Detection of early neuron degeneration and accompanying microglial responses in the retina of a rat model of glaucoma

PURPOSE: To characterize the early reaction of retinal ganglion cells (RGCs) in a rat model of glaucoma using in vivo imaging and to examine the involvement of retinal microglia in glaucomatous neuropathy. METHODS: Glaucoma was induced in adult female Sprague-Dawley rats by cauterizing two episcleral veins, which resulted in a 1.6-fold increase in intraocular pressure (IOP). Retinal ganglion cells were retrogradely labeled with the fluorescent dye, 4-[didecylaminostyryl]-N-methyl-pyridinium-iodide (4-Di-10ASP) and monitored in vivo after elevation of IOP using fluorescence microscopy imaging. The number of RGCs was quantified on retinal flatmounts. Dying RGCs were surrounded by activated microglia that became visible after taking up the fluorescent debris. Immunocytochemistry was conducted to characterize further the ganglion cells and microglia. RESULTS: Cauterizing two of the four episcleral veins resulted in a consistent increase of IOP to 25.3 +/- 2.0 mm Hg, as measured with a handheld tonometer. IOP remained high for at least 3 months in glaucomatous eyes. The earliest sign of RGC death was detected in anesthetized animals 20 hours after induction of glaucoma. RGCs continued to decrease in number over time, with 40% of RGCs having degenerated after 2.5 months. Fundoscopic examination of the optic nerve head revealed cupping 2 months after induction of glaucoma. In addition, microglia were detected on retinal flatmounts as early as 72 hours after induction. Activated microglia and RGCs were also identified immunocytochemically, with an antibody against ionized calcium-binding adaptor molecule (Iba)-1 and an antibody specific to the 200-kDa subunit of the neurofilament protein, respectively. CONCLUSIONS: Occlusion of episcleral veins is a reproducible method that mimics human glaucoma, with chronically elevated IOP-induced RGC loss. This study shows that in vivo imaging permits the detection of ganglion cells in the living animal in the early stages of the disease and highlights the importance of in vivo imaging in understanding ophthalmic disorders such as glaucoma. Secondly, activation of intraretinal microglia coincides with degeneration of RGCs in glaucoma.     

Three experimental glaucoma models in rats: comparison of the effects of intraocular pressure elevation on retinal ganglion cell size and death

Glaucoma is a chronic and progressive optic nerve neuropathy involving the death of retinal ganglion cells (RGCs). Elevated intraocular pressure (IOP) is considered to be the major risk factor associated with the development of this neuropathy. The objective of the present study was to compare the effects on RGC survival of three different experimental methods to induce chronic elevation of IOP in rats. These methods were: (i) injections of latex microspheres into the eye anterior chamber; (ii) injections into the anterior chamber of a mixture of microspheres plus hydroxypropylmethylcellulose (HPM) and (iii) cauterization of three episcleral veins. The IOP of right (control) and left (glaucomatous) eyes was measured with an applanation tonometer in awake animals. Thirteen to 30 weeks later, RGCs were retrogradely labeled with 3% fluorogold. Subsequently, we analyzed the density of RGCs, as well as the major axis length and area of RGC soma resulting from the application of each method. A significant increase in IOP was found following application of each of the three methods. Cell death was evident in the glaucomatous eyes as compared to controls. However, no statistical differences were found between the extent of cell death associated with each of the three methods. IOP increase also induced a significant increase in the size of the soma of the remaining RGCs. In conclusion, the three methods used to increase IOP induce a similar degree of RGC death. Moreover, the extent of cell death was similar when the retinas were maintained under conditions of elevated IOP for 24 weeks in comparison to 13 weeks.     

Retinal damage after 3 to 4 months of elevated intraocular pressure in a rat glaucoma model

PURPOSE: To characterize a long-term elevated intraocular pressure (IOP) glaucoma model in the rat with respect to electroretinographic (ERG) changes and the pattern and mechanism of retinal ganglion cell (RGC) death. METHODS; An approximate doubling of IOP was induced in one eye (G) of female Wistar rats (150-180 g) by cautery of 3 episcleral/limbal veins. At intervals over 3 to 4 months, measurements of IOP and ERG changes (contact-lens electrode) were made in both the G and contralateral normal (N) eyes. At the end of 3 to 4 months of elevated IOP, RGCs were fluorescently labeled with Fluorogold (retrogradely from the superior colliculus), or retinas were labeled by intravitreal injection of a mitochondrial potential indicator dye and stained for apoptotic nuclei with a DNA dye. Flatmounts of fixed, dye-labeled retinas were examined by epifluorescence, confocal, or interference contrast microscopy. RESULTS: Elevated IOP was consistently maintained for up to 4 months in G eyes, but ERG a- and b-waves showed a statistically significant decline, of 30% to 40% in amplitude, after 3 months. Loss of RGCs in G retinas was primarily focal with no statistically significant loss demonstrable outside of the focal areas when assessed by an area sampling method for counting RGCs, which totaled 2% to 3% of the entire retinal area. Mitochondrial membrane potential of cells in the RGC layer was reduced by 17.5% (P: < 0.05) in regions surrounding areas of focal loss compared with comparable locations in control N eyes. After 3.5 months' elevated IOP the G retinas showed cell nuclei at various stages of apoptosis, from initial DNA condensation to fragmentation. CONCLUSIONS: The three-vein episcleral/limbal vein occlusion model for inducing glaucomatous pathology in the rat eye gives a consistent long-term elevation of IOP. After 3 to 4 months of approximately 100% increased IOP, the ERG responses begin to decline, there is a variable focal loss of RGCs, and some of the remaining RGCs show characteristics of stress and apoptosis. These changes seem consistent with retinal damage in human glaucoma (focal field defects), and this rat model appears to mimic some features of primary open-angle glaucoma.     

Characterization of retinal damage in the episcleral vein cauterization rat glaucoma model

Episcleral vein cauterization (EVC) is used in rats to generate a glaucoma model with high intraocular pressure (IOP). The long-term retinal damage in this glaucoma model, however, has not been accurately quantified. We report the location and amount of retinal ganglion cell (RGC) damage caused by (EVC) induced IOP elevation in two rat strains. IOP was raised in one eye of Wistar (N = 5) and Brown-Norway(B-N)(N = 7) rats by EVC and monitored monthly until IOP in contralateral eyes equalized at 5 months post-surgery. Animals were maintained for 3.5-4.5 additional months. B-N rats (N = 7) that had no EVC served as controls for this strain. Scotopic flash ERGs were recorded at baseline and just prior to euthanasia. Automated counts of all retrogradely labeled RGCs in retinal flat-mounts were determined and compared between contralateral eyes. RGC density maps were constructed and RGC size distribution was determined. Oscillatory potentials in the group of eyes which had elevated IOP were decreased at the time of euthanasia, when IOP had returned to normal. The group of normal B-N rats had similar RGC counts between contralateral eyes. In the experimental group the mean number of RGCs was not significantly different between control and experimental eyes, but 1 of 5 Wistar and 2 of 7 B-N experimental eyes had at least 30% fewer RGCs than contralateral control eyes. Total retinal area in B-N experimental eyes was higher compared to contralateral eyes. Cumulative IOP exposure of the experimental eyes was modestly correlated with RGC loss while oscillatory potentials appeared to be inversely related to RGC loss. In retinas with extensive (> 30% RGC loss) but not complete damage, smaller cells were preserved better than larger ones. The above results indicate that RGC loss in both Wistar and B-N strains is variable after a prolonged elevation of IOP via EVC. Such variability despite equivalent IOP levels and ERG abnormalities, suggests unknown factors that can protect IOP-stressed RGCs. Identification and enhancement of such factors could prove useful for glaucoma therapy.     

Neuroprotection of retinal ganglion cells with GDNF-Loaded biodegradable microspheres in experimental glaucoma

Glaucoma is the second leading cause of blindness worldwide, and also the most common optic neuropathy. The ultimate cause of vision loss in glaucoma is thought to be retinal ganglion cell (RGC) death. Neuroprotection of RGC is therefore an important goal of glaucoma therapy. Currently, glaucoma treatment relies on pharmacologic or surgical reduction of intraocular pressure (IOP). It is critical to develop treatment approaches that actively prevent the death of RGCs at risk in glaucoma. Neurotrophic factors have the ability to promote the survival and influence the growth of neurons. Neurotrophic factor deprivation has been proposed as one mechanism leading to RGC death in glaucoma. Effective neuroprotection in glaucoma likely requires the consistent availability of the active agent for prolonged periods of time. Biodegradable microspheres are especially attractive as drug delivery vehicles for a number of reasons. Sustained GDNF delivery by biodegradable microspheres offers significant neuroprotection to injured RGC in experimental glaucoma. PLGA microsphere-delivered GDNF represents an important neuroprotective strategy in the treatment of glaucomatous optic neuropathy and provides direction for further investigations of this hypothesis.     

Neuroprotective and intraocular pressure-lowering effects of (-)Delta9-tetrahydrocannabinol in a rat model of glaucoma

In glaucoma, retinal ganglion cell (RGC) death is induced by many risk factors, including ocular hypertension. It has been proposed that glutamate-mediated oxidative stress may also contribute to this RGC death. Cannabinoids are known to possess therapeutic properties including ocular hypotension and antioxidation. In this study, we test the hypothesis that (-)Delta(9)-tetrahydrocannabinol (THC) lowers intraocular pressure (IOP) and prevents RGC death in a rat model of glaucoma. Arat model of experimental glaucoma with chronic, moderately elevated IOP was produced unilaterally by cauterization of episcleral vessels. Rats received weekly injections of THC at a level of 5 mg/kg or vehicle for 20 weeks. IOP of both eyes was measured weekly on anesthetized animals immediately before THC treatment. RGCs were labeled in a retrograde fashion and counted in whole-mounted retinas. IOP was elevated in all operated eyes 1 day after the operation and remained elevated in the vehicle-treated rats throughout 20 weeks. In THC-treated rats, IOP elevation in operated eyes was diminished 2 weeks after operation and remained reduced. IOP in the contralateral control eyes was not affected by THC. In the operated eyes of vehicle-treated animals, there was a loss of approximately 50 and 40% of the RGCs in the peripheral and central retina, respectively. The RGC loss in the operated eyes of the THC-treated animals was reduced to 10-20%. These results demonstrate that THC is a neuroprotectant that preserves RGCs in an experimental model of glaucoma, possibly through a reduction in IOP.     

Glaucoma 2.0: neuroprotection, neuroregeneration, neuroenhancement

Glaucoma is a progressive neurodegenerative disease of retinal ganglion cells (RGCs) associated with characteristic axon degeneration in the optic nerve. Clinically, our only method of slowing glaucomatous loss of vision is to reduce intraocular pressure (IOP), but lowering IOP is only partially effective and does not address the underlying susceptibility of RGCs to degeneration. We review the recent steps forward in our understanding of the pathophysiology of glaucoma and discuss how this understanding has given us a next generation of therapeutic targets by which to maintain RGC survival, protect or rebuild RGC connections in the retina and brain, and enhance RGC function.     

Apoptotic retinal ganglion cell death in the DBA/2 mouse model of glaucoma

The DBA/2 mouse has been used as a model for spontaneous secondary glaucoma. We attempted to determine the in vivo time course and spatial distribution of retinal ganglion cells (RGCs) undergoing apoptotic death in DBA/2 mice. Female DBA/2 mice, 3, 9-10, 12, 15, and 18 months of age, received intravitreal injections of Annexin-V conjugated to AlexaFluor 1h prior to euthanasia. Retinas were fixed and flat-mounted. Annexin-V-positive RGCs in the hemiretina opposite the site of injection were counted, and their locations were recorded. Positive controls for detection of apoptotic RGCs by Annexin-V labeling included rats subjected to optic nerve ligation, and C57BL/6 mice subjected to either optic nerve ligation or intravitreal injection of NMDA. To verify that Annexin-V-labeled cells were RGCs, intravitreal Annexin-V injections were also performed on retinas pre-labeled retrogradely with FluoroGold or with DiI. Annexin-V-positive RGC locations were analyzed to determine possible clustering and areas of preferential loss. Annexin-V labeled apoptotic RGCs in eyes after optic nerve ligation, intravitreal NMDA injection, as well as in aged DBA/2 animals. In glaucomatous DBA/2 mice 95-100% of cells labeled with Annexin-V were also FluoroGold- and DiI-positive. This confirms that Annexin-V can be used to specifically detect apoptotic RGCs in rodent retinas. In DBA/2 mice, apoptotic RGC death is maximal from the 12th to the 15th month of age (ANOVA, p<0.001, Fisher's post hoc test) and occurs in clusters. These clusters are initially located in the midperipheral retina and progressively occur closer to the optic nerve head with increasing age. Retrograde axonal transport of FluoroGold in the glaucomatous mouse retina is functional until at least 2-3days prior to initiation of apoptotic RGC death.     

Diabetes Exacerbates the Intraocular Pressure-Independent Retinal Ganglion Cells Degeneration in the DBA/2J Model of Glaucoma

PurposeGlaucoma is a multifactorial disease, causing retinal ganglion cells (RGCs) and optic nerve degeneration. The role of diabetes as a risk factor for glaucoma has been postulated but still not unequivocally demonstrated. The purpose of this study is to clarify the effect of diabetes in the early progression of glaucomatous RGC dysfunction preceding intraocular pressure (IOP) elevation, using the DBA/2J mouse (D2) model of glaucoma.MethodsD2 mice were injected with streptozotocin (STZ) obtaining a combined model of diabetes and glaucoma (D2 + STZ). D2 and D2 + STZ mice were monitored for weight, glycemia, and IOP from 3.5 to 6 months of age. In addition, the activity of RGC and outer retina were assessed using pattern electroretinogram (PERG) and flash electroretinogram (FERG), respectively. At the end point, RGC density and astrogliosis were evaluated in flat mounted retinas. In addition, Müller cell reactivity was evaluated in retinal cross-sections. Finally, the expression of inflammation and oxidative stress markers were analyzed.ResultsIOP was not influenced by time or diabetes. In contrast, RGC activity resulted progressively decreased in the D2 group independently from IOP elevation and outer retinal dysfunction. Diabetes exacerbated RGC dysfunction, which resulted independent from variation in IOP and outer retinal activity. Diabetic retinas displayed decreased RGC density and increased glial reactivity given by an increment in oxidative stress and inflammation.ConclusionsDiabetes can act as an IOP-independent risk factor for the early progression of glaucoma promoting oxidative stress and inflammation-mediated RGC dysfunction, glial reactivity, and cellular death.     

Translimbal laser photocoagulation to the trabecular meshwork as a model of glaucoma in rats

PURPOSE: To develop and characterize a model of pressure-induced optic neuropathy in rats. METHODS: Experimental glaucoma was induced unilaterally in 174 Wistar rats, using a diode laser with wavelength of 532 nm aimed at the trabecular meshwork and episcleral veins (combination treatment group) or only at the trabecular meshwork (trabecular group) through the external limbus. Intraocular pressure (IOP) was measured by a tonometer in rats under ketamine-xylazine anesthesia. Possible retinal vascular compromise was evaluated by repeated fundus examinations and by histology. The degree of retinal ganglion cell (RGC) loss was assessed by a masked, semiautomated counting of optic nerve axons. Effects of laser treatment on anterior ocular structures and retina were judged by light microscopy. RESULTS: After the laser treatment, IOP was increased in all eyes to higher than the normal mean IOP of 19.4 +/- 2.1 mm Hg (270 eyes). Peak IOP was 49.0 +/- 6.1 mm Hg (n = 108) in the combination group that was treated by a laser setting of 0.7 seconds and 0.4 W and 34.0 +/- 5.7 mm Hg (n = 46) in the trabecular group. Mean IOP after 6 weeks was 25.5 +/- 2.9 mm Hg in glaucomatous eyes in the combination group compared with 22.0 +/- 1.8 mm Hg in the trabecular group. IOP in the glaucomatous eyes was typically higher than in the control eyes for at least 3 weeks. In the combination group, RGC loss was 16.1% +/- 14.4% at 1 week (n = 8, P = 0.01), 59.7% +/- 25.7% at 6 weeks (n = 88, P < 0.001), and 70.9% +/- 23.6% at 9 weeks (n = 12, P < 0.001). The trabecular group had mean axonal loss of 19.1% +/- 14.0% at 3 weeks (n = 9, P = 0.004) and 24.3% +/- 20.2% at 6 weeks (n = 25, P < 0.001), increasing to 48.4% +/- 32.8% at 9 weeks (n = 12, P < 0.001). Laser treatment led to closure of intertrabecular spaces and the major outflow channel. The retina and choroid were normal by ophthalmoscopy at all times after treatment. Light microscopic examination showed only loss of RGCs and their nerve fibers. CONCLUSIONS: Increased IOP caused by a laser injury to the trabecular meshwork represents a useful and efficient model of experimental glaucoma in rats.     

Regeneration of retinal ganglion cell axons in organ culture is increased in rats with hereditary buphthalmos

This study used organ cultures to examine whether retinal ganglion cells (RGCs) retain their ability to regenerate axons in buphthalmos. A rat mutant with hereditary buphthalmos was used to (1) determine whether the extent of RGC loss corresponds to the severity and duration of elevated intraocular pressure (IOP), (2) examine whether RGCs exposed to an elevated IOP are able to regenerate their axons in a retina culture model, and (3) analyze the proteome of the regenerating retina in order to identify putative regeneration-associated proteins. Retrograde labeling of RGCs revealed a decrease in their numbers in the retinas of buphthalmic eyes that increased with age. Quantification of axons growing out of retinal explants taken at different stages of the disease demonstrated that buphthalmic RGCs possess a remarkable potential to regrow axons. As expected, immunohistochemistry and immunoblotting revealed that elevated IOP was associated with upregulation of certain known proteins, such as growth-associated protein 43, glial fibrillary acidic protein, and endothelin-1. In addition, two-dimensional polyacrylamide gel electrophoresis and mass spectrometry revealed several spots corresponding to proteins that were specifically regulated when buphthalmic RGCs were permitted to regrow their axons. Out of the proteins identified, heat-shock protein (HSP)-60 was constantly expressed during axonal growth at all stages of the disease. Antibodies against HSP-60 reduced axonal growth, indicating the involvement of this protein in regenerative axonal growth. These data are the first to show that diseased retinal neurons can grow their axons, and that HSP-60 supports neuritogenesis. This model may help to elucidate the fundamental mechanisms of optic neuropathy at stages preceding death caused by chronic injury, and aid in the development of neuroprotective strategies.     

The pig eye as a novel model of glaucoma

We validated the pig eye as a model of glaucoma, based on chronic elevation of intraocular pressure (IOP). IOP was elevated by cauterising three episcleral veins in each of the left eyes of five adult pigs. Right eyes were used as controls. Measurement of IOP was performed during the experiment with an applanation tonometer (Tono-Pen). Five months after episcleral vein occlusion, retinal ganglion cells (RGCs) from both cauterised and control eyes were retrogradely backfilled with Fluoro-Gold. Analysis of RGC loss and morphometric as characterization of surviving RGCs was performed using whole-mounted retinas. Elevation of IOP was apparent after three weeks of episcleral vein cauterisation and it remained elevated for at least 21 weeks (duration of the experiments). Analysis of RGC loss after chronic elevation of IOP revealed that RGC death was significant in the mid-peripheral and peripheral retina, mainly in the temporal quadrants of both retinal regions. Moreover the mean soma area of remaining RGCs was observed to increase and we found a greater loss of large RGCs in the mid-peripheral and peripheral retina. We conclude that the pattern of RGC death induced in the pig retina by episcleral vein cauterisation resembles that found in human glaucoma. On the basis of this study, the pig retina may be considered as a suitable model for glaucoma-related studies, based on its similarity with human and on its affordability.     

Topically administered timolol and dorzolamide reduce intraocular pressure and protect retinal ganglion cells in a rat experimental glaucoma model

AIMS: This study sought to elucidate the effects of timolol and dorzolamide on intraocular pressure (IOP) and retinal ganglion cell (RGC) death in an experimental model of glaucoma in rat. METHODS: Mild elevation of IOP was induced in rats by intracameral injection of India ink and subsequent laser trabecular photocoagulation. IOP was measured before the surgical procedures and weekly thereafter. Timolol (0.5%), timolol XE (0.5%), dorzolamide (1%), and artificial tears (vehicle) were topically applied daily. Retinal sections were prepared for histology to determine RGC number. RESULTS: Timolol, timolol XE, and dorzolamide induced a significant reduction in IOP (p<0.05) and counteracted the reduction in RGC number that occurred in vehicle treated glaucomatous eyes (p<0.05). The coefficient of correlation between RGC number and IOP was significant in the dorzolamide treated group (r = -0.908, p<0.005), but not in other groups (p>0.05). CONCLUSIONS: Both timolol formulation and dorzolamide reduced IOP and protected RGCs in a rat model of experimental glaucoma. It cannot be ruled out that timolol might protect RGCs by additional mechanisms other than simply lowering of IOP.     

Retinal ganglion cells death in glaucoma--mechanism and potential treatment. Part I

Glaucoma is a kind of optic neuropathy where selective retinal ganglion cell loss is the major hallmark. Frequently glaucoma is associated with elevated intraocular pressure, but this condition is neither necessary nor sufficient for onset and progression of the disease. The exact mechanism of ganglion cell death in glaucoma and fully effective treatment of glaucomatous neuropathy still remain unknown. This article is a review of the recent researches relevant to IOP independent risk factors, mechanisms of RGC death and modern potential therapeutic strategies in glaucoma. Part one includes review of blood flow changes, neurotrophic factors deprivation and apoptotic dysregulation findings in glaucoma.     

The effect of experimental glaucoma and optic nerve transection on amacrine cells in the rat retina

PURPOSE: To detect alterations in amacrine cells associated with retinal ganglion cell (RGC) depletion caused by experimental optic nerve transection and glaucoma. METHODS: Intraocular pressure (IOP) was elevated unilaterally in 18 rats by translimbal trabecular laser treatment, and eyes were studied at 1 (n = 6), 2 (n = 5), and 3 (n = 7) months. Complete optic nerve transection was performed unilaterally in nine rats with survival for 1 (n = 4) and 3 (n = 5) months. Serial cryosections (five per eye) were immunohistochemically labeled with rabbit anti-gamma-aminobutyric acid (GABA) and anti-glycine antibodies. Cells in the ganglion cell and inner nuclear layers that labeled for GABA or glycine were counted in a masked fashion under bright-field microscopy. Additional labeling with other RGC and amacrine antigens was also performed. RGC loss was quantified by axon counts. RESULTS: Amacrine cells identified by GABA and glycine labeling were not significantly affected by experimental glaucoma, with a mean decrease of 15% compared with bilaterally untreated control cells (557 +/- 186 neurons/mm [glaucoma] versus 653.9 +/- 114.4 neurons/mm [control] of retina; P = 0.15, t-test). There was no significant trend for amacrine cell counts to be lower in eyes with fewer RGCs (r = -0.39, P = 0.11). By contrast, there was highly significant loss of GABA and glycine staining 3 months after nerve transection, both in the treated and the fellow eyes (P < 0.0001, t-test). However, there was a substantial number of remaining amacrine cells in transected retinas, as indicated by labeling for calretinin and calbindin. CONCLUSIONS: Experimental glaucoma causes minimal change in amacrine cells and their expression of neurotransmitters. After nerve transection, neurotransmitter presence declines, but many amacrine cell bodies remain. Differences among optic nerve injury models, as well as effects on "untreated" fellow eyes, should be recognized.     

Dorzolamide and timolol saves retinal ganglion cells in glaucomatous adult rats.

PURPOSE: This study was designed to evaluate the effects of a dorzolamide-timolol combination or dorzolamide on retinal ganglion cell (RGC) density and intraocular pressure (IOP) in glaucomatous eyes of adult rats. METHODS: Glaucoma was induced in the right eye of adult Wistar rats by episcleral venous occlusion. One experimental group was administered dorzolamide 2%-timolol 0.5% combination eye drops, while the other experimental group was administered dorzolamide 2% eye drops. Control groups had surgery without drug administration. Drug application was initiated either 2 weeks before surgery (Group A), from the day of surgery (Group B), 2 weeks after surgery (Group C), or 4 weeks after surgery (Group D). RGCs were labeled by intratectal Fluorogold injections and counted from flat-mount preparations, and IOP was measured using Tonopen. RESULTS: Both dorzolamide-timolol combination and dorzolamide, when applied topically, significantly reduced IOP and improved RGC densities in experimental eyes when compared to control eyes. Earlier initiation, as well as longer duration of drug application, resulted in higher RGC densities. CONCLUSIONS: Topical application of a dorzolamide-timolol combination or dorzolamide saved RGCs to a significant extent and reduced IOP in glaucomatous rat eyes.     

青光眼发病机制:从临床复杂表型剖析到基本科学问题探索

青光眼是一类复杂疾病综合征,其共同临床表现为"特征性视神经病变",实际病因则千差万别。青光眼的发病机制亟待剖析,重点在于梳理其错综复杂的临床表型,围绕眼压改变、视网膜神经节细胞(RGCs)/轴突损伤、非眼压因素等进行合理分型,还原为基础研究手段可以系统探索的基本科学问题。本文将青光眼分为两大类型:Ⅰ型:真实眼压显著升高,直接导致大量RGCs/轴突原发性损害,并在继发性神经免疫炎症参与下造成青光眼视神经病变(GON)。Ⅱ型:检测到的眼压不能或者不足以直接导致大量RGCs/轴突损害和GON,此时神经免疫炎症可能在青光眼的起始发病机制中起到更重要的作用。根据病因机制不同,本文又将前者进一步细分为5型,后者进一步细分为4型。     

Head-up tilt lowers IOP and improves RGC dysfunction in glaucomatous DBA/2J mice

The inbred DBA/2J (D2) mouse strain is a well established model of spontaneously elevated intraocular pressure (IOP), progressive glaucomatous loss of retinal ganglion cells (RGCs), and early damage of RGC axons at the level of optic nerve head. Pattern electroretinogram (PERG) studies have shown that surviving RGCs in mice 6-12-month-old may be dysfunctional. RGC dysfunction seems to be IOP-dependent, since it may be exacerbated by means of acute IOP elevation with head-down body tilt. Here we test the hypothesis that head-up body posture lowers IOP, resulting in improvement of PERG amplitude in aged D2 mice with glaucoma. We show that head-up body tilt induces age-independent IOP lowering whose magnitude increases with the angle of tilt. For a fixed angle (−60°) of head-up tilt, IOP progressively decreases with a time constant of about 5 min and stabilizes at a value lower by about 5-6 mm Hg compared to the baseline. Head-up tilt also results in an improvement of PERG amplitude in older D2 mice with glaucoma but not in younger D2 mice without glaucoma. Improvement of PERG amplitude in aged D2 mice upon head-up-induced IOP lowering is consistent with the idea that RGCs undergo a stage of IOP-dependent, reversible dysfunction before death. The head-up IOP/PERG protocol may represent a non-invasive way to probe the potential for recovery of RGC dysfunction in D2 mice.     

Neuroprotective effect of N-methyl-D-aspartate receptor antagonists in an experimental glaucoma model in the rat

PURPOSE: To evaluate the neuroprotective effect of memantine and dizocilpine, which are noncompetitive open-channel blockers of the N-methyl-D-aspartate (NMDA) receptor, on glaucomatous optic neuropathy in an experimental glaucoma model in the rat. METHODS: Experimental glaucoma was induced in the right eyes of 30 Wistar albino rats by intracameral injection of India ink followed by laser trabecular photocoagulation 4 days later. The left eye served as a control. Either memantine, dizocilpine, or phosphate-buffered saline (PBS) was injected intraperitoneally just before trabecular photocoagulation. Five days later, 3% fast blue was injected into both superior colliculi. The eyes were enucleated another 3 days later and flat mounts of the retinas were prepared. Labeled ganglion cells were counted in the area 1 mm away from the optic disc. RESULTS: Five days after laser application, no significant intraocular pressure (IOP) change in the right eye was found among the 3 groups. In eyes treated with memantine or dizocilpine, significantly more ganglion cells were labeled. CONCLUSION: Systemically applied memantine and dizocilpine had a neuroprotective effect against experimental glaucomatous optic neuropathy in the rat.