Purpose. 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.
In cases of bilateral corneal blindness in which traditional penetrating keratoplasty has either failed repeatedly or has no chance of survival, as in patients with progressive cicatrizing ocular surface disease and some chemical burns, a keratoprosthesis (KPro) may offer the only means of visual rehabilitation. Several keratoprosthesis designs are in use for this purpose. The two most common styles include those composed of a central cylinder with an implantable skirt composed of various materials and those utilizing a collar button configuration that sandwiches the corneal tissue around a central stem between front and back plates (Fig. 1). The polymethylmethacrylate (PMMA) Dohlman-Doane keratoprosthesis is of the latter collar button type and has been implanted into over 190 eyes since 1990. Two variants of the device have been developed to serve, on one hand, patients with good ocular surface hydration (type I) and, on the other hand, those with very dry eyes (type II) (Fig. 2). A description of this keratoprosthesis and the surgical technique for its placement has been reported elsewhere. 1,2
In the course of treatment with a KPro, several complications can arise which threaten long-term prognosis. These include the formation of a retroprosthesis membrane, corneal necrosis and melting, epithelial ingrowth, glaucoma, retinal detachment, and endophthalmitis. In some instances, treatment of these complications involves removal and replacement of the KPro and its supporting corneal graft. 3
The histopathology of tissue removed during reoperations or from eyes obtained postmortem while bearing an uncomplicated Dohlman-Doane KPro has not previously been described in the literature. In this paper, we describe and compare the histologic features of three KPro–cornea complexes explanted due to various complications with that from one KPro/corneal specimen taken postmortem from a relatively uncomplicated eye.