Placental growth factor contributes to micro-vascular abnormalization and blood-retinal barrier breakdown in diabetic retinopathy.

OBJECTIVE: There are controversies regarding the pro-angiogenic activity of placental growth factor (PGF) in diabetic retinopathy (DR). For a better understanding of its role on the retina, we have evaluated the effect of a sustained PGF over-expression in rat ocular media, using ciliary muscle electrotransfer (ET) of a plasmid encoding rat PGF-1 (pVAX2-rPGF-1). MATERIALS AND METHODS: pVAX2-rPGF-1 ET in the ciliary muscle (200 V/cm) was achieved in non diabetic and diabetic rat eyes. Control eyes received saline or naked plasmid ET. Clinical follow up was carried out over three months using slit lamp examination and fluorescein angiography. After the control of rPGF-1 expression, PGF-induced effects on retinal vasculature and on the blood-external barrier were evaluated respectively by lectin and occludin staining on flat-mounts. Ocular structures were visualized through histological analysis. RESULTS: After fifteen days of rPGF-1 over-expression in normal eyes, tortuous and dilated capillaries were observed. At one month, microaneurysms and moderate vascular sprouts were detected in mid retinal periphery in vivo and on retinal flat-mounts. At later stages, retinal pigmented epithelial cells demonstrated morphological abnormalities and junction ruptures. In diabetic retinas, PGF expression rose between 2 and 5 months, and, one month after ET, rPGF-1 over-expression induced glial activation and proliferation. CONCLUSION: This is the first demonstration that sustained intraocular PGF production induces vascular and retinal changes similar to those observed in the early stages of diabetic retinopathy. PGF and its receptor Flt-1 may therefore be looked upon as a potential regulatory target at this stage of the disease.

Krypton laser photocoagulation induces retinal vascular remodeling rather than choroidal neovascularization.

The purpose of this study is to analyze the retina and choroid response following krypton laser photocoagulation. Ninety-two C57BL6/Sev129 and 32 C57BL/6J, 5-6-week-old mice received one single krypton (630 nm) laser lesion: 50 microm, 0.05 s, 400 mW. On the following day, every day thereafter for 1 week and every 2-3 days for the following 3 weeks, serial sections throughout the lesion were systematically collected and studied. Immunohistology using specific markers or antibodies for glial fibrillary acidic protein (GFAP) (astrocytes, glia and Muller's cells), von Willebrand (vW) (vascular endothelial cells), TUNEL (cells undergoing caspase dependent apoptosis), PCNA (proliferating cell nuclear antigen) p36, CD4 and F4/80 (infiltrating inflammatory and T cells), DAPI (cell nuclei) and routine histology were carried out. Laser confocal microscopy was also performed on flat mounts. Temporal and spatial observations of the created photocoagulation lesions demonstrate that, after a few hours, activated glial cells within the retinal path of the laser beam express GFAP. After 48 h, GFAP-positive staining was also detected within the choroid lesion center. "Movement" of this GFAP-positive expression towards the lasered choroid was preceded by a well-demarcated and localized apoptosis of the retina outer nuclear layer cells within the laser beam path. Later, death of retinal outer nuclear cells and layer thinning at this site was followed by evagination of the inner nuclear retinal layer. Funneling of the entire inner nuclear and the thinned outer nuclear layers into the choroid lesion center was accompanied by "dragging" of the retinal capillaries. Thus, from days 10 to 14 after krypton laser photocoagulation onward, well-formed blood capillaries (of retinal origin) were observed within the lesion. Only a few of the vW-positive capillary endothelial cells stained also for PCNA p36. In the choroid, dilatation of the vascular bed occurred at the vicinity of the photocoagulation site and around it. Confocal microscopy demonstrates that the vessels throughout the path lesion are located within the neuroretina while in the choroid (after separation of the neural retina) only GFAP-positive but no lectin-positive cells can be seen. The involvement of infiltrating inflammatory cells in these remodeling and healing processes remained minimal throughout the study period. During the 4 weeks following krypton laser photocoagulation in the mouse eye, processes of wound healing and remodeling appear to be driven by cells (and vessels) originating from the retina.

Retinal embolisation with localised retinal detachment following retrobulbar anaesthesia.

BACKGROUND: The aim of this communication is to describe an unusual and serious complication of retrobulbar anaesthesia for cataract surgery. HISTORY AND SIGNS: A 78-year-old female was referred for visual loss (light perception) 24 hours after apparently uneventful cataract surgery with retrobulbar anaesthesia in her left eye. Fundus examination revealed multiple arterial emboli and a localised retinal detachment. MRI revealed a retrobulbar hypersignal of the optic nerve associated with perineuritis. The cardiovascular examination was normal. We assumed this condition resulted from injection of the anaesthetic mixture into the optic nerve. THERAPY AND OUTCOME: In order to improve retinal circulation and oxygenation, the intraocular pressure was maximally lowered and anticalcic therapy administered, expecting optimal arterial dilatation. Methylprednisolone (1 g/day 3 days i. v., then rapidly tapered) was also added. The retina slowly reattached but visual acuity remained unchanged. CONCLUSIONS: Retrobulbar anaesthesia is routinely used for ocular surgery. Serious complications may still happen, however. This case adds to the previously reported spectrum of complications from retrobulbar anaesthesia.

VEGF is a mediator of retinal pigment epithelium permeability leading to photoreceptor cell death in light-induced retinal degeneration : gene therapy strategy to prevent AMD-disorders

ABSTRACTIn normal tissues, a balance between pro- and anti-angiogenic factors tightly controls angiogenesis. Alterations of this balance may have pathological consequences. For instance, concerning the retina, the vascular endothelial growth factor (VEGF) is a potent pro-angiogenic factor, and has been identified has a key player during ocular neovascularization implicated in a variety of retinal diseases. In the exudative form (wet-form) of age-related macular degeneration (AMD), neovascularizations occurring from the choroidal vessels are responsible for a quick and dramatic loss of visual acuity. In diabetic retinopathy and retinopathy of prematurity, sprouting from the retinal vessels leads to vision loss. Furthermore, the aging of the population, the increased- prevalence of diabetes and the better survival rate of premature infants will lead to an increasing rate of these conditions. In this way, anti-VEGF strategy represents an important therapeutic target to treat ocular neovascular disorders.In addition, the administration of Pigmented Epithelial growth factor, a neurotrophic and an anti- angiogenic factor, prevents photoreceptor cell death in a model of retinal degeneration induced by light. Previous results analyzing end point morphology reveal that the light damage (LD) model is used to mimic retinal degenerations arising from environmental insult, as well as aging and genetic disease such as advanced atrophic AMD. Moreover, light has been identified as a co-factor in a number of retinal diseases, speeding up the degeneration process. This protecting effect of PEDF in the LD retina raises the possibility of involvement of the balance between pro- and anti-angiogenic factors not only for angiogenesis, but also in cell survival and maintenance.The aim of the work presented here was to evaluate the importance of this balance in neurodegenerative processes. To this aim, a model of light-induced retinal degeneration was used and characterized, mainly focusing on factors simultaneously controlling neuron survival and angiogenesis, such as PEDF and VEGF.In most species, prolonged intense light exposure can lead to photoreceptor cell damage that can progress to cell death and vision loss. A protocol previously described to induce retinal degeneration in Balb/c mice was used. Retinas were characterized at different time points after light injury through several methods at the functional and molecular levels. Data obtained confirmed that toxic level of light induce PR cell death. Variations were observed in VEGF pathway players in both the neural retina and the eye-cup containing the retinal pigment epithelium (RPE), suggesting a flux of VEGF from the RPE towards the neuroretina. Concomitantly, the integrity of the outer blood-retinal-barrier (BRB) was altered, leading to extravascular albumin leakage from the choroid throughout the photoreceptor layer.To evaluate the importance of VEGF during light-induced retinal degeneration process, a lentiviral vector encoding the cDNA of a single chain antibody directed against all VEGF-A isoforms was developed (LV-V65). The bioactivity of this vector to block VEGF was validated in a mouse model of laser-induced choroidal neovascularization mediated by VEGF upregulation. The vector was then used in the LD model. The administration of the LV-V65 contributed to the maintenance of functional photoreceptors, which was assessed by ERG recording, visual acuity measurement and histological analyses. At the RPE level, the BRB integrity was preserved as shown by the absence of albumin leakage and the maintenance of RPE cell cohesion.These results taken together indicate that the VEGF is a mediator of light induced PR degeneration process and confirm the crucial role of the balance between pro- and anti-angiogenic factors in the PR cell survival. This work also highlights the prime importance of BRB integrity and functional coupling between RPE and PR cells to maintain the PR survival. VEGF dysregulation was already shown to be involved in wet AMD forms and our study suggests that VEGF dysregulation may also occur at early stages of AMD and could thus be a potential therapeutic target for several RPE related diseases.RESUMEDans les différents tissues de l'organisme, l'angiogenèse est strictement contrôlée par une balance entre les facteurs pro- et anti-angiogéniques. Des modifications survenant dans cette balance peuvent engendrer des conséquences pathologiques. Par exemple, concernant la rétine, le facteur de croissance de l'endothélium vasculaire (VEGF) est un facteur pro-angiogénique important. Ce facteur a été identifié comme un acteur majeur dans les néovascularisations oculaires et les processus pathologiques angiogéniques survenant dans l'oeil et responsables d'une grande variété de maladies rétiniennes. Dans la forme humide de la dégénérescence maculaire liée à l'âge (DMLA), la néovascularisation choroïdienne est responsable de la perte rapide et brutale de l'acuité visuelle chez les patients affectés. Dans la rétinopathie diabétique et celle lié à la prématurité, l'émergence de néovaisseaux rétiniens est la cause de la perte de la vision. Les néovascularisations oculaires représentent la principale cause de cécité dans les pays développés. De plus, l'âge croissant de la population, la progression de la prévalence du diabète et la meilleure survie des enfants prématurés mèneront sans doute à l'augmentation de ces pathologies dans les années futures. Dans ces conditions, les thérapies anti- angiogéniques visant à inhiber le VEGF représentent une importante cible thérapeutique pour le traitement de ces pathologies.Plusieurs facteurs anti-angiogéniques ont été identifiés. Parmi eux, le facteur de l'épithélium pigmentaire (PEDF) est à la fois un facteur neuro-trophique et anti-angiogénique, et l'administration de ce facteur au niveau de la rétine dans un modèle de dégénérescence rétinienne induite par la lumière protège les photorécepteurs de la mort cellulaire. Des études antérieures basées sur l'analyse morphologique ont révélé que les modifications survenant lors de la dégénération induite suite à l'exposition à des doses toxiques de lumière représente un remarquable modèle pour l'étude des dégénérations rétiniennes suite à des lésions environnementales, à l'âge ou encore aux maladies génétiques telle que la forme atrophique avancée de la DMLA. De plus, la lumière a été identifiée comme un co-facteur impliqué dans un grand nombre de maladies rétiniennes, accélérant le processus de dégénération. L'effet protecteur du PEDF dans les rétines lésées suite à l'exposition de des doses toxiques de lumière suscite la possibilité que la balance entre les facteurs pro- et anti-angiogéniques soit impliquée non seulement dans les processus angiogéniques, mais également dans le maintient et la survie des cellules.Le but de ce projet consiste donc à évaluer l'implication de cette balance lors des processus neurodégénératifs. Pour cela, un modèle de dégénération induite par la lumière à été utilisé et caractérisé, avec un intérêt particulier pour les facteurs comme le PEDF et le VEGF contrôlant simultanément la survie des neurones et l'angiogenèse.Dans la plupart des espèces, l'exposition prolongée à une lumière intense peut provoquer des dommages au niveau des cellules photoréceptrices de l'oeil, qui peut mener à leur mort, et par conséquent à la perte de la vision. Un protocole préalablement décrit a été utilisé pour induire la dégénération rétinienne dans les souris albinos Balb/c. Les rétines ont été analysées à différents moments après la lésion par différentes techniques, aussi bien au niveau moléculaire que fonctionnel. Les résultats obtenus ont confirmé que des doses toxiques de lumière induisent la mort des photorécepteurs, mais altèrent également la voie de signalisation du VEGF, aussi bien dans la neuro-rétine que dans le reste de l'oeil, contenant l'épithélium pigmentaire (EP), et suggérant un flux de VEGF provenant de ΙΈΡ en direction de la neuro-rétine. Simultanément, il se produit une altération de l'intégrité de la barrière hémato-rétinienne externe, menant à la fuite de protéine telle que l'albumine, provenant de la choroïde et retrouvée dans les compartiments extravasculaires de la rétine, telle que dans la couche des photorécepteurs.Pour déterminer l'importance et le rôle du VEGF, un vecteur lentiviral codant pour un anticorps neutralisant dirigée contre tous les isoformes du VEGF a été développé (LV-V65). La bio-activité de ce vecteur a été testé et validée dans un modèle de laser, connu pour induire des néovascularisations choroïdiennes chez la souris suite à l'augmentation du VEGF. Ce vecteur a ensuite été utilisé dans le modèle de dégénération induite par la lumière. Les résultats des électrorétinogrammes, les mesures de l'acuité visuelle et les analyses histologiques ont montré que l'injection du LV-V65 contribue à la maintenance de photorécepteurs fonctionnels. Au niveau de l'EP, l'absence d'albumine et la maintenance des jonctions cellulaires des cellules de l'EP ont démontré que l'intégrité de la barrière hémato-rétinienne externe est préservée suite au traitement.Par conséquent, tous les résultats obtenus indiquent que le VEGF est un médiateur important impliquée dans le processus de dégénération induit par la lumière et confirme le rôle cruciale de la balance entre les facteurs pro- et anti-angiogéniques dans la survie des photorécepteurs. Cette étude révèle également l'importance de l'intégrité de la barrière hémato-rétinienne et l'importance du lien fonctionnel et structurel entre l'EP et les photorécepteurs, essentiel pour la survie de ces derniers. Par ailleurs, Cette étude suggère que des dérèglements au niveau de l'équilibre du VEGF ne sont pas seulement impliqués dans la forme humide de la DMLA, comme déjà démontré dans des études antérieures, mais pourraient également contribuer et survenir dans des formes précoces de la DMLA, et par conséquent le VEGF représente une cible thérapeutique potentielle pour les maladies associées à des anomalies au niveau de l'EP.

Placental growth factor-1 and epithelial haemato-retinal barrier breakdown: potential implication in the pathogenesis of diabetic retinopathy.

AIMS/HYPOTHESIS: Disruption of the retinal pigment epithelial (RPE) barrier contributes to sub-retinal fluid and retinal oedema as observed in diabetic retinopathy. High placental growth factor (PLGF) vitreous levels have been found in diabetic patients. This work aimed to elucidate the influence of PLGF-1 on a human RPE cell line (ARPE-19) barrier in vitro and on normal rat eyes in vivo. METHODS: ARPE-19 permeability was measured using transepithelial resistance and inulin flux under stimulation of PLGF-1, vascular endothelial growth factor (VEGF)-E and VEGF 165. Using RT-PCR, we evaluated the effect of hypoxic conditions or insulin on transepithelial resistance and on PLGF-1 and VEGF receptors. The involvement of mitogen-activated protein kinase (MEK, also known as MAPK)/extracellular signal-regulated kinase (ERK, also known as EPHB2) signalling pathways under PLGF-1 stimulation was evaluated by western blot analysis and specific inhibitors. The effect of PLGF-1 on the external haemato-retinal barrier was evaluated after intravitreous injection of PLGF-1 in the rat eye; evaluation was by semi-thin analysis and zonula occludens-1 immunolocalisation on flat-mounted RPE. RESULTS: In vitro, PLGF-1 induced a reversible decrease of transepithelial resistance and enhanced tritiated inulin flux. These effects were specifically abolished by an antisense oligonucleotide directed at VEGF receptor 1. Exposure of ARPE-19 cells to hypoxic conditions or to insulin induced an upregulation of PLGF-1 expression along with increased transcellular permeability. The PLGF-1-induced RPE cell permeability involved the MEK signalling pathway. Injection of PLGF-1 in the rat eye vitreous induced an opening of the RPE tight junctions with subsequent sub-retinal fluid accumulation, retinal oedema and cytoplasm translocation of junction proteins. CONCLUSIONS/INTERPRETATION: Our results indicate that PLGF-1 may be a potential regulation target for the control of diabetic retinal and macular oedema.

Ultrastructural and morphometric aspects of ageing in the retinal capillaries of rats

Age-related morphological, ultrastructural and morphometric changes in the capillaries of the superficial and deep plexuses of the rat retina were studied in animals aged from 3 to 15 months. Our results suggest that age-related morphological alterations start occurring in the retina of rats at about 12 months of age. Increased glycogen deposits, pinocytotic vesicles, residual bodies and cell debris were observed in both the endothelial and pericytic cells of 12- and 15-month-old animals. In addition, heterogeneous osmiophilic accumulations, electron-transparent spaces were observed in the basement membrane as well as projections of the basement membrane towards the neighboring cells. Morphometric examination of the two vascular plexuses studied did not show differences in the area of the endothelial or pericytic cells, basement membrane or vascular lumen between rats of different ages.

Endothelial survival factors and spatial completion, but not pericyte coverage of retinal capillaries determine vessel plasticity

Pericyte loss and capillary regression are characteristic for incipient diabetic retinopathy. Pericyte recruitment is involved in vessel maturation, and ligand-receptor systems contributing to pericyte recruitment are survival factors for endothelial cells in pericyte-free in vitro systems. We studied pericyte recruitment in relation to the susceptibility toward hyperoxia-induced vascular remodeling using the pericyte reporter X-LacZ mouse and the mouse model of retinopathy of prematurity (ROP). Pericytes were found in close proximity to vessels, both during formation of the superficial and the deep capillary layers. When exposure of mice to the ROP was delayed by 24 h, i.e., after the deep retinal layer had formed [at postnatal (p) day 8], preretinal neovascularizations were substantially diminished at p18. Mice with a delayed ROP exposure had 50% reduced avascular zones. Formation of the deep capillary layers at p8 was associated with a combined up-regulation of angiopoietin-1 and PDGF-B, while VEGF was almost unchanged during the transition from a susceptible to a resistant capillary network. Inhibition of Tie-2 function either by soluble Tie-2 or by a sulindac analog, an inhibitor of Tie-2 phosphorylation, resensitized retinal vessels to neovascularizations due to a reduction of the deep capillary network. Inhibition of Tie-2 function had no effect on pericyte recruitment. Our data indicate that the final maturation of the retinal vasculature and its resistance to regressive signals such as hyperoxia depend on the completion of the multilayer structure, in particular the deep capillary layers, and are independent of the coverage by pericytes.

Vascular endothelial growth factor-B and retinal vascular development in the mouse

Purpose: Vascular endothelial growth factor-A (VEGF-A) is crucial to retinal vascular growth, both normal and pathological. VEGF-B, recently characterized, is reported to be expressed in retinal tissues, but the importance of VEGF-B to retinal vascular development remained unknown. The aim of this study was to analyse retinal vascular growth in the Vegfb (-/-) knockout mouse. Methods: Retinal vascular growth was measured in Vegfb (-/-) knockout mice raised under normal conditions, and Vegfb (-/-) knockout mice with an oxygen-induced proliferative retinopathy. Wild type Vegfb (+/+) mice served as controls. Vessels were perfused with ink and retinal flatmounts secondarily labelled with FITC-lectin (BS-1, Griffonia simplicifolia ). Area and diameter of retinal growth and retinal vascular growth were recorded over days 0-20, and capillary density and mean diameter recorded from day 17 pups. Results: A variety of techniques confirmed that Vegfb (+/+) mice expressed VEGF-B and that VEGF-B expression was absent in Vegfb (-/-) mice. Vegfb (-/-) mice raised in room air showed no significant differences from Vegfb (+/+) controls. No differences were found in oxygen-induced retinopathy between Vegfb (-/-) and Vegfb (+/+) pups in either the extent of the initial oxygen-induced ablation, or in the regrowth of retinal vessels or vitreal (neovascular) sprouts; vitreal sprouts are important markers of the abnormal proliferative response, and are maximally expressed on day 17 in this model of oxygen-induced retinopathy. Conclusions: These results indicate that a lack of VEGF-B does not significantly affect development of the retinal vasculature under normal conditions, nor does it appear to affect the proliferative retinal responses seen in oxygen-induced retinopathy.

Regional differences in oxygen saturation in retinal arterioles and venules

BACKGROUND: Retinal vessel oxygenation saturation measurements have been the focus of much attention in recent years as a potential diagnostic parameter in a number of ocular and systemic pathologies. This interest has been heightened by the ability to measure oxygen saturation in vivo using a photographic technique. METHODS: Retinal vessel oxygenation in venules and arterioles of 279 retinal vessels of 12 healthy Caucasian participants (mean age: 30 SD (+/- 6) years) were measured consecutively three times to evaluate short-term variation in oxygen saturation and regional variability of retinal vessel oxygen saturation using dual-wavelength technology (Oxymetry Modul, Imedos, Germany). All subjects underwent standard optometric assessment including non-contact intra-ocular pressure assessment as well as having their systemic blood pressure measured. RESULTS: Vessels were grouped as either near-macula or peripheral, depending on their location. Peripheral arterioles and venules exhibited significantly lower oxygen saturation compared to their near-macula counterparts (arterioles: 94.7% (SD 3.9) vs. 99.7% (SD 3.2); venules: 65.1% (SD 7.2) vs. 90.3% (SD 6.7)). Both arterioles and venules, main branches, and those feeding and draining the retina near the macula and periphery showed low short-term variability of oxygen saturation (arterioles: COV 1.2-1.8%; venules: COV 2.9-4.9%). CONCLUSIONS: Retinal arterioles and venules exhibit low short-term variation of oxygen saturation in healthy subjects. Regional differences in oxygen saturation could be a potential useful marker for risk stratification and diagnostic purposes of area-specific retinal pathology such as age-related macula degeneration and diabetic maculopathy.

The effect of simulated cataract light scatter on retinal vessel oximetry

To assess the impact of light scatter, similar to that introduced by cataract on retinal vessel blood oxygen saturation measurements using poly-bead solutions of varying concentrations. Eight healthy, young, non-smoking individuals were enrolled for this study. All subjects underwent digital blood pressure measurements, assessment of non-contact intraocular pressure, pupil dilation and retinal vessel oximetry using dual wavelength photography (Oximetry Module, Imedos Systems, Germany). To simulate light scatter, cells comprising a plastic collar and two plano lenses were filled with solutions of differing concentrations (0.001, 0.002 and 0.004%) of polystyrene microspheres (Polysciences Inc., USA). The adopted light scatter model showed an artifactual increase in venous optical density ratio (p=0.036), with the 0.004% condition producing significantly higher venous optical density ratio values when compared to images without a cell in place. Spectrophotometric analysis, and thus retinal vessel oximetry of the retinal vessels, is altered by artificial light scatter. © 2013 Elsevier Ltd.

Retinal vascular dysfunction relates to cognitive impairment in Alzheimer's disease

Cerebral vascular dysregulation has been increasingly implicated as a risk factor in the development of Alzheimer disease (AD)1; however, because of the difficulties associated with assessing and visualizing the cerebral vasculature directly, the ability to detect such dysregulation, noninvasively, is currently limited.2 Consequently, one concept that is being increasingly explored is the possibility of using the eye as a "window to the brain"; this approach has reasonable scientific validity as the retinal and brain vessels share a large number of embryological, anatomic, and functional similarities.2 Indeed, previous research has demonstrated a correlation between cognition and the geometry of the retinal vessels in elderly people.3 The aim of this pilot study, therefore, was to explore whether microvascular functional anomalies are evident at the retinal level in mild AD patients and to determine whether these anomalies relate to the degree of concurrent cognitive deficit..

The fractal properties of the retinal vascular architecture

Purpose: The human retinal vasculature has been demonstrated to exhibit fractal, or statistically self similar properties. Fractal analysis offers a simple quantitative method to characterise the complexity of the branching vessel network in the retina. Several methods have been proposed to quantify the fractal properties of the retina. Methods: Twenty five healthy volunteers underwent retinal photography, retinal oximetry and ocular biometry. A robust method to evaluate the fractal properties of the retinal vessels is proposed; it consists of manual vessel segmentation and box counting of 50 degree retinal photographs centred on the fovea. Results: Data is presented on the associations between the fractal properties of the retinal vessels and various functional properties of the retina. Conclusion Fractal properties of the retina could offer a promising tool to assess the risk and prognostic factors that define retinal disease. Outstanding efforts surround the need to adopt a standardised protocol for assessing the fractal properties of the retina, and further demonstrate its association with disease processes.

The time course of changes in retinal vessel diameter in response to differing durations of flicker light provocation

Purpose: To determine the response of retinal vessels to differing durations of flicker light (FL) sitmulation. Methods: We recorded retinal arterial and venous vessel dilation to 12.5 Hz flicker light provocation (Retinal Vessel Analyzer, Imedos Systems) of varying duration (5, 7, 10 and 20 seconds) in twelve healthy young individuals (age range 26-45 yrs). All participants underwent a full ocular examination including intraocular pressure and blood pressure measurements. Results: Maximum dilation (MD) did not show a significant dependence on flicker duration in arteries whereas maximum constriction (MC) did. However, in veins MD significantly increased with flicker duration. Approximately 80-90% of MD in arteries is reached within 10 seconds of flicker light stimulation. Conclusions: The vast majority of arterial dilatory capacity is reached within 10 seconds of flicker light stimulation even though venous dilation continues strongly. Since the MC of arteries shows a significant dependence on flicker duration measurements at two different durations can provide more information about the retinal vascular system than at a single flicker duration alone.

Macroglial and retinal changes in hypercholesterolemic rabbits after normalization of cholesterol levels

This study evaluates hypercholesterolemic rabbits, examining the retinal changes in Müller cells and astrocytes as well as their variations after a period of normal blood-cholesterol values induced by a standard diet. New Zealand rabbits were divided into three groups: G0, fed a standard diet; G1A, fed a 0.5% cholesterol-enriched diet for 8 months; and G1B, fed as G1A followed by standard diet for 6 months. Eyes were processed for transmission electron microscopy and immunohistochemistry (GFAP). While G1B resembled G0 more than did G1A, they shared alterations with G1A: a) as in G1A, Müller cells were GFAP+, filled spaces left by axonal degeneration, formed glial scars and their nuclei were displaced to the nerve-fibre layer. The area occupied by the astrocytes associated with the nerve-fibre bundles (AANFB) and by perivascular astrocytes (PVA) in G1A and G1B was significantly lower than in controls. However, no significant differences in PVA were found between G1A and G1B. In G1B, type I PVA was absent and replaced by hypertrophic type II cells; b) Bruch's membrane (BM) was thinner in G1B than in G1A; c) the retinal pigment epithelium (RPE) cytoplasm contained fewer lipids in G1B than in G1A; d) in G1A and G1B choriocapillaris and retinal vessel showed alterations with respect to G0; e) cell death and axonal degeneration in the retina were similar in G1A and G1B. The substitution of a hyperlipemic diet by a standard one normalizes blood-lipid levels. However, the persistence of damage at retinal vessels and BM-RPE could trigger chronic ischemia.

Lack of Spontaneous Venous Pulsation: Possible Risk Indicator in Normal Tension Glaucoma?

PURPOSE: Recently, the absence of spontaneous venous pulsation (SVP) has been suggested as a vascular risk factor for primary open-angle glaucoma (POAG). As the mechanism behind this phenomenon is still unknown, the authors have studied this vascular component using colour Doppler imaging (CDI). METHODS: A total of 236 patients were divided into three diagnostic groups: healthy controls (81), POAG (86) and normal tension glaucoma (NTG; 69). All subjects were submitted to CDI studies of the retrobulbar circulation, intraocular pressure measurements and assessment of SVP existence. Mann-Whitney, chi-square contingency tables and Spearman correlations were used to explore differences and correlations between variables in the diagnostic groups. RESULTS: Eighty-two percent of healthy controls had SVP (66/81), while a smaller numbers were registered in both glaucoma groups: POAG - 50% (43/86); NTG - 51% (35/69). In NTG patients, but not in POAG patients, the prevalence of the SVP phenomenon decreases with increased glaucoma damage (p = 0.04; p = 0.55, respectively). Overall glaucoma patients from both groups had lower central retinal vein (CRV) velocities than the healthy controls (p < 0.05). NTG patients with SVP had less severe visual field defects (mean defect -6.92 versus -11.1, p < 0.05), higher [correction added after online publication 21 September 2012; the word 'higher' has been inserted to replace the word 'lower'] peak systolic and mean flow velocities in the central retinal artery (p < 0.01; p < 0.05, respectively) as well as higher [correction added after online publication 21 September 2012; the word higher has been inserted to replace the word lower] maximal velocities and RI of the CRV (p < 0.02; p < 0.05, respectively). CONCLUSIONS: Glaucoma patients have a decrease in CRV velocities. SVP is less prevalent in glaucoma patients than in healthy individuals. This phenomenon apparently reflects different hemodynamic patterns in the central retinal vessels. This variable may be of particular importance in NTG patients, where it may be associated with more advanced functional damage.