Retinal glutamate transporter changes in experimental glaucoma and after optic nerve transection in the rat

PURPOSE: High levels of glutamate can be toxic to retinal ganglion cells. Effective buffering of extracellular glutamate by retinal glutamate transporters is therefore important. This study was conducted to investigate whether glutamate transporter changes occur with two models of optic nerve injury in the rat. METHODS: Glaucoma was induced in one eye of 35 adult Wistar rats by translimbal diode laser treatment to the trabecular meshwork. Twenty-five more rats underwent unilateral optic nerve transection. Two glutamate transporters, GLAST (EAAT-1) and GLT-1 (EAAT-2), were studied by immunohistochemistry and quantitative Western blot analysis. Treated and control eyes were compared 3 days and 1, 4, and 6 weeks after injury. Optic nerve damage was assessed semiquantitatively in epoxy-embedded optic nerve cross sections. RESULTS: Trabecular laser treatment resulted in moderate intraocular pressure (IOP) elevation in all animals. After 1 to 6 weeks of experimental glaucoma, all treated eyes had significant optic nerve damage. Glutamate transporter changes were not detected by immunohistochemistry. Western blot analysis demonstrated significantly reduced GLT-1 in glaucomatous eyes compared with control eyes at 3 days (29.3% +/- 6.7%, P = 0.01), 1 week (55.5% +/- 13.6%, P = 0.02), 4 weeks (27.2% +/- 10.1%, P = 0.05), and 6 weeks (38.1% +/- 7.9%, P = 0.01; mean reduction +/- SEM, paired t-tests, n = 5 animals per group, four duplicate Western blot analyses per eye). The magnitude of the reduction in GLT-1 correlated significantly with mean IOP in the glaucomatous eye (r(2) = 0.31, P = 0.01, linear regression). GLAST was significantly reduced (33.8% +/- 8.1%, mean +/- SEM) after 4 weeks of elevated IOP (P = 0.01, paired t-test, n = 5 animals per group). In contrast to glaucoma, optic nerve transection resulted in an increase in GLT-1 compared with the control eye (P = 0.01, paired t-test, n = 15 animals). There was no significant change in GLAST after transection. CONCLUSIONS: GLT-1 and GLAST were significantly reduced in an experimental rat glaucoma model, a response that was not found after optic nerve transection. Reductions in GLT-1 and GLAST may increase the potential for glutamate-induced injury to RGC 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.     

Retinal nerve fiber layer measurements using laser scanning polarimetry in different stages of glaucomatous optic nerve damage

PURPOSE: To evaluate the diagnostic value of polarimetric measurements of the retinal nerve fiber layer (RNFL) thickness in different stages of glaucomatous optic nerve damage. METHODS: The study included 92 eyes of 46 controls (age 41.0+/-13.7 years) and a heterogeneous group of 232 eyes of 135 patients with different stages of glaucomatous optic nerve damage (age 54.0+/-10.2 years; 68 patients with primary open-angle glaucoma, 56 with normal-pressure glaucoma and 11 patients with secondary glaucoma due to primary dispersion syndrome or pseudoexfoliation syndrome). All control subjects and patients underwent complete ophthalmological examinations including scanning laser polarimetry of the RNFL using the GDx (Laser Diagnostic Technologies, San Diego, Calif.) and 15 degrees color stereo optic disc photographs. Only subjects and patients with disc area less than 3.4 mm(2) were included in the study. The total glaucoma group were divided into four subgroups according to the morphological criteria of the neuroretinal rim. RESULTS: The stage of morphological glaucomatous optic nerve damage was classified as follows: stage 0: n=92, stage 1: n=103, stage 2: n=65, stage 3: n=40, and stage 4: n=19. Differences in mean polarimetric retardation between controls and eyes with glaucoma were significant for all parameters except the variable symmetry. The most significant differences between controls and eyes with glaucomatous optic nerve damage were found with the "number" variable assigned by the neural network analysis ( P<0.001). With increasing stage of glaucomatous optic nerve damage, separation of the variable "the number" increased significantly. At a predetermined specificity of 90% the sensitivity of the groups with different stages of morphological glaucomatous optic nerve damage increased from 32% for stage 1 to 90% for stage 4. CONCLUSION: Polarimetric measurement of the RNFL thickness is significantly associated with morphological glaucomatous optic nerve damage. The fast performance, easy handling, and low cost of RNFL polarimetry mean that it can be included in the routine examination of glaucoma patients. Further study and refinement of this technique are indicated to improve its usefulness in both clinical diagnosis and in population-based case identification.     

Differences in parapapillary atrophy between glaucomatous and normal eyes: the Beijing Eye Study

PURPOSE: To determine in a population-based study whether parapapillary atrophy is associated with glaucoma. DESIGN: Population-based cross-sectional study. METHODS: The Beijing Eye Study included 4,439 of 5,324 subjects invited to participate (response rate, 83.4%). Mean age was 56.2 +/- 10.6 years (range, 40 to 101 years). Color optic disk photographs (30 degrees) were examined morphometrically. Parapapillary atrophy was divided into alpha and beta zones. Glaucomatous optic nerve atrophy was defined by a glaucomatous optic nerve head appearance. RESULTS: After excluding highly myopic eyes, data from 4,003 (90.2%) subjects entered the statistical analysis. Glaucomatous optic nerve damage was detected in 93 (2.3%) subjects. The beta zone of parapapillary atrophy as a whole and measured separately in four disk sectors was significantly larger and occurred significantly more frequently in the glaucomatous group than in the nonglaucomatous group (beta zone total area, 1.21 +/- 1.92 mm2 vs 0.32 +/- 0.99 mm2; P < .001). In multiple regression analysis, area of beta zone was significantly associated with age (P < .001), myopic refractive error (P < .001), and presence of glaucomatous optic nerve damage (P < .001), with no significant difference between chronic open-angle glaucoma (n = 72) and chronic angle-closure glaucoma (n = 21; beta zone area, 1.20 +/- 0.39 mm2 vs 1.19 +/- 0.46 mm2; P = .69). CONCLUSIONS: In a population-based setting, the beta zone of parapapillary atrophy is significantly larger and occurs more frequently in glaucomatous eyes than in normal eyes of Chinese adults, with no marked difference between chronic open-angle glaucoma and primary angle-closure glaucoma.     

Measurement of amino acid levels in the vitreous humor of rats after chronic intraocular pressure elevation or optic nerve transection

PURPOSE: To investigate whether the levels of free amino acids and protein in the vitreous of rat eyes are altered with chronic intraocular pressure (IOP) elevation or after optic nerve transection. MATERIALS AND METHODS: The concentrations of 20 amino acids in the vitreous humor were measured by high-performance liquid chromatography in both eyes of 41 rats with unilateral IOP elevation induced by translimbal photocoagulation. Eyes were studied 1 day and 1, 2, 4, and 9 weeks after initial IOP elevation. The same amino acids were measured in 41 rats 1 day and 2, 4, and 9 weeks after unilateral transection of the orbital optic nerve. The intravitreal protein level was assayed in additional 22 rats with IOP elevation and 12 rats after nerve transection. Two masked observers evaluated the amount of optic nerve damage with a semiquantitative, light-microscopic technique. RESULTS: In rats with experimental glaucoma, amino acid concentrations were unchanged 1 day after treatment. At 1 week, 4 of 20 amino acids (aspartate, proline, alanine, and lysine) were higher than in control eyes ( < or = 0.01), but this difference was nonsignificant after Bonferroni correction for multiple simultaneous amino acid comparisons (none achieved < 0.0025). No amino acid was significantly different from control in the nerve transection groups (all > 0.05). Vitreous protein level was significantly higher in glaucomatous eyes than their paired controls at 1 day ( < 0.0001) and 1 week ( < 0.002). One day and 1 week after optic nerve transection, vitreal proteins were significantly elevated compared with control eyes from untreated animals ( < 0.0020 and < 0.0022, respectively), though not compared with their fellow eyes ( = 0.25 and 0.10). CONCLUSION: Chronic experimental glaucoma and transection of the optic nerve increase the amount of protein in the rat vitreous above control levels. In the vitreous of rats with experimental glaucoma, a number of free amino acids were transiently elevated to a modest degree, but no significant difference in vitreous glutamate concentration was detected ( > 0.01).     

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.     

Optical coherence tomography measurement of the retinal nerve fiber layer in normal and juvenile glaucomatous eyes

The aim of this study was to quantitatively assess and compare the thickness of the retinal nerve fiber layer (RNFL) in normal and glaucomatous eyes of children using the optical coherence tomograph. The mean RNFL thickness of normal eyes (n=26) was compared with that of glaucomatous eyes (n=26). The eyes were classified into diagnostic groups based on conventional ophthalmological physical examination, Humphrey 30-2 visual fields, stereoscopic optic nerve head photography, and optical coherence tomography. The mean RNFL was significantly thinner in glaucomatous eyes than in normal eyes: 95+/-26.3 and 132+/-24.5 microm, respectively. More specifically, the RNFL was significantly thinner in glaucomatous eyes than in normal eyes in the inferior quadrant: 87+/-23.5 and 122+/-24.2 microm, respectively. The mean and inferior quadrant RFNL thicknesses as measured by the optical coherence tomograph showed a statistically significant correlation with glaucoma. Optical coherence tomography may contribute to tracking of juvenile glaucoma progression.     

Correlation between retinal ganglion cell death and chronically developing inherited glaucoma in a new rat mutant

Glaucoma is a progressive optic neuropathy with characteristic optic disc changes, retinal ganglion cell loss and progressive visual field defects. Elevated intraocular pressure is considered to be a major risk factor in glaucomatous neuropathy. This study aimed to characterize and document a new chronic glaucoma model in the rat with respect to the effect of elevated intraocular pressure on overall retinal dysfunction and retinal ganglion cell loss, and to elucidate the possible mechanisms underlying this cell loss. Intraocular pressure (IOP) was measured in rats using a Tonopen. RGCs were retrogradely labeled with the fluorescent dye, 4-[didecylaminostyryl]-N-methyl-pyridinium-iodide (4-Di-10 ASP) and quantified on retinal flat mounts using fluorescence microscopy. The optic nerve head was examined fundoscopically. Changes in the histological appearance of the whole eyes was studied in paraffin sections, and immunohistochemistry was carried out on cryostat sections. The levels of mRNA for several genes were compared between control and glaucomatous retinae using semi-quantitative RT-PCR. Mutant animals are affected with either a unilateral or bilateral enlargement of the globes having an IOP that ranged from 25 to 45 mmHg, as compared to control values of 12-16 mmHg. The IOP of glaucomatous eyes increased significantly with age to attain a value of 35+/-7.3 at 1.5 years. Concomitant with the rise in IOP, the number of labeled RGCs continued to decrease in number with age. A total of 1887+/-117RGC mm(-2) could be labeled in wild-type control and juvenile mutant pre-glaucomatous retinas, whereas this number dropped to 92+/-26RGC mm(-2) at 1.5 years. Ophthalmoscopy revealed atrophied optic nerve heads in the affected eyes. The pars plicata and the pars plana of the ciliary body of glaucomatous eyes were hypertrophied and elongated, respectively. The anterior chamber was narrow and the irido-corneal angle open in glaucoma eyes. The mRNA of glial-fibrillary-acidic protein, endothelin-1, STAT-3 and STAT-6 increased in the retinas correlating with the severity and duration of the disease. Changes in the expression of GFAP and endothelin-1 could be confirmed using immunohistochemistry. This model may help to address several fundamental issues in the pathogenesis of glaucoma and aid in the development of neuroprotective strategies.     

Videographic measurements of optic nerve topography in glaucoma

Topographic measurements of the optic nerve head were made with computerized videographic image analysis (Rodenstock Analyzer) in one eye each of 36 normal controls, 41 glaucoma suspects and 46 glaucoma patients matched for age. Glaucoma suspects had elevated intraocular pressures and normal visual fields in both eyes. Glaucoma patients had typical visual field defects. Disc measurements were corrected for the optical dimensions of individual eyes. One-way analysis of variance revealed statistically significant differences among the diagnostic groups for cup-disc ratio (P = 0.0006), disc rim area (P less than 0.0001) and cup volume (P = 0.0001). Mean (+/- SEM) disc rim area was 1.14 +/- 0.04 mm2 for controls, 1.10 +/- 0.04 mm2 for glaucoma suspects and 0.87 +/- 0.05 mm2 for glaucoma patients. Mean (+/- SEM) optic nerve cup volume was 0.35 +/- 0.02 mm3 for controls, 0.44 +/- 0.04 mm3 for glaucoma suspects and 0.60 +/- 0.05 mm3 for glaucoma patients. Planimetric measurements of disc rim area were made from manual tracings of stereoscopic disc photographs of the same eyes. There was a statistically significant correlation between the computerized videographic measurements and the manual photographic measurements of disc rim area (r = 0.73, P less than 0.0001). The broad range of values for these optic nerve structural parameters in normal eyes and their overlap with values in glaucomatous eyes prevents their use to reliably predict which patients are normal and which have glaucomatous visual field loss. New parameters are required to fully describe the depth information generated with new quantitative techniques.     

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.     

Nerve fiber layer assessment with scanning laser polarimetry in glaucoma patients and glaucoma suspects.

PURPOSE: To investigate whether scanning laser polarimeter can differentiate glaucoma and suspected glaucoma patients from normals. METHODS: Polarimetric measurements were obtained using the nerve fiber analyzer (NFA)-I from 80 eyes of patients with glaucoma with mostly moderate glaucomatous optic nerve damage (37 eyes with primary open angle glaucoma, 21 with normal tension glaucoma, 17 with pseudoexfoliative glaucoma, 3 with angle closure glaucoma, and 2 with juvenile glaucoma), 53 eyes of patients suspected of glaucoma based on disc appearance, and from age-matched healthy volunteers as control groups. Ratios (superior/nasal, inferior/nasal, superior/inferior) were used for assessing nerve fiber layer (NFL) thickness. Student's t-test and linear regression analysis were used for statistical analysis. RESULTS: Both the glaucoma patients and glaucoma suspects had significantly lower NFL ratios (mean S/N 2.34 +/- 0.47, I/N 2.46 +/- 0.52, S/I 0.94 +/- 0.18) than the control groups (respectively 2.88 +/- 0.48, 2.88 +/- 0.48, 1.00 +/- 0.13) (p<0.05). There was an ample overlap between the patient groups and the normals. The superior and inferior NFL ratios in glaucoma patients gradually decreased as the mean defect in visual field increased (linear regression analysis, p<0.05). CONCLUSIONS: The NFL of glaucomatous eyes and eyes suspected of glaucoma based on disc appearance was significantly less thick than normals. NFA-I detects pathological abnormalities in some patients with glaucomatous optic nerve damage and normal visual fields as measured by conventional achromatic computerized perimetry. NFA-I, however, is unable to distinguish these patients from normals, at least using these parameters, because of the considerable overlap.     

Central corneal thickness correlated with glaucoma damage and rate of progression

PURPOSE: To evaluate whether the amount of glaucomatous optic nerve damage at presentation of the patient and the rate of progression of glaucoma during follow-up are related to central corneal thickness. METHODS: The prospective observational clinical study included 861 eyes of 454 white subjects (239 normal eyes of 121 subjects, 250 ocular hypertensive eyes of 118 patients, 372 eyes of 215 patients with chronic open-angle glaucoma). For 567 eyes (304 patients) with ocular hypertension or chronic open-angle glaucoma, follow-up examinations were performed, with a mean follow-up time of 62.7 +/- 33.2 months (median, 60.8; range, 6.2-124.9). All patients underwent qualitative and morphometric evaluation of color stereo optic disc photographs and white-on-white visual field examination. Central corneal thickness was measured by corneal pachymetry. RESULTS: Central corneal thickness correlated significantly (P < 0.001) and positively with the area of the neuroretinal rim and negatively with the loss of visual field. Development or progression of glaucomatous visual field defects detected in 119 (21.0%) eyes was statistically independent of central corneal thickness, in univariate (P = 0.99) and multivariate Cox regression analyses (P = 0.19). CONCLUSIONS: At the time of patient referral, the amount of glaucomatous optic nerve damage correlated significantly with a thin central cornea. Progression of glaucomatous optic nerve neuropathy was independent of central corneal thickness, suggesting that central corneal thickness may not play a major role in the pathogenesis of progressive glaucomatous optic nerve damage.     

Effect of glatiramer acetate on primary and secondary degeneration of retinal ganglion cells in the rat

PURPOSE: After crush injury to the optic nerve, elevated intraocular pressure, and glutamate toxicity, the immune modulator glatiramer acetate (GA, Cop-1; Copaxone; Teva Pharmaceutical Industries, Pitach Tikva, Israel) has been shown to reduce the delayed cell death of retinal ganglion cells (RGCs). This study was undertaken to confirm the protective effect of GA on secondary degeneration of RGCs in the rat, by using a spatial, rather than temporal, model. METHODS: A total of 131 Wistar rats divided into 10 groups underwent bilateral stereotactic injection of fluorescent tracer (Fluorogold; Fluorochrome, Denver, CO) into the superior colliculus to label RGCs. They received a concurrent subcutaneously injection of (1) GA mixed with complete Freund's adjuvant (CFA), (2) CFA alone, or (3) saline. One week later, the superior one third of the left optic nerve was transected in animals in the six partial transection groups. Optic nerves in four additional groups underwent full transection. Rats were killed and retinas harvested from both eyes 1 or 4 weeks after partial transection and 1 or 2 weeks after full transection. RGC densities were calculated from retinal wholemounts, and differences between right (control) and left (transected) eyes were compared across treatment groups. RESULTS: Among the partial transection groups, differences in the mean percentage of RGC loss in the inferior retinas were not significant at 1 or 4 weeks (ANOVA; P = 0.20, P = 0.12, respectively). After full transection, there was significantly more RGC loss in the GA group than in the CFA group when comparing whole retinas at 1 week, but not at 2 weeks (two-tailed t-test; P = 0.04, P = 0.36, respectively). CONCLUSIONS: There is no evidence that GA has a neuroprotective effect after optic nerve transection, either for primarily injured or secondarily involved RGC.     

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.     

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.     

Analysis of macular volume in normal and glaucomatous eyes using optical coherence tomography

PURPOSE: To evaluate macular volume in normal and glaucomatous eyes using optical coherence tomography (OCT). DESIGN: Case control study. METHOD: The authors assessed 272 eyes of 164 subjects as part of an institutional study at New England Eye Center in Boston, Massachusetts; 202 eyes were in the study group and 70 eyes in the control group. Eyes were categorized as normal (70 eyes of 43 subjects), glaucoma suspect (70 eyes of 44 subjects), early glaucoma (70 eyes of 47 subjects), or advanced glaucoma (62 eyes of 43 subjects). Subjects underwent analysis with the commercially available OCT1 unit. Optical coherence tomography macular neurosensory retinal thickness maps were used to calculate macular volume for comparison to Humphrey visual field testing, intraocular pressure measurement, and stereo biomicroscopy of the optic nerve head and nerve fiber layer. RESULTS: Using repeated measures regression, macular volume in normal (2.37 +/- 0.11 mm(3)) glaucoma suspect (2.33 +/- 0.16 mm(3)), and early glaucoma eyes (2.27 +/- 0.13 mm(3)) was significantly greater than in eyes with advanced glaucoma (2.12 +/- 0.23 mm(3), P =.0001, P =.0001, and P =.0008, respectively). Macular volume in normal eyes was significantly greater than in early glaucoma eyes (P =.01). CONCLUSIONS: Optical coherence tomography retinal macular volume correlates with known structural defects of glaucoma, providing a potential objective and quantitative parameter for evaluation. Our data show a significant difference in macular volume between normal, glaucoma suspect, and early glaucoma eyes, compared with advanced glaucomatous eyes as well as between normal and early glaucomatous eyes. This correlates with a trend of decreasing macular volume in eyes with more advanced disease.     

Quantitative evaluation of the optic nerve head in patients with unilateral visual field loss from primary open-angle glaucoma

Measurable structural alterations of the optic nerve head may precede visual field abnormalities in early open-angle glaucoma. The authors studied the optic nerve heads of 10 patients with unilateral visual field loss from primary open-angle glaucoma, and 12 age- and sex-matched normal subjects. Topographic optic nerve head parameters were measured with a system of computerized image analysis (Rodenstock Analyzer, G. Rodenstock Instrumente GMBH, Munich, W. Germany). In patients with asymmetric primary open-angle glaucoma, eyes with normal visual fields had a slightly larger mean (+/- standard error of the mean) disc rim area (0.90 +/- 0.04 mm2) than eyes with glaucomatous visual field defects (0.78 +/- 0.05 mm2). However, both sets of eyes in the asymmetric primary open-angle glaucoma patients had smaller mean disc rim areas (P less than 0.0007) than did the control group (1.27 +/- 0.09 mm2). These findings support the hypothesis that loss of the optic disc rim can be detected before perimetric abnormalities develop in primary open-angle glaucoma.     

Parapapillary autofluorescence as indicator for glaucoma

BACKGROUND: A pronounced fundus autofluorescence (lipofuscin) occurs in eyes with AMD. Parapapillary lipofuscin accumulation in the retinal pigment epithelial cells was observed in eyes with advanced glaucoma histologically. The aim of this study was to evaluate the parapapillary autofluorescence (PAF) in vivo in healthy eyes (controls), and in eyes with primary open angle glaucoma (POAG), pseudoexfoliation glaucoma (PSXG) or normal tension glaucoma (NTG). PATIENTS AND METHODS: Controlled cross-sectional analysis was performed on 281 consecutive eyes (98 controls, 95 POAG, 32 PSXG, 56 NTG). Eyes with fundus pathologies were excluded. The confocal scanning laser ophthalmoscope HRA II (Heidelberg Retina Angiograph II) was used after lipofuscin-excitation with an argon blue laser (488 nm) to detect PAF in the spectrum above 500 nm. PAF area and PAF distance to the optic nerve head were analyzed using the HRA standard software. Two experienced ophthalmologists classified independently the stage of glaucomatous optic nerve head atrophy (GONHA) using 15 degrees fundus photographs. RESULTS: Vital optic nerve heads had smaller PAF areas (stage 0: 0.07 +/- 0.09 mm (2)) in contrast to advanced stages of GONHA (stages 1 to 4: 0.27 +/- 0.46 mm (2); p < 0.001; logistic regression Cox and Snell: r = 0.7; p = 0.015). The PAF distance to the optic nerve head was lower in controls (0.12 +/- 0.08 mm) than in eyes with POAG, PSXG, or NTG (0.25 +/- 0.21 mm, Bonferroni: p < 0,004). The PAF area correlated significantly with the stage of GONHA (stage 1: 0.23 +/- 0.23 mm (2), stage 2: 0.24 +/- 0.19 mm (2), stages 3 and 4: 0.34 +/- 0.73 mm (2), p < 0.01). No significant difference of PAF area was found between the glaucoma types. However, the distance between PAF and optic nerve head was higher in POAG (0.28 +/- 0.26 mm) than in NTG (0.24 +/- 0.07 mm) or in PSXG (0.18 +/- 0.07 mm, Bonferroni: p < 0.03). CONCLUSIONS: A pronounced fundus autofluorescence was detected as a sign of increased lipofuscin accumulation in the parapapillary atrophic zone of eyes with POAG, PSXG, and NTG in contrast to controls. The PAF analysis may provide an indicator for glaucomas in the future.     

The retinal nerve fiber layer in normal eyes and in glaucoma. I. Semiquantitative data of 398 eyes with glaucoma

Atrophy of the optic nerve is associated with changes of the retinal fiber layer (RNFL). Using red-free photographs the authors examined the RNFL of 398 eyes with chronic primary open-angle glaucoma and compared it with the RNFL of 234 normal eyes. The glaucoma group was divided into five stages and the fundus into four sectors. Differences between the normal and glaucoma eyes were: (1) The sequence of the sectors, with regard to the best visibility of the retinal nerve fiber bundles, was changed. In the normal eyes the nerve fiber bundles were most often best visible in the inferior temporal sector, followed by the superior temporal sector, the temporal horizontal area and finally the nasal region. In the glaucoma group the nerve fiber bundles were significantly more often best detectable in the superior temporal sector and the temporal horizontal area. (2) The degree of visibility of the retinal nerve fibers decreased significantly with increasing glaucoma stage. (3) Localized defects were seen in 15% of the eyes with glaucoma and none of the normal eyes. The specificity of this qualitative parameter was, therefore, 100%. The defects were found most often in the superior and inferior temporal regions. These differences between normal and glaucomatous eyes were also significant for the first glaucoma stage of this study. The localization of the foveola below the optic disk center (0.53 +/- 0.34 mm in the glaucoma group and 0.55 +/- 0.29 mm in the normal eyes) was not significantly different.     

Scanning laser tomography in the diagnosis of juvenile glaucoma]

The aim of our research was to evaluate the optic nerve head parameters of children with juvenile glaucoma with the scanning laser ophthalmoscope from Laser Diagnostic Technologies Inc. The material consisted of 46 eyes of 25 children aged from 7 to 18 years. There were 18 glaucomatous eyes (I group) and 28 eyes without glaucoma (II group) as a control group. The three examinations were repeated every three months. Mean values of Vol. B in the glaucomatous group were -0.327 +/- 0.098, first visit; -0.390 +/- 0.130, second visit; 0.344 +/- 0.096 mm3, third visit. These values in the control group were--0.234 +/- 0.73; -0.224 +/- 0.071; -0.252 +/- 0.069 mm3. The difference was statistically significant. Mean values of Volume A were significantly lower in the I group: 0.216 +/- 0.034, 0.207 +/- 0.033, 0.203 +/- 0.030 mm3 than in the II group: 0.269 +/- 0.039, 0.283 +/- 0.032, 0.271 +/- 0.042 mm3. CD ratio was higher in the glaucomatous eyes: 0.447 +/- 0.080; 0.491 +/- 0.069; 0.484 +/- 0.074 in comparison with the control group: 0.376 +/- 0.060; 0.368 +/- 0.067; 0.399 +/- 0.056. It was significant difference. More changes of biomorphometric parameters of the optic nerve head were observed in the glaucomatous group during follow-up period. The role of laser scanning ophthalmoscopic tomography is very important in the diagnosis of early forms of juvenile glaucoma in the youth.