Vasospasm in Glaucoma: Clinical and Laboratory Aspects

Caveolin-1 in vascular health and glaucoma: A critical vascular regulator and potential therapeutic target

Caveolin-1 (Cav-1) is an integral scaffolding membrane protein found in most cell types. Cav-1 has been found to contribute significantly to ocular function, with mutations of Cav-1 being associated with a genetic risk of glaucoma development. Raised intraocular pressure (IOP) is a major modifiable risk factor for glaucoma. Cav-1 may be involved in both IOP-dependent and independent mechanisms involving vascular dysregulation. Systemic vascular diseases including hypertension, diabetes and hyperlipidaemia, have been shown to be associated with glaucoma development. Cav-1 is closely interlinked with endothelial nitric oxide synthase pathways that mediate vascular function and prevent cardiovascular diseases. Endothelial nitric oxide synthase and endothelin-1 are key vasoactive molecules expressed in retinal blood vessels that function to autoregulate ocular blood flow (OBF). Disruptions in the homeostasis of OBF have led to a growing concept of impaired neurovascular coupling in glaucoma. The imbalance between perfusion and neuronal stimulation arising from Cav-1 depletion may result in relative ischemia of the optic nerve head and glaucomatous injury. OBF is also governed by circadian variation in IOP and systemic blood pressure (BP). Cav-1 has been shown to influence central BP variability and other circadian rhythms such as the diurnal phagolysosomal digestion of photoreceptor fragments and toxic substrates to maintain ocular health. Overall, the vast implications of Cav-1 on various ocular mechanisms leading to glaucoma suggest a potential for new therapeutics to enhance Cav-1 expression, which has seen success in other neurodegenerative diseases.

Status of Rho kinase inhibitors in glaucoma therapeutics-an overview

Medical management remains the cornerstone of glaucoma management despite advances in the surgical or laser procedures. After a leap of almost two decades of the advent of prostaglandin analogues, recently a new class of drug, Rho kinase (ROCK) inhibitors, has come to limelight because of their varied therapeutic potential in different clinical conditions of eye, especially glaucoma. Their efficacy of lowering intraocular pressure (IOP) by virtue of an entirely different mechanism of decreasing outflow resistance has ignited a series of clinical trials evaluating their potential as monotherapy or as adjunct to existing antiglaucoma medications, and three of them ripasudil, netarsudil and roclatan have even been approved for clinical use in the recent past. There are evidences suggesting their beneficial effects in glaucoma patients even via non-IOP-dependent mechanisms like neuroprotection by improving blood flow to the optic nerve and increasing ganglion cell survival. They can even act as antifibrotic agents and reduce bleb scarring after glaucoma surgery. Hence, their effective role in glaucomatous optic neuropathy is multifaceted primary being improved drainage through the conventional pathway. On the other hand, certain local adverse effects like conjunctival hyperaemia have been reported in substantial proportion of patients, while some others like blepharitis, subconjunctival haemorrhages and cornea verticillata constitute less common side effects. The purpose of this review is to summarize the discovery, evolution and recent update of clinical trials on Rho kinase inhibitors as antiglaucoma medicine and to delineate their role in existing management protocol.

Tackling retinal ganglion cell apoptosis in glaucoma: role of adenosine receptors

INTRODUCTION

The role of adenosine receptors as therapeutic targets for neuroprotection is now widely recognized. Their role, however, in protection against retinal ganglion cell (RGC) apoptosis in glaucoma needs further investigation. Hence, in this review, we look into the possibility of adenosine receptors as potential therapeutic targets by exploring their role in modulating various pathophysiological mechanisms underlying glaucomatous RGC loss.

AREAS COVERED

This review presents a summary of the adenosine receptor distribution in retina and the cellular functions mediated by them. The major pathophysiological mechanisms such as excitotoxicity, vascular dysregulation, loss of neurotrophic signaling, and inflammatory responses involved in glaucomatous RGC loss are discussed. The literature showing the role of adenosine receptors in modulating these pathophysiological mechanisms is discussed. The literature search was conducted using Pubmed search engine using key words such as 'RGC apoptosis,' 'adenosine,' adenosine receptors' 'retina' 'excitotoxicity,' 'neurotrophins,' 'ischemia', and 'cytokines' individually and in various combinations.

EXPERT OPINION

Use of adenosine receptor agonists and antagonists, for preservation of the RGCs in glaucomatous eyes independent of the level of intraocular pressure seems a very useful strategy. Future application of this strategy would require appropriate designing of drug formulation for tissue and disease-specific receptor targeting. Furthermore, the modulation of physiological functions and potential adverse effects need further investigations.

Correlation of Visual Field With Peripapillary Vessel Density Through Optical Coherence Tomography Angiography in Normal-Tension Glaucoma

Purpose

To investigate the retinal vessel density (VD) in healthy and normal-tension glaucoma (NTG) eyes through optical coherence tomography angiography (OCTA) and to determine the correlation between VD and the retinal nerve fiber layer (RNFL) thickness and functional visual field (VF) defects for different locations.

Methods

A total of 74 NTG eyes and 24 healthy eyes were included. OCTA VD at 4.5 × 4.5 mm peripapillary region and 3.0 × 3.0 mm macula area, RNFL thickness, and VF pattern deviation results were individually analyzed on the basis of the Garway-Heath sectorization. Correlations between VD and VF/RNFL and VF were compared.

Results

In the NTG group, peripapillary VD, superficial macula VD, RNFL thickness, and ganglion cell complex thickness were significantly lower. In the whole peripapillary area and inferotemporal sector, anatomic correlations between VD and VF pattern deviation values were significantly higher than those between the RNFL thickness and VF values. In the subgroup analysis, VD was anatomically correlated with VF in early-, moderate-, and severe-stage NTG eyes, whereas the RNFL thickness was correlated with VF in moderate- and severe-stage NTG eyes.

Conclusions

We observed VD reduction in the peripapillary retina and superficial macula area in NTG eyes. The microvascular dropout of VD in the peripapillary retina, especially in the inferotemporal sector, provided a more accurate anatomic correlation with functional VF defects than that of the RNFL thickness, especially in early-stage NTG eyes.

Translational Relevance

In patients who cannot comply VF exam, VD is a good tool for disease detection.

Peripheral vascular disease - a new vascular disease associated with normal tension glaucoma: a case report

INTRODUCTION

Normal-tension glaucoma is known as a multifactorial optic neuropathy. A number of lines of evidence suggested that vascular factors played a significant role in the development of normal-tension glaucoma. The mechanisms underlying the abnormal ocular blood flow in normal-tension glaucoma are still not clear. Peripheral vascular disease seems to be associated with glaucoma populations independent of other cardiovascular risk factors. We found this presentation, for the first time, to our knowledge, as another probable vascular abnormality related to our patient with normal-tension glaucoma, although it is necessary to confirm its pathological effect in future studies.

CASE PRESENTATION

Our patient was a 48-year-old Spanish man without any personal and family history of interest except for circulatory problems of the lower limbs with repetitive ulcers at the frontal and lateral aspects of his legs. His chief complaint was vision loss when he came to consult us. In exploration, his best corrected visual acuity was 20/20 in both eyes; initial intraocular pressure in the right eye was 14-16 mmHg and in the left eye was 16-18 mmHg, with a mild sclerosis of the lens in slit-lamp examination. No inflammation or pigmented lesion was detected in the anterior chamber. Open angle confirmed by Goldman four quadrants gonioscopy. Funduscopic examination revealed a vertical cup disc ratio of 0.6 in the right eye and 0.8 in the left eye. The patient's neuroretinal rim was normal in the right eye, and superior thinning in the left eye was determined. Examination of the patient's visual field showed inferior mild probable nasal scotoma in the right eye and an inferior deep arcuate scotoma defect in the left eye. His optical coherence tomography examination revealed thinning of the peripapillary nerve fiber layer thickness in the left eye and superior loss of macular retinal ganglion cells in the left eye. Normal intraocular pressure values were measured on the intraocular pressure curve without treatment (maximum value, 18-20 mmHg), discarding higher intraocular pressures measured out of office. Ultrasonic pachymetry measured 515/520 μm, and normal intraocular pressure measured with a PASCAL tonometer ruled out probable corneal biomechanical underestimations. The patient's polysomnography study was normal and excluded sleep apnea syndrome. The patient's serial mean blood pressure was normal, especially in the lower limbs (mean value, 125/70 mmHg), ruling out the possibility of systemic hypotension. Thyroidal and coagulation abnormalities, autoimmune disease, and inflammatory disease were excluded. Normal immunologic study and normal vascular biopsy were observed, as well as normal brain magnetic resonance imaging and a normal carotid vascular study. The primary diagnosis was moderate medium peripheral arterial disease in the lower limbs, which was confirmed by echography after ruling out other probable vascular abnormalities related to normal-tension glaucoma.

CONCLUSION

After ruling out other systemic diseases and vascular abnormalities related to normal-tension glaucoma, we found peripheral arterial disease as a probable vascular abnormality related to normal-tension glaucoma in our patient. To our knowledge, this is the first time such a case has been reported. Thus, further research is needed to determine the relevance of these results to the general population.

Foveal Avascular Zone in Normal Tension Glaucoma Measured by Optical Coherence Tomography Angiography

Aim

To measure diameter of foveal avascular zone (FAZ), FAZ area, and vessel density using Optical Coherence Tomography Angiography (OCT-A) in patients with normal tension glaucoma (NTG) and to establish the possible role of OCT-A in diagnosis and follow-up of patients with NTG.

Methods

Twenty-one eyes of 21 patients with NTG and 30 eyes of 30 healthy subjects underwent complete ophthalmic examination as well as OCT-A on ZEISS AngioPlex. 3 × 3 macula scans were used to measure vertical, horizontal, and maximum diameter of FAZ by two graders. Mean values and interobserver variability were analyzed. Image J was used for analysis of FAZ area and vessel density.

Results

Mean vertical diameter (t = 5.58, p < 0.001), horizontal diameter (t = 3.59, p < 0.001), maximum diameter (t = 5.94, p < 0.001), and FAZ area (t = 5.76, p < 0.001) were statistically significantly enlarged in the NTG group compared to those in the control group. Vessel density (t = -5.80, p < 0.001) was statistically significantly decreased in the NTG group compared to that in the control group.

Conclusion

OCT-A could have an important role in the future in diagnosis of patients with NTG. In patients with NTG, there is larger FAZ area, while the vessel density is reduced in comparison to the control group.

Arteriolar Diameters in Glaucomatous Eyes with Single-Hemifield Damage

PURPOSE

To examine the association between retinal arteriolar caliber and lumen, retinal sensitivity (RS), and retinal nerve fiber layer (RNFL) thickness in glaucomatous eyes with single-hemifield loss.

METHODS

We conducted a prospective, nonrandomized, case-control study of 20 eyes of 20 patients with glaucoma with visual field damage confined to a single hemifield. The control group was composed of 20 eyes of 20 normal subjects. For all the eyes, we performed optical coherence tomography to assess the RNFL and standard automated perimetry to evaluate RS. External and internal arteriolar diameters were assessed in vivo using scanning laser Doppler flowmetry.

RESULTS

The RNFL was significantly thinner in glaucomatous eyes than in normal eyes (p < 0.001). In glaucomatous eyes, a positive correlation between sectorial RNFL thickness and the corresponding external and internal arteriolar diameters was found (r = 0.43, p = 0.05; r = 0.63, p = 0.003, respectively). The internal arteriolar diameter significantly correlated with RS in the corresponding abnormal hemifield (r = 0.44, p = 0.04). Compared with the normal hemifield, the internal arteriolar diameter, RNFL thickness, and RS were significantly reduced, whereas the external arteriolar diameter was unchanged in the abnormal hemifield.

CONCLUSIONS

In glaucomatous eyes with single-hemifield damage, attenuation of retinal vessels was associated with a thinner RNFL and reduced RS. Moreover, a narrower lumen with increased wall-to-lumen ratio was found in the abnormal hemifield, supporting the hypothesis that vessel narrowing is likely secondary to a lower demand for blood flow in the glaucomatous areas of the retina.

Accuracy of isolated-check visual evoked potential technique for diagnosing primary open-angle glaucoma

PURPOSE

The aim of this study was to determine the diagnostic accuracy, sensitivity and specificity of isolated-check visual evoked potentials (icVEP) in primary open-angle glaucoma (POAG).

METHODS

Ninety POAG patients and sixty-six healthy controls were recruited consecutively. All subjects underwent icVEP and visual field testing. Swept icVEP response functions were obtained by increasing contrast in six stimulus steps, recording the electroencephalogram synchronized to the stimulus display's frame rate and calculating the corresponding signal-to-noise ratio (SNR) of the response at the fundamental frequency to evaluate visual function. Depth of modulation of the check luminance was increased as follows: 2, 4, 8, 14, 22 and 32%, about an equal level of standing contrast, so that the pattern appeared and disappeared at a frequency of 10.0 Hz. SNR above 0.85 was deemed to be significant at the 0.1 level and SNR above 1 significant at the 0.05 level.

RESULTS

The results show that SNR is contrast dependent. It significantly rose as contrast increased. The areas under receiver-operating-characteristic curves (AUCs) indicating classification accuracy for all POAG cases in comparison with normal subjects were 0.790 (sensitivity 91.1%, specificity 69.7%) with the cutoff SNR of 0.85, and 0.706 (sensitivity 95.6%, specificity 51.5%) with the cutoff SNR of 1. The AUC of early glaucoma cases (EG) in comparison with normal subjects was 0.801 (sensitivity 93.3%, specificity 69.7%) with the cutoff SNR of 0.85, and 0.717 (sensitivity 97.8%, specificity 51.5%) with the cutoff SNR of 1.

CONCLUSION

icVEP has good diagnostic accuracy (high sensitivity and moderate specificity) in distinguishing early POAG patients from healthy subjects. It might be a promising device to use in conjunction with complementary functional and structural measures for early POAG detection.

Management of glaucoma as a neurodegenerative disease

Glaucoma is a neurodegenerative disease with an estimated prevalence of 60 million people, and the most common cause of irreversible blindness worldwide. The mainstay of treatment has been aimed at lowering intraocular pressure, currently the only modifiable risk factor. Unfortunately, despite adequate pressure control, many patients go on to suffer irreversible visual loss. We first briefly examine currently established intraocular pressure lowering-treatments, with a discussion of their roles in neuroprotection as demonstrated by both animal and clinical studies. The review then examines currently available intraocular pressure independent agents that have shown promise for possessing neuroprotective effects in the management of glaucoma. Finally, we explore potential future treatments such as immune-modulation, stem cell therapy and neural regeneration as they may provide further protection against the neurodegenerative processes involved in glaucomatous optic neuropathy.

Association Between Nocturnal Blood Pressure Dips and Optic Disc Hemorrhage in Patients With Normal-Tension Glaucoma

PURPOSE

To investigate the effect of nocturnal blood pressure (BP) dips on the occurrence of optic disc hemorrhage (ODH) in normal-tension glaucoma (NTG) patients and determine whether ODH is associated with greater likelihood of visual field progression (VFP).

DESIGN

Prospective case-control study.

METHODS

This study enrolled 698 eyes of 349 consecutive NTG patients who were ≥40 years old, underwent 24-hour intraocular pressure and ambulatory BP monitoring in the habitual position, were examined for ODH every 4-6 months with optic disc photography, and had ≥5 reliable visual field tests with minimum follow-up of 3 years. NTG patients were classified into 2 groups: "nonphysiologic" dippers, including nondippers and overdippers, and "physiologic" dippers. Odds ratios for the association between the "nonphysiologic" group and ODH were calculated using logistic regression models. Kaplan-Meier analyses were performed to compare outcomes with reference to the presence of ODH for VFP.

RESULTS

Overall, ODH and VFP were detected in 107 (15.3%) eyes and 60 (8.6%) eyes among total 698 eyes, respectively. Overdippers showed a significantly greater frequency of ODH than nondippers or dippers. Being an overdipper was a significant and an independent risk factor for ODH occurrence during follow-up. The rates of VFP were 6%, 7%, and 24% for dippers, nondippers, and overdippers, respectively. Eyes with ODH were associated with greater likelihoods of subsequent VFP than those without. VFP occurred only in eyes with ODH.

CONCLUSIONS

Being an overdipper is a significant risk factor for ODH in NTG eyes. The detection of ODH during follow-up is a potent predictor of future VFP.

Association between open-angle glaucoma and neovascular age-related macular degeneration: a case-control study

PurposeTo investigate the relationship between previously diagnosed open-angle glaucoma (OAG) and neovascular age-related macular degeneration (AMD) using a routine insurance dataset.MethodsThis study retrieved data from the Taiwan Longitudinal Health Insurance Database 2005. We found 3282 patients with neovascular AMD as cases and 13 128 sex- and age-matched subjects without neovascular AMD as controls. Conditional logistic regressions were performed to evaluate the association of neovascular AMD with previously diagnosed OAG among the sampled patients.ResultsOf the 16 410 sampled patients, 2.55% had previously diagnosed OAG, 5.06 and 1.92% for the cases and controls, respectively. The logistic regression analysis showed that the odds ratio (OR) of previously diagnosed OAG for cases was 2.45 (OR: 2.45; 95% confidence interval: 1.99-3.01) compared with the controls after adjusting for potential confounders. In addition, the adjusted ORs for previously diagnosed OAG were similar for patients with AMD in both genders (with an adjusted OR of 2.49 for males and 2.39 for females). Furthermore, it shows that OAG was significantly associated with neovascular AMD regardless of sex even after adjusting for monthly income, geographic region, urbanisation level, and comorbidities (with adjusted ORs of 2.49 for males and 2.39 for females).ConclusionsThis study demonstrated that patients with neovascular AMD had a higher odds of previously diagnosed OAG compared with those patients without neovascular AMD regardless of sex.

Prospective Study of Oral Health and Risk of Primary Open-Angle Glaucoma in Men: Data from the Health Professionals Follow-up Study

PURPOSE

Tooth loss or periodontal disease is associated with systemic endothelial dysfunction, which has been implicated in primary open-angle glaucoma (POAG). The relationship between oral health and POAG has received limited attention. Thus, we evaluated the association between oral health history and risk of POAG and POAG subtypes.

DESIGN

Prospective cohort study.

PARTICIPANTS

Health Professionals Follow-up Study participants (40 536 men) followed biennially from 1986 to 2012. At each 2-year risk period, eligible participants were aged 40+ years, were free of POAG, and reported eye examinations.

METHODS

By using validated questions, we updated participants' status on number of natural teeth, teeth lost, periodontal disease with bone loss, and root canal treatments.

MAIN OUTCOME MEASURES

During follow-up, 485 incident cases of POAG were confirmed with medical records and classified into subtypes defined by intraocular pressure (IOP; ≥ or <22 mmHg) or visual field (VF) loss pattern at diagnosis (peripheral loss only or early paracentral loss). Multivariable relative risks (MVRRs) and 95% confidence intervals (CIs) were estimated.

RESULTS

Number of natural teeth, periodontal disease, and root canal treatment were not associated with POAG. However, compared with no report of tooth loss, a report of losing teeth within the past 2 years was associated with a 1.45-fold increased risk of POAG (95% CI, 1.06-1.97); in particular, a report within the past 2 years of both losing teeth and having a prevalent diagnosis of periodontal disease was associated with a 1.85-fold increased risk of POAG (95% CI, 1.07-3.18). The associations with recent tooth loss were not significantly different for the POAG subtypes (P for heterogeneity ≥0.36), although associations were strongest in relation to the POAG subtypes with IOP <22 mmHg (MVRR, 1.93; 95% CI, 1.09-3.43) and early paracentral VF loss (MVRR, 2.27; 95% CI, 1.32-3.88).

CONCLUSIONS

Although the number of natural teeth was not associated with risk of POAG, recent tooth loss was associated with an increased risk of POAG. Because these findings may be due to chance, they need confirmation in larger studies.

Microvascular endothelial function and severity of primary open angle glaucoma

PurposeThe role of microvascular endothelial dysfunction on severity of primary open angle glaucoma (POAG) was investigated in this study.Patients and methodsA prospective cohort study was conducted. One hundred and fourteen ethnically Malay patients (114 eyes) with POAG treated at the eye clinic of Hospital University Sains Malaysia between April 2012 and December 2014 were recruited. Patients aged between 40 and 80 years with two consecutive reliable and reproducible Humphrey visual field 24-2 analyses were selected. Patients who were diagnosed with any other type of glaucoma, previous glaucoma-filtering surgery, or other surgeries except uncomplicated cataract and pterygium surgery were excluded. Humphrey visual field analysis 24-2 was used to stratify the severity of glaucoma using Advanced Glaucoma Intervention Study (AGIS) score at the time of recruitment. Microvascular endothelial function was assessed using Laser Doppler fluximetry and iontophoresis. Iontophoresis process with acetylcholine (ACh) and sodium nitroprusside (SNP) was used to measure microvascular endothelium-dependent and -independent vasodilatation, respectively.ResultsBased on the AGIS score, 55 patients showed mild glaucoma, with 29 moderate and 30 severe. There was statistically significant difference in microvascular endothelial function (ACh% and ACh_max) between mild and moderate POAG cases (P=0.023) and between mild and severe POAG cases (P<0.001). There was negative correlation between microvascular endothelial function and severity of POAG (r=-0.457, P<0.001).ConclusionMicrovascular endothelial dysfunction may have a role in influencing the severity of POAG in Malay patients.

Ocular Blood Flow and Influencing Factors for Glaucoma

Open-angle glaucoma (OAG) is characterized by optic nerve fiber atrophy and deterioration of the visual field, corresponding to damage to the optic nerve head. Intraocular pressure (IOP) is currently the only evidence-based, treatable risk factor for OAG. However, normal-tension glaucoma, the most common type of OAG in Asia, is a type of glaucoma with an unclear pathogenesis. Glaucoma is suspected to be a multifactorial disease with IOP-dependent and IOP-independent risk factors, including decreased ocular blood flow (OBF), oxidative stress, decreased axoplasmic flow, and genetic background. A number of epidemiological studies have generated strong evidence that OBF may be an especially important risk factor for the progression of glaucoma. Recent innovations in laser speckle flowgraphy and optical coherence tomography-based angiography have allowed us to noninvasively monitor changes in the microcirculation of the optic nerve head with high reproducibility. Laser speckle flowgraphy-derived measurement parameters include mean blur rate and pulse wave form parameters, whereas the main optical coherence tomography angiography-derived parameter is the vessel index. Decreases in these parameters are associated with the severity of glaucomatous damage, and changes are detectible even in the earliest, preperimetric stage of glaucoma. In the future, OBF analysis may improve significantly because of continuing progress in the development of the relevant instruments. This review will summarize possible connections between systemic and OBF abnormalities and OAG, describe the scientific rationale for these connections, and discuss their potential implications. Thus, this review will summarize the role of OBF in glaucoma pathogenesis and discuss the wide range of IOP-independent risk factors.

Risk Factors in Normal-Tension Glaucoma and High-Tension Glaucoma in relation to Polymorphisms of Endothelin-1 Gene and Endothelin-1 Receptor Type A Gene

The aim of the research is to analyse the influence of polymorphisms of endothelin-1 gene and endothelin-1 receptor type A gene on the clinical condition of patients with primary open angle glaucoma. Methods. 285 Polish patients took part in the research (160 normal-tension glaucoma and 125 high-tension glaucoma). DNA was isolated by standard methods and genotype distributions of four polymorphisms in genes encoding endothelin-1 (K198N) and endothelin-1 receptor type A polymorphisms (C1222T, C70G, and G231A) were determined. Genotype distributions were compared between NTG and HTG groups. The clinical condition of participants was examined for association with polymorphisms. Results. A similar frequency of occurrence of the polymorphic varieties of the studied genes was observed in patients with NTG and HTG. There is no relation between NTG risk factors and examined polymorphisms. NTG patients with TT genotype of K198N polymorphism presented with the lowest intraocular pressure in comparison to GG + GT genotype (p = 0.03). In NTG patients with CC genotype of C1222T polymorphism (p = 0.028) and GG of C70G polymorphism (p = 0.03) the lowest values of mean blood pressure were observed. Conclusions. The studied polymorphic varieties (K198N, C1222T) do have an influence on intraocular pressure as well as arterial blood pressure in NTG patients.

Ocular Blood Flow Autoregulation Mechanisms and Methods

The main function of ocular blood flow is to supply sufficient oxygen and nutrients to the eye. Local blood vessels resistance regulates overall blood distribution to the eye and can vary rapidly over time depending on ocular need. Under normal conditions, the relation between blood flow and perfusion pressure in the eye is autoregulated. Basically, autoregulation is a capacity to maintain a relatively constant level of blood flow in the presence of changes in ocular perfusion pressure and varied metabolic demand. In addition, ocular blood flow dysregulation has been demonstrated as an independent risk factor to many ocular diseases. For instance, ocular perfusion pressure plays key role in the progression of retinopathy such as glaucoma and diabetic retinopathy. In this review, different direct and indirect techniques to measure ocular blood flow and the effect of myogenic and neurogenic mechanisms on ocular blood flow are discussed. Moreover, ocular blood flow regulation in ocular disease will be described.

Ocular Blood Flow and Normal Tension Glaucoma

Normal tension glaucoma (NTG) is known as a multifactorial optic neuropathy characterized by progressive retinal ganglion cell death and glaucomatous visual field loss, even though the intraocular pressure (IOP) does not exceed the normal range. The pathophysiology of NTG remains largely undetermined. It is hypothesized that the abnormal ocular blood flow is involved in the pathogenesis of this disease. A number of evidences suggested that the vascular factors played a significant role in the development of NTG. In recent years, the new imaging techniques, fluorescein angiography, color Doppler imaging (CDI), magnetic resonance imaging (MRI), and laser speckle flowgraphy (LSFG), have been used to evaluate the ocular blood flow and blood vessels, and the impaired vascular autoregulation was found in patients with NTG. Previous studies showed that NTG was associated with a variety of systemic diseases, including migraine, Alzheimer's disease, primary vascular dysregulation, and Flammer syndrome. The vascular factors were involved in these diseases. The mechanisms underlying the abnormal ocular blood flow in NTG are still not clear, but the risk factors for glaucomatous optic neuropathy likely included oxidative stress, vasospasm, and endothelial dysfunction.

Optic disc hemorrhage is related to various hemodynamic findings by disc angiography

BACKGROUND

To investigate the hemodynamic characteristics of glaucoma eyes with disc hemorrhage (DH) by disc fluorescein angiography, and its relationship with glaucomatous changes of the optic disc and surrounding retinal nerve fiber layer (RNFL).

METHODS

This study included 35 glaucoma eyes with DH who were followed up at least 5 years and had DH at presentation. Eyes were classified as eyes with DH at the border of localized RNFL defects and eyes with DH not related to localized RNFL defects. Prevalence of DH and location of the proximal border were recorded from disc photographs. Fluorescein angiography was performed 3 months after detecting the DH. Arm-retina time, arteriovenous transit time, disc filling time, choroidal filling time, and venous filling time were measured as retinal circulation parameters. The presence of disc filling defects and disc leaks were evaluated.

RESULTS

There were 19 (54.3%) eyes with DH accompanying localized RNFL defects. The arm-retina time was prolonged in eyes with DH not related to RNFL defects (P = 0.044) and the arteriovenous transit time was prolonged in eyes with DH accompanying RNFL defects (P = 0.029). Among eyes with DH accompanying RNFL defects, 11 (57.9%) had vessel filling defects or delayed filling indicating blood flow stasis at the cup margin proximal to where DH occurred. Eyes with DH not related to RNFL defects did not show vessel filling defects or delayed filling.

CONCLUSIONS AND RELEVANCE

Eyes with DH related to RNFL defects showed prolonged arteriovenous transit time and had frequent vessel filling defects or delayed filling indicating blood flow stasis and thrombus formation at the site DH occurred. These findings suggest that vascular and hemodynamic changes due to glaucomatous structural changes cause DH in relation to localized RNFL defects.

Discovery of novel inhibitors for the treatment of glaucoma

INTRODUCTION

Glaucoma is a neurodegenerative disease with heterogeneous causes that result in retinal ganglionic cell (RGC) death. The discovery of ocular antihypertensives has shifted glaucoma therapy, largely, from surgery to medical intervention. Indeed, several intraocular pressure (IOP)-lowering drugs, with different mechanisms of action and RGC protective property, have been developed.

AREAS COVERED

In this review, the authors discuss the main new class of kinase inhibitors used as glaucoma treatments, which lower IOP by enhancing drainage and/or lowering production of aqueous humor. The authors include novel inhibitors under preclinical evaluation and investigation for their anti-glaucoma treatment. Additionally, the authors look at treatments that are in clinics now and which may be available in the near future.

EXPERT OPINION

Treatment of glaucoma remains challenging because the exact cause is yet to be delineated. Neuroprotection to the optic nerve head is undisputable. The novel Rho-associated kinase inhibitors have the capacity to lower IOP and provide optic nerve and RGC protection. In particular, the S-isomer of roscovitine has the capacity to lower IOP and provide neuroprotection. Combinations of selected drugs, which can provide maximal and sustained IOP-lowering effects as well as neuroprotection, are paramount to the prevention of glaucoma progression. In the near future, microRNA intervention may be considered as a potential therapeutic target.

Morphological and morphometric changes in rat optic nerve microvessels in a glaucoma experimental model

AIM

To study the morphological and morphometric changes produced in the capillaries of the optic nerve (ON) head and initial portion after the experimental increase in intraocular pressure (IOP).

MATERIAL AND METHODS

Wistar rats underwent cauterization of three episcleral veins, which produced an immediate increase in the IOP, and was maintained for 3 months. Sagittal sections of the eyeball were studied with immunohistochemical techniques, using a primary antibody to GLUT-1. The GLUT-1 positive capillaries were counted, and measurements were made of the area, perimeter and mean diameter.

RESULTS

Microscopic examination of sections of the ON of control rats revealed a lower density and larger caliber of capillaries in the prelaminar region as compared with the other regions of the ON (P<.05). Comparison between the control and the experimental groups showed a reduction in capillary density (except in the prelaminar region) and a smaller size in all the areas of the ON studied, but less evident in the initial portion (P<.05).

CONCLUSIONS

The increase in IOP was associated with significant qualitative and quantitative changes in the capillaries of the laminar and poslaminar regions of the ON head. These changes appear to return towards parameters compatible with normality in the initial portion of the ON, an area where the vascular collapse was less evident. These findings might explain the significant reduction in ocular blood flow seen in patients with primary open-angle glaucoma.

The current research status of normal tension glaucoma

Normal tension glaucoma (NTG) is a progressive optic neuropathy that mimics primary open-angle glaucoma, but lacks the findings of elevated intraocular pressure or other mitigating factors that can lead to optic neuropathy. The present review summarized the causes, genetics, and mechanisms underlying NTG in both animal models and human patients. We also proposed that the neurovascular unit is a therapeutic target for NTG management.

Flammer syndrome

The new term Flammer syndrome describes a phenotype characterized by the presence of primary vascular dysregulation together with a cluster of symptoms and signs that may occur in healthy people as well as people with disease. Typically, the blood vessels of the subjects with Flammer syndrome react differently to a number of stimuli, such as cold and physical or emotional stress. Nearly all organs, particularly the eye, can be involved. Although the syndrome has some advantages, such as protection against the development of atherosclerosis, Flammer syndrome also contributes to certain diseases, such as normal tension glaucoma. The syndrome occurs more often in women than in men, in slender people than in obese subjects, in people with indoor rather than outdoor jobs, and in academics than in blue collar workers. Affected subjects tend to have cold extremities, low blood pressure, prolonged sleep onset time, shifted circadian rhythm, reduced feeling of thirst, altered drug sensitivity, and increased general sensitivity, including pain sensitivity. The plasma level of endothelin-1 is slightly increased, and the gene expression in lymphocytes is changed. In the eye, the retinal vessels are stiffer and their spatial variability larger; the autoregulation of ocular blood flow is decreased. Glaucoma patients with Flammer syndrome have an increased frequency of the following: optic disc hemorrhages, activated retinal astrocytes, elevated retinal venous pressure, optic nerve compartmentalization, fluctuating diffuse visual field defects, and elevated oxidative stress. Further research should lead to a more concise definition, a precise diagnosis, and tools for recognizing people at risk. This may ultimately lead to more efficient and more personalized treatment.

The influence of new beta-adrenolytics nebivolol and carvedilol on intraocular pressure and iris blood flow in rabbits

BACKGROUND

The aim of this study was to assess the influence of propranolol, nebivolol, and carvedilol on intraocular pressure and blood flow in vessels of rabbit's (New Zealand White) eyeball.

METHODS

The study was carried out on New Zealand white rabbits. Intraocular pressure was measured with the applanation tonometer Möller-Wedel and Icare; blood flow was measured with Doppler Laser Blood Flow Monitor MBD3.

RESULTS

Following a single administration into a conjunctival sac, all drugs decreased intraocular pressure. Iris blood flow was decreased following administration of propranol, but increased by nebivolol and carvedilol. After single and repeated oral administration of nebivolol and carvedilol an IOP decrease was demonstrated, but with no effect of all applied doses on iris or retina/choroid blood flow.

CONCLUSION

Studies performed on an animal model indicate that it is possible to reduce the intraocular pressure and increase ocular blood flow in humans, following topical administration of carvedilol and nebivolol. Confirmation of those results in clinical trials may lead to development of a new anti-glaucoma treatment. Further clinical studies of long-term nebivolol and carvedilol are recommended. They are necessary for evaluation of usefulness of those drugs for selected groups of patients, for example those with glaucoma and arterial hypertension.

Effects of dorzolamide-timolol and brimonidine-timolol on retinal vascular autoregulation and ocular perfusion pressure in primary open angle glaucoma

PURPOSE

To assess whether dorzolamide 2%-timolol 0.5% (D/T) and/or brimonidine 0.2%-timolol 0.5% (B/T) alters retinal vascular autoregulation (RVA) and seated ocular perfusion pressure (sOPP) in primary open angle glaucoma (POAG) patients who demonstrate retinal vascular dysregulation (RVD) on timolol 0.5% alone.

METHODS

In this prospective, observer-masked, crossover study, 21 POAG patients with untreated intraocular pressure (IOP) >21 mmHg were treated for 6 weeks with timolol 0.5%. Subsequently, we measured inferior temporal retinal artery blood flow in the left eye with subjects seated and then while reclined for 30 min using the Canon Laser Blood Flowmeter. Subjects with a change in retinal blood flow in response to posture change outside of the range previously found in healthy subjects were designated as having RVD and randomized to either D/T or B/T for 6 weeks and re-tested. This was followed by treatment with the opposite medication.

RESULTS

Seven of the 21 subjects demonstrated RVD in response to posture change following timolol 0.5%. Multiple linear regression analysis indicated that lower sOPP was the main determinant of RVD (P=0.033). After treatment with D/T, all 7 converted from RVD to normal RVA status (P=0.001). Four of 6 subjects showed a similar return to normal RVA following B/T (P=0.066). Mid-morning sOPP was 41.1±5.5 mmHg post-timolol, 46.3±6.5 mmHg post-D/T, and 38.6±6.0 mmHg post-B/T (D/T vs. B/T, P=0.026).

CONCLUSIONS

D/T significantly improved RVA in POAG patients exhibiting RVD while on timolol 0.5% alone. D/T also increased sOPP compared to B/T. There was no significant difference (P=0.37) between D/T and B/T in improving RVA.

Effect of Lycium barbarum Polysaccharides on the expression of endothelin-1 and its receptors in an ocular hypertension model of rat glaucoma

Lycium barbarum, a traditional Chinese anti-aging herb, has been shown to protect retinal ganglion cells (RGCs) in a rat chronic ocular hypertension (COH) model. Here, we investigated the expression of endothelin-1 (ET-1), a strong vasoconstrictor, and its receptors, ETA and ETB, in the COH model and assessed the effects of Lycium barbarum on the ET-1 axis. Elevated intraocular pressure (IOP) was induced in the right eye of SD rats using argon laser photocoagulation. (1) The expression of ET-1, ETA and ETB in normal and COH retinas was studied. (2) Some COH rats were fed daily with Lycium barbarum Polysaccharides (LBP) using 1 mg/kg or phosphate-buffered saline (PBS) for 3 weeks (started 1 week before photocoagulation). The effects of LBP on the expression of ET-1 and its receptors, ETA and ETB, in COH retina were evaluated. A semi-quantitative analysis of staining intensity was used to evaluate the expression levels of ET-1, ETA and ETB in retinal vasculature. We found that (1) Under COH condition, the immunoreactivity of ET-1 was increased in retina associated with an increase of ETB receptor immunoreactivity and a decrease of ETA receptor immunoreactivity. (2) After feeding COH rats with LBP, the expression of ET-1 was decreased with an increase of ETA expression and a decrease of ETB expression in the retina, especially in RGCs. (3) By comparing the staining intensity in the vasculature of COH retina in LBP-fed group with PBS-fed group, there was a decrease in the expression of ET-1 and ETA and an increase in ETB. In summary, ET-1 expression was up-regulated in the retina in COH model. LBP could decrease the expression of ET-1 and modulate the expression of its receptors, ETA and ETB, under the condition of COH. The neuroprotective effect of LBP on RGCs might be related to its ability to regulate the ET-1-mediated biological effects on RGCs and retinal vasculature.

The effect of vasopressin on choroidal blood flow, intraocular pressure, and orbital venous pressure in rabbits

PURPOSE

To investigate the effects of arginine-vasopressin (AVP) on intraocular pressure (IOP), orbital venous pressure (OVP), and choroidal blood flow (ChorBF) regulation in anesthetized rabbits.

METHODS

Mean arterial pressure (MAP), IOP, and OVP were measured by direct cannulation of the central ear artery, the vitreous, and the orbital venous sinus, respectively. Laser Doppler flowmetry was used to record ChorBF. To change the perfusion pressure (PP), MAP was manipulated mechanically with occluders around the aorta and vena cava. In the first group of animals (n = 11) the dose-response relationship was measured. In the second group of animals (n = 8) pressure-flow relationships were determined at baseline and in response to intravenous application of a low (0.08 ng/kg/min) and a high (1.33 ng/kg/min) infusion rate of AVP.

RESULTS

AVP caused a dose-dependent increase of MAP and choroidal vascular resistance (ChorR), whereas IOP, OVP, ChorBF, and heart rate (HR) were decreased. In contrast to the high infusion rate, the low infusion rate of AVP had no effect on baseline ChorBF. However, the pressure-flow relationship was shifted downward significantly by both infusion rates at PP below baseline.

CONCLUSIONS

AVP reduces IOP and OVP significantly and is a potent vasoconstrictor in the choroidal vascular bed. In the choroid, the effect of AVP is not only dose-dependent, but also PP-dependent, which is indicated by the reduced perfusion relative to control with low-dosed AVP at low PP.

Ischemic tolerance protects the rat retina from glaucomatous damage

Glaucoma is a leading cause of acquired blindness which may involve an ischemic-like insult to retinal ganglion cells and optic nerve head. We investigated the effect of a weekly application of brief ischemia pulses (ischemic conditioning) on the rat retinal damage induced by experimental glaucoma. Glaucoma was induced by weekly injections of chondroitin sulfate (CS) in the rat eye anterior chamber. Retinal ischemia was induced by increasing intraocular pressure to 120 mmHg for 5 min; this maneuver started after 6 weekly injections of vehicle or CS and was weekly repeated in one eye, while the contralateral eye was submitted to a sham procedure. Glaucoma was evaluated in terms of: i) intraocular pressure (IOP), ii) retinal function (electroretinogram (ERG)), iii) visual pathway function (visual evoked potentials, (VEPs)) iv) histology of the retina and optic nerve head. Retinal thiobarbituric acid substances levels were assessed as an index of lipid peroxidation. Ischemic conditioning significantly preserved ERG, VEPs, as well as retinal and optic nerve head structure from glaucomatous damage, without changes in IOP. Moreover, ischemia pulses abrogated the increase in lipid peroxidation induced by experimental glaucoma. These results indicate that induction of ischemic tolerance could constitute a fertile avenue for the development of new therapeutic strategies in glaucoma treatment.

Dysfunctional regulation of ocular blood flow: A risk factor for glaucoma?

Primary open angle glaucoma (OAG) is a multifactorial optic neuropathy characterized by progressive retinal ganglion cell death and associated visual field loss. OAG is an emerging disease with increasing costs and negative outcomes, yet its fundamental pathophysiology remains largely undetermined. A major treatable risk factor for glaucoma is elevated intraocular pressure (IOP). Despite the medical lowering of IOP, however, some glaucoma patients continue to experience disease progression and subsequent irreversible vision loss. The scientific community continues to accrue evidence suggesting that alterations in ocular blood flow play a prominent role in OAG disease processes. This article develops the thesis that dysfunctional regulation of ocular blood flow may contribute to glaucomatous optic neuropathy. Evidence suggests that impaired vascular autoregulation renders the optic nerve head susceptible to decreases in ocular perfusion pressure, increases in IOP, and/or increased local metabolic demands. Ischemic damage, which likely contributes to further impairment in autoregulation, results in changes to the optic nerve head consistent with glaucoma. Included in this review are discussions of conditions thought to contribute to vascular regulatory dysfunction in OAG, including atherosclerosis, vasospasm, and endothelial dysfunction.

Effect of brimonidine on retinal blood flow autoregulation in primary open-angle glaucoma

PURPOSE

To determine whether topically applied brimonidine affects the retinal hemodynamic autoregulatory response to posture change in patients with normal tension glaucoma.

METHODS

Six patients with normal tension glaucoma (primary open-angle glaucoma and maximum untreated intraocular pressure <22 mmHg) in each eye were studied. We retrospectively reviewed retinal hemodynamic data acquired when the patients were off and on treatment with brimonidine 0.15% (twice a day, both eyes) during the course of their care. At each testing session, vessel diameter and blood speed at the same site along the inferior temporal retinal artery of 1 eye were measured while sitting, while reclining for 30 min, and again while sitting using a retinal laser Doppler instrument. Blood flow was computed automatically. Brachial artery blood pressure and heart rate were also measured. The Wilcoxon signed rank test was used to assess the statistical significance of the differences in each measured parameter while subjects were on and off brimonidine.

RESULTS

Off brimonidine, the mean blood flow rate increased by 68.0%±34.3% (range: +17% to +108%) after 30 min in reclined posture compared to baseline-seated measures. On brimonidine, the mean blood flow rate increased by 8.9%±16.8% (range: -9.7 to +28.0%) after 30 min in reclined posture compared to baseline-seated measures. The difference in the posture-induced changes for blood flow rate while on brimonidine compared to off brimonidine was statistically significant (P=0.027).

CONCLUSIONS

Off brimonidine, the patients exhibited marked increases in retinal blood flow while reclining. On brimonidine, the hemodynamic changes were consistent with normal autoregulatory control of retinal blood flow.

Clinical clues of vascular dysregulation and its association with glaucoma

Vascular dysregulation is a condition in which blood flow is not properly distributed to meet the demands of different tissues and could lead to overperfusion or underperfusion. Vascular dysregulation can be primary (occurring alone) or secondary (associated with other disorders, usually autoimmune diseases), and is caused by an imbalance between vasodilator and vasoconstrictor substances produced mainly locally by the vascular endothelium. In most circumstances of vascular dysregulation, the level of endothelin-1 is increased, leading to vasospasm. Vascular dysregulation is present in at least some subgroups of patients with glaucoma, and in these individuals it might have some important therapeutic consequences. In this article we review the evidence linking vascular dysregulation and glaucoma, and evaluate the clinical characteristics that might suggest the presence of vascular dysregulation in the glaucoma patient.

Protective effects of epigallocatechin gallate after UV irradiation in cultured human retinal pigment epithelial cells

Purpose

To evaluate the protective effects of Epigallocatechin gallate (EGCG) against UV irradiation in cultured human retinal pigment epithelial (RPE) cells.

Methods

UV irradiation was produced by a UV lamp for 30 seconds with an irradiance of 3.3 mW/cm². After 5 minutes and 1 hour, we administered different concentrations of EGCG (0, 5, 10, 15, 25, 50, 100 uM). The cell count was determined under a microscope using a counting chamber and the cell activity was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay.

Results

The cell count of cultured human RPE cells after UV irradiation was markedly increased in the EGCG administration group, compared with the non-administrated group. The cell activity of the cultured human RPE cells after UV irradiation was markedly increased in the EGCG administration group and was increased in a dose-dependent way as determined by the MTT assay.

Conclusions

The administration of EGCG increased the cell count and the cell activity after UV irradiation in cultured human retinal pigment epithelial cells; this suggests that EGCG provided protection against UV damage in cultured human retinal pigmented epithelial cells.

What is the link between vascular dysregulation and glaucoma?

The need of blood flow to different organs varies rapidly over time which is why there is sophisticated local regulation of blood flow. The term dysregulation simply means that blood flow is not properly adapted to this need. Dysregulative mechanisms can lead to an over- or underperfusion. A steady overperfusion may be less critical for long-term damage. A constant underperfusion, however, can lead to some tissue atrophy or in extreme situations to infarction. Unstable perfusion (underperfusion followed by reperfusion) leads to oxidative stress. There are a number of causes that lead to local or systemic vascular dysregulation. Systemic dysregulation can be primary or secondary of nature. A secondary dysregulation is due to other autoimmune diseases such as rheumatoid arthritis, giant cell arteritis, systemic lupus erythematodes, multiple sclerosis, colitis ulcerosa, or Crohns disease. Patients with a secondary vascular dysregulation normally have a high level of circulating endothelin-1 (ET-1). This increased level of ET-1 leads to a reduction of blood flow both in the choroid and the optic nerve head but has little influence on autoregulation. In contrast, primary vascular dysregulation has little influence on baseline ocular blood flow but interferes with autoregulation. This, in turn, leads to unstable oxygen supply, which seems to be a relevant component in the pathogenesis of glaucomatous optic neuropathy.

Retinal blood flow response to posture change in glaucoma patients compared with healthy subjects

PURPOSE

To characterize the retinal vascular autoregulatory response to ocular perfusion pressure (OPP) changes in patients with glaucoma and in healthy control subjects.

DESIGN

Observational cohort study.

PARTICIPANTS

Eighteen patients with open-angle glaucoma (OAG) and 8 control subjects, all females ages 40 to 60 years, were studied. Only subjects with known maximum intraocular pressure less than 22 mmHg in both eyes were included.

METHODS

Arterial diameter and blood speed in the inferior temporal retinal artery of the left eye were measured simultaneously at baseline while sitting, while reclining for approximately 30 minutes, and once again sitting using a retinal laser Doppler instrument. Blood flow rate was computed automatically. Brachial artery blood pressure and heart rate also were measured.

MAIN OUTCOME MEASURE

Change in blood flow rate while reclining for approximately 30 minutes compared with baseline blood flow rate measured while seated.

RESULTS

In control subjects, arterial diameter decreased by 7.5+/-3.4% (P = 0.0003) and blood speed increased by 24.6+/-10.8% (P = 0.004) while reclining compared with baseline. The concomitant change in the blood flow rate (6.5+/-12.0%; P = 0.15) compared with baseline was not statistically significant. In contrast, OAG patients showed a much broader range of blood flow changes in response to posture change (14.9+/-37.7%; P = 0.086) compared with baseline. Although there were no significant differences in the flow changes compared with baseline in either group, there was a significant difference in the variance of the blood flow changes in the OAG patients compared with the controls (P = 0.0025). Division of the OAG patients into subgroups revealed a significant (P = 0.031) association between baseline OPP and the retinal blood flow response to posture change.

CONCLUSIONS

The authors describe the hemodynamic details of retinal vascular autoregulation in response to posture-induced changes in OPP in healthy subjects and document the lack of such autoregulation in a selected group of patients with OAG.

Rho GTPase/Rho kinase inhibition as a novel target for the treatment of glaucoma

Rho kinase (ROCK1 and ROCK2) is a serine/threonine kinase that serves as an important downstream effector of Rho GTPase, and plays a critical role in regulating the contractile tone of smooth muscle tissues in a calcium-independent manner. Several lines of experimental evidence indicate that modulating ROCK activity within the aqueous humor outflow pathway using selective inhibitors could achieve very significant benefits for the treatment of increased intraocular pressure in patients with glaucoma. The rationale for such an approach stems from experimental data suggesting that both ROCK and Rho GTPase inhibitors can increase aqueous humor drainage through the trabecular meshwork, leading to a decrease in intraocular pressure. In addition to their ocular hypotensive properties, inhibitors of both ROCK and Rho GTPase have been shown to enhance ocular blood flow, retinal ganglion cell survival and axon regeneration. These properties of the ROCK and Rho GTPase inhibitors indicate that targeting the Rho GTPase/ROCK pathway with selective inhibitors represents a novel therapeutic approach aimed at lowering increased intraocular pressure in glaucoma patients.

Epigallocatechin gallate, an active ingredient from green tea, attenuates damaging influences to the retina caused by ischemia/reperfusion

The aim of this study was to examine whether the antioxidant epigallocatechin gallate (EGCG), a catechin-base flavonoid derived from green tea protects retina neurones in situ from ischemia/reperfusion and in vitro from an oxidative stress insult of hydrogen peroxide (H(2)O(2)). Similar results were obtained when rats were injected by two different regimes of EGCG. Ischemia was delivered by raising the intraocular pressure above the systolic blood pressure (120 mm Hg) generally for 45 min. The electroretinogram (ERG) was measured prior to ischemia and 5 days after reperfusion. Rats were killed 7 days after ischemia and processed for immunohistochemistry and for determining of mRNA and protein levels by RT-PCR and electrophoresis/western blotting, respectively. In addition, optic nerves 7 days after ischemia were subjected to protein analysis. Ischemia/reperfusion caused a significant reduction in the a- and b-wave amplitudes of the ERGs, a decrease in retinal ganglion cell and photoreceptor specific proteins and mRNAs, an increase in retinal caspase-3 mRNA and protein, an increase in retinal caspase-8 mRNA, an increase in retinal GFAP protein and mRNA and a decrease in optic nerve proteins associated with ganglion cell axons. All these changes were significantly counteracted by EGCG. Moreover, EGCG clearly blunted ischemia/reperfusion-induced changes in the localisation of retinal Thy-1 and ChAT immunoreactivities. EGCG also significantly reduced the apoptosis to retinal ganglion cells (RGC-5 cells) in culture caused by H(2)O(2). The results of the study demonstrate that EGCG provides protection to retinal neurones from oxidative stress and ischemia/reperfusion.