The global burden of visual impairment is substantial. According to a report published by the World Health Organization in 2009, there are an estimated 314 million visually impaired individuals globally, representing approximately 5% of the world population. Forty-five million of these people were considered blind. Corneal disease accounted for 8 million blind, with 1.5 million of those being children.
In areas of Africa, nearly 90% of blindness is caused by corneal disease, with trachoma as the major cause. Untreated primary corneal ulceration continues to be a major cause of global corneal blindness. In the United States, the incidence of corneal ulceration is approximately 11 ulcers per 100 000 people per year, whereas in southern India and Nepal, the respective rates are 10 and 80-fold greater.
Role of Corneal Allotransplantation
Corneal allograft has been the mainstay of therapy for severe corneal disease for the last 40 years. Well-conceived regulation of tissue banking in the United States, general social acceptance of organ and tissue donation, and the resultant abundance of quality regional eye banks across the country now ensure an excellent supply of corneal donor tissue. However, outside the United States, the supply of donor corneas suitable for transplantation falls far short of demand and varies widely by region because of legal, cultural, religious, and socioeconomic constraints. Therefore, a procedure appropriate for the nonindustrialized world is needed urgently.
Keratoprosthesis
The concept of using a prosthetic cornea to replace a diseased one dates back to the work of Guilaume Pellier de Quengsy during the time of the French Revolution. Although many designs were tried, the Boston keratoprosthesis type I, developed at the Massachusetts Eye & Ear Infirmary over the last 40 years, is now the keratoprosthesis used most commonly, with more than 3500 devices implanted worldwide. The Boston keratoprosthesis type I seems applicable for a broad array of corneal conditions not amenable to allotransplantation, although severe dry eye and cicatrizing ocular surface disease remain relative contraindications.
The Boston keratoprosthesis type I consists of 2 curved polymethyl methacrylate plates sandwiched around a corneal autograft or allograft. A soft contact lens is used after surgery to prevent corneal dehydration and to minimize the risk of ulceration. Implantation is performed in 1 stage, and the technique and operative time are similar to that of standard corneal transplantation.
The overall retention rate of the Boston keratoprosthesis type I in the United States recently was reported to be 95% at 8.5 months and 60% at 24 months. The latter study, however, included patients with recalcitrant autoimmune diseases. Unpublished data suggest that retention in nonautoimmune patients is closer to 90% at 2 years (Ament J, Todani A, Ciolino J, Belin M. Multicenter KPro retention data. KPro Study Group, Albany, New York. Ongoing study). To put these numbers in perspective, a large outcome study of repeat corneal allotransplantation showed that approximately 80% of second allografts had failed by 5 years after surgery and essentially that all third and subsequent regrafts failed within the same period. Visual restoration with the device has been dramatic. According to a large multicenter study, only 3.6% of preoperative keratoprosthesis candidates could be corrected to 20/200 or better. After keratoprosthesis implantation, visual acuity at 1 year was 20/200 or better in 56% and 20/40 or better in 23% of operated eyes. Perioperative complications are similar to those of standard corneal allotransplantation. Long-term complications associated with the device include glaucoma, retroprosthetic membrane formation, and sterile vitritis.
Keratoprosthesis
The concept of using a prosthetic cornea to replace a diseased one dates back to the work of Guilaume Pellier de Quengsy during the time of the French Revolution. Although many designs were tried, the Boston keratoprosthesis type I, developed at the Massachusetts Eye & Ear Infirmary over the last 40 years, is now the keratoprosthesis used most commonly, with more than 3500 devices implanted worldwide. The Boston keratoprosthesis type I seems applicable for a broad array of corneal conditions not amenable to allotransplantation, although severe dry eye and cicatrizing ocular surface disease remain relative contraindications.
The Boston keratoprosthesis type I consists of 2 curved polymethyl methacrylate plates sandwiched around a corneal autograft or allograft. A soft contact lens is used after surgery to prevent corneal dehydration and to minimize the risk of ulceration. Implantation is performed in 1 stage, and the technique and operative time are similar to that of standard corneal transplantation.
The overall retention rate of the Boston keratoprosthesis type I in the United States recently was reported to be 95% at 8.5 months and 60% at 24 months. The latter study, however, included patients with recalcitrant autoimmune diseases. Unpublished data suggest that retention in nonautoimmune patients is closer to 90% at 2 years (Ament J, Todani A, Ciolino J, Belin M. Multicenter KPro retention data. KPro Study Group, Albany, New York. Ongoing study). To put these numbers in perspective, a large outcome study of repeat corneal allotransplantation showed that approximately 80% of second allografts had failed by 5 years after surgery and essentially that all third and subsequent regrafts failed within the same period. Visual restoration with the device has been dramatic. According to a large multicenter study, only 3.6% of preoperative keratoprosthesis candidates could be corrected to 20/200 or better. After keratoprosthesis implantation, visual acuity at 1 year was 20/200 or better in 56% and 20/40 or better in 23% of operated eyes. Perioperative complications are similar to those of standard corneal allotransplantation. Long-term complications associated with the device include glaucoma, retroprosthetic membrane formation, and sterile vitritis.
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