A rationale for membrane peeling in the repair of stage 4 macular holes.

AIM: To examine the histological and immunocytochemical characteristics of epiretinal membranes (ERM) associated with stage 4 macular holes (MH) so as to establish a vitreoretinal rationale for surgery in stage 4 MH. METHOD: Consecutive patients with stage 4 MH undergoing vitrectomy and membrane peeling were recruited. Preoperatively, the eyes were examined for ERM formation over the macula and completeness of posterior hyaloid membrane (PHM) separation from the retina. ERM peel specimens obtained during surgery were sent for histological and immunocytochemical studies and were compared with the PHM specimens taken from a previous post-mortem study of eyes with physiological posterior vitreous detachment but without macular holes. RESULT: A total of 13 patients with stage 4 MH fulfilled the inclusion criteria and were recruited. Preoperatively, all eyes had an ERM over the macula and incomplete separation of the PHM seen as a defect in the PHM on specular biomicroscopy. Histologically, the ERM specimens had very similar morphological characteristics to PHM, consisting of an eosinophilic membrane of varying thickness with scattered spindle-shaped cells. The membranes stained positively for type IV collagen while the cells were glial fibrillary acidic protein positive. Postoperatively, successful closure of MH was achieved in all cases. CONCLUSION: Stage 4 MH is characterised by incomplete separation of the PHM from the retina with remnants overlying the macula manifesting as ERM. Removal of the ERM is required during vitrectomy in order to relieve the tangential forces involved in the development of MH.

Hyperconvolution of the inner limiting membrane in vitreomaculopathies.

BACKGROUND: This study investigates the similarities and differences between epiretinal membranes in four clinically distinct types of vitreomaculopathy. We propose a hypothesis on the origin of the predominant cell type and its potential role in causing these conditions. METHODS: Epiretinal membranes (ERMs) surgically removed from a prospective, consecutive series of vitrectomies for macular pucker associated with an untreated peripheral horseshoe tear (MP), cellophane maculopathy (CM), stage 4 macular hole (MH) and vitreomacular traction syndrome (VMT) were examined by light microscopy and by immunocytochemistry (ICC) using antibodies marking type IV collagen, type II collagen, glial fibrillary acidic protein (GFAP), and low- and high-molecular-weight cytokeratin (MNF116). These specimens were compared with post-mortem control eyes with and without physiological posterior vitreous detachment (PVD). Light microscopy was carried out on 5-microm-thick sections cut from formalin-fixed, paraffin-embedded tissue blocks. Appropriate autoclave or enzyme pre-digestion steps were deployed to retrieve antigens for ICC. No patient had undergone previous vitreoretinal surgery or peripheral retinopexy. RESULTS: From a series of 38 patients, (13 CM, 8 MP, 16 MH and 1 VMT) a total of 20 specimens contained sufficient tissue for histology and immunocytochemistry. All specimens contained portions of inner limiting membrane (ILM) coated by GFAP-positive cells. Specimens from patients with MP and CM exhibited hyperconvolution of the ILM, which was not found in the specimens from patients with MH or VMT or in the control eyes. Hyperconvolution was associated with increased glial cell density, GFAP staining intensity and duplication of ILM basement membrane. Three cases of ERMs from the MP group contained, in addition, cytokeratin-positive cells. In the control group; post-mortem eyes with PVDs showed patchy staining of the posterior hyaloid membrane for GFAP and type 4 collagen. Post-mortem eyes with attached gel showed weak positivity of the ILM for type 4 collagen, and a monolayer of GFAP-positive cells lined the vitreous aspect of the ILM. CONCLUSIONS: These results indicate that glial cells are fundamentally important in the formation of ERMs found in this group of vitreomaculopathies. The hyperconvolution and duplication of the ILM in CM and MP were striking and distinctive features and suggest a mechanism by which these membranes exert tractional forces on the retina. Post-mortem control eyes contained a similar (but more dispersed) population of GFAP-positive cells in the region of the ILM, suggesting the primary aetiology for CM and MP may originate within the ILM. ERMs from MP cases may, in addition, contain cytokeratin-positive cells, of probable RPE origin.

Clinical, histological and ultrastructural studies of the posterior hyaloid membrane.

AIMS: To investigate the histological, immunohistochemical and ultrastructural features of the posterior hyaloid membrane (PHM) in its naturally separated state in patients without previous surgery and slit-lamp documentation of antemortem posterior vitreous detachment (PVD). METHODS: A prospective study was commenced in 1992 to recruit patients with physiological PVD from an unselected group of general medical inpatients and ascertain the prevalence of PVD. Postmortem specimens subsequently available were studied to analyse the clinicopathological correlation and processed using standard techniques for histology, immunohistochemistry and electron microscopy. RESULTS: Eighty-five patients were examined with ages ranging from 68 to 98 yrs (mean 83.4 yrs). The posterior hyaloid membrane had clearly separated from the retina in 66% of eyes. Twenty-nine eyes from 15 patients were subsequently studied pathologically. The posterior hyaloid membrane exhibited a uniform cellular component, most densely populated around the Weiss' ring. The cells were characterised by oval or round nuclei, indistinct cytoplasm and were only seen within, or abutting, the weakly eosinophilic posterior hyaloid membrane. The posterior aspect of the posterior hyaloid membrane showed a convoluted appearance staining lightly with haematoxylin and eosin. The detached posterior hyaloid membrane exhibited focal positivity for GFAP and type IV collagen. Electron microscopy demonstrates both fibres and basement membrane associated with the cellular component including hemi-desmosome attachment plaques between the cells and basement membrane. CONCLUSIONS: This study illustrates some of the structural differences between the posterior hyaloid membrane and the cortical vitreous gel it envelopes and demonstrates the presence of cells intimately associated with the posterior hyaloid membrane in its naturally separated state. We propose the cellular population integral to the PHM to be designated as laminocytes in order to emphasise their type IV collagen/basement membrane association and planar array within the membrane which separates at posterior vitreous detachment.