When the cornea becomes severely damaged or diseased, it can often spell out pain, opacification and loss of vision for a patient. Many providers opt to treat with a corneal transplantation from human donors to remedy the situation. While it may work for some people, corneal transplantation sometimes fails for a number of reasons, including graft rejection or endothelial decompensation.
Keratoprosthesis, or more specifically, the Boston Keratoprosthesis, has paved the way for alternative treatment in recent years. Clinical experts discussed this ‘artificial cornea’ treatment at a symposium held at the 34th Congress of Asia-Pacific Academy of Ophthalmology (APAO) in Bangkok, Thailand.
Origins and Advantages of the Boston Keratoprosthesis
Keratoprosthesis involves the replacement of a damaged cornea with an artificial cornea. But why exactly do we need a permanent keratoprosthesis? According to Dr. Kimberly Sippel, from the Weill Cornell Medical College at New York-Presbyterian Hospital, while corneal transplant surgery can produce highly successful outcomes, ophthalmologists can often find themselves in situations where an ophthalmic environment is simply not able to support a clear corneal transplant. Therefore, the need for an artificial cornea is warranted as a permanent keratoprosthesis.
There are several different types of keratoprosthesis: the Boston Keratoprosthesis (B-KPro), osteo-odonto keratoprosthesis (OOKP), Moscow Eye Microsurgery Complex in Russia (MICOF) keratoprosthesis, and tibial bone keratoprosthesis. The B-KPro, however, is the most common implant – developed by Claes Dohlman at the Massachusetts Eye and Ear Infirmary, it was approved by the US Food and Drug Administration (FDA) in 1992. To date, there have been 13,000 implantation procedures performed worldwide.
The type 1 model (B-KPro) consists of two plates; the front plate and back plate are made up of polymethylmethacrylate (PMMA). Dr. Sippel mentioned the use of titanium for the back plate which may help reduce the incidence of retro-prosthetic membrane formation. “Sandwiched between the two plates is a corneal button to complete the device,” she explained. “The assembled device is then sutured into position in standard penetrating keratoplasty fashion.”
Boston Keratoprosthesis vs. Standard Corneal Transplant
“The Boston Keratoprosthesis holds several advantages over a standard corneal transplant,” commented Dr. Sippel. “For example, even if the carrier corneal tissue becomes opacified, the stem remains clear with the B-KPro.” She continued to explain further advantages including a front plate that is not deformable, which translates to less issues with astigmatism and a quick visual recovery. By the same token, Dr. Sippel remarked that a prompt visual recovery is also aided by immediate clearance of corneal edema.
While the B-KPro can be expensive for some people, lower cost alternatives have become available, such as the Lucia keratoprosthesis. Despite the cost, aphakic and pseudophakic powers mean no intraocular lens needs to be present. Requirements for corneal tissue quality is also not as stringent. In other words, the patient’s own cornea may be used in certain instances.
Managing the Boston Keratoprosthesis
The B-KPro is not without a risk for complications, which include glaucoma, erosion/extrusion, retro-prosthetic membranes and keratitis. In considering the post-op management of the B-KPro, Dr. Peter Zloty, an accomplished anterior segment surgeon and recipient of the 2019 APAO Achievement Award, contributed to the discussion.
According to Dr. Zloty: “Since the KPro procedure is one of exceptional needs and indications, it only makes sense that the post-surgical care would also need to be exceptional.”
The three main tenets of B-KPro management are inflammation control, pressure control and the maintenance of ocular surface health in the patient.
For the prevention of inflammation and infection, Dr. Zloty recommends a topical antibiotic such as a fluoroquinolone four times daily. While using antibiotics, he said it is best to avoid aminoglycosides. “Unique to KPro is also the use of an anti-collagenolytic antibiotic such as tetracycline,” he said.
“In addition, topical steroids such as prednisolone acetate or dexamethasone can be used post-op to further treat inflammation.”
To help prevent post-op pressure spikes, Dr. Zloty advocates the use of a topical glaucoma agent, such as apraclonidine, routinely used after surgery.
“If the patient has good lid closure and normal tear film, they will likely do well,” said Dr. Zloty. “The better the ocular surface, the less likely keratolysis or infection will develop.” Additionally, the use of bandage contact lens can also help prevent erosions and melting to maintain the ocular surface. Dr. Zloty recommends changing the lens every three to six months to prevent infection.
Overall, diagnosis and management are crucial to the success and full advantages of the B-KPro. Patients need to be observed often when possible to ensure proper restoration of vision. Intraocular pressure needs to be assessed, therapeutic contact lens needs to be replaced, and vision needs to be verified during each follow-up.
Although it may be a lifetime commitment for both the patient and the physician, survival studies show greater than 90% retention after five years. Compared to corneal transplantation, the B-KPro is miles ahead in driving positive visual outcomes.
Editor’s Note: The APAO 2019 Congress was held in Bangkok, Thailand, on March 6-9, 2019. Reporting for this story also took place at APAO 2019. Media MICE Pte Ltd, CAKE Magazine’s parent company, was the official media partner at APAO 2019.
