Efficacy and Safety of Memantine Treatment for Reduction of Changes Associated with Experimental Glaucoma in Monkey, II: Structural Measures

PURPOSE

To determine, using anatomic measurements, whether daily oral dosing with memantine is both safe and effective to reduce the injury associated with experimental glaucoma in primates.

METHODS

Argon laser treatment of the anterior chamber angle was used to induce chronic ocular hypertension (COHT) in the right eyes of 18 macaque monkeys. Nine animals were daily orally dosed with 4 mg/kg memantine while the other nine animals received vehicle only. Measurements of intraocular pressure (IOP) from both eyes of all animals were made at regular intervals. Appearance of the optic nerve head, retinal vessels, and surrounding retina was documented with stereo fundus photographs obtained at multiple time points throughout the study. Measurements of optic nerve head topography were obtained from confocal laser scans made from animals with the highest IOPs at approximately 3, 5, and 10 months after elevation of IOP. At approximately 16 months after IOP elevation, animals were killed and histologic counts of cells in the retinal ganglion cell (RGC) layer were made.

RESULTS

Histologic measurements showed that, for animals with moderate elevation of IOP, memantine treatment was associated with an enhanced survival of RGCs in the inferior retina. Measurements of optic nerve head topography showed less IOP-induced change in memantine-treated animals. This effect was seen in measurements of both the cup and the neuroretinal rim. A comparison of these same histologic and morphologic measurements in normotensive eyes from the two treatment groups showed that memantine treatment was not associated with any significant effects on these eyes.

CONCLUSIONS

Histologic measurements of RGC survival as well as tomographic measurements of nerve head topography show that systemic treatment with memantine, a compound which does not lower intraocular pressure, is both safe and effective to reduce changes associated with experimental glaucoma.

Alterations in neurofilament light in optic nerve in rat kainate and monkey ocular hypertension models

The purpose of this study is to evaluate the changes in neurofilament light (NF-L) protein in the optic nerve in rat kainate and monkey ocular hypertension models. In the rat model, optic nerve damage was induced by kainate injection into the vitreous body. In the monkey model, photocoagulation of the trabecular meshwork led to laser-induced ocular hypertension. NF-L in optic nerve extract was quantified by quantitative immunoblot using an imaging analyzer. The amount of NF-L in optic nerve was compared between normal and kainate-treated groups at 7 days after kainate injection. Specimens from rat optic nerves and retinas were evaluated histologically to examine the correlations between damage and amount of NF-L in the optic nerve. In monkeys, the amount of NF-L in the optic nerve was compared between control fellow and ocular hypertensive eyes. Injection of kainate induced morphological optic nerve and retinal damage in rats. The amount of NF-L in the optic nerve was significantly reduced in kainate-treated eyes (vs. normal eyes). The amount of NF-L correlated with the cell count in the ganglion cell layer and the axon number in the optic nerve at 7 days after kainate injection. Further, 6-cyano-7-nitro-quinoxaline-2,3-dione, a non N-methyl-D-aspartate receptor antagonist, suppressed the kainate-induced reduction in NF-L and retinal damage. In the monkey model, ocular hypertension and morphological optic nerve damage were shown by laser-treated eyes. The amount of NF-L in the optic nerve was reduced in laser-treated eyes. In conclusion, in rat kainate and monkey ocular hypertension models, immunoblot evaluation of NF-L shows the reduction of the amount of NF-L in the optic nerves of treated-eyes. The amount of NF-L correlated with the morphological retinal and optic nerve damage in rats. These findings indicate that immunoblot evaluation of NF-L in the optic nerve may provide a quantitative index of optic nerve damage.

Effect of corneal parameters on measurements using the pulsatile ocular blood flow tonograph and Goldmann applanation tonometer

AIMS

To investigate the effect of central corneal thickness and corneal curvature on intraocular pressure measurements using the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer, and to assess the agreement between the pulsatile ocular blood flow tonograph and the Goldmann applanation tonometer in intraocular pressure measurement.

METHODS

479 subjects underwent intraocular pressure measurements with the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph. Of these, 334 patients underwent additional measurement of central corneal thickness with an ultrasonic pachymeter and corneal curvature measurement with a keratometer.

RESULTS

The intraocular pressure measurements obtained with both the Goldmann applanation tonometer and the pulsatile ocular blood flow tonograph varied with central corneal thickness and mean keratometric reading. Intraocular pressure measured using the Goldmann applanation tonometer increased by 0.027 mm Hg per micro m increase in central corneal thickness. Intraocular pressure measured using the pulsatile ocular blood flow tonograph increased by 0.048 mm Hg per micro m increase in central corneal thickness. For an increase of 1 mm of mean corneal curvature there was rise in intraocular pressure of 1.14 mm Hg measured by the Goldmann applanation tonometer and of 2.6 mm Hg measured by the pulsatile ocular blood flow tonograph. When compared to the Goldmann applanation tonometer, the pulsatile ocular blood flow tonograph underestimated at low intraocular pressure and overestimated at higher intraocular pressure.

CONCLUSION

Central corneal thickness and corneal curvature affected measurements obtained with the pulsatile ocular blood flow tonograph more than they affected measurements obtained with the Goldmann applanation tonometer.

Symmetry Analysis for Detecting Early Glaucomatous Changes in Ocular Hypertension Using Optical Coherence Tomography

PURPOSE

To compare symmetry analysis of the retinal nerve fiber layer (RNFL) in ocular-hypertensive, normal, and glaucomatous eyes using optical coherence tomography (OCT).

METHODS

Thirty-three consecutive ocular-hypertensive patients (33 eyes), 25 normal volunteers (25 eyes), and 35 open-angle glaucoma patients (35 eyes) were enrolled in this study. Circular OCT scans were obtained using a diameter of 3.4 mm around the optic disc. RNFL thickness was measured, and a symmetry analysis was performed using symmetry ratios. To calculate the symmetry ratios, the circle was divided into the superior and inferior hemiretina. The superior hemiretina was further subdivided into three (area I, temporal 45 degrees; area II, superior 90 degrees; and area III, nasal 45 degrees ) or five (with areas 1-5, each spanning 36 degrees ) zones. The symmetry ratios were defined as the ratios comparing the RNFL thickness within each of the zones with that in the analogous zone in the inferior hemiretina.

RESULTS

RNFL thickness measurements could distinguish glaucomatous eyes from other groups, but could not distinguish ocular-hypertensive from normal eyes. However, the symmetry analysis revealed differences between ocular-hypertensive and normal eyes in area II (mean +/- SD, 0.77 +/- 0.16 vs. 0.85 +/- 0.12, P = 0.0379).

CONCLUSIONS

Early glaucomatous RNFL changes might exist in some areas of ocular-hypertensive eyes, and a symmetry analysis may be a useful method for detecting these changes.

Hyphema and elevated intraocular pressure in a neonate

A female neonate delivered vaginally at term was noted 12 hours after birth to have a 20% hyphema, layered temporally. Intraocular pressure in the affected eye was 46 mm Hg. She was treated with intravenous and topical medications, with normalization of pressure within 6 hours. The hyphema cleared completely within 72 hours.

Age-dependent decrease of retinal kynurenate and kynurenine aminotransferases in DBA/2J mice, a model of ocular hypertension

The study examines age-dependent changes of kynurenic acid (KYNA) content and kynurenine aminotransferases (KAT I and KAT II) celluar expression in the retinas of DBA/2J mice. Retinas were obtained from DBA/2J mice of different ages (3, 6 and 11 months). C57BL6 mice were used as controls. As measured with HPLC, KYNA content decreased (p < 0.01) in the retinas of 6-month-old DBA/2J mice and continued to decrease (p < 0.0074) in the retinas of 11-month-old animals compared to the controls. Immunohistochemistry showed that expression of both KAT I and KAT II decreased markedly in the retinas of 11-month-old DBA/2J mice compared to controls. The impairment in KYNA biosynthesis in the retinas of DBA/2J mice may be one of the mechanisms of retinal neurodegeneration related to ocular hypertension.

Retinal neurodegeneration in the DBA/2J mouse-a model for ocular hypertension

Mice of the DBA/2J strain spontaneously develop complex ocular abnormalities, including glaucomatous loss of retinal ganglion cells (RGC). In the present study ultrastructural features of retinal neurodegeneration in DBA/2J mice of different age (3, 6, 8 and 11 months) are described. By 3 months, RGC apoptosis characterized by electron-dense karioplasm and cytoplasm of ganglion cells was observed. The occurrence of apoptotic ganglion cells peaked at the age of 6 months. Past this age, necrosis characterized by swelling and electron-rare cytoplasm appeared to be the prevailing form of cell death. Müller glia activation increased with age, but there were no signs of leukocyte infiltration. At 8 and 11 months, signs of neoangiogenesis were found both at the ultrastructural level and in clinical examinations. In these older animals myelin-like bodies, most probably representing the intracellular aggregates of phospholipids in irreversibly injured cells, were also seen. Photoreceptor cells were not affected at any age. Our observations suggest that retinal degeneration in the DBA/2J mice does not involve recruitment of blood-borne inflammatory/phagocytosing cells, and that apoptosis is gradually replaced by necrosis as the predominant pathway of RGC death. Retinal degeneration in 3- to 11-month-old DBA/2J mice partially resembles human pigment dispersion syndrome and pigmentary glaucoma with characteristic anterior segment changes and elevation of intraocular pressure. However, neovasculogenesis and myelin-like bodies are observed during aging. Therefore, the DBA/2J model requires judicious interpretation as a glaucoma model.

CNTF promotes survival of retinal ganglion cells after induction of ocular hypertension in rats: the possible involvement of STAT3 pathway

We examined the neuroprotective effect of ciliary neurotrophic factor (CNTF) on retinal ganglion cells (RGCs) in a rat glaucoma model with increased intraocular pressure (IOP) and studied the CNTF-mediated activation of Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway. Elevated IOP was induced by laser photocoagulation of the episcleral and limbal veins. The survival of RGCs was studied using Fluoro-Gold labelled in ocular hypertensive eyes with or without CNTF intravitreal injection. Immunochemical staining and immunoblot analysis for CNTF and phosphorylated STAT3 (pSTAT3) were performed. There was a significant and progressive loss of RGCs in the retinas following the induction of elevated IOP. A single intravitreal injection of 2 microg in 2 microL CNTF significantly protected RGCs up to 4 weeks. pSTAT3 was only transiently expressed in ocular hypertensive eyes. However, in eyes treated with CNTF, pSTAT3 was observed up to 2 weeks after the induction of elevated IOP. In ocular hypertensive eyes, CNTF-positive cells were found in the inner nuclear layer (INL), and there was a transient increase in the pSTAT3 cells in the ganglion cell layer and INL. Immunoblots showed that STAT3 was transiently phosphorylated after IOP increase, but with an injection of CNTF, pSTAT3 protein was observed up to 2 weeks after hypertensive glaucoma induction. Laser-induced chronic ocular hypertension in rats resulted in the death of RGCs and a transient activation of STAT3 in the retina. Intravitreal injection of CNTF showed a significant protection of RGCs, and the JAK-STAT signalling could be one of the important pathways that underlie the mechanism of CNTF neuroprotection in this rat glaucoma model.

Characteristics of optic nerve damage induced by chronic intraocular hypertension in rat

PURPOSE

To set up the Sharma's chronic intraocular hypertension model and investigate the intraocular pressure (IOP) as well as the optic nerve damage of this model in rat.

METHODS

The operations of the chronic intraocular hypertension model were performed as described by Sharma in 60 Male Lewis albino rats. IOP was measured using the Tono-Pen XL immediately after surgery and then at 5 day, 2 week or 4 week intervals. Cresyl violet staining of whole-mounted retinas was used to label retinal ganglion cells (RGCs), then RGCs were counted. Paraphenylenediamine (PPD) staining was performed in the semi-thin cross sections of optic nerve of rat, in order to know whether the axons of optic nerve were degenerated or not.

RESULTS

There were 47 rats with higher IOP after the episcleral veins cauterized in 60 rats. The ratio of elevated IOP was 78.3%. The IOPs were stable in 4 weeks. After cresyl violet staining, the RGCs loss was 11.0% and 11.3% was found in the central and peripheral retina respectively after 2 weeks of increased IOP. After 4 weeks of increased IOP, the loss of RGCs was 17% for the central retina and 24.6% for the peripheral retina. In the retinas without higher IOP, there was no loss of RGCs. PPD staining showed that optic nerve of rat with about 5.3% damage of axons located at the superior temporal region. Region of affected optic nerve 1 mm posterior to the globe by light microscope showed evidence of damaged axons with axonal swelling and myelin debris.

CONCLUSION

Sharma's chronic intraocular hypertension model is a reproducible and effective glaucoma model, which mimics human glaucoma with chronically elevation IOP and induced RGCs loss and damage of optic nerve.

Intraobserver and interobserver reproducibility in the evaluation of ultrasonic pachymetry measurements of central corneal thickness

PURPOSE

To assess reproducibility of central corneal thickness (CCT) measurement by means of ultrasonic pachymetry.

METHODS

Fifty one volunteers underwent three sessions of CCT measurements, each consisting of three CCT measurements, performed by each of three different observers. Intra- and interobserver reproducibility was calculated by means of intraclass correlation coefficient (ICC). The expected range of variability between two independent evaluations was calculated using scatter plots of each test-retest difference against their mean. The standard deviation of the mean differences in the test-retest scores was used to describe the differences in the score spread.

RESULTS

The ICC ranges of the intra- and interobserver evaluations were 0.95-0.97 and 0.89-0.95 respectively; the expected variability was < or = +/-1% and < or = +/- 2% respectively (95% confidence interval).

CONCLUSIONS

The measurement of CCT by means of ultrasonic pachymetry is highly reproducible.

Diabetes has an additive effect on neural apoptosis in rat retina with chronically elevated intraocular pressure

PURPOSE

Diabetes mellitus (DM) is a risk factor for open-angle glaucoma, although the mechanistic interrelationship of the two is debatable. The purpose of this study is to test whether DM augments neural apoptosis in rat retina with chronically elevated intraocular pressure (IOP).

METHODS

Sprague-Dawley rats were made diabetic by intraperitoneal injection of streptozotocin (STZ). At one month after STZ injection, three episcleral veins in one eye were cauterized to elevate IOP. Rats without STZ injection were treated likewise as diabetic controls. At 2 weeks, 1 month, and 2 months after cauterization, the retina was dissected, flat-mounted, and subjected to terminal dUTP nick end labeling (TUNEL) staining. TUNEL positive cells per unit area of the whole retina were measured.

RESULTS

DM did not affect base line IOP or augment IOP elevation due to episcleral vein cauterization. TUNEL positive cells, which primarily consisted of the neurons and glial cells in the inner retina including retinal ganglion cell (RGC), were counted consistently eight times more in the diabetic retina without IOP elevation than diabetic controls (n = 9, p < 0.001). The cauterization significantly elevated IOP up to 28.9 mmHg (p < 0.001), which was reduced over time, and substantially induced apoptosis in a IOP-dependent fashion (p < 0.001). Ocular hypertensive retinas with DM had significantly more TUNEL positive cells than those without DM despite of the similar time course of IOP changes (p < 0.001).

CONCLUSIONS

DM has an additive effect on apoptosis induction by chronic elevation of IOP. Diabetes may act as a risk factor of open-angle glaucoma by increasing susceptibility of retinal cells including retinal ganglion cells to apoptosis triggered by additional stresses such as elevated IOP.

Changes in retinal expression of neurotrophins and neurotrophin receptors induced by ocular hypertension

Open angle glaucoma is defined as a progressive and time-dependent death of retinal ganglion cells concomitant with high intraocular pressure, leading to loss of visual field. Because neurotrophins are a family of growth factors that support neuronal survival, we hypothesized that quantitative and qualitative changes in neurotrophins or their receptors may take place early in ocular hypertension, preceding extensive cell death and clinical features of glaucoma. We present molecular, biochemical, and phenotypic evidence that significant neurotrophic changes occur in retina, which correlate temporally with retinal ganglion cell death. After 7 days of ocular hypertension there is a transient up-regulation of retinal NGF, while its receptor TrkA is up-regulated in a sustained fashion in retinal neurons. After 28 days of ocular hypertension there is sustained up-regulation of retinal BDNF, but its receptor TrkB remains unchanged. Throughout, NT-3 levels remain unchanged but there is an early and sustained increase of its receptor TrkC in Müller cells but not in retinal ganglion cells. These newly synthesized glial TrkC receptors are truncated, kinase-dead isoforms. Expression of retinal p75 also increases late at day 28. Asymmetric up-regulation of neurotrophins and neurotrophin receptors may preclude efficient neurotrophic rescue of RGCs from apoptosis. A possible rationale for therapeutic intervention with Trk receptor agonists and p75 receptor antagonists is proposed.

Correlation between morphological and functional retinal impairment in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis and Alzheimer's disease

In this article the correlations between the morphological evaluation of the nerve fiber layer (NFL) thickness (by OCT) and retinal functional assessment (by Pattern ERG recordings) performed in patients affected by ocular hypertension (OHT), glaucoma (OAG), demyelinating optic neuritis (MSON), and Alzheimer's disease (AD) are reported. In OHT eyes with ocular hypertension we observed that the inter-individual variation in NFL thickness is correlated with the variability of the PERG responses (the thinner the layer, the worse the visual function). In our OAG, MSON and AD eyes we observed a significant reduction in NFL thickness when compared with controls. In OHT, OAG, MSON and AD eyes abnormal PERG responses with delayed implicit times and reduced amplitudes were found. The impairment in the PERG parameters was significantly correlated to the reduction in NFL thickness. Our results suggest that in patients affected by ocular hypertension, glaucoma, demyelinating optic neuritis, and Alzheimer's Disease there is a reduction of NFL thickness evaluated "in vivo" by OCT, and this morphological involvement is correlated with electrophysiological responses assumed to be originating from the innermost retinal layers.

Laser-induced mouse model of chronic ocular hypertension

PURPOSE

To develop an inducible mouse model of glaucoma.

METHODS

An obstruction of aqueous humor outflow in adult C57BL6/J mice was induced by combined injection of indocyanine green (ICG) dye into the anterior chamber and diode laser treatment. To evaluate intraocular pressure (IOP), tonometry was performed with a modified Goldmann tonometer. The function of the retina was evaluated with electroretinography (ERG).

RESULTS

IOP was significantly elevated in surgical eyes compared with control eyes: before surgery, 15.2 +/- 0.6 mm Hg; 10 days after surgery, 33.6 +/- 1.5 mm Hg (P < 0.001); and 30 days after surgery, 27.4 +/- 1.2 mm Hg (P < 0.001). However, 60 days after surgery, IOP in the surgical eyes decreased to 19.5 +/- 0.9 mm Hg and was not significantly different compared with control eyes (control, 17.3 +/- 0.7 mm Hg; P = 0.053). ERG amplitudes, expressed as a ratio (surgical/control), were decreased in surgical eyes. The amplitudes for b-wave were: before surgery, 107.6% +/- 4.6%; 28 days after surgery, 61% +/- 4% (P < 0.001); and 56 days after surgery, 62% +/- 5.6% (P < 0.001). Oscillatory potentials were the most dramatically affected: before surgery, 108.6% +/- 6.7%; 28 days after surgery, 57.5% +/- 5% (P < 0.01); and 56 days after surgery, 57% +/- 8.5% (P < 0.001). Amplitudes of the a-waves had relatively smaller but still significant deficits: before surgery, 105.8% +/- 6.9%; 28 days after surgery, 72.2% +/- 5.4% (P < 0.01); and 56 days after surgery, 79.8% +/- 11.0% (P < 0.01). Histologic analysis of the surgical eyes revealed development of anterior synechia, loss of retinal ganglion cells (RGCs), and thinning of all retinal layers. Electron microscopy of optic nerve cross sections revealed swelling and degeneration of the large diameter axons and gliosis.

CONCLUSIONS

Diode laser treatment of ICG saturated episcleral veins causes a chronic elevation of IOP and sustained ERG deficits.

Experimental mouse ocular hypertension: establishment of the model

PURPOSE

To establish an experimental model of ocular hypertension in the mouse.

METHODS

Twenty-two black Swiss mice were used. After anesthesia and pupil dilation, the anterior chamber was flattened by the aspiration of aqueous humor. Laser photocoagulation (532-nm wavelength, 200-mW power, 0.05-second duration, 200- micro m spot size) then was performed at the limbus. Intraocular pressure (IOP) was measured weekly for 4 weeks and biweekly for 12 weeks, by a microneedle method. Slit lamp biomicroscopy was performed throughout the period and the structural changes were assessed histologically. A treatment response was considered to be a success if either the mean of IOP measurements collected during the first 4 weeks was increased by 30% or more, or the mean of all measurements collected during the 12 week study period was increased by 30% or more.

RESULTS

Laser-treated eyes showed significantly higher IOP than control eyes from 1 to 6 weeks (P < 0.001). The average IOP in treated eyes during the first 4 and 12 weeks was significantly higher than the control IOP (P < 0.001). These IOP increases were 7.1 and 3.8 mm Hg, respectively. During the first 4 weeks, sustained elevation of IOP was obtained in 64% (14/22) of the treated eyes. During the entire 12-week study, increased IOP was successfully maintained in 37% (7/19) of the treated eyes. After 6 weeks, elevated IOP often returned to normal or several mm Hg below normal. Histologic analysis at the end of the 12-week study showed no inflammatory cells in the anterior segment and confirmed that the angle was closed by the laser photocoagulation treatment.

CONCLUSIONS

This method produces persistent IOP elevation in mouse eyes and may be a promising experimental model for the investigation of the biological mechanisms of glaucomatous optic neuropathy.

Glaucoma phenotype in pedigrees with the myocilin Thr377Met mutation

OBJECTIVE

To investigate the phenotype and age-related penetrance of primary open-angle glaucoma (POAG) in Australian families with the myocilin mutation Thr377Met.

METHOD AND DESIGN

Cross-sectional genetic study. Four unrelated pedigrees carrying the Thr377Met mutation were ascertained from more than 2000 consecutive cases of POAG in the Glaucoma Inheritance Study in Tasmania and from families with glaucoma referred to the study from throughout Australia. Index cases and available family members were examined for signs of glaucoma, and the presence of the GLC1A Thr377Met mutation was ascertained by single-strand conformation polymorphism analysis and subsequent direct sequencing.

RESULTS

From the 4 pedigrees carrying the Thr377Met mutation, 23 individuals with either ocular hypertension (OHT) or POAG were found, with a mean +/- SD age at diagnosis of 41.2 +/- 11.5 years, and a mean peak intraocular pressure of 31.7 +/- 9.9 mm Hg. A further 9 mutation carriers older than 18 years were studied who as yet showed no signs of OHT or POAG (6 of these 9 were younger than 30 years). A single individual with POAG was identified who did not carry the Thr377Met mutation. For Thr377Met carriers, age-related penetrance for OHT or POAG was 88% at age 30 years. A positive family history of POAG was present for 3 of the 4 index cases. Thirteen (57%) of the 23 Thr377Met carriers with OHT or POAG had undergone glaucoma drainage surgery. Although the glaucoma in these families appears to be pressure dependent, 2 individuals showed optic disc cupping before detected elevation in intraocular pressure. One family was of British origin, with a different background haplotype from the other 3 families from Greece or Macedonia, who shared a common haplotype.

CONCLUSIONS

The GLC1A Thr377Met mutation is associated with POAG that, in the pedigrees studied, had a younger age at onset and higher peak intraocular pressure than in pedigrees with the more common Gln368STOP mutation. In addition, patients with glaucoma with the Thr377Met mutation were more likely to have undergone glaucoma drainage surgery.

[In-vivo measurement of autofluorescence in the parapapillary atrophic zone of optic discs with and without glaucomatous atrophy]

BACKGROUND

To assess the level of autofluorescence (lipofuscin) of atrophic parapapillary zones in different stages of glaucomatous optic disc atrophy.

METHODS

Controlled cross-sectional prospective analysis of 79 consecutive eyes (15 normals as controls, 26 with ocular hypertension, 38 with primary open angle glaucoma). Eyes with retinal diseases or retinal pigment epithelial pathologies were excluded. The confocal scanning laser ophthalmoscope (HRA, Heidelberg Retina Angiograph) was used after lipofuscin excitation with argon blue laser (488 nm) to detect parapapillary autofluorescence in a spectrum above 500 nm. Size, extension of the parapapillary autofluorescent area and its mean distance to the optic nerve head were measured using the HRA standard software. Additional optic nerve head photographs taken with the 15 degrees Zeiss telecentric fundus camera (30 degrees camera with 2 x magnifier) were examined by two experienced ophthalmologists to determine the stage of glaucomatous optic disc atrophy (stages 0 to 4).

RESULTS

Very small autofluorescent areas were found in vital discs (optic nerve glaucoma stage 0) in the parapapillary atrophic area (0.08 +/- 0.12 mm (2)) in contrast to glaucomatous discs in stage 1 (0.24 +/- 0.26 mm (2)) and stages 2, 3 and 4 (0.59 +/- 1.29 mm (2), logistic regression analysis r = 0.71; P = 0.029). The circular extension of the autofluorescent area correlated borderlined with the stage of the glaucomatous disc atrophy (higher glaucoma stages: r = 0.82; P = 0.09). The autofluorescent area was larger in OHT than in controls (0.11 mm (2) vs. 0.04 mm (2), P < 0.03). The circular extension of the autofluorescent area was longer in OHT than in controls (0.5 mm vs. 1.15 mm, P < 0.04).

CONCLUSIONS

As a sign of pronounced lipofuscin accumulation in the parapapillary atrophic zone higher degrees of fundus autofluorescence can be detected in OHT and manifest primary open angle glaucoma in contrast to normals. The lipofuscin accumulation is correlated with the stage of progression of glaucoma and the stage of optic disc atrophy. The detection of active parapapillary autofluorescent areas especially in OHT may offer the ophthalmologist an important tool for early diagnosis.

Corneal thickness and endothelial cell density measured by non-contact specular microscopy and pachymetry in Rhesus macaques (Macaca mulatta) with laser-induced ocular hypertension

PURPOSE

Sustained increase in intraocular pressure (IOP) in humans results in a loss of corneal endothelial cells and an increase of corneal thickness. The effects of chronically elevated IOP on the corneal endothelium of monkeys with laser-induced ocular hypertension, a commonly used animal model of human glaucoma have not been documented. This study examined the central corneal thickness (CCT), the corneal endothelial cell density (ECD), and the corneal endothelial cell size (ACS) in Rhesus monkeys with experimental ocular hypertension. Materials and methods. Ten male monkeys with argon laser-induced ocular hypertension in one eye for an average duration of 2.4+/-0.7 years, were sedated with ketamine hydrochloride, and the CCT, ECD, and ACS measured at the center of the cornea of both eyes with a Topcon SP-2000P non-contact specular microscope (Topcon America Corporation((R)), Paramus, NJ, USA). CCT was also measured using a DHG-500 Pachette ultrasonic pachymeter (DHG Technology Inc., Exton, PA, USA). Mean and standard deviation (S.D.) of CCT, ECD and ACS for each eye was calculated and statistically compared.Results. Mean CCT in the hypertensive and normal eyes measured by specular microscopy was 0.477+/-0.023mm and 0.468+/-0.020 mm, respectively. Mean ECD in the hypertensive and normal eyes was 2601.7+/-631.8 and 3990.2+/-402.9 cells mm(-2), respectively. The mean size of the endothelial cells was 252.4+/-23.9 micro m(2) in the normal eye and 408.7+/-115.0 microm m(2) in the hypertensive eye. No significant difference in the measurement of CCT was observed between the specular microscope and the pachymeter (p=0.46). No significant difference in the mean CCT was observed between the two eyes (p=0.4820), whereas the mean ECD was significantly lower in the hypertensive eye than in the normal eye (p<0.001). The ECD was inversely related to the length of IOP elevation (p<0.001).

CONCLUSIONS

No difference in the corneal thickness measurement was observed between the specular microscopy and the pachymetry techniques. Chronic ocular hypertension did not significantly affect the CCT, but caused a significant loss of endothelial cells in the center of the cornea of the laser treated eyes compared to the normotensive eyes. The duration of elevated IOP was the most important factor affecting the ECD.

[Effect of negative pressure suction on rabbit optic nerve and retina]

OBJECTIVE

To study the effect of acute intraocular pressure (IOP) elevation on the optic nerve and retina in laser in situ keratomileusis (LASIK).

METHODS

Acute IOP was increased to 65 mm Hg for different period of time (30 s, 1 min and 3 min) by using scleral suction on rabbit eyes. The tissues of retina and optic nerve of immediately extirpated group (instant group), of 2 weeks later extirpated group (recovery group) both after the negative pressure suction and of normal rabbit eyes were examined with electron and light microscope.

RESULTS

After the negative pressure suction for 30 s, 1 min, and 3 min respectively, the optic nerve and retinal cells changed lightly; some part of optic nerve and retinal cells changed; optic nerve fibers and retinal cells changed sharply.

CONCLUSION

Ultrastructural changes of retina and optic nerve may be induced by acute IOP elevation in LASIK. The longer the time, the more apparent the changes.

Early glial responses after acute elevated intraocular pressure in rats

PURPOSE

To study the responses of glial cells to a short-term elevation in intraocular pressure (IOP) in rats.

METHODS

Adult Sprague-Dawley albino rats, 45 to 55 days old, were given India ink intracamerally. After 7 days, 200 spots of laser burn over 360 degrees were delivered by an Argon laser (620-637 nm; 200 mW; 200 mm; 0.2 seconds) aimed at the ink deposits in the trabecular meshwork. IOP was recorded and eye tissues at 12 hours and 1, 3, 5, 7, or 14 days after laser were examined by immunohistochemistry with antibodies against glial fibrillary acidic protein (GFAP), vimentin, S-100, ED1, and OX42. To evaluate neuronal loss, the number of cells in the retinal ganglion cell layer (RGCL) was counted on flat preparations of retinas at various times after elevation of IOP.

RESULTS

Significant elevation of IOP from 1 to 7 days and loss of cells in the RGCL from 3 days onward were noted after trabecular laser photocoagulation. In the inner retina, there was a gradual and sustained increase in GFAP and S-100 immunoreactivity, but only a transient increase in vimentin immunoreactivity. No remarkable changes in GFAP, vimentin, and S-100 immunoreactivity were noted at the optic nerve head (ONH). ED1- and OX42-labeled cells were noted in the choroidal plexus, the parapapillary region of the optic nerve, and the ONH from 3 days onward, whereas expression in the retina was unremarkable.

CONCLUSIONS

There is differential expression of glial cell markers in the retina and the ONH, with early loss of cells in the RGCL in response to the elevation of IOP. Macroglia such as astrocytes and Müller cells may be involved in the pathophysiology of retinal ganglion cell death or retinal repair, and activated microglial/phagocytic cells may play an important role in modulating the changes in the ONH that occur with the elevation of IOP.

Occurrence of catecholaminergic nerve fibers in the human uveoscleral tissue in conditions of normal and raised intraocular pressure

The distribution of catecholaminergic nerve fibers (CNF) in human uveoscleral tissue was studied in six human eyes with normal intraocular pressure and in five eyes with increased pressure. The eyes with increased pressure had no visual field alterations and the patients did not have any glaucoma-related optic neuropathies. The amount of norepinephrine in these structures was also analysed. Catecholaminergic nerve fibers were detected by means of fluorescence microscopy and were counted using the quantitative analysis of images. Our results demonstrate that the occurrence of catecholaminergic nerve fibers (expressed in Conventional Units = C.U.) in human uveoscleral tissue is 15.4 +/- 1.6 C.U. in eyes with normal intraocular pressure. In eyes with increased intraocular pressure, these values were 12.2 +/- 1.2 C.U. Moreover, the amount of norepinephrine in tissue homogenates of the same eyes was evaluated and found to be 21.7 +/- 1.3 microg/gr tissue fresh weight of the human uveoscleral tissue in eyes with normal intraocular pressure. This value decreased to 18.8 +/- 1.1 microg/gr tissue fresh weight in the same tissue in conditions of raised intraocular pressure. In these experiments, the small number of eyes examined made it difficult to draw general conclusions. However, the role of human uveoscleral tissue was emphasized by the rich catecholaminergic innervation. A decrease of catecholaminergic nerve fibers and norepinephrine occurs when intraocular pressure is elevated. The modifications of these parameters, involved in the sympathetic control of aqueous humor outflow, may support the hypothesis of a possible relevant role for the human uveoscleral tissue in different pathological conditions.

A mouse model of elevated intraocular pressure: retina and optic nerve findings

PURPOSE

To develop and characterize a mouse model of elevated intraocular pressure (IOP) as a means to investigate the underlying cellular and genetic mechanisms of glaucomatous optic neuropathy.

METHODS

An experimental increase in IOP was induced in one eye of each adult C57BL/6J mouse by argon laser photocoagulation of the episcleral and limbal veins. The IOP of both eyes of each mouse was measured using an indentation tonometer prior to treatment and once a week thereafter. The mouse retinal ganglion cells (RGCs) were identified immunocytochemically using an antiserum against Thy1,2, CD90.2, and the number of RGCs was measured with confocal microscopy. The reduction in the number of RGCs was compared in the experimental and control eyes. The mechanism of RGC death after IOP elevation was investigated using TdT-mediated dUTP nick end labeling (TUNEL) staining. The pathologic changes of optic nerve following elevated IOP were characterized by light and electron microscopy.

RESULTS

After laser treatment, mean IOP was increased in the treated eyes from the control mean of 13 +/- 1.8 mm Hg to 20.0 +/- 2.8 mm Hg at 4 weeks. Peak IOP was 32 +/- 2.5 mm Hg in the experimental group. RGC loss was 16.9% +/- 7.8% at 2 weeks (n = 6, P < .05) and 22.4% +/- 7.5% at 4 weeks (n = 6, P < .05) after laser photocoagulation. TUNEL staining showed that there were marked increases in the number of apoptotic nuclei in the ganglion cell layer in the treated eyes; moreover, these TUNEL-positive cells were mostly distributed in the peripheral areas of the retina. The optic nerve axons from the eyes with elevated IOP were observed to demonstrate greater degeneration compared with the control group.

CONCLUSIONS

The magnitude and duration of the elevation of the IOP supports the use of this model as a surrogate for glaucomatous optic neuropathy. The presumed apoptotic mechanism of RGC death is consistent with this assumption. Laser-induced increased IOP appears to be a viable means for future investigations of the genetic mechanisms of glaucoma.

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.

A case-control comparison of the clinical characteristics of glaucoma and ocular hypertensive patients with and without the myocilin Gln368Stop mutation

PURPOSE

To determine whether primary open-angle glaucoma (POAG) and ocular hypertensive (OHT) patients who harbor the myocilin Gln368Stop mutation differ in phenotype or clinical course from patients without the mutation.

DESIGN

Case-control study.

METHODS

A retrospective case-control study compared all known POAG patients (n = 18) and OHT patients (n = 4) harboring the Gln368Stop mutation evaluated by the University of Iowa Glaucoma Service with control patients from the same population. Patients and control subjects were matched for diagnosis, age, sex, and race and were compared for phenotype and clinical course.

RESULTS

Mean age of disease onset and mean peak intraocular pressures (IOPs) of cases were similar to those reported by other studies. There was no statistically significant difference between cases and controls for the following variables: age at onset, peak intraocular pressure, Snellen visual acuity, number of medications, Humphrey visual field (HVF) mean deviation, HVF pattern deviation, number of filtering surgeries performed, time intervals from diagnosis to argon laser trabeculoplasty (ALT), diagnosis to first filtering surgery, ALT to first filtering surgery, and percent change in IOP after ALT and after first filtering surgery.

CONCLUSIONS

There is no statistically significant difference between the onset and clinical course of POAG and OHT caused by the Gln368Stop mutation and POAG and OHT not associated with the mutation.

Scanning laser polarimetric analysis of retinal nerve fiber layer thickness in Turkish patients with glaucoma and ocular hypertension

PURPOSE

To assess the thickness of the retinal nerve fiber layer (RNFL) in patients with different stages of glaucoma, in comparison with ocular hypertensive (OHT) and healthy subjects in a Turkish population.

METHODS

Scanning laser polarimetry was done with a GDx Nerve Fiber Analyzer (NFA, GDx version, 1.0.08) on 270 eyes with glaucoma, 52 OHT eyes, and 81 normal eyes. The eyes were classified as having early (146 eyes), moderate (66 eyes) and severe (58 eyes) glaucoma based on the Humphrey Visual Field indices. We compared 14 NFA parameters by analysis of variance (ANOVA) and Scheffe multiple comparison analysis. Receiver operator characteristic curves (ROC) and Fisher linear discriminant analysis (LDF) were used to measure the sensitivity and specificity of the NFA parameters.

RESULTS

Except for symmetry, all NFA parameters showed significant differences between the groups (p<0.05). The eyes with glaucoma had significantly thinner RNFL than healthy eyes (p<0.01). The RNFL retardation measurements of OHT eyes were lower than controls, but higher than the early glaucoma group. The sensitivity and specificity of the GDx System were 87% and 72.8%, respectively. Applying LDF, the group with the highest sensitivity and specificity (85.9% and 74.1%) was determined as inferior ratio, superior/nasal ratio, superior maximum and the Number.

CONCLUSIONS

Assessment of RNFL thickness with scanning laser polarimetry can distinguish glaucoma, OHT and normal subjects with relatively high sensitivity and specificity.