Inflammatory demyelination induces axonal injury and retinal ganglion cell apoptosis in experimental optic neuritis

Optic neuritis is an inflammatory disease of the optic nerve that often occurs in patients with multiple sclerosis and leads to permanent visual loss mediated by retinal ganglion cell (RGC) damage. Optic neuritis occurs with high frequency in relapsing-remitting experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, with significant loss of RGCs. In the current study, mechanisms of RGC loss in this model were examined to determine whether inflammation-induced axonal injury mediates apoptotic death of RGCs. RGCs were retrogradely labeled by injection of fluorogold into superior colliculi of 6-7 week old female SJL/J mice. EAE was induced one week later by immunization with proteolipid protein peptide. Optic neuritis was detected by inflammatory cell infiltration on histological examination as early as 9 days after immunization, with peak incidence by day 12. Demyelination occurred 1-2 days after inflammation began. Loss of RGC axons was detected following demyelination, with significant axonal loss occurring by day 13 post-immunization. Axonal loss occurred prior to loss of RGC bodies at day 14. Apoptotic cells were also observed at day 14 in the ganglion cell layer of eyes with optic neuritis, but not in control eyes. Together these results suggest that inflammatory cell infiltration mediates demyelination and leads to direct axonal injury in this model of experimental optic neuritis. RGCs die by an apoptotic mechanism triggered by axonal injury. Potential neuroprotective therapies to prevent permanent RGC loss from optic neuritis will likely need to be initiated prior to axonal injury to preserve neuronal function.     

SIRT1 activation confers neuroprotection in experimental optic neuritis

PURPOSE: Axonal damage and loss of neurons correlate with permanent vision loss and neurologic disability in patients with optic neuritis and multiple sclerosis (MS). Current therapies involve immunomodulation, with limited effects on neuronal damage. The authors examined potential neuroprotective effects in optic neuritis by SRT647 and SRT501, two structurally and mechanistically distinct activators of SIRT1, an enzyme involved in cellular stress resistance and survival. METHODS: Experimental autoimmune encephalomyelitis (EAE), an animal model of MS, was induced by immunization with proteolipid protein peptide in SJL/J mice. Optic neuritis developed in two thirds of eyes with significant retinal ganglion cell (RGC) loss detected 14 days after immunization. RGCs were labeled in a retrograde fashion with fluorogold by injection into superior colliculi. Optic neuritis was detected by inflammatory cell infiltration of the optic nerve. RESULTS: Intravitreal injection of SIRT1 activators 0, 3, 7, and 11 days after immunization significantly attenuated RGC loss in a dose-dependent manner. This neuroprotective effect was blocked by sirtinol, a SIRT1 inhibitor. Treatment with either SIRT1 activator did not prevent EAE or optic nerve inflammation. A single dose of SRT501 on day 11 was sufficient to limit RGC loss and to preserve axon function. CONCLUSIONS: SIRT1 activators provide an important potential therapy to prevent the neuronal damage that leads to permanent neurologic disability in optic neuritis and MS patients. Intravitreal administration of SIRT1 activators does not suppress inflammation in this model, suggesting that their neuroprotective effects will be additive or synergistic with current immunomodulatory therapies.     

Suppression of mitochondrial oxidative stress provides long-term neuroprotection in experimental optic neuritis

PURPOSE: Axonal loss is thought to contribute to the persistence of visual loss in optic neuritis and multiple sclerosis (MS). The mechanisms of injury are poorly understood. The authors investigated the contribution of mitochondrial oxidative stress and the effects of modulating mitochondrial antioxidant gene expression in the optic nerves of mice induced with experimental allergic encephalomyelitis (EAE), with a focus on long-term neuroprotection. METHODS: Optic nerves from mice with EAE were probed for reactive oxygen species (ROS) with the use of dichlorofluorescein diacetate (DCFDA), dihydroethidium, and cerium chloride. To modulate mitochondrial oxidative stress, recombinant AAV containing the human SOD2 gene or a ribozyme targeting murine SOD2 was injected into the vitreous. Control eyes received the recombinant virus without a therapeutic gene. Mice were sensitized for EAE and were monitored by serial contrast-enhanced MRI. The effects of SOD2 modulation on the EAE optic nerve were gauged by computerized analysis of optic nerve volume, myelin fiber area, and retinal ganglion cell loss at 1, 3, and 12 months after sensitization for EAE. RESULTS: ROS were detected in the EAE optic nerve as early as 3 days after antigenic sensitization. Colocalization suggested mitochondria as the source of ROS activity in the absence of inflammation. The ribozyme suppressing SOD2 gene expression increased myelin fiber injury by 27%. Increasing SOD2 levels twofold in the optic nerve by virally mediated gene transfer ameliorated myelin fiber injury by 51% and RGC loss fourfold, limiting it to 7% in EAE at 1 year. CONCLUSIONS: Amelioration of mitochondrial oxidative stress by SOD2 gene delivery may be a therapeutic strategy for suppressing neurodegeneration in optic neuritis.     

Protective effects of catalase on retinal ischemia/reperfusion injury in rats

Retinal ischemia/reperfusion (I/R) injury causes profound tissue damage, especially retinal ganglion cell (RGC) death. The aims of the study were to investigate whether catalase (CAT) has a neuroprotective effect on RGC after I/R injury in rats, and to determine the possible antioxidant mechanism. Wistar female rats were randonmized into four groups: normal control group (Control group), retinal I/R with vehicle group (I/R with vehicle group), retinal I/R with AAV-CAT group (I/R with AAV-CAT group), and normal retina with AAV-CAT group (normal with AAV-CAT group). One eye of each rat was pretreated with recombinant adeno-associated virus containing catalase gene (I/R with AAV-CAT group or normal with AAV-CAT group) and recombinant adeno-associated virus containing GFP gene (I/R with vehicle group) by intravitreal injection 21 days before initiation of I/R injury. Retinal I/R injury was induced by elevating intraocular pressure to 100 mmHg for 1 h. The number of RGC and inner plexiform layer (IPL) thickness were measured by fluorogold retrograde labeling and hematoxylin and eosin staining at 6 h, 24 h, 72 h and 5d after injury. Hydrogen peroxide (H₂O₂), the number of RGC, IPL thickness, malondialdehyde(MDA), 8-hydroxy-2-deoxyguanosine (8-OHdG), CAT activity and nitrotyrosine were measured by fluorescence staining, immunohistochemistry and enzyme-linked immunosorbent assay analysis at 5 days after injury. Electroretinographic (ERG) evaluation was also used. Pretreatment of AAV-CAT significantly decreased the levels of H₂O₂, MDA, 8-OHdG and nitrotyrosine, increased the catalase activity, and prevented the reduction of a- and b- waves in the I/R with AAV-CAT group compare with the I/R with vehicle group (p < 0.01). Catalase attenuated the I/R-induced damage of RGC and IPL and retinal function. Therefore, catalase can protect the rat retina from I/R-induced injury by enhancing the antioxidative ability and reducing oxidative stress, which suggests that catalase may be relevant for the neuroprotection of inner retina from I/R-related diseases.     

Obstructed axonal transport of BDNF and its receptor TrkB in experimental glaucoma

PURPOSE: In both animal model system and in human glaucoma, retinal ganglion cells (RGCs) die by apoptosis. To understand how RGC apoptosis is initiated in these systems, the authors studied RGC neurotrophin transport in experimental glaucoma using acute intraocular pressure (IOP) elevations in rats and chronic IOP elevation and unilateral optic nerve transections in monkeys. METHODS: Eyes were studied in masked fashion by light and electron microscopy and by immunohistochemistry with antibodies directed against the tyrosine kinase receptors (TrkA, B, and C) and against brain-derived neurotrophic factor (BDNF), as well as by autoradiography to identify retrograde axonal transport of 125I-BDNF injected into the superior colliculus. RESULTS: With acute glaucoma in the rat, RGC axons became abnormally dilated, accumulating vesicles presumed to be moving in axonal transport at the optic nerve head. Label for TrkB, but not TrkA, was relatively increased at and behind the optic nerve head with IOP elevation. Abnormal, focal labeling for TrkB and BDNF was identified in axons of monkey optic nerve heads with chronic glaucoma. With acute IOP elevation in rats, radiolabeled BDNF arrived at cells in the RGC layer at less than half the level of control eyes. CONCLUSIONS: Interruption of BDNF retrograde transport and accumulation of TrkB at the optic nerve head in acute and chronic glaucoma models suggest a role for neurotrophin deprivation in the pathogenesis of RGC death in glaucoma.     

Reduced retina microglial activation and improved optic nerve integrity with minocycline treatment in the DBA/2J mouse model of glaucoma

PURPOSE: In the context of the retinal ganglion cell (RGC) axon degeneration in the optic nerve that occurs in glaucoma, microglia become activated, then phagocytic, and redistribute in the optic nerve head. The authors investigated the potential contribution of retinal microglia activation to glaucoma progression in the DBA/2J chronic mouse glaucoma model. METHODS: The authors treated 6-week-old DBA/2J mice for 25 weeks with minocycline, a tetracycline derivative known to reduce microglia activation and to improve neuronal survival in other models of neurodegenerative disease. They quantified RGC numbers and characterized microglia activation, gliosis, and both axonal integrity and retrograde tracer transport by RGCs in mice systemically treated with minocycline or vehicle only. RESULTS: Minocycline reduced microglial activation and improved RGC axonal transport and integrity, yet it had no effect on the characteristic age-related ocular changes that lead to chronically elevated pressure and did not alter Müller or astrocyte gliosis. Specifically, minocycline increased the fraction of microglia with resting ramified morphology and reduced levels of Iba1 mRNA and protein, a microglia-specific calcium ligand linked to activation. The reduction in microglial activation was coupled to significant improvement in RGC axonal transport, as measured by neuronal retrograde tracing from the superior colliculus. Finally, minocycline treatment significantly decoupled RGC axon loss from increased intraocular pressure. CONCLUSIONS: These observations suggest that in glaucoma, retina and optic nerve head microglia activation may be a factor in the early decline in function of the optic nerve and its subsequent degeneration.     

Neuron stress and loss following rodent anterior ischemic optic neuropathy in double-reporter transgenic mice

PURPOSE: Nonarteritic anterior ischemic optic neuropathy (NAION) is an optic nerve infarct involving axons of retinal ganglion cell (RGC) neurons. The rodent NAION model (rAION) can use transgenic mouse strains to reveal unique characteristics about the effects of sudden optic nerve ischemia on RGCs and their axons. The impact of rAION on RGC stress patterns, RGC loss, and their axons after axonal infarct were evaluated. METHODS: A double-transgenic mouse strain was used, containing a construct with cyan fluorescent protein (CFP) under Thy-1 promoter control, and a construct with beta-galactosidase (lacZ) linked to the stress gene c-fos promoter. Thy-1 in the retina is expressed predominantly in RGCs, enabling stereologic analysis of CFP(+) RGC numbers and loss post-rAION-using confocal microscopy. RGC loss was correlated with axonal counts using transmission electron microscopy (TEM). LacZ immunohistochemistry was used to evaluate retinal cell stress after rAION. RESULTS: The 45,000 CFP(+) cells in the RGC layer of control animals compared with previous RGC quantitative estimates. rAION produced RGC stress, defined as lacZ expression, in patterns corresponding with later RGC loss. rAION-associated RGC loss correlated with regional nerve fiber layer loss. Axonal loss correlates with stereologically determined RGC loss estimates in transgenic mice retinas. CONCLUSIONS: Post-ON infarct RGC stress patterns correlate with regional RGC loss. Cellular lacZ levels in most RGCs are low, suggesting rAION-affected RGCs express c-fos only transiently. CFP(+) cell loss correlates closely with quantitative axonal loss, suggesting that the Thy-1 (CFP) transgenic mouse strain is appropriate for RGC stereologic analyses.     

Neuroprotective effect of memantine in different retinal injury models in rats

PURPOSE: To evaluate the neuroprotective effect of memantine, an NMDA receptor channel blocker, in two retinal ganglion cell (RGC) injury models in rats. METHODS: Neuroprotective effect of memantine was tested in partial optic nerve injury and chronic ocular hypertensive models. In the optic nerve injury model, memantine (0.1 - 30 mg/kg) was injected intraperitoneally immediately after injury. Two weeks later, optic nerve function was determined by measuring compound action potential and surviving RGC was determined by retrograde labeling with dextran tetramethyl rhodamine. Chronic ocular hypertension was attained by laser photocoagulation of episcleral and limbal veins. Memantine (5 or 10 mg/kg) was administered continuously each day with an osmotic pump, either immediately after or 10 days after first laser photocoagulation, for 3 weeks, after which RGC survival was determined. RESULTS: Two weeks after partial optic nerve injury, there was approximately 80% reduction in RGC number. Memantine (5 mg/kg) caused a twofold increase in compound action potential amplitude and a 1.7-fold increase in survival of RGCs, respectively. In the chronic ocular hypertension model there was 37% decrease in RGCs after 3 weeks of elevated intraocular pressure. Memantine (10 mg/kg daily) reduced ganglion cell loss to 12% when applied immediately after first laser photocoagulation, and prevented any further loss when applied 10 days after first laser photocoagulation. CONCLUSION: The protective effect of memantine suggests that excessive stimulation of NMDA receptors by glutamate is involved in causing cell damage in these RGC injury models.     

神经生长因子对脱髓鞘性视神经炎小鼠视网膜神经组织保护作用的实验研究

目的 研究神经生长因子（NGF）对脱髓鞘性视神经炎小鼠视网膜神经组织的保护作用.方法 实验研究.50只C57BL/6小鼠按随机数字表法分为对照组（10只）、BSS组（20只）和NGF组（20只）,取右眼为实验眼.后两组应用MOG35-55多肽加完全弗氏佐剂皮下注射建立实验性视神经炎小鼠模型,每天对各组小鼠进行称重及神经功能评分.NGF组和BSS组分别于免疫后的第4天和第10天,对右眼进行玻璃体腔注射3μg/μl NGF或2 μl BSS.分别于免疫当天、免疫后的第7天和免疫后的第14天,对每组小鼠进行闪光视觉诱发电位（f-VEP）和闪光视网膜电图（f-ERG）检查;采用HE染色、LFB染色、Bielschowsky银染分别评估视神经炎性细胞浸润、髓鞘脱失、轴突病理改变;使用TUNEL法检测视网膜神经节细胞凋亡并计算凋亡指数.对两组实验数据采用t检验进行统计学分析.结果 NGF组与BSS组小鼠发病时间和临床评分比较,差异均无统计学意义（t=-1.844,P=0.079;t=-2.012,P=0.059）.在不同时间点,NGF组和BSS组的f-VEP差异均无统计学意义（P＞0.05）.在免疫后的第14天,NGF组f-ERG b波潜伏期较BSS组缩短,振幅较BSS组增大,两组差异有统计学意义（t=5.909,P=0.000;t=3.602,P=0.043）.LFB染色示,NGF组和BSS组视神经的脱髓鞘面积占横截面比例分别为（31.50±8.72）%、（29.91±10.00）%,差异无统计学意义（t=0.298,P=0.709）.TUNEL检测结果示,NGF组小鼠视网膜神经节细胞凋亡指数[（15.18±3.36）%]低于BSS组[（34.14±3.83）%],差异有统计学意义（t=11.790,P=0.000）.结论 NGF可以促进脱髓鞘性视神经炎小鼠视网膜神经节细胞的存活,对其视网膜神经组织可能具有一定的保护作用.     

The pathogenic role of transforming growth factor-β2 in glaucomatous damage to the optic nerve head

In patients with primary open angle glaucoma (POAG), the optic nerve head (ONH) shows characteristic cupping correlated with visual field defects. The progressive optic neuropathy is characterized by irreversible loss of retinal ganglion cells (RGC). The critical risk factor for axonal damage at the ONH is an elevated intraocular pressure (IOP). The increase in IOP correlates with axonal loss in the ONH, which might be due to an impaired axoplasmatic flow leading to the loss of RGCs. Damage to the optic nerve is thought to occur in the lamina cribrosa (LC) region of the ONH, which is composed of characteristic sieve-like connective tissue cribriform plates through which RGC axons exit the eye. The cupping of the optic disc, and the compression and excavation of LC are characteristic signs of glaucomatous ONH remodelling. In ONH of POAG patients a disorganized distribution and deposition of elastic fibers and a typical pronounced thickening of the connective tissue septae surrounding the optic nerve fibers is found.Transforming growth factor (TGF)-β2 could be one of the pathogenic factors responsible for the structural alterations in POAG patients as the TGF-β2 levels in the ONH of glaucomatous eyes are elevated as well as in the aqueous homour. TGF-β2 leads to an increased synthesis of extracellular matrix (ECM) molecules mediated by connective tissue growth factor and to an impaired ECM degradation in cultured ONH astrocytes. Bone morphogenetic protein (BMP)-4 effectively antagonizes the effects of TGF-β2 on matrix deposition. The BMP antagonist gremlin blocks this inhibition, allowing TGF-β2 stimulation of ECM synthesis. Overall, the ECM in the ONH is kept in balance in the OHN by factors that augment or block the activity of TGF-β2.     

Oxidative stress is an early event in hydrostatic pressure induced retinal ganglion cell damage

PURPOSE: To determine whether oxidative adduct formation or heme oxygenase-1 (HO-1) expression are altered in retinal ganglion cell (RGC) cultures exposed to elevated hydrostatic pressure and in a mouse model of glaucoma. METHODS: Cultured RGC-5 cells were subjected to 0, 30, 60, or 100 mm Hg hydrostatic pressure for 2 hours, and the cells were harvested. Parallel experiments examined the recovery from this stress, the effect of direct 4-hydroxy-2-nonenal (HNE) treatment, and the effect of pretreatment with resveratrol or quercetin. Mice were anesthetized and intraocular pressure was increased to 30, 60, or 100 mm Hg for 1 hour; then the retinas were harvested. HNE adduct formation and HO-1 expression were assessed by immunocytochemistry and immunoblotting. RESULTS: Increases of HNE-protein adducts (up to 5-fold) and HO-1 expression (up to 2.5 fold) in pressure-treated RGC-5 cells were dose dependent. During recovery experiments, HNE-protein adducts continued to increase for up to 10 hours; in contrast, HO-1 expression decreased immediately. HNE, at a concentration as low as 5 muM, led to neurotoxicity in RGC-5 cells. HNE adducts and HO-1 expression increased in the mouse retina and optic nerve after acute IOP elevation up to 5.5-fold and 2-fold, respectively. Antioxidant treatment reduced the oxidative stress level in pressure-treated RGC-5 cells. CONCLUSIONS: This study demonstrates that oxidative stress is an early event in hydrostatic pressure/IOP-induced neuronal damage. These findings support the view that oxidative damage contributes early to glaucomatous optic neuropathy.     

Recovery of visual field defects in ischemic optic neuropathy and idiopathic optic neuritis]

Fifty-four eyes of 41 patients with optic nerve disease demonstrating acute visual field defects without any traumatic, compressive, or other known etiology were classified into four categories. Those showing poor recovery of visual field defects were ischemic optic neuropathy which was subclassified into either anterior ischemic optic neuropathy (AION) or posterior ischemic optic neuropathy (PION) according to the ophthalmoscopic changes in the optic nerve head. Those showing good recovery of visual field defects were idiopathic optic neuritis which was subclassified into either papillitis or retrobulbar neuritis according to the ophthalmoscopic pathology of the optic disc. Patients with ischemic optic neuropathy were significantly older than those with optic neuritis. All eyes with optic neuritis showed good recovery of vision, whereas those with ischemic optic neuropathy showed varying outcomes of vision. With regard to the pattern of field defect, central or paracentral scotoma was predominant in all but eyes with AION in which altitude defect predominated. Pale swelling of the optic nerve head and angiographic evidence of circulatory disturbance in the optic disc or adjacent choroid were common findings in eyes with AION, whereas such findings were never observed in eyes with papillitis. The amplitude of pattern visual evoked potential was significantly lower in eyes with PION than in those with retrobulbar optic neuritis. Four patients classified as optic neuritis developed into multiple sclerosis in the follow-up study. It was concluded that poor recovery of visual field defect is one of the most convincing evidences for the diagnosis of ischemic optic neuropathy.     

MRI lesions of the optic nerves in optic neuritis

Magnetic resonance imaging (MRI) was performed in 14 patients with optic neuritis. Three patients suffered from multiple sclerosis but the etiologies of the remaining 11 cases could not be identified. They were bilateral in 6, and unilateral in 8. The MR images were compared with the symptomatic lesions of optic neuritis and pattern reversal VECP. The STIR mode (short time inversion recovery), was employed for the MRI in the orbit and T2-weighted mode in the brain. In 11 eyes with hyperemia of the optic disc, 7 eyes showed a high signal in the optic nerve with the MRI, and 9 eyes showed an abnormal pattern VECP. Seven eyes with normal disc and two eyes with a pale disc showed a high signal in the optic nerve with MRI, those 9 eyes had abnormal pattern VECP. The high signal in the optic nerve was not related to visual acuity or visual field abnormalities of patients. However, the degree of the high signal of the optic nerve lesion in MRI was associated with the clinical course and prognosis of the optic neuritis. The degree of the high signal of the optic nerve lesion decreased with the recovery of visual acuity in optic neuritis.     

A model to study differences between primary and secondary degeneration of retinal ganglion cells in rats by partial optic nerve transection

PURPOSE: To use a rat model of optic nerve injury to differentiate primary and secondary retinal ganglion cell (RGC) injury. METHODS: Under general anesthesia, a modified diamond knife was used to transect the superior one third of the orbital optic nerve in albino Wistar rats. The number of surviving RGC was quantified by counting both the number of cells retrogradely filled with fluorescent gold dye injected into the superior colliculus 1 week before nerve injury and the number of axons in optic nerve cross sections. RGCs were counted in 56 rats, with 24 regions examined in each retinal wholemount. Rats were studied at 4 days, 8 days, 4 weeks, and 9 weeks after transection. The interocular difference in RGCs was also compared in five control rats that underwent no surgery and in five rats who underwent a unilateral sham operation. It was confirmed histologically that only the upper optic nerve had been directly injured. RESULTS: At 4 and 8 days after injury, superior RGCs showed a mean difference from their fellow eyes of -30.3% and -62.8%, respectively (P = 0.02 and 0.001, t-test, n = 8 rats/group), whereas sham-operation eyes had no significant loss (mean difference between eyes = 1.7%, P = 0.74, t-test). At 8 days, inferior RGCs were unchanged from control, fellow eyes (mean interocular difference = -4.8%, P = 0.16, t-test). Nine weeks after transection, inferior RGC had 34.5% fewer RGCs than their fellow eyes, compared with 41.2% fewer RGCs in the superior zones of the injured eyes compared with fellow eyes. Detailed, serial section studies of the topography of RGC axons in the optic nerve showed an orderly arrangement of fibers that were segregated in relation to the position of their cell bodies in the retina. CONCLUSIONS: A model of partial optic nerve transection in rats showed rapid loss of directly injured RGCs in the superior retina and delayed, but significant secondary loss of RGCs in the inferior retina, whose axons were not severed. The findings confirm similar results in monkey eyes and provide a rodent model in which pharmacologic interventions against secondary degeneration can be tested.     

米诺环素对急性视神经炎大鼠视网膜神经节细胞的保护作用

目的:探讨米诺环素对大鼠视神经炎视网膜神经节细胞(RGCs)的影响,并与甲基强的松龙比较。方法:选取22只雌性Wistar大鼠随机分为正常对照组和实验组,实验组又分为实验对照组(EAE组)、米诺环素组、甲基强的松龙组(MP组)。HE染色观察视神经病理改变,TUNEL法检测RGCs凋亡率。结果:EAE组视神经纤维空泡样变性,轴突不规则肿胀,大量炎性细胞浸润,轴突内空泡样变性,髓鞘松解脱落,微丝微管消失,EAE大鼠视神经病理变化符合脱髓鞘性视神经炎改变。正常大鼠几乎未见RGCs凋亡,EAE组、米诺环素组、MP组较正常组相比,差异均有显著统计学意义(P<0.01),EAE组、MP组较米诺环素组相比,差异均有统计学意义(P<0.05),MP组与EAE组间的差异有统计学意义(P<0.05)。结论:采用豚鼠脊髓匀浆诱导建立大鼠EAE模型,其视神经病理学改变符合脱髓鞘性视神经炎的表现。米诺环素可抑制脱髓鞘性视神经炎RGCs凋亡,而甲基强的松龙对脱髓鞘性视神经炎RGCs无直接保护作用。     

Quantitative Analysis of Changes in Macular Layers Following Optic Neuritis

The effects of optic neuritis in patients with multiple sclerosis (MS) on the thickness of individual macular layers was analysed by means of optical coherence tomography (OCT). Data of 15 patients (mean age 37.2 years, range 16–50) with multiple sclerosis and 15 normal subjects (mean age 37.7 years, range 17–67) were analysed. Twelve patients had suffered from an attack of acute unilateral optic neuritis in one or both eyes. OCT scans of the circumpapillary retinal nerve fibre layer (RNFL) and of the macula were obtained by means of fast scan protocols. The characteristic sequence of five intensity maxima and four intensity minima was attributed to the mean location of the individual macular layers. The eyes affected by optic neuritis showed significant (p < 0.05) reductions of RNFL thickness by 30.5%, of macular volume (MV) by 12.8%, and of inner macular layers. The mean reduction was 16.2% (macular nerve fibre layer), 31.1% (ganglion cell layer [GCL]), and 25.9% (inner plexiform layer [IPL]), respectively. However, significant reductions of RNFL thickness (by 9.0%), MV (by 5.0%), CGL (by 10.3%), and IPL (by 10.8%) were found also in the unaffected eyes of MS patients. Thus, the quantitative analysis of the axial reflectivity profiles from exported OCT images offers an appropriate method for the characterisation of the location of macular changes after optic neuritis. The shrinking of inner macular layers is a more sensitive parameter of postneuritic optic atrophies than the reduction of MV.     

A novel neuroprotectant against retinal ganglion cell damage in a glaucoma model and an optic nerve crush model in the rat

PURPOSE: To investigate the effects of repeated treatments with a neuroprotective compound, R(-)-1-(benzo [b] thiophen-5-yl)-2-[2-(N, N-diethylamino) ethoxy] ethanol hydrochloride (T-588), on retinal ganglion cell (RGC) survival in rat eyes with elevated intraocular pressure (IOP) or after optic nerve crush. METHODS: An increase in IOP was induced by a single laser treatment to the trabecular meshwork in one eye of adult Wistar rats. Crush injury was unilaterally produced by clipping the optic nerve 2 mm behind the globe. RGC density was estimated by counting fluorescent dye-labeled cells in the flatmount of the retina. The optic nerve damage in the crush model was also evaluated histologically. RESULTS: In the elevated IOP model, RGC survival decreased to 72.9% +/- 3.8% (mean +/- SEM) of that of the contralateral control eye on the eighth day after laser irradiation. Repeated treatments with T-588 at 30 mg/kg twice daily significantly enhanced RGC survival (86.0% +/- 2.2%, P = 0.0242) without the reduction of IOP. In the optic nerve crush model, RGC survival diminished to 37.2% +/- 8.4% of that of the contralateral control eye after 4 weeks. Repeated applications with T-588 at 10 mg/kg twice daily significantly enhanced RGC survival (77.8% +/- 2.1%, P = 0.0038). Histologically, the rat optic nerve in the group treated with T-588 at 10 mg/kg retained a near-normal morphology. CONCLUSIONS: T-588 has a neuroprotective effect against RGC death caused by elevated IOP and optic nerve crush in the rat.     

Optic nerve transection in monkeys may result in secondary degeneration of retinal ganglion cells

PURPOSE: Interest in neuroprotection for optic neuropathies is, in part, based on the assumption that retinal ganglion cells (RGCs) die, not only as a result of direct (primary) injury, but also indirectly as a result of negative effects from neighboring dying RGCs (secondary degeneration). This experiment was designed to test whether secondary RGC degeneration occurs after orbital optic nerve injury in monkeys. METHODS: The superior one third of the orbital optic nerve on one side was transected in eight cynomolgus monkeys (Macaca fascicularis). Twelve weeks after the partial transection, the number of RGC bodies in the superior and inferior halves of the retina of the experimental and control eyes and the number and diameter of axons in the optic nerve were compared by detailed histomorphometry. Vitreous was obtained for amino acid analysis. A sham operation was performed in three additional monkeys. RESULTS: Transection caused loss of 55% +/- 13% of RGC bodies in the superior retina of experimental compared with fellow control eyes (mean +/- SD, t-test, P < 0.00,001, n = 7). Inferior RGCs, not directly injured by transection, decreased by 22% +/- 10% (P = 0.002). The loss of superior optic nerve axons was 83% +/- 12% (mean +/- SD, t-test, P = 0.0008, n = 5) whereas, the inferior loss was 34% +/- 20% (P = 0.02, n = 5). Intravitreal levels of glutamate and other amino acids in eyes with transected nerves were not different from levels in control eyes 12 weeks after injury. Fundus examination, fluorescein angiography, and histologic evaluation confirmed that there was no vascular compromise to retinal tissues by the transection procedure. CONCLUSIONS: This experiment suggests that primary RGC death due to optic nerve injury is associated with secondary death of surrounding RGCs that are not directly injured.     

Measurements of Pupillary Responses to Light in Term and Preterm Infants

This study was conducted to assess ocular pulse amplitude and retinal nerve fibre layer in patients with multiple sclerosis and their correlation with disease duration and with severity. Retinal nerve fibre layer thickness was measured by Heidelberg Retinal Tomography II (HRT-II; Heidelberg Engineering, Dossenheim, Germany) and ocular pulse amplitude was measured by dynamic contour tonometry (Ziemer Ophthalmic Systems, Port, Switzerland) in 37 multiple sclerosis patients and 72 age- and gender-matched controls. Ocular pulse amplitude was significantly reduced and retinal nerve fibre layer was significantly thinner in temporal, superotemporal, and nasal sectors in patients with multiple sclerosis regardless of having an optic neuritis attack. The retinal nerve fibre layer was thinner in eyes with a previous optic neuritis attack compared with the eyes without an attack, but the difference was not significant. Ocular pulse amplitude showed a positive correlation with visual evoked potential amplitude and a negative correlation with visual evoked potential latency. Retinal nerve fibre layer thickness showed a significant negative correlation with the disease duration but not with visually evoked potential, disease severity, nor previous optic neuritis. These findings indicate that the process of degeneration starts in the early period of the disease, as our study group is composed of early–middle-stage multiple sclerosis patients, and is independent of relapses.     

Understanding glaucomatous damage: anatomical and functional data from ocular hypertensive rodent retinas

Glaucoma, the second most common cause of blindness, is characterized by a progressive loss of retinal ganglion cells and their axons, with a concomitant loss of the visual field. Although the exact pathogenesis of glaucoma is not completely understood, a critical risk factor is the elevation, above normal values, of the intraocular pressure. Consequently, deciphering the anatomical and functional changes occurring in the rodent retina as a result of ocular hypertension has potential value, as it may help elucidate the pathology of retinal ganglion cell degeneration induced by glaucoma in humans. This paper predominantly reviews the cumulative information from our laboratory’s previous, recent and ongoing studies, and discusses the deleterious anatomical and functional effects of ocular hypertension on retinal ganglion cells (RGCs) in adult rodents. In adult rats and mice, perilimbar and episcleral vein photocauterization induces ocular hypertension, which in turn results in devastating damage of the RGC population. In wide triangular sectors, preferentially located in the dorsal retina, RGCs lose their retrograde axonal transport, first by a functional impairment and after by mechanical causes. This axonal damage affects up to 80% of the RGC population, and eventually causes their death, with somal and intra-retinal axonal degeneration that resembles that observed after optic nerve crush. Importantly, while ocular hypertension affects the RGC population, it spares non-RGC neurons located in the ganglion cell layer of the retina. In addition, functional and morphological studies show permanent alterations of the inner and outer retinal layers, indicating that further to a crush-like injury of axon bundles in the optic nerve head there may by additional insults to the retina, perhaps of ischemic nature.