Keratoprosthesis implantation potentially helpful, but tricky

October 12, 2016

A permanent keratoprosthesis (KPro) can help restore the vision of patients with severe corneal disease, but clinicians must watch out for complications, according to Donald J. D’Amico, MD. Dr. D’Amico of the Weill Cornell Medical College, New York, described some of those complications in his Pyron Award Lecture during the American Society of Retina Specialists 2016 Annual Meeting.

Reviewed by Donald J. D’Amico, MD

A permanent keratoprosthesis (KPro) can help restore the vision of patients with severe corneal disease, but clinicians must watch out for complications, according to Donald J. D’Amico, MD.

Dr. D’Amico of the Weill Cornell Medical College, New York, described some of those complications in his Pyron Award Lecture during the American Society of Retina Specialists 2016 Annual Meeting.

The “permanent KPro is increasingly used in ophthalmology and if you haven’t seen patients with a KPro, you soon will,” he said.

KPros are typically used in patients whose corneal transplants have failed, in patients with chemical burns, and in Stevens-Johnson Syndrome, he said. “It compares favorably to repeat biologic penetrating keratoplasty in many eyes, even after a single failed corneal transplant,” he added.

He focused on the Boston KPro, which he referred to as the Dohlman KPro in deference to its original designer, Claes Dohlman, MD, PhD.

Two versions

There are two types of Boston KPro. Type 1 consists of a plastic front and back plates with a donut of donor corneal tissue sandwiched between them, and a locking ring to hold it together.

The type 2 Boston KPro, designed for severe, end-stage ocular surface disorders, is similar to the type 1 device but requires a permanent tarsorrhaphy to be performed through which a small anterior nub of the type 2 model protrudes.

Recent models have featured a titanium back plate intended to enhance biointegration. Since some patients don’t like the way the titanium looks, so experiments are underway to dye the titanium a more natural color.

Successful implantation begins with a careful history and detailed exam with ultrasound, and it is helpful to look at the optic nerve to see whether it is cupped out, said Dr. D’Amico. A wide-field camera provides a good view, he added, and should be used routinely to examine the fundus.

In patients with uncertain visual potential, Dr. D’Amico and his team will often perform a brief exploratory surgery and endoscopy in a separate sitting to see if it is worth going forward with a KPro subsequently.

Retro KPro membrane is opened with a bent needle during vitrectomy. Image courtesy of Donald J. D'Amico, MDIf the patient has decided to have a KPro implanted, it is important to manage the patient’s expectations. “Counsel patients that they will need contact lens and drops lifelong or as long as the KPro is in place,” he recommended.

At Weill Cornell, Dr. D’Amico and his colleagues prefer to place a KPro in an aphakic patient rather than in a pseudophakic one. They perform a full pars plana vitrectomy at the time of implantation, routinely 25-gauge. They enter 4.5 mm to 7 mm from the center of the device, and always examine the posterior segment carefully while the eye is open prior to KPro placement.

 

“Any time the eye is open for a corneal procedure, even a straight transplant, just simply put light pipe above or into the vitreous lake and get a view of the posterior segment,” Dr. D’Amico advised. “It’s ridiculous to be struggling for a view on the first postoperative day when you had an unroofed eye earlier that offered a wonderful view.”

Dr. D’Amico and his colleagues recently have recorded surprising findings after more recent implantations. “Recently, we’ve noted biointegration of the new devices and we don’t quite know why,” he said.

They are investigating a theory that epithelium growing over the device may help reduce the risk of infection. He also advised using anterior segment optical coherence tomography to monitor the wound integrity surrounding the implanted device.

Common postop complications

In addition to glaucoma and vitreous hemorrhage, the following are some of the most common postoperative complications associated with KPro implantation.

Retroprosthetic membrane. The growth of this membrane occurs in about half of all KPro implantations. For this reason, Dr. D’Amico prefers to place a KPro in an aphakic patients–having to remove a membrane in the presence of an intraocular lens makes a membranectomy that more difficult.

An Nd:YAG laser can sometimes open the membrane, but vitrectomy is frequently necessary. “Bent needle and forceps are typically the way to go,” said Dr. D’Amico.

The intraoperative view of a retinal detachment repair in an eye with a KPro. Image courtesy of Donald J. D'Amico, MD

Sterile inflammation is “surprisingly common,” Dr. D’Amico said. “You’ll be afraid that some of these eyes are infected but many of them are not.” It has typically been treated with peribulbar injection of triamcinolone or dexamethasone, followed by intense topical steroids.

Endophthalmitis can occur. There are new guidelines for checking for candida colonization, and for preventing infection with this organism, Dr. D’Amico said. Injection of the appropriate antimicrobial agent is the first line of treatment, followed by surgery.

Retinal detachment can occur years after the KPro implantation. Reattachment often proves difficult, said Dr. D’Amico. It typically involves pars plana vitrectomy and silicone oil. Although about half of these cases can be repaired, fewer patients regain vision.

Choiroidal detachment also may occur years after the initial KPro surgery, said Dr. D’Amico. Some may resolve on their own, but treatment with drainage may be appropriate in others.

Vitreous hemorrhage may result from inflammation, intraoperative steroid use, or diabetes, said Dr. D’Amico. Those that don’t resolve on their own may require vitrectomy, which is usually quite successful.

Hypotony may be associated with glaucoma drainage devices, choroidal detachment, choroidal effusion, or suprachoroidal hemorrhage, said Dr. D’Amico. In cases in which a prior glaucoma tube shunt ligation has not improved intraocular pressure (IOP), intracameral injection of viscoelastic or vitrectomy and silicone oil tamponade may be employed to restore IOP, said Dr. D’Amico.

 

Donald J. D’Amico, MD

E: djd2003@med.cornell.edu