ELECTRON MICROSCOPIC AND HISTOLOGICAL EVALUATION OF LAMELLAR CHANNEL DEPOSITS ON ICRS EXPLANTED FROM HUMAN EYES.

Abstract

Abstract: : Purpose: Intrastromal Corneal Ring Segments (ICRS – INTACS), are crescent–shaped arcs of polymethylmethacrylate (PMMA) plastic inserted in the stroma to correct myopia. Postoperatively, lamellar channel deposits have been observed with slitlamp and confocal microscopy and optical coherence tomography, yet, little is known regarding their nature. Methods: ICRS from 12 patients (13 quiet eyes) with an uneventful implantation were explanted due to residual refractory error. The segments were evaluated by histological staining as well as by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to better understand the nature of the deposits. Electron Microscopy: Following explantation, the segments were fixed in 3% cacodylate buffered glutaraldehyde and standard EM processing. Each segment was bisected and mounted on opposite sides of an aluminum stub to enable imaging both the anterior and posterior. Histology: The segments were formalin fixed and paraffin embedded. Resulting blocks were then cut and stained. Results: Microscopically, TEM and SEM of the ICRS surfaces revealed a relatively amorphous focal film with occasional cells (probably fibroblasts?). Histology: Changes characteristic of abundant nonspecific eosinopilic background within which were embedded numerous very small, granular pieces of material. Immunohistochemistry: Sections showed fragments of an amorphous substance which were both vimentin– and cytokeratin–positive. Conclusions: Electron microsopy (TEM) suggested the presence of intact cells adhering to the sides of the implants, consistent with sporadic fibroblasts (nucleus and cellular features seen) and degradation products of stromal cells within a mild inflammatory response (seen in 2 patients). Granular material was mostly non–cellular, without clinical significance, although the specific identity of it has not been determined. Immunohistology staining, however, has shown no evidence of cell wall, nucleus, or other cell–like features. There is no evidence of microbial contamination, epithelial downgrowth or active cellular necrosis. Despite deposit formation, all corneas were clinically stable and patients had normal visual acuity.

Keywords: refractive surgery: complications • microscopy: electron microscopy • immunohistochemistry