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Anita Shukla, Andrea Cruzat, Juan-Carlos Abad, Claes H. Dohlman, Kathryn A. Colby; Results of the Boston keratoprosthesis type 1 larger backplate. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6069.
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It is possible that retroprosthetic membrane formation after Boston Keratoprosthesis surgery is due to unrestricted swelling of the host cornea wound, allowing stromal keratocytes to migrate and form the membrane. Therefore, enlarging the backplate diameter might clamp the wound more effectively and reduce membrane formation. In this study, we report using anterior segment OCT (AS-OCT) to study the anatomy of the graft host junction after standard and larger backplate surgery and compare their clinical outcomes.
5 patients with 9.5 mm titanium Boston Kpro backplates and 5 patients with standard 8.5 mm backplates were imaged by AS-OCT. All patients had a standard 8.5 mm carrier graft placed into an 8.0 mm trephined host. The location of the graft host junction in relation to the backplate, the corneal thickness in the graft-host junction, and the chamber angle were assessed. For each parameter, 4 representative images of the different quadrants were analyzed by 2 observers. A retrospective review of the clinical course and incidence of retroprosthetic membrane formation was performed. The clinical outcomes of 5 additional patients with larger backplates from an outside center were included in the analysis.
With the larger 9.5 mm backplate, the wound was completely clamped on both sides, restricting swelling. However, with the standard 8.5 mm backplate, there was clamping of the graft but not the host in most cases resulting in a significantly thicker graft host junction (p<0.05). The angle was open in all cases with no statistical difference in size between both groups. Over an average 9 month follow-up period (range 4.5 to 20 months) none of the patients in the larger backplate group developed retroprosthetic membranes however one of the patients developed a corneal melt.
An important complication of the Boston keratoprosthesis has been the formation of retroprosthetic membranes which limit visual acuity by blocking the optical axis. In this study, we demonstrate that a larger 9.5 mm Boston Kpro backplate clamps the graft host junction creating a barrier against the growth of retroprosthetic membranes from the host cornea wound.
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