystrophy. They sought to simply replace the endothelium using DMEK, with the idea of doing as minimal surgery as they could for these patients. “With DMEK, the trick is once you put the cells into the eye, you want it to stick to the back of the cornea,” Dr. Parker said. “The question was whether these incisions in the cornea made by the RK were going to interfere with the process of unfolding the cells in the eye or the action of sticking those cells to the back of the cornea where they belong.”

Fixing corneal shape

The study assessed outcomes in these cases. “Dogma with DMEK is that when you replace the back of the cornea, the shape of the cornea doesn’t change,” Dr. Parker said. “When you replace just the back 5% of the cornea, you don’t expect the front 95% to have very much of a change of shape.”
Prior to surgery, investigators observed that not only did patients have scars from their RK incisions, but the corneas had lost most of their structural support. “They’re drooping, sagging, or twisted in all sorts of undesirable ways,” Dr. Parker said. “It’s not just that they’re riddled with scars, but also the shape is totally irregular.” While the temptation is to replace the whole structure, investigators found that just replacing the back 5% of the cornea dramatically improved the shape in every case. “If you can improve the shape just by fixing the back, you can have a much smaller surgery and you expose the patient to fewer risks,” he said.
If the endothelium goes bad, the cornea starts to swell, and while many times the cornea looks soggy, sometimes that swelling is not obvious. “Probably when the cornea swells and it has lost its structural support it starts to bulge,” he said. “Probably after DMEK, the new cells reverse that swelling; when you fix the swelling, those changes seem to be at least partially reversible.”
Investigators were concerned that irregularities on the back of the RK from scarred corneas would interfere with the graft sticking and were surprised to find this was not the case. “The detachment rate was exactly the same in all of the previous reports so that didn’t seem to be a contraindication for this operation,” Dr. Parker said.
When it came to best corrected spectacle acuity, 80% attained visual acuity of 20/40 or better by the 6-month postoperative mark.
Dr. Parker hopes that physicians come away from the study understanding that abnormalities in shape or bulging of the cornea from RK or Fuchs’ dystrophy do not necessarily require a full-thickness corneal transplant. “They can be dramatically improved just by replacing the back of the cornea,” he said.

About the doctor
Jack Parker, MD, PhD

Parker Cornea
Birmingham, Alabama

Reference

1. Parker JS, et al. Clinical outcomes of Descemet membrane endothelial keratoplasty in eyes with previous radial keratotomy. Cornea. 2018;37:1351–1354.

Financial interests
Parker
: None

Contact information
Parker
: Jack.parker@gmail.com

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