Acute retinal ischemia caused by controlled low ocular perfusion pressure in a porcine model. Electrophysiological and histological characterisation

Review of a new concept of glaucoma pathogenesis based on the glymphatic theory of cerebrospinal fluid circulation

General aspects of glaucoma: Glaucoma is a heterogeneous multi-factorial disease that is one of the main causes of blindness, along with degeneration of retinal ganglion cells and optic nerve atrophy.

Theories of pathogenesis: There are three theories of glaucoma pathogenesis: biomechanical, vascular, and biochemical.

Basic theory of the glymphatic system: The classical knowledge of cerebrospinal fluid circulation has been revised, and in 2012 a new concept of glial-perivascular – glymphatic perfusion of the brain parenchyma was introduced. Due to experimental and clinical studies, it is approved by many scientists, especially in relation to Alzheimer’s disease (AD), in which amyloid pathology is the result of dysfunction of the para-/perivascular transport/cleansing pathways.

Features of the optic nerve and the cribriform plate: The cribriform plate forms a barrier at the border of intraocular (IOP) and intracranial (ICP) pressures, thus affecting the para-/periarterial flow of cerebrospinal fluid to the optic nerve and retina, as well as the para-/perivenous cleansing outflow.

Morphofunctional evidence of an ocular glymphatic system: The presence of an ocular glymphatic system is confirmed by in vivo experiments with the transfer of labeled substances through para-/perivascular structures from the ventricular or subarachnoid space to the optic nerve and by postmortem morphology.

Clinical evidence for the glymphatic system hypothesis: There is some clinical, including case-based, and epidemiological evidence for similarities between glaucomatous optic nerve/retinal injuries and AD, since both occur in the form of improper secretion of neurotoxic metabolites, and both are often diagnosed together.

Retinal Cell Protection in Ocular Excitotoxicity Diseases. Possible Alternatives Offered by Microparticulate Drug Delivery Systems and Future Prospects

Excitotoxicity seems to play a critical role in ocular neurodegeneration. Excess-glutamate-mediated retinal ganglion cells death is the principal cause of cell loss. Uncontrolled glutamate in the synapsis has significant implications in the pathogenesis of neurodegenerative disorders. The exploitation of various approaches of controlled release systems enhances the pharmacokinetic and pharmacodynamic activity of drugs. In particular, microparticles are secure, can maintain therapeutic drug concentrations in the eye for prolonged periods, and make intimate contact by improving drug bioavailability. According to the promising results reported, possible new investigations will focus intense attention on microparticulate formulations and can be expected to open the field to new alternatives for doctors, as currently required by patients.

Hypotensive efficacy of topical brimonidine for intraocular pressure spikes following intravitreal injections of antivascular endothelial growth factor agents: a randomised crossover trial

PURPOSE

To determine the effect of topical brimonidine tartrate prophylaxis on intraocular pressure (IOP) spikes following intravitreal injection of antivascular endothelial growth factor (anti-VEGF) agents.

METHODS

This is a randomised crossover trial of consecutive non-glaucomatous eyes receiving intravitreal anti-VEGF injections between December 2016 and July 2017. All eyes were randomly assigned to no prophylaxis or topical brimonidine tartrate 0.15 % administered 20 min prior to injection in one of two consecutive visits. Measurements of IOP were obtained immediately (T0), 10 min (T10) and 20 min (T20) after injection during the visits with and without prophylaxis.

RESULTS

Among the 58 eyes of 55 patients (116 visits), the mean (SD) age was 74.3 (11.6), and 62% were female. The mean baseline IOP was 15.3 (2.3) mm Hg (range: 11-20). On average, the immediate postinjection IOP during the visit without prophylaxis was 41.6 (12) mm Hg (range: 17-81). Compared with no prophylaxis, the visit with preadministered topical brimonidine tartrate had a lower IOP at T0 (p<0.001), T10 (p=0.001) and T20 (p=0.043), and a smaller proportion of eyes with IOP elevation of greater than 20 mm Hg from preinjection (p=0.002) and IOP greater than 50 mm Hg at T0 (p=0.036). Without prophylaxis, two eyes (two patients) had an IOP of greater than 70 mm Hg at T0 and thus underwent anterior chamber paracentesis.

CONCLUSION

Topical brimonidine tartrate prophylaxis for intravitreal injection of anti-VEGF agents effectively reduces IOP spikes in non-glaucomatous eyes and may be easily incorporated into ophthalmologists' current practice.

TRIAL REGISTRATION NUMBER

NCT03513172.

Neuropeptide Y treatment induces retinal vasoconstriction and causes functional and histological retinal damage in a porcine ischaemia model

PURPOSE

To investigate the effects of intravitreal neuropeptide Y (NPY) treatment following acute retinal ischaemia in an in vivo porcine model. In addition, we evaluated the vasoconstrictive potential of NPY on porcine retinal arteries ex vivo.

METHODS

Twelve pigs underwent induced retinal ischaemia by elevated intraocular pressure clamping the ocular perfusion pressure at 5 mmHg for 2 hr followed by intravitreal injection of NPY or vehicle. After 4 weeks, retinas were evaluated functionally by standard and global-flash multifocal electroretinogram (mfERG) and histologically by thickness of retinal layers and number of ganglion cells. Additionally, the vasoconstrictive effects of NPY and its involved receptors were tested using wire myographs and NPY receptor antagonists on porcine retinal arteries.

RESULTS

Intravitreal injection of NPY after induced ischaemia caused a significant reduction in the mean induced component (IC) amplitude ratio (treated/normal eye) compared to vehicle-treated eyes. This reduction was accompanied by histological damage, where NPY treatment reduced the mean thickness of inner retinal layers and number of ganglion cells. In retinal arteries, NPY-induced vasoconstriction to a plateau of approximately 65% of potassium-induced constriction. This effect appeared to be mediated via Y1 and Y2, but not Y5.

CONCLUSION

In seeming contrast to previous in vitro studies, intravitreal NPY treatment caused functional and histological damage compared to vehicle after a retinal ischaemic insult. Furthermore, we showed for the first time that NPY induces Y1- and Y2- but not Y5-mediated vasoconstriction in retinal arteries. This constriction could explain the worsening in vivo effect induced by NPY treatment following an ischaemic insult and suggests that future studies on exploring the neuroprotective effects of NPY might focus on other receptors than Y1 and Y2.

Retinal Cryo-sections, Whole-Mounts, and Hypotonic Isolated Vasculature Preparations for Immunohistochemical Visualization of Microvascular Pericytes

Retinal pericytes play an important role in many diseases of the eye. Immunohistochemical staining techniques of retinal vessels and microvascular pericytes are central to ophthalmological research. It is vital to choose an appropriate method of visualizing the microvascular pericytes. We describe retinal microvascular pericyte immunohistochemical staining in cryo-sections, whole-mounts, and hypotonic isolated vasculature using antibodies for platelet-derived growth factor receptor β (PDGFRβ) and nerve/glial antigen 2 (NG2). This allows us to highlight advantages and shortcomings of each of the three tissue preparations for the visualization of the retinal microvascular pericytes. Cryo-sections provide transsectional visualization of all retinal layers but contain only a few occasional transverse cuts of the microvasculature. Whole-mount provides an overview of the entire retinal vasculature, but visualization of the microvasculature can be troublesome. Hypotonic isolation provides a method to visualize the entire retinal vasculature by the removal of neuronal cells, but this makes the tissue very fragile.

Assessment of Ocriplasmin Effects on the Vitreoretinal Compartment in Porcine and Human Model Systems

Ocriplasmin (Jetrea®) is a recombinant protease used to treat vitreomacular traction. To gain insight into vitreoretinal observations reported after ocriplasmin treatment, we have developed an in vivo porcine ocriplasmin-induced posterior vitreous detachment (PVD) model in which we investigated vitreoretinal tissues by optical coherence tomography, histology, and cytokine profiling. Eight weeks postinjection, ocriplasmin yielded PVD in 82% of eyes. Subretinal fluid (85%) and vitreous hyperreflective spots (45%) were resolved by week 3. Histological analysis of extracellular matrix (ECM) proteins such as laminin, fibronectin, and collagen IV indicated no retinal ocriplasmin-induced ECM distribution changes. Retinal morphology was unaffected in all eyes. Cytokine profiles of ocriplasmin-treated eyes were not different from vehicle. In cell-based electrical resistance assays, blood-retinal barrier permeability was altered by ocriplasmin concentrations of 6 μg/mL and higher, with all effects being nontoxic, cell-type specific, and reversible. Ocriplasmin was actively taken up by RPE and Müller cells, and our data suggest both lysosomal and transcellular clearance routes for ocriplasmin. In conclusion, transient hyperreflective spots and fluid in a porcine ocriplasmin-induced PVD model did not correlate with retinal ECM rearrangement nor inflammation. Reversible in vitro effects on blood-retinal barrier permeability provide grounds for a hypothesis on the mechanisms behind transient subretinal fluid observed in ocriplasmin-treated patients.

Short-term changes of intraocular pressure and ocular perfusion pressure after intravitreal injection of bevacizumab or ranibizumab

Background

The aim of this study was to investigate the effect of intravitreal anti-vascular endothothelial growth factor (VEGF) injection on intraocular pressure (IOP) and mean ocular perfusion pressure (MOPP).

Methods

MOPP results were obtained by measuring mean arterial pressure (MAP) and IOP just before the injection, immediately after the injection, at 30 min, 1 day, and 1 week after injection from 65 eyes of 42 patients.

Results

Pre-injection mean IOP was 16.66 ± 3.50 mmHg, and mean IOP was 43.81 ± 9.69 mmHg immediately after the injection, 17.57 ± 4.44 mmHg at 30 min, 15.00 ± 4.21 mmHg at 1 day, and 15.90 ± 3.63 mmHg at 1 week after the injection. Pre-injection mean MOPP was 46.39 ± 5.78 mmHg, and mean MOPP was 25.14 ± 8.79 mmHg immediately after the injection, 45.87 ± 6.31 mmHg at 30 min, 46.93 ± 6.25 mmHg at 1 day, and 46.50 ± 4.94 mmHg at 1 week after the injection.

Conclusion

The instant increase in IOP by intravitreal anti-VEGF injection led to a transient decrease in MOPP. Based on this finding, the instant increase in IOP after intravitreal anti-VEGF injection does not significantly impair retinal blood flow.

Retinal vessel diameter changes induced by transient high perfusion pressure

AIM

To investigate the effects of transient high perfusion pressure on the retinal vessel diameter and retinal ganglion cells.

METHODS

The animals were divided into four groups according to different infusion pressure and infusion time (60 mm Hg-3min, 60 mm Hg-5min, 100 mm Hg-3min, 100 mm Hg-5min). Each group consisted of six rabbits. The left eye was used as the experimental eye and the right as a control. Retinal vascular diameters were evaluated before, during infusion, immediately after infusion, 5min, 10min and 30min after infusion based on the fundus photographs. Blood pressure was monitored during infusion. The eyes were removed after 24h. Damage to retinal ganglion cell (RGC) was analyzed by histology.

RESULTS

Retina became whiten and papilla optic was pale during perfusion. Measurements showed significant decrease in retinal artery and vein diameter during perfusion in all of the four groups at the proximal of the edge of the optic disc. The changes were significant in the 100 mm Hg-3min group and 100 mm Hg-5min group compared with 60 mm Hg-3min group (P1=0.025, P2=0.000). The diameters in all the groups recovered completely after 30min of reperfusion. The number of RGC showed no significant changes at the IOP in 100 mm Hg with 5min compared with contralateral untreated eye (P>0.05).

CONCLUSION

Transient fluctuations during infusion lead to temporal changes of retinal vessels, which could affect the retinal blood circulation. The RGCs were not affected by this transient fluctuation. Further studies are necessary to evaluate the effect of pressure during real-time phacoemusification on retinal blood circulation.

Vascular considerations in glaucoma patients of African and European descent

Glaucoma is the leading cause of blindness in individuals of African descent (AD). While open-angle glaucoma (OAG) disproportionately affects individuals of AD compared with persons of European descent (ED), the physiological mechanisms behind this disparity are largely unknown. The more rapid progression and greater severity of the disease in persons of AD further raise the concern for identifying these underlying differences in disease pathophysiology between AD and ED glaucoma patients. Ocular structural differences between AD and ED patients, including larger optic disc area, cup:disc ratio and thinner corneas, have been found. AD individuals are also disproportionately affected by systemic vascular diseases, including hypertension, cardiovascular disease, stroke and diabetes mellitus. Abnormal ocular blood flow has been implicated as a risk factor for glaucoma, and pilot research is beginning to identify localized ocular vascular differences between AD and ED OAG patients. Given the known systemic vascular deficits and the relationship between glaucoma and ocular blood flow, exploring these concepts in terms of glaucoma risk factors may have a significant impact in elucidating the mechanisms behind the disease disparity in the AD population.

Recent advances in cellular and molecular aspects of mammalian retinal ischemia

Retinal ischemia is a common clinical entity and, due to relatively ineffective treatment, remains a common cause of visual impairment and blindness. Generally, ischemic syndromes are initially characterized by low homeostatic responses which, with time, induce injury to the tissue due to cell loss by apoptosis. In this respect, retinal ischemia is a primary cause of neuronal death. It can be considered as a sort of final common pathway in retinal diseases and results in irreversible morphological and functional changes. This review summarizes the recent knowledge on the effects of ischemia in retinal tissue and points out experimental strategies/models performed to gain better comprehension of retinal ischemia diseases. In particular, the nature of the mechanisms leading to neuronal damage (i.e., excess of glutamate release, oxidative stress and inflammation) will be outlined as well as the potential and most intriguing retinoprotective approaches and the possible therapeutic use of naturally occurring molecules such as neuropeptides. There is a general agreement that a better understanding of the fundamental pathophysiology of retinal ischemia will lead to better management and improved clinical outcome. In this respect, to contrast this pathological state, specific pharmacological strategies need to be developed aimed at the many putative cascades generated during ischemia.

Acute retinal ischemia inhibits endothelium-dependent nitric oxide-mediated dilation of retinal arterioles via enhanced superoxide production

PURPOSE

Because retinal vascular disease is associated with ischemia and increased oxidative stress, the vasodilator function of retinal arterioles was examined after retinal ischemia induced by elevated intraocular pressure (IOP). The role of superoxide anions in the development of vascular dysfunction was assessed.

METHODS

IOP was increased and maintained at 80 to 90 mm Hg for 30, 60, or 90 minutes by infusing saline into the anterior chamber of a porcine eye. The fellow eye with normal IOP (10-20 mm Hg) served as control. In some pigs, superoxide dismutase mimetic TEMPOL (1 mM) or vehicle (saline) was injected intravitreally before IOP elevation. After enucleation, retinal arterioles were isolated and pressurized without flow for functional analysis by recording diameter changes using videomicroscopic techniques. Dihydroethidium (DHE) was used to detect superoxide production in isolated retinal arterioles.

RESULTS

Isolated retinal arterioles developed stable basal tone and the vasodilations to endothelium-dependent nitric oxide (NO)-mediated agonists bradykinin and L-lactate were significantly reduced only by 90 minutes of ischemia. However, vasodilation to endothelium-independent NO donor sodium nitroprusside was unaffected after all time periods of ischemia. DHE staining showed that 90 minutes of ischemia significantly increased superoxide levels in retinal arterioles. Intravitreal injection of membrane-permeable radical scavenger but not vehicle before ischemia prevented elevation of vascular superoxide and preserved bradykinin-induced dilation.

CONCLUSIONS

Endothelium-dependent NO-mediated dilation of retinal arterioles is impaired by 90 minutes of ischemia induced by elevated IOP. The inhibitory effect appears to be mediated by the alteration of NO signaling via vascular superoxide.

Toxicity profiles of subretinal indocyanine green, Brilliant Blue G, and triamcinolone acetonide: a comparative study

BACKGROUND

This study introduces a novel porcine model to examine the histopathological and electrophysiological consequences of retinotoxicity exerted by dyes commonly used for internal limiting membrane (ILM) staining.

METHODS

Indocyanine green (ICG) 0.5 mg/ml, Brilliant Blue G (BBG) 0.25 mg/ml and triamcinolone acetonide (TA) 13 mg/ml was injected subretinally in 12 vitrectomized pig eyes. At 6 weeks, retinas were examined by multifocal electroretinography (mfERG), ophthalmoscopy, fluorescein angiograpy, histopathology, and apoptosis assay.

RESULTS

mfERG responses were significantly lower in ICG-injected eyes than in healthy fellow eyes (p = 0.039). The ratio between injected eyes and healthy fellow eyes was lower in the ICG group than in the BBG (p = 0.009) and TA group (p = 0.025). No difference between BBG and TA existed. All retinas were reattached, and fluorescein angiographies showed a window defect corresponding to the injected areas but no blood-retina barrier break-down. Histopathology confirmed damage to the outer retina after ICG, but not after BBG and TA. No apoptosis was found at 6 weeks.

CONCLUSIONS

Subretinal ICG induces histological and functional damage to the retina, suggesting that ICG should be used with caution in macular hole surgery, where subretinal migration can occur. In contrast, BBG and TA appear safe after subretinal injection.

The effect of subretinal viscoelastics on the porcine retinal function

The functional consequence of long-term retinal detachment in the porcine model is examined by multifocal electroretinography (mfERG). Retinal detachment (RD) in humans leaves permanent visual impairment, despite anatomical successful reattachment surgery. To improve treatment, adjuvant pharmaceutical therapy is needed, and can only be tested in a suitable animal model. The porcine model is promising and the mfERG is well validated in this model. RD was induced in 18 pigs by vitrectomy and healon injection of various concentrations. Preoperatively and 6 weeks postoperatively eight animals were examined by mfERG. The major component P1 was analyzed statistically. Indirect ophthalmoscopy and bilateral color fundus photography (FP) were performed. Selected animals underwent high-resolution optical coherence tomography (OCT). Examination by ophthalmoscopy and FP showed that the RDs remained detached for the 6 weeks of follow-up. The P1 amplitude of the mfERG did not differ significantly between the detached areas, the surrounding attached areas, and the healthy eye (p = 0.25). Similarly, P1 implicit time did not differ between the areas (p = 0.85). The lack of functional consequences of long-term RD makes the porcine model unsuitable for examining adjuvant pharmaceutical RD treatment. Future studies should focus on foveated primates.

Guinea pig horizontal cells express GABA, the GABA-synthesizing enzyme GAD 65, and the GABA vesicular transporter

Gamma-aminobutyric acid (GABA) is likely expressed in horizontal cells of all species, although conflicting physiological findings have led to considerable controversy regarding its role as a transmitter in the outer retina. This study has evaluated key components of the GABA system in the outer retina of guinea pig, an emerging retinal model system. The presence of GABA, its rate-limiting synthetic enzyme glutamic acid decarboxylase (GAD(65) and GAD(67) isoforms), the plasma membrane GABA transporters (GAT-1 and GAT-3), and the vesicular GABA transporter (VGAT) was evaluated by using immunohistochemistry with well-characterized antibodies. The presence of GAD(65) mRNA was also evaluated by using laser capture microdissection and reverse transcriptase-polymerase chain reaction. Specific GABA, GAD(65), and VGAT immunostaining was localized to horizontal cell bodies, as well as to their processes and tips in the outer plexiform layer. Furthermore, immunostaining of retinal whole mounts and acutely dissociated retinas showed GAD(65) and VGAT immunoreactivity in both A-type and B-type horizontal cells. However, these cells did not contain GAD(67), GAT-1, or GAT-3 immunoreactivity. GAD(65) mRNA was detected in horizontal cells, and sequencing of the amplified GAD(65) fragment showed approximately 85% identity with other mammalian GAD(65) mRNAs. These studies demonstrate the presence of GABA, GAD(65), and VGAT in horizontal cells of the guinea pig retina, and support the idea that GABA is synthesized from GAD(65), taken up into synaptic vesicles by VGAT, and likely released by a vesicular mechanism from horizontal cells.

Immunocytochemical evidence for SNARE protein-dependent transmitter release from guinea pig horizontal cells

Horizontal cells are lateral interneurons that participate in visual processing in the outer retina but the cellular mechanisms underlying transmitter release from these cells are not fully understood. In non-mammalian horizontal cells, GABA release has been shown to occur by a non-vesicular mechanism. However, recent evidence in mammalian horizontal cells favors a vesicular mechanism as they lack plasmalemmal GABA transporters and some soluble NSF attachment protein receptor (SNARE) core proteins have been identified in rodent horizontal cells. Moreover, immunoreactivity for GABA and the molecular machinery to synthesize GABA have been found in guinea pig horizontal cells, suggesting that if components of the SNARE complex are expressed they could contribute to the vesicular release of GABA. In this study we investigated whether these vesicular and synaptic proteins are expressed by guinea pig horizontal cells using immunohistochemistry with well-characterized antibodies to evaluate their cellular distribution. Components of synaptic vesicles including vesicular GABA transporter, synapsin I and synaptic vesicle protein 2A were localized to horizontal cell processes and endings, along with the SNARE core complex proteins, syntaxin-1a, syntaxin-4 and synaptosomal-associated protein 25 (SNAP-25). Complexin I/II, a cytosolic protein that stabilizes the activated SNARE fusion core, strongly immunostained horizontal cell soma and processes. In addition, the vesicular Ca(2+)-sensor, synaptotagmin-2, which is essential for Ca(2+)-mediated vesicular release, was also localized to horizontal cell processes and somata. These morphological findings from guinea pig horizontal cells suggest that mammalian horizontal cells have the capacity to utilize a regulated Ca(2+)-dependent vesicular pathway to release neurotransmitter, and that this mechanism may be shared among many mammalian species.

A battery of cell- and structure-specific markers for the adult porcine retina

The pig is becoming an increasingly used non-primate model in experimental studies of human retinal diseases and disorders. The anatomy, size, and vasculature of the porcine eye and retina closely resemble their human counterparts, which allows for application of standard instrumentation and diagnostics used in the clinic. Despite many reports that demonstrate immunohistochemistry as a useful method for exploring neuropathological changes in the mammalian central nervous system, including the pig, the porcine retina has been sparsely described. Hence, to facilitate further immunohistochemical analysis of the porcine retina, we report on the successful use of a battery of antibodies for staining of paraformaldehyde-fixed cryosectioned retina. The following antibodies were evaluated for neuronal cells and structures: recoverin (cones and rods), Rho4D2 (rods), transducin-gamma (cones), ROM-1 (photoreceptor outer segments), calbindin (horizontal cells), PKC-alpha (bipolar cells), parvalbumin (amacrine and displaced amacrine cells), and NeuN (ganglion cells and displaced amacrines). For detecting synaptic connections in fiber layers, we used an antibody against synaptobrevin. For detecting retinal pigment epithelium, we studied antibodies against cytokeratin and RPE65, respectively. The glial cell markers used were bFGF (Müller cells and displaced amacrine cells), GFAP (Müller cells and astrocytes), and vimentin (Müller cells). Each staining effect was evaluated with regard to its specificity, sensitivity, and reproducibility in the identification of individual cells, specific cell structures, and fiber layers, respectively. The markers parvalbumin and ROM-1 were tested here for the first time for the porcine retina. All antibodies tested resulted in specific staining of high quality. In conclusion, all immunohistochemical protocols presented here will be applicable in fixed, cryosectioned pig retina.

Delayed administration of glial cell line-derived neurotrophic factor (GDNF) protects retinal ganglion cells in a pig model of acute retinal ischemia

This study investigates whether intravitreal administration of glial cell line-derived neurotrophic factor (GDNF) enhances survival of NeuN positive retinal cells in a porcine model of retinal ischemia. 16 pigs were subjected to an ischemic insult where intraocular pressure was maintained at 5 mmHg below mean arterial blood pressure for 2 h. The mean IOP during the ischemic insult was 79.5 mmHg (s.e.m. 2.1 mmHg, n = 15). Three days after the insult the pigs received an intravitreal injection of GDNF microspheres or blank microspheres. The pigs were evaluated by way of multifocal electroretinography (mfERG), quantification of NeuN positive cells and evaluation of the degree of retinal perivasculitis and inflammation 6 weeks after the insult. In the post-injection eyes (days 14, 28 and 42), the ratios of the iN1 and the iP2 amplitudes were 0.10 (95% CI: 0.05-0.15) and 0.09 (95% CI: 0.04-0.16) in eyes treated with blank microspheres, and 0.24 (95% CI: 0.18-0.32) and 0.23 (95% CI: 0.15-0.33) in eyes treated with GDNF microspheres. These differences were statistically significant (P < 0.05). The number of NeuN positive cells in the area of the visual streak area was significantly higher in eyes injected with GDNF microspheres compared to eyes injected with blank microspheres. In eyes injected with GDNF microspheres the ganglion cell count was 9.5/field (s.e.m.: 2.1, n = 8), in eyes injected with blank microspheres it was 3.5/field (s.e.m.: 1.2, n = 7). This difference was statistically significant (P < 0.05). There was also a significant difference (P < 0.01) in the degree of perivasculiitis between GDNF treated eyes (median perivasculitis score 1.5) and blank treated eyes (median perivasculitis score 3.0). In conclusion, injection of GDNF microspheres 3 days after an ischemic insult results in functional and morphological rescue of NeuN positive cells in a porcine model of acute ocular ischemia.