Histopathology of explanted collar button keratoprostheses: a clinicopathologic correlation.

Objective: To compare the histopathology of three PMMA collar button type keratoprosthesis (KPro)/corneal specimens, explanted due to various complications, with that from one KPro/corneal specimen taken postmortem from an otherwise "healthy" enucleated eye.

Methods: Patient 1 (chemical injury) had no problems for 3 years after KPro placement; the entire eye was obtained postmortem. Patient 2 (repeated graft failures, nonautoimmune disease) developed an "unlaserable" retroprosthesis membrane 4 months after KPro placement. A new KPro was placed. Patient 3 [ocular cicatricial pemphigoid (OCP)] developed tissue melt at the KPro-cornea interface 7 months after KPro placement, and the KPro was replaced. Patient 4 (OCP) developed progressive corneal melt around the KPro 3.5 years after placement resulting in replacement. All KPro/cornea specimens were processed and sectioned for histology with the KPro in place.

Results: All patients exhibited growth of corneal or conjunctival derived epithelium under the KPro front plate. In patients 1 and 2, no epithelial downgrowth was noted and the keratocyte density appeared normal with few inflammatory cells present. Dense fibrous tissue was present behind the KPro in patient 2. Patients 3 and 4 showed massive inflammatory cell infiltration and tissue necrosis with "melt" adjacent to the stem resulting in epithelial downgrowth.

Conclusions: Corneal inflammation and degradation after KPro placement correlate well with the preoperative diagnostic category. Patients with immune-related corneal surface disease can exhibit marked inflammatory responses leading to necrosis, stromal melting, and the formation of an epithelial fistula. In contrast, patients without autoimmune corneal disease demonstrate a remarkably noninflamed cornea with intact keratocytes and without epithelial ingrowth, commensurate with their clinical appearance.