Issue: June 10, 2015
June 10, 2015
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Researcher: Long-term visual acuity results for KPro ‘sobering’

Study finds the chance of maintaining best-ever visual acuity with the device is 48% at 3 years.

Issue: June 10, 2015
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Glaucoma and other IOP-related problems are the main reasons for visual acuity loss in patients with a Boston type 1 keratoprosthesis, according to a study.

A retrospective chart review of 59 adult eyes implanted with the KPro device between January 2006 and March 2012 found the risk for glaucomatous visual acuity loss was 15% at 2 years and 27% at 3 years. Overall, the probability of eyes maintaining their best-ever vision was 71% at 1 year, 59% at 2 years and 48% at 3 years.

Vision loss at 3 years

“These results are sobering,” co-author Pradeep Y. Ramulu, MD, PhD, an associate professor of ophthalmology at Wilmer Eye Institute, said. “While most eyes have an initial improvement in vision, usually to a level that would allow a restricted driver’s license, by 2 years’ time most of these eyes have lost at least three lines of vision.”

Among the numerous causes for vision loss, “intraocular pressure issues — too high or too low — were the most common reason,” Ramulu told Ocular Surgery News.

Eyes that experienced loss of vision after primary KPro implantation were “likely reflecting that eyes not suitable for conventional transplantation from the beginning are complex situations that pose many postoperative hazards,” Ramulu said. Primary KPro implantation was done in 22% of eyes in the study, whereas in 78% of eyes, KPro implantation was done secondarily after failed corneal transplantation.

“We knew these were complex eyes, but the rate of postoperative vision loss was surprising,” Ramulu said. “That being said, we suspect that the rate of vision loss may already be less in more recent cases, where aggressive treatment of glaucoma (typically with a glaucoma tube shunt) is typically initiated prior to, or concurrent with, KPro implantation.”

Glaucoma was the main reason for vision loss in 39% of eyes in the study.

Ramulu and colleagues undertook the study to identify which patients were good or poor candidates for the KPro procedure and to identify the major reasons why patients did not maintain visual improvement after surgery.

“The procedure offers unique hope to patients who are not suitable for traditional corneal transplantation, for example, patients who have failed numerous conventional transplantations,” Ramulu said.

Merits of KPro

KPro is effective because the artificial cornea itself cannot become opaque, according to Ramulu.

“Although other problems can arise, such as infections that may destroy the retina or glaucoma which destroys the optic nerve, at the very least a clear central visual axis can be maintained,” he said.

Ramulu said it is critical for patients to understand the considerable risks associated with the procedure.

“Also, treat the glaucoma early by placing a tube shunt very early — at or before KPro implantation, if there is any consideration of glaucoma,” he said.

Ramulu said that while study results appear discouraging, “there are certainly patients who did extraordinarily well, maintaining good vision for several years.”

For example, 40% of eyes maintained their best-ever vision through the follow-up period, which had a mean duration of 37.8 months. Furthermore, even though more than 50% of eyes lost vision from their best-ever postoperative vision, “many still were seeing better than their preop vision,” he said.

In total, 25% of eyes required explantation during the follow-up period, at a mean of 23 months after implantation.

The ophthalmic community needs to contemplate “more clever ways to monitor for glaucoma and other problems in these eyes, perhaps with implantable IOP sensors or other techniques,” Ramulu said.

Because it is difficult to follow glaucoma or check IOP in eyes with a KPro, Ramulu and colleagues are involved in an ongoing study to examine different measures of vision and evaluate the optic nerve to determine what might be most useful in identifying glaucomatous progression in these eyes. – by Bob Kronemyer

Reference:
Ahmad S, et al. Am J Ophthalmol. 2015;doi:10.1016/j.ajo.2014.12.024.
For more information:
Pradeep Y. Ramulu, MD, PhD, can be reached at Wilmer Eye Institute, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Maumenee B-110, Baltimore, MD 21287-9238; email: pramulu@jhmi.edu.
Disclosure: Ramulu reports no relevant financial disclosures.