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Indications for Keratoprosthesis


Key Concepts

  • Widespread use of keratoprosthesis devices has led to indications of improved vision in many patients with no other treatment options.

  • The prognosis for keratoprosthesis recipients can be classified into three main groups, in decreasing order of success: (a) corneal allograft failure, (b) chemical injury, and (c) autoimmune-related, cicatricial, keratoconjunctival scarring.

  • The two designs used most commonly in the United States and Europe are the Boston keratoprosthesis type 1 and osteo-odonto-keratoprosthesis (OOKP).

  • Whereas corneal transplant failure is the most common indication for keratoprosthesis implantation in the United States, chemical injury is a more common indication internationally.

Introduction

Corneal transplantation is currently considered the most successful solid organ transplantation, with more than 70,000 corneal grafts implanted every year in the United States, and rates of corneal graft survival reportedly above 80% after 5 years under optimal circumstances. However, long-term viability of full-thickness keratoplasty has been reported to be 55% at 15 years postoperatively, and there remain patients with visually significant corneal opacity in whom standard penetrating or lamellar keratoplasty performs poorly. Keratoprosthesis surgery, or artificial corneal replacement, is increasingly used for visual restoration of corneal blindness. The history of keratoprosthesis can be traced back to the work of Guillaume Pellier de Quengsy, who first proposed in 1789 that an artificial cornea could be implanted in place of an opacified cornea. Initially considered to be a last resort treatment for patients who had experienced multiple failed corneal transplants, today the indications for keratoprosthesis encompass a wide array of corneal disorders. In standard corneal transplantation, keratoconus and corneal dystrophies are the conditions associated with the best graft survival with success rates of 93 and 89% 5 years after surgery, respectively. However, corneal allograft survival rates are lower in the setting of limbal stem cell failure, aniridia, after chemical injury, in Stevens-Johnson syndrome (SJS) and mucous membrane pemphigoid (MMP), and in the presence of extensive corneal vascularization, in which primary corneal transplantation can be associated with allograft survival rates well below 25% and rates of 20/40 best corrected vision near zero. In a study from India, the overall 5-year survival rate for corneal transplantation was less than 50%. Limbal stem cell deficiency ruins many otherwise perfect grafts by preventing normal corneal epithelial transparency. Moreover, refractive failure may result in poor vision despite an otherwise perfectly clear and compact allograft. Postoperative astigmatism, anisometropia, and/or an inability to tolerate refractive contact lens wear are common. Only approximately one-third of patients with penetrating keratoplasty in the most optimal circumstances achieve 20/40 vision with spectacle correction, and patients with high astigmatism may remain legally blind with spectacle correction alone. Finally, when a corneal allograft has failed, success is less likely with each successive graft, with 5-year survival rates as low as 25% for second grafts and 0% for third grafts. ,

Keratoprosthesis Designs Currently in Wide Use

Although numerous keratoprosthesis designs have been proposed and attempted, the two designs used in the United States and Europe, respectively, more than any others are the Boston keratoprosthesis type 1 and the osteo-odonto-keratoprosthesis (OOKP). Each device has its strengths and weaknesses in specific clinical conditions, and therefore the indications for each device are different.

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