Keratoprosthesis a viable option

March 15, 2011

Keratoprosthesis is a viable therapeutic option for many patients with end-stage corneal diseases who are poor candidates for traditional corneal transplantation.

Baltimore-Keratoprosthesis is a viable therapeutic option for many patients with end-stage corneal diseases who are poor candidates for traditional corneal transplantation, said Esen K. Akpek, MD, here at the 23rd annual Current Concepts in Ophthalmology meeting, held in association with Ophthalmology Times.

"Keratoprosthesis may be the way to go, especially globally, in patients with corneal blindness," said Dr. Akpek, associate professor of ophthalmology and director of the Ocular Surface Disease and Dry Eye Clinic, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore. "Excellent visual acuity is possible. You can get 20/20 the day after surgery, and I've never seen that in other patients with donor corneal transplants."

Corneal transplantations are one of the most successful tissue transplantations performed today, explained Dr. Akpek. More than 40,000 procedures are performed annually in the United States alone. In low-risk patients, the success rate of corneal transplantation is more than 90% at 1 year, and more than 80% at 10 years.

She explained that the two groups of patients who tend not to do well after corneal transplantation are patients with ocular surface diseases from infections, autoimmune diseases, and trauma; along with pediatric patients with congenital corneal abnormalities.

"Due to technical challenges and the heightened immune system in these patients, the rejection rate and aphakia [are] very high," Dr. Akpek said. "Even when you have a clear cornea at the end of your follow-up period, it doesn't necessarily translate into good enough vision."

Exploring the options

Since 2004, Dr. Akpek and her colleagues at the Wilmer Institute have completed more than 80 keratoprosthesis procedures. Surgeons at Wilmer Eye Institute were the first to perform keratoprosthesis in children, Dr. Akpek noted.

Another reason for keratoprosthesis is the scarcity of corneas worldwide, she continued.

"We don't feel the problem here in the United States, but especially in the Middle East, Africa, and even in India, where corneal blindness is most prevalent, they don't have good eye banking systems," she said. "Even in some European countries, patients may have to get on a waiting list and wait for several years."

Two devices for keratoprosthesis are FDA approved in the United States: AlphaCor (Cooper Vision Surgical) and the Boston KPro.

The AlphaCor is an FDA-approved synthetic cornea that measures 7.0 mm in diameter and 0.5 mm in thickness. Surgery with this device is usually reserved for patients in whom traditional corneal transplants have failed, those in whom they have been rejected due to an autoimmune dysfunction, and in those who have a highly vascularized cornea that is a contraindication for traditional corneal transplantation.

The Boston KPro is a collar-button design keratoprosthesis, composed of a front plate with a stem, which houses the optical portion of the device, a back plate, and a titanium locking c-ring. The Type 1 Boston KPro is most commonly used, while the Type II unit is usually reserved for severe end-stage dry eye conditions. It is similar in design to the Type I unit, but has a 2-mm anterior nub that is designed to penetrate through a tarsorrhaphy.

The Type I Boston KPro is available in single standard pseudophakic power or customized aphakic optic in an 8.5-mm adult-sized or 7.0-mm pediatric-sized back plate. During implantation, this device is assembled with a donor corneal graft positioned between the front and back plate, which is sutured into place as a corneal transplant is.