Idiopathic epiretinal membrane management and prognosis: a review

Idiopathic epiretinal membrane is one of the most common disorders encountered by vitreoretinal surgeons. While it precise pathogenic mechanism, by definition, is unknown, there are some steps that seem to explain its formation and effects. It is characteristically a semitranslucent, avascular, contractile fibrocellular tissue situated on the internal limiting membrane of the retina. Loss of vision is attributed to a variety of mechanisms, but most prominent and important are the effects of traction forces that may either directly or indirectly compromise macular function. The advent of optical coherence tomography has contributed greatly to the diagnosis and understanding of the pathoanatomy, and may be an important treatment guide, but may also lead the clinician to overattribute visual loss to the epiretinal membrane, possibly prompting unnecessary surgery. It is important to realize that vast majority of afflicted eyes do not develop visual symptoms sufficient to justify intervention. The aim of this review is to provide prognostic and treatment information for management of epiretinal membranes in the optical coherence tomography era

Fate and transport of metals in H₂S-rich waters at a treatment wetland

<p/> <p>The aqueous geochemistry of Zn, Cu, Cd, Fe, Mn and As is discussed within the context of an anaerobic treatment wetland in Butte, Montana. The water being treated had a circum-neutral pH with high concentrations of trace metals and sulfate. Reducing conditions in the wetland substrate promoted bacterial sulfate reduction (BSR) and precipitation of dissolved metal as sulfide minerals. ZnS was the most common sulfide phase found, and consisted of framboidal clusters of individual spheres with diameters in the submicron range. Some of the ZnS particles passed through the subsurface flow, anaerobic cells in suspended form. The concentration of "dissolved" trace metals (passing through a 0.45 μm filter) was monitored as a function of H₂S concentration, and compared to predicted solubilities based on experimental studies of aqueous metal complexation with dissolved sulfide. Whereas the theoretical predictions produce "U-shaped" solubility curves as a function of H₂S, the field data show a flat dependence of metal concentration on H₂S. Observed metal concentrations for Zn, Cu and Cd were greater than the predicted values, particularly at low H₂S concentration, whereas Mn and As were undersaturated with their respective metal sulfides. Results from this study show that water treatment facilities employing BSR have the potential to mobilize arsenic out of mineral substrates at levels that may exceed regulatory criteria. Dissolved iron was close to equilibrium saturation with amorphous FeS at the higher range of sulfide concentrations observed (>0.1 mmol H₂S), but was more likely constrained by goethite at lower H₂S levels. Inconsistencies between our field results and theoretical predictions may be due to several problems, including: (i) a lack of understanding of the form, valence, and thermodynamic stability of poorly crystalline metal sulfide precipitates; (ii) the possible influence of metal sulfide colloids imparting an erroneously high "dissolved" metal concentration; (iii) inaccurate or incomplete thermodynamic data for aqueous metal complexes at the conditions of the treatment facility; and (iv) difficulties in accurately measuring low concentrations of dissolved sulfide in the field.</p

Challenges in ophthalmic pathology: The vitreoretinal membrane biopsy

The introduction of vitreoretinal microsurgery has produced a new type of biopsy; that of the vitreoretinal membrane. This review investigates methods by which these scar-like tissues are handled in the laboratory and explores the implications of the results of such evaluations. The study of vitreoretinal membrane biopsies has provided much information concerning the pathobiology of the various conditions which may give rise to the tissue as well as insights into how membranes themselves develop. Moreover, the application of new laboratory techniques is expected to enhance our understanding of the formation of vitreoretinal membranes, and lead to further advances in their surgical and medical management.link_to_subscribed_fulltex

Pathobiology of epiretinal and subretinal membranes: Possible roles for the matricellular proteins thrombospondin 1 and osteonectin (SPARC)

Epiretinal and subretinal membranes are fibrocellular proliferations which form on the surfaces of the neuroretina as a sequel to a variety of ocular diseases. When these proliferations complicate rhegmatogenous retinal detachment (a condition known as proliferative vitreoretinopathy or PVR), the membranes often contain numerous retinal pigment epithelial (RPE) cells and a variety of extracellular proteins. The extracellular proteins include adhesive proteins like collagen, laminin and fibronectin. In addition, several matricellular proteins with potential counter-adhesive functions are present in the membranes. Two such matricellular proteins, thrombospondin 1 and osteonectin (or SPARC: Secreted Protein Acidic and Rich in Cysteine), tend to be codistributed with the RPE cells in PVR membranes. By virtue of their counter-adhesive properties, thrombospondin 1 and SPARC may reduce RPE cell-matrix adhesion and so permit key RPE cellular activities (for example, migration or shape change) in periretinal membrane development. Furthermore, within a 'cocktail' containing other proteins such as the metalloproteinases and growth factors like the scatter factor/hepatocyte growth factor family, matricellular proteins may play a role in the RPE cell dissociation from Bruch's membrane, which characterises early PVR.link_to_OA_fulltex