Annegret Dahlmann-Noor

VEGF-A Is Necessary and Sufficient for Retinal Neuroprotection in Models of Experimental Glaucoma

Vascular endothelial growth factor A (VEGF-A) is a validated therapeutic target in several angiogenic- and vascular permeability–related pathological conditions, including certain cancers and potentially blinding diseases, such as age-related macular degeneration and diabetic retinopathy. We and others have shown that VEGF-A also plays an important role in neuronal development and neuroprotection, including in the neural retina. Antagonism of VEGF-A function might therefore present a risk to neuronal survival as a significant adverse effect. Herein, we demonstrate that VEGF-A acts directly on retinal ganglion cells (RGCs) to promote survival. VEGF receptor-2 signaling via the phosphoinositide-3-kinase/Akt pathway was required for the survival response in isolated RGCs. These results were confirmed in animal models of staurosporine-induced RGC death and experimental hypertensive glaucoma. Importantly, we observed that VEGF-A blockade significantly exacerbated neuronal cell death in the hypertensive glaucoma model. Our findings highlight the need to better define the risks associated with use of VEGF-A antagonists in the ocular setting.

Quantitative Mapping of Scleral Fiber Orientation in Normal Rat Eyes

PURPOSE Previous work has suggested a major role of scleral biomechanics in the pathogenesis of glaucoma. Since fiber orientation in connective tissues is a key determinant of tissue biomechanics, experimental characterization of scleral fiber orientation is needed to fully understand scleral biomechanics. This is a report of baseline experimental measurements of fiber orientation in whole normal rat scleras. METHODS Twenty ostensibly normal Norway brown rat eyes were fixed in 4% paraformaldehyde. The scleras were cleaned of intra- and extraorbital tissues and dissected into five patches, and each patch was glycerol treated to maximize its transparency. Fiber orientation was measured using small-angle light scattering (SALS). Scattering patterns were analyzed to extract two microstructural parameters at each measurement location-the preferred fiber orientation and the degree of alignment-yielding a fiber orientation map for each sclera. RESULTS Rat sclera is structurally anisotropic with several consistent features. At the limbus, fibers were highly aligned and organized primarily into a distinct ring surrounding the cornea. In the equatorial region, the fibers were primarily meridionally aligned. In the posterior and peripapillary region, the scleral fibers were mostly circumferential but less aligned than those in the anterior and equatorial regions. CONCLUSIONS Circumferential scleral fibers may act as reinforcing rings to limit corneal and optic nerve head deformations, whereas equatorial meridional fibers may either provide resistance against extraocular muscle forces or limit globe axial elongation.

Current approaches and future prospects for stem cell rescue and regeneration of the retina and optic nerve

The 3 most common causes of visual impairment and legal blindness in developed countries (age-related macular degeneration, glaucoma, and diabetic retinopathy) share 1 end point: the loss of neural cells of the eye. Although recent treatment advances can slow down the progression of these conditions, many individuals still suffer irreversible loss of vision. Research is aimed at developing new treatment strategies to rescue damaged photoreceptors and retinal ganglion cells (RGC) and to replace lost cells by transplant. The neuroprotective and regenerative potential of stem and progenitor cells from a variety of sources has been explored in models of retinal disease and ganglion cell loss. Continuous intraocular delivery of neurotrophic factors via stem cells (SC) slows down photoreceptor cells and RGC loss in experimental models. Following intraocular transplantation, SC are capable of expressing proteins and of developing a morphology characteristic of photoreceptors or RGC. Recently, recovery of vision has been achieved for the first time in a rodent model of retinal dystrophy, using embryonic SC differentiated into photoreceptors prior to transplant. This indicates that clinically significant synapse formation and acquisition of the functional properties of retinal neurons, and restoration of vision, are distinct future possibilities.

Modulation of wound healing during and after glaucoma surgery.

Following all types of glaucoma filtration surgery (GFS), scarring still poses the major threat to long-term success. The healing and scarring determine the percentage of patients achieving low final intraocular pressures (IOPs) that are associated with virtually no glaucoma progression. The use of antifibrotic agents to inhibit scarring of trabeculectomy blebs is now a well-established clinical practice. Unfortunately, severe complications such as leakage, infection, hypotony, and endophthalmitis with complete loss of vision may occur. In addition, surgery still fails in some individuals despite maximal doses of current antifibrotics. Better therapeutic agents are needed. Many promising new agents are being evaluated clinically and in vitro. In this chapter, we will discuss our current understanding of the wound healing process after glaucoma surgery and promising new treatment modalities.

Strategies for optic nerve rescue and regeneration in glaucoma and other optic neuropathies

Glaucoma is the most common age-related optic nerve disease and also the most common neuropathy, affecting approximately 60 million people worldwide in its most common forms. This figure is expected to rise to 80 million by 2020. Glaucoma is a neurodegenerative disease in which various triggers induce cascades of secondary events, which ultimately lead to apoptotic retinal ganglion cell (RGC) death. The main risk factor for glaucomatous nerve damage is raised pressure in the eye. Understanding the cascades mediating optic nerve damage enables the development of new, neuroprotective treatment strategies that might not only target the initial insult but also prevent or delay secondary neurodegeneration. Furthermore, neuroregeneration and repopulation of the visual pathway by stem or neural precursor cells is becoming possible. Increasing understanding of the pathways involved in directed axon growth and manipulation of stem and progenitor cells towards an RGC fate have facilitated first successes in animal models of glaucoma.

Vision screening in children by Plusoptix Vision Screener compared with gold-standard orthoptic assessment

Background/aims: To evaluate a new autorefractor, the Plusoptix Vision Screener (PVS), as a screening tool to detect risk factors for amblyopia by comparing it with gold-standard orthoptic vision screening in children. Methods: Community-based screening study including 288 children age 4–7 years who were screened with the PVS and by orthoptic assessment (distance acuity, cover test, extraocular movements, 20 PD prism test, Lang stereotest). Follow-up comprehensive eye examination of screening-positive children included manual cycloplegic retinoscopy. Results: Testability was high for both methods. Orthoptic screening identified 36 children with reduced vision and/or factors associated with amblyopia (referral rate 12.5%). The PVS identified 16 children with potential vision problems (referral rate 5.6%), indicating only moderate sensitivity (44%; 95% CI 27.9 to 61.9%), but high specificity (100%; 95% CI 98.5 to 100%) to detect factors associated with amblyopia. The PVS underestimated visually significant refractive errors. Conclusions: Use of the PVS as single screening test in young children may miss a significant number of children with amblyopia or amblyogenic risk factors.

The effect of MMP inhibitor GM6001 on early fibroblast-mediated collagen matrix contraction is correlated to a decrease in cell protrusive activity

Although fibroblasts play an essential part during the wound healing response, the mechanisms by which they mediate tissue remodelling and contraction are still unclear. Using live cell and matrix imaging within 3D free-floating fibroblast-populated collagen lattices as a model for tissue contraction, we compared the behaviour of a range of fibroblasts with low and high contraction abilities and analysed the effect of the broad spectrum MMP-inhibitor GM6001 on cell behaviour and matrix contraction. We identified two mechanisms underlying matrix contraction, one via direct cell-mediated contractile activity, the second through matrix degradation. These appear to be linked to cell morphology and regulated by the collagen concentration within the matrix. Cells with a rounded morphology proliferated in the matrix but did not remodel it efficiently, resulting in a poor ability to contract matrices. Cells with an elongated morphology showed higher levels of protrusive activity, leading to efficient matrix remodelling and contraction. GM6001 inhibited week-long matrix contraction to various extents with the different cell lines. However, quantitative analysis of the cell protrusive activity showed that GM6001 consistently decreased cell dynamics in 3D by about 20%, and this was correlated with a significant reduction in early matrix contraction. Overall our results suggest that although fibroblast-mediated matrix contraction depends on both cell dynamics and MMP-mediated matrix degradation, the efficiency of GM6001 treatment in preventing contraction might be linked to a direct effect on cell dynamics.

Comparison of handheld rebound tonometry with Goldmann applanation tonometry in children with glaucoma: a cohort study

Objective To test agreement of two methods to measure intraocular pressure (IOP): rebound tonometry (RBT) and gold standard Goldmann applanation tonometry (GAT) in children with glaucoma. Design Observational prospective cohort study. Setting Tertiary paediatric glaucoma clinic at a single centre. Participants 102 individuals attending a paediatric glaucoma clinic, mean (SD) age 11.85 (3.17), of whom 53 were male. Primary and secondary outcome measures Intraocular pressure, central corneal thickness, child preference for measurement method. Results Limits of agreement for intraobserver and interobserver were, respectively, (−2.71, 2.98) mm Hg and (−5.75, 5.97) mm Hg. RBT frequently gave higher readings than GAT and the magnitude of disagreement depend on the level of IOP being assessed. Differences of 10 mm Hg were not uncommon. RBT was the preferred method for 70% of children. Conclusions There is poor agreement between RBT and GAT in children with glaucoma. RBT frequently and significantly overestimates IOP. However, ‘normal’ RBT readings are likely to be accurate and may spare children an examination under anaesthesia (EUA). High RBT readings should prompt the practitioner to use another standard method of IOP measurement if possible, or consider the RBT measurement in the context of clinical findings before referring the child to a specialist clinic or considering EUA.

Advancing the Treatment of Conjunctival Scarring A Novel Ex Vivo Model

OBJECTIVES To develop and validate a novel ex vivo model of conjunctival contraction. METHODS Ex vivo segments of conjunctiva were maintained in culture for 4 weeks in permeable support plates. Digital images were obtained twice a week to monitor contraction using tissue area changes and weekly weight measurements. Investigated were the effects of known contraction stimulators (fetal bovine serum and transforming growth factor β(2)) and of the matrix metalloproteinase inhibitor GM6001. Microscopic contraction, tissue organization, and cell viability (using the cell vital dye carboxyfluorescein diacetate) were monitored by confocal reflection and 2-photon microscopy, revealing detailed real-time kinetics of tissue remodeling. RESULTS Fetal bovine serum and transforming growth factor β(2) induced significant tissue contraction in conjunctiva segments, with no changes in cell viability. This correlated with dramatic and specific degradation of the collagen component in the tissue. Contraction and collagen degradation were reduced in the presence of GM6001. CONCLUSIONS Ex vivo segments of conjunctiva can be used as an integral model system to provide a higher level of understanding about the efficacy of antiscarring therapies and can help bridge the current gap between in vitro and in vivo models. CLINICAL RELEVANCE Scarring leads to the failure of several ocular surgical procedures. This novel ex vivo model recapitulates tissue contraction (with kinetics close to that of in vivo scarring) and allows for a more physiological analysis of conjunctival scarring, which could better evaluate potential therapeutic targets.

Saccadic vector optokinetic perimetry in children with neurodisability or isolated visual pathway lesions: observational cohort study

Background/aims Children and adults with neurological impairments are often not able to access conventional perimetry; however, information about the visual field is valuable. A new technology, saccadic vector optokinetic perimetry (SVOP), may have improved accessibility, but its accuracy has not been evaluated. We aimed to explore accessibility, testability and accuracy of SVOP in children with neurodisability or isolated visual pathway deficits. Methods Cohort study; recruitment October 2013–May 2014, at childrens eye clinics at a tertiary referral centre and a regional Child Development Centre; full orthoptic assessment, SVOP (central 30° of the visual field) and confrontation visual fields (CVF). Group 1: age 1–16 years, neurodisability (n=16), group 2: age 10–16 years, confirmed or suspected visual field defect (n=21); group 2 also completed Goldmann visual field testing (GVFT). Results Group 1: testability with a full 40-point test protocol is 12.5%; with reduced test protocols, testability is 100%, but plots may be clinically meaningless. Children (44%) and parents/carers (62.5%) find the test easy. SVOP and CVF agree in 50%. Group 2: testability is 62% for the 40-point protocol, and 90.5% for reduced protocols. Corneal changes in childhood glaucoma interfere with SVOP testing. All children and parents/carers find SVOP easy. Overall agreement with GVFT is 64.7%. Conclusions While SVOP is highly accessible to children, many cannot complete a full 40-point test. Agreement with current standard tests is moderate to poor. Abnormal saccades cause an apparent non-specific visual field defect. In children with glaucoma or nystagmus SVOP calibration often fails.