This article discusses the kinds of cases for which the Rochester Eye Institute Team used the Boston KPro device, and it addresses some of the underlying reasons for the selection of this modality. This article does not report in detail on the risks, benefits, and complications associated with keratoprosthesis surgery in general or those specifically related to the Boston device.
Recent Keratoprosthesis History
For more than half a century, keratoprosthesis (KPro) has been perceived by corneal surgeons as well as by the general ophthalmological community as an infrequently performed procedure, indicated only in bilateral blindness where no alternatives were possible, and associated with poor prognosis and a high rate of complication. Over the last decade, only a handful of these procedures were performed annually throughout the world. Recent reports seem to indicate an altered utilization pattern associated with the modified Boston KPro device.
As a result of a number of changes in the design of the Boston device,1 the techniques for surgical implantation,2 as well as routines of postoperative management, the procedure has taken on a new identity.3 A recent review of more than 250 cases performed at the University of Rochester Eye Institute over a period of 48 months revealed a wide set of indications and a low rate of complications.
Current Design
The Boston KPro is composed of polymethylmethacrylate and consists of a 3.2 mm optical cylinder that is passed through a central 3 mm aperture in an 8.5 mm or 8.75 mm donor corneal button. A fenestrated back plate clips on to secure donor tissue to the front plate (optical cylinder). A locking titanium ring prevents uncoupling of the device (diagram 1).
Courtesy of James V. Aquavella, MD
Diagram 1. Depicts the donor cornea situated between the front optical cylinder and back retaining plate.
Coupling the device with a piece of donor tissue assists in the assembly process and enables rapid implantation in the style of a cornea transplant utilizing 10-0 interrupted nylon sutures. The fenestrations allow for the free passage of metabolites, a modification perceived to be primarily responsible for the new stability of the implanted device.
A large-diameter hydrophilic bandage contact lens is placed over the implanted device and is worn continuously, affording protection to the ocular surface. Long-term prophylactic antibiotic coverage is thought to be responsible for the paucity of postoperative infections, in contrast to the problems associated with previous iterations of this procedure.3
Current Indications for Keratoprosthesis
In the current series of cases performed at the University of Rochester Eye Institute, device utilization was found to fall into 3 broad categories.
The first category consists of adult cases in which routine corneal transplantation was considered complicated and associated with a guarded prognosis. The second category consists of primary procedures performed in lieu of routine corneal transplantation. The third category consists of infants and young children (Table 1).
Table 1 |
Indications for Keratoprosthesis |
1. Poor prognosis keratoplasty |
a. Autoimmune |
b. Nonautoimmune |
2. Primary keratoprosthesis in cases with good prognosis for corneal transplant |
3. Pediatric keratoprosthesis |
Category 1 can be divided into groups with and without associated autoimmune involvement. In the absence of autoimmune disease, there were no extrusions, and there was 100% retention despite a preoperative diagnostic array that included keratitis sicca, neurotropic and chemical keratitis, repeated graft failure, herpes simplex, graft vs. host disease, stem-cell deficiency, glaucoma, and aniridia.
The prime motivating factor in this group of patients was to avoid the prospect of allograft rejection. The initial cases fell into this category, and all of these as well as subsequent cases were characterized by a return to full visual potential within a matter of weeks after surgery.
The absence of astigmatism and the ability to essentially ignore neovascularization were benefits realized in the early postoperative period. The researchers were not confronted with persistent epithelial defects or other evidence of ocular surface disease, which frequently threaten graft survival following penetrating keratoplasty. Management of glaucoma was straightforward and unimpeded by the presence of the device. Fundus evaluation and photography were unimpeded as were routine visual fields.
Some patients had undergone earlier glaucoma surgery including trabeculectomy and aqueous shunts. In 3 patients, shunts were implanted at the time of prosthesis surgery; in 3 others, implantation followed prosthesis surgery. Figures 1 and 2 show the pre- and postoperative appearance of a patient with xerophthalmia secondary to trachoma.