title: Characterization of retrokeratoprosthetic membranes in the Boston type 1 keratoprosthesis.
abstract: OBJECTIVE
  To evaluate retroprosthetic membranes that can occur in 25% to 65% of patients with the Boston type 1 keratoprosthesis (KPro).
  
  
  METHODS
  Two patients with Peter anomaly and 2 with neurotrophic scarred corneas underwent revisions of their type 1 KPros because of visually compromising retroprosthetic membranes. The excised membranes were studied by light microscopy with hematoxylin-eosin, periodic acid-Schiff, and toluidine blue stains. Immunohistochemical and transmission electron microscopic examination were also used.
  
  
  RESULTS
  Light microscopic examination revealed that the retro-KPro fibrous membranes originated from the host's corneal stroma. These mildly to moderately vascularized membranes grew through gaps in the Descemet membrane to reach behind the KPro back plate and adhere to the anterior iris surface, which had undergone partial lysis. In 2 cases, the fibrous membranes merged at the pupil with matrical portions of metaplastic lens epithelium, forming a bilayered structure that crossed the optical axis. Retro-KPro membranes stained positively for α-smooth muscle actin but negatively for pancytokeratin. Electron microscopy confirmed the presence of actin filaments within myofibroblasts and small surviving clusters of metaplastic lens epithelial cells.
  
  
  CONCLUSIONS
  Stromal downgrowth, rather than epithelial downgrowth, was the major element of the retro-KPro membranes in this series. Metaplastic lens epithelium also contributed to opacification of the visual axis. Florid membranous inflammation was not a prominent finding and thus probably not a requisite stimulus for membrane development. Further advances in prosthetic design and newer antifibroproliferative agents may reduce membrane formation.
authors.affiliation: David G. Cogan Laboratory of Ophthalmic Pathology, Massachusetts Eye and Ear Infirmary, and Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Stacy
authors.forename: Frederick A
authors.initials: FA
authors.lastname: Jakobiec
authors.forename: Norman A
authors.initials: NA
authors.lastname: Michaud
authors.forename: Claes H
authors.initials: CH
authors.lastname: Dohlman
authors.forename: Kathryn A
authors.initials: KA
authors.lastname: Colby
mesh_terms: D000199:Actins / Q000378:metabolism; D000328:Adult; D000368:Aged; D000869:Anterior Eye Segment / Q000002:abnormalities / Q000601:surgery; D001187:Artificial Organs; D002675:Child, Preschool; D003315:Cornea; D003318:Corneal Opacity / Q000601:surgery; D020878:Device Removal; D005124:Eye Abnormalities / Q000601:surgery; D005260:Female; D005355:Fibrosis / Q000473:pathology; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008566:Membranes / Q000378:metabolism / Q000473:pathology* / Q000648:ultrastructure; D008875:Middle Aged; D019736:Prostheses and Implants; D011475:Prosthesis Failure; D012086:Reoperation
chemical_list: C541116:ACTA2 protein, human; D000199:Actins