The Boston Keratoprosthesis (KPro) is an artificial cornea designed to restore vision in individuals experiencing severe corneal blindness. This prosthetic device serves as a solution when traditional corneal transplants are not suitable or have failed. The Boston KPro provides an alternative to address complex cases of vision loss.
Understanding Boston Keratoprosthesis
The Boston Keratoprosthesis is a “collar button” shaped artificial cornea, typically composed of a front optical part made from polymethylmethacrylate (PMMA), a back plate, and a titanium locking c-ring. During implantation, a donor corneal graft is positioned between the front and back plates of the device. This assembly is then secured, allowing light to enter the eye through the prosthetic optical component.
The device functions by providing a clear pathway for light to reach the retina, bypassing a damaged or opaque natural cornea. The Boston KPro was first developed in 1965 by Dr. Claes Henrik Dohlman and his team at the Massachusetts Eye and Ear Infirmary, undergoing refinements over several decades. It received approval from the U.S. Food and Drug Administration in 1992. Early designs included a “screw-in” mechanism, which later evolved to a threadless design where the plates snap together. Holes were added to the back plate in 1996 to allow aqueous humor to nourish the donor graft.
Who Benefits from Boston Keratoprosthesis?
The Boston Keratoprosthesis is a treatment option for corneal disorders that cannot be effectively addressed by standard corneal transplantation. It is often considered a last resort for patients with severe and complex corneal conditions. This includes individuals who have experienced multiple failed corneal transplants.
Specific conditions where the Boston KPro is frequently indicated include severe chemical burns and ocular cicatricial pemphigoid. Other challenging cases involve Stevens-Johnson syndrome, aniridia (absence of the iris), and certain pediatric congenital corneal opacities like Peter’s anomaly. The device is typically offered to patients with vision worse than 20/400, especially if the vision in the other eye is also significantly impaired.
The Surgical Journey
The implantation of a Boston Keratoprosthesis involves a surgical procedure known as prosthokeratoplasty. Before the surgery, careful planning is undertaken, and any advanced glaucoma or retinal pathology is typically evaluated. The procedure begins with the assembly of the Boston KPro device, where a donor corneal graft is prepared and positioned between the front and back plates of the prosthesis. This creates a unified device that includes both the artificial and donor components.
Once the device is assembled, the patient’s eye is prepared. A circular section of the patient’s damaged cornea is precisely removed, making space for the new KPro-donor complex. The assembled device, with the donor cornea, is then carefully sutured into the eye, similar to how a traditional corneal transplant is secured. Immediate post-operative care involves monitoring the eye, and patients typically begin their initial recovery in the hospital setting.
Living with a Boston Keratoprosthesis
Living with a Boston Keratoprosthesis requires a commitment to lifelong follow-up care to maintain vision and manage potential complications. Regular eye examinations are necessary to monitor the device’s stability and the overall health of the eye. Patients must adhere to a strict regimen of topical medications, which commonly include antibiotics to prevent infection and glaucoma drops to control intraocular pressure. This ongoing medication use helps to reduce the risk of long-term issues.
One common long-term complication is the formation of a retroprosthetic membrane (RPM), a fibrous tissue that can grow behind the device and obscure vision. RPM occurs in a significant number of patients, with reported rates ranging from approximately 25% to 44% in various studies. Glaucoma, characterized by increased pressure within the eye that can damage the optic nerve, is another concern, observed in about 15% to 18% of cases. These complications are managed with medications or, if necessary, additional surgical interventions.
Infection is a serious, though less frequent, complication that requires prompt treatment with antibiotics. While cases of infectious endophthalmitis were not reported in some series, it remains a potential risk. Despite these challenges, the Boston KPro can improve visual outcomes and enhance the quality of life for patients who were severely visually impaired. Studies have indicated that a substantial percentage of patients, around 75%, achieve a visual acuity of 20/200 or better, allowing for greater independence and engagement in daily activities.