Charanjit Sethi

Complement factor H deficiency in aged mice causes retinal abnormalities and visual dysfunction.

Age-related macular degeneration is the most common form of legal blindness in westernized societies, and polymorphisms in the gene encoding complement factor H (CFH) are associated with susceptibility to age-related macular degeneration in more than half of affected individuals. To investigate the relationship between complement factor H (CFH) and retinal disease, we performed functional and anatomical analysis in 2-year-old CFH-deficient (cfh−/−) mice. cfh−/− animals exhibited significantly reduced visual acuity and rod response amplitudes on electroretinography compared with age-matched controls. Retinal imaging by confocal scanning laser ophthalmoscopy revealed an increase in autofluorescent subretinal deposits in the cfh−/− mice, whereas the fundus and vasculature appeared normal. Examination of tissue sections showed an accumulation of complement C3 in the neural retina of the cfh−/− mice, together with a decrease in electron-dense material, thinning of Bruchs membrane, changes in the cellular distribution of retinal pigment epithelial cell organelles, and disorganization of rod photoreceptor outer segments. Collectively, these data show that, in the absence of any specific exogenous challenge to the innate immune system, CFH is critically required for the long-term functional health of the retina.

Matrix Metalloproteinases in Disease and Repair Processes in the Anterior Segment

The pathogenesis of many anterior segment disorders and ocular complications following surgery are secondary to the wound healing response. The extent of clinical damage observed is closely related to the amount of scarring and tissue contraction. Matrix metalloproteinases (MMPs) are a family of enzymes that play a vital role in all stages of the wound healing process. They degrade all extracellular matrix components and also have the ability to synthesize collagen and extracellular matrix members, and are therefore important in the remodeling of a wound. Overexpression of MMPs results in excessive extracellular matrix degradation, leading to tissue destruction and loss of organ function. In the case of the anterior segment, this may mean the loss of visual function. This review focuses on the role MMPs have in the development of various anterior segment disorders. The importance of MMPs in the wound healing response and its potential modulation to manipulate the scarring response is being recognized, and current developments will be described.

Proliferative vitreoretinopathy—developments in adjunctive treatment and retinal pathology

Proliferative vitreoretinopathy (PVR) remains a difficult management problem despite advances in vitreoretinal surgery. There is still a significant incidence of PVR in rhegmatogenous retinal detachment and other forms of retinal disease. Surgery for PVR now has a high anatomical success rate although visual results are often disappointing. The use of adjunctive treatments to prevent cellular proliferation holds promise for the prevention of PVR or recurrences after surgery. Control of proliferation and strategies aimed at improving visual outcome are important areas of future research in PVR and other forms of retinal disease. Studies of the intraretinal and peri-retinal pathology of PVR have demonstrated characteristic changes which may have a significant influence on visual outcome and surgical management.

Animal models of retinal detachment and reattachment: identifying cellular events that may affect visual recovery

Retinal detachment continues to be a significant cause of visual impairment, either through the direct effects of macular detachment or through secondary complications such as subretinal fibrosis or proliferative vitreoretinopathy. Animal models can provide us with an understanding of the cellular mechanisms at work that account for the retinopathy induced by detachment and for the generation of secondary effects. As we understand the mechanisms involved, animal models can also provide us with opportunities to test therapeutic agents that may reduce the damaging effects of detachment or improve the outcome of reattachment surgery. They may also reveal information of use to understanding other causes of blindness rooted in retinal defects or injuries. Understanding the effects of detachment (and reattachment) are likely to become even more important as surgeons gain skills in subretinal surgical techniques and macular translocation, both of which will generate short-lived detachments. Here we discuss the fundamental events that occur after detachment, present changes associated with reattachment, and discuss retinal changes that may affect the return of vision.

Silicone oil concentrates fibrogenic growth factors in the retro-oil fluid

Aim: To determine whether silicone oil concentrates protein and growth factors in the retro-oil fluid. Methods: A laboratory analysis of intraocular fluid and vitreous specimens obtained from patients undergoing removal of silicone oil, revision vitrectomy, or primary vitrectomy for macular hole, proliferative vitreoretinopathy (PVR), or retinal detachment. Patients were prospectively recruited from routine vitreoretinal operating lists. Vitreous cavity fluid and vitreous samples were analysed for the presence of transforming growth factor beta (TGF-β2), basic fibroblast growth factor (bFGF), interleukin 6 (IL-6), and total protein using either commercially available enzyme linked immunosorbent assays (ELISA) or protein assay kits. Results: The median levels of bFGF, IL-6, and protein in the retro-oil fluid were raised (p<0.05) compared to all the other vitreous and vitreous cavity fluid samples. bFGF, IL-6, and protein levels were raised in PVR vitreous compared to non-PVR vitreous. TGF-β2 levels were not significantly raised in retro-oil fluid or in PVR vitreous. Conclusions: The concentration of fibrogenic (bFGF) and inflammatory (IL-6) growth factors and protein is raised in retro-silicone oil fluid. This may contribute to the process of retro-oil perisilicone proliferation and subsequent fibrocellular membrane formation.

Experimental retinal reattachment: a new perspective.

In the feline model, retinal detachment initiates a cascade of changes that include photoreceptor-cell “deconstruction,” apoptotic death of some photoreceptors, neurite outgrowth from second-and third-order neurons, remodeling of photoreceptor synaptic terminals, and Müller-cell gliosis. We have previously shown that reattachment within 24 h halts or reverses many of these presumed detrimental changes. However, in patients with retinal detachments, reattachment cannot always be performed within this 24-h window. Moreover, recovery of vision following successful reattachment surgery in the macula is often imperfect. Here, we examine the ability of relatively long-term reattachment (28 d) to stop or reverse several cellular events that occur at 3 d of detachment. In contrast to earlier studies of reattachment, which focused on the regeneration of outer segments, we focus our attention here on other cellular events such as neuronal remodeling and gliosis. Some of these changes are reversed by reattachment, but reattachment itself appears to stimulate other changes that are not associated with detachment. The implications of these events for the return of vision are unknown, but they do indicate that simply reattaching the retina does not return the retina to its pre-detachment state within 28 d.

Intraretinal and periretinal pathology in anterior proliferative vitreoretinopathy

ObjectivesTo determine the intraretinal and periretinal pathological changes in early anterior proliferative vitreoretinopathy (APVR).DesignObservational case series.ParticipantsEighteen patients undergoing retinectomy for APVR.MethodsRetinectomy specimens removed at vitrectomy surgery were analysed by (a) semithin light microscopy, (b) immunohistochemistry and (c) electron microscopy.ResultsThe specimens showed consistent outer retinal degenerative changes, marked Muller cell hypertrophy and glial continuity to epiretinal membranes. Photoreceptor outer and inner segments were markedly disrupted and occasional photoreceptor nuclear had pyknosis and chromatin clumping consistent with apoptosis. Muller cells expressed upregulated levels of glial fibrillary acid protein (GFAP) and extended through glial bridges to complex epiretinal membranes which in some areas had a bilaminar structure with a glial-negative inner lamina.ConclusionRetinal degeneration and photoreceptor apoptosis occur in retinal detachment complicated by proliferative vitreoretinopathy (PVR), although during the early stages of the process neural retinal cells remain present, suggesting potential for recovery. The intraretinal glial response appears to be centrally involved in the formation of contractile epiretinal membranes. The retina retains the capacity for a degree of functional recovery following surgery for PVR. Surgical separation of anterior epiretinal membranes in PVR may be difficult and incomplete and alternative surgical strategies may be necessary to prevent recurrence.

Identification of ganglion cell neurites in human subretinal and epiretinal membranes

Aim: To determine whether neural elements are present in subretinal and epiretinal proliferative vitreoretinopathy (PVR) membranes as well as in diabetic, fibrovascular membranes removed from patients during vitrectomy surgery. Methods: Human subretinal and epiretinal membranes of varying durations were immunolabelled with different combinations of antibodies to glial fibrillary acidic protein, vimentin, neurofilament protein and laminin. Results: Anti-neurofilament-labelled neurites from presumptive ganglion cells were frequently found in epiretinal membranes and occasionally found in subretinal membranes. In addition, the neurites were only observed in regions that also contained glial processes. Conclusions: These data demonstrate that neuronal processes are commonly found in human peri-retinal cellular membranes similar to that demonstrated in animal models. These data also suggest that glial cells growing out of the neural retina form a permissive substrate for neurite growth and thus may hold clues to factors that support this growth.

Acute macular pucker.

PURPOSE To describe the presenting features, histopathology, and surgical outcome in a group of patients with rapidly progressive macular pucker. DESIGN Retrospective interventional noncomparative case series. PARTICIPANTS Five patients. METHODS Review of case notes and the existing literature. RESULTS All five patients had rapidly progressive visual loss and metamorphopsia over 2 weeks to 3 months, secondary to macular pucker after retinal tears or detachment. Vitrectomy and epiretinal membrane removal was performed within 1 month of diagnosis. In the absence of complications, there was rapid recovery of the visual acuity with resolution of metamorphopsia within 6 weeks to 3 months. Surgical complications limited the visual outcome in two cases. Histopathologic examination of epiretinal membrane removed from two of the cases suggests that these tend to form tubuloacinar structures and contain more retinal pigment epithelium-derived cells than tissue excised from cases with idiopathic macular pucker. CONCLUSIONS Patients with acute macular pucker have precipitous visual loss caused by epiretinal membrane formation after retinal tear or detachment. Early surgery in these patients results in rapid recovery of visual acuity and resolution of metamorphopsia. The clinical features and comparative immunohistochemistry suggest that acute macular pucker is a distinct clinicopathologic entity.

Staining and Peeling of the Internal Limiting Membrane in the Cat Eye

Purpose: To investigate the cat vitreomacular interface using trypan blue (TB) and indocyanine green (ICG) and to determine the validity of the cat model in terms of staining and peeling of the internal limiting membrane (ILM). Methods: Lensectomy and vitrectomy were performed in four eyes of two cats. The ILM of two eyes was stained with TB (0.15%). ILM peeling was performed in one eye. Two eyes were stained with ICG (0.5%). One eye was illuminated for 3 min. Light and transmission electron microscopy and confocal microscopy were performed. Results: Clinically, both dyes stained the cat ILM similar to human ILM. TB staining resulted in a normal ultrastructure and antigenity of the retina. ILM peeling was associated with intraretinal bleeding. There were fragments of Müller cells adherent to the retinal side of the ILM, and Müller cell endfeet were ruptured and avulsed. ICG staining of the ILM followed by illumination caused severe inner retinal damage. ICG without illumination resulted in focal ILM detachments associated with tearing of Müller cell endfeet. Conclusions: The cat can be used as a model to study the effect of TB and ICG on the central area of the cat retina, as previous results from clinical and experimental postmortem settings in human eyes were confirmed in the current study. Peeling of the ILM as a sheet as performed in human macular surgery is not feasible. Differences in the ultrastructure of the ILM and a strong adhesion of the ILM to Müller cell endfeet may account for this observation.