Activation of the coagulation cascade in untreated primary open-angle glaucoma

Complement System Proteins in the Human Aqueous Humor and Their Association with Primary Open-Angle Glaucoma

This study discovers the complement protein profile in the aqueous humor (AH) of human subjects and investigates its association with primary open-angle glaucoma (POAG) pathogenesis. Among the 32 complement proteins identified, 22 were highly abundant and detected in more than 50% of AH samples. The most predominant active complement proteins in the AH are C3, C4B, C4A, CFB, CFD, and C9. Additionally, the most prevalent complement regulators and receptors include CLU, SERPING1, F2, CFH, CFI, and VTN. Significant alterations in complement proteins were observed in individuals with POAG compared to those with cataracts. Specifically, complement protein F2 was upregulated, while C8G, C6, and CFH were downregulated in POAG samples. Stratification of the samples by race and sex revealed distinct alterations of complement proteins in patients with POAG. In the African American cohort, five complement proteins (C4A, C4B, F2, C7, and C3) were upregulated in POAG compared to cataract patients. In the Caucasian cohort, eight complement proteins (C3, SERPING1, CFI, CLU, CFHR1, C8G, C6, and CFH) were downregulated in the POAG samples compared to the cataract samples. Within the male cohort, three complement proteins (CLU, C6, and CFH) were downregulated in POAG patients compared to those with cataracts. Whereas, within the female cohort, two complement proteins (C4B and F2) were upregulated and one (C8G) downregulated in the POAG samples when compared to cataracts. Discerning these changes in the AH complement protein profile will assist in the development of tailored therapies to modulate the complement system for managing ocular disorders. These insights may also lead to novel biomarkers for diagnosing and monitoring disease progression.

The aqueous humor proteome of primary open angle glaucoma: An extensive review

BACKGROUND

We reviewed the literature on the aqueous humor (AH) proteome of primary open angle glaucoma (POAG) patients in order to obtain deeper insight into the pathophysiology of POAG.

METHODS

We searched Pubmed and Embase up to May 2019 for studies that compared AH protein composition between POAG (cases) and cataract (controls). Untargeted studies (measuring the whole proteome, by LC-MS/MS) were divided into two subgroups depending on the type of surgery during which POAG AH was collected: glaucoma filtration surgery (subgroup 1) or cataract surgery (subgroup 2). We reanalyzed the raw data (subgroup 1) or combined the reported data (subgroup 2) to perform GO enrichment (GOrilla) and pathway analysis (Pathvisio).

RESULTS

Out of 93 eligible proteomic studies, seven were untargeted studies that identified 863 AH proteins. We observed 73 differentially expressed proteins in subgroup 1 and 87 differentially expressed proteins in subgroup 2. Both subgroups were characterized by activation of the acute immune response, dysregulation of folate metabolism and dysregulation of the selenium micronutrient network. For subgroup 1 but not for subgroup 2, proteins of the complement system were significantly enriched.

CONCLUSION

AH proteome of POAG patients shows strong activation of the immune system. In addition, analysis suggests dysregulation of folate metabolism and dysregulation of selenium as underlying contributors. In view of their glaucoma surgery, POAG patients of subgroup 1 most likely are progressive whereas POAG patients in subgroup 2 most likely have stable POAG. The proteome difference between these subgroups suggests that the complement system plays a role in POAG progression.

Discovery and Validation of Circulating Hsa-miR-210-3p as a Potential Biomarker for Primary Open-Angle Glaucoma

Purpose

Blood-based examination tools for glaucoma diagnosis in clinical practice, which can be useful for screening patients when traditional ophthalmic examinations cannot be utilized, are not available thus far. This study aimed to identify circulating microRNAs (miRNAs) associated with primary open-angle glaucoma (POAG) and explore their utility as diagnostic markers.

Methods

A total of 136 POAG patients and controls were enrolled. Next-generation RNA sequencing was used to explore the expression profile of circulating miRNAs in the sequencing set, and potential miRNAs from independent samples in both the screening and validation sets were validated by quantitative real-time polymerase chain reaction (qRT-PCR). Receiver operating characteristic (ROC) analysis was used to evaluate the ability of certain miRNAs to distinguish POAG patients from control subjects.

Results

Using sequencing and qRT-PCR, hsa-miR-210-3p was found to be elevated in POAG patients in all sets. ROC analysis of the screening and validation sets revealed that hsa-miR-210-3p differentiated between POAG patients and matched controls with an area under the curve (AUC) of 0.846 (sensitivity: 84.6%; specificity: 80.8%) and 0.813 (sensitivity: 84.8%; specificity: 69.7%), respectively. In case of all nonsequencing participants, analysis revealed that hsa-miR-210-3p differentiated between severe POAG patients and controls with an AUC of 0.880 (sensitivity: 85.4%; specificity: 85.7%). In addition, the expression of hsa-miR-210-3p was associated with visual field defects of |mean deviation| (β = 0.237; P = 0.022) and average retinal nerve fiber layer thickness (β = -5.792; P = 0.014).

Conclusions

Circulating hsa-miR-210-3p may serve as a potential diagnostic marker for POAG (especially for severe POAG patients).

Parafoveal and optic disc vessel density in patients with obstructive sleep apnea syndrome: an optical coherence tomography angiography study

AIMS

To compare optic disc perfusion, radial peripapillary capillaries (RPC) and macular vascular density, between normal subjects and subjects with obstructive sleep apnea syndrome (OSAS) using spectral-domain OCT angiography (OCTA).

METHODS

Sixteen eyes of patients with mild OSAS, 17 eyes with moderate OSAS, 20 eyes with severe OSAS on polygraphy and 28 controls were evaluated with OCTA RT XR Avanti (AngioVue software, Optovue Inc., Fremont, CA). Optic nerve head (ONH), RPC and macular vessel density were measured. Clinical data, visual field parameters, and Spectral Domain OCT evaluation (retinal nerve fiber layer (RNFL) thickness and ganglion cell complex (GCC) thickness) were recorded for all patients.

RESULTS

ONH vascular flow (p = 0,396), RPC vascular density (automatized data "whole" p = 0,913, "peripapillary" p = 0,539, and segmented analysis with a topographic grid) and macular vascular density (foveal p = 0,484, parafoveal p = 0,491) were not significantly different between the four groups. FDT-Matrix™ and Humphrey 24/2 mean deviation were significantly lower in eyes with severe OSAS and were correlated to the apnea-hypopnea index. Retinal nerve fiber layer (RNFL) thickness, Cup/Disc ratio, rim area, and ganglion cell complex (GCC) were not significantly modified.

CONCLUSIONS

OCTA did not detect reduced ONH, RPC, neither macular blood vessel density in eyes with OSAS. The precise mechanisms that link OSAS with optic nerve pathologies remain unclear: our study was not able to demonstrate a vascular impact by OCTA examination.

Association between coagulation function and patients with primary angle closure glaucoma: a 5-year retrospective case-control study

OBJECTIVE

To evaluate the association between coagulation function and patients with primary angle closure glaucoma (PACG).

DESIGN

A retrospective, hospital-based, case-control study.

SETTING

Shanghai, China.

PARTICIPANTS

A total of 1778 subjects were recruited from the Eye & ENT Hospital of Fudan University from January 2010 to December 2015, including patients with PACG (male=296; female=569) and control subjects (male=290; female=623).

OUTCOME MEASURES

Sociodemographic data and clinical data were collected. The one-way analysis of variance test was used to compare the levels of laboratory parameters among the mild, moderate and severe PACG groups. Multivariate logistic regression analyses were performed to identify the independent risk factors for PACG. The nomogram was constructed based on the logistic regression model using the R project for statistical computing (R V.3.3.2).

RESULTS

The activated partial thromboplastin time (APTT) of the PACG group was approximately 4% shorter (p<0.001) than that of the control group. The prothrombin time (PT) was approximately 2.40% shorter (p<0.001) in patients with PACG compared with the control group. The thrombin time was also approximately 2.14% shorter (p<0.001) in patients with PACG compared with the control group. The level of D-dimer was significantly higher (p=0.042) in patients with PACG. Moreover, the mean platelet volume (MPV) of the PACG group was significantly higher (p=0.013) than that of the control group. A similar trend was observed when coagulation parameters were compared between the PACG and control groups with respect to gender and/or age. Multiple logistic regression analyses revealed that APTT (OR=1.032, 95% CI 1.000 to 1.026), PT (OR=1.249, 95% CI 1.071 to 1.457) and MPV (OR=1.185, 95% CI 1.081 to 1.299) were independently associated with PACG.

CONCLUSION

Patients with PACG had a shorter coagulation time. Our results suggest that coagulation function is significantly associated with patients with PACG and may play an important role in the onset and development of PACG.

Perspectives on biomechanical growth and remodeling mechanisms in glaucoma()

Glaucoma is a blinding diseases in which damage to the axons results in loss of retinal ganglion cells. Experimental evidence indicates that chronic intraocular pressure elevation initiates axonal insult at the level of the lamina cribrosa. The lamina cribrosa is a porous collagen structure through which the axons pass on their path from the retina to the brain. Recent experimental studies revealed the extensive structural changes of the lamina cribrosa and its surrounding tissues during the development and progression of glaucoma. In this perspective paper we review the experimental evidence for growth and remodeling mechanisms in glaucoma including adaptation of tissue anisotropy, tissue thickening/thinning, tissue elongation/shortening and tissue migration. We discuss the existing predictive computational approaches that try to elucidate the potential biomechanical basis of theses growth and remodeling mechanisms and highlight open questions, challenges, and avenues for further development.

Glaucoma and obstructive sleep apnoea syndrome

Glaucoma is increasingly recognized as a manifestation of both ocular and systemic risk factors. A number of disorders associated with reduced blood flow and ischaemia, collectively termed vascular risk factors, such as migraine, Raynaud's phenomenon, atrial fibrillation and reduced nocturnal blood pressure, lead to decreased ocular perfusion pressure. During sleep, alterations occur in cardiovascular physiology that are balanced by autoregulation to maintain homeostasis. However, in obstructive sleep apnoea (OSA), the normal physiological balance is upset. A potentially modifiable risk factor, OSA has been increasingly associated with glaucoma independent of intraocular pressure. OSA may alter blood flow to the optic nerve head and, in combination with other predisposing factors, lead to decreased ocular perfusion pressure. This in turn may directly affect the optic nerve or it may indirectly increase its susceptibility to other insults. The purpose of this review is to shed light on the association between OSA and glaucoma.

Glaucomatous cupping of the lamina cribrosa: a review of the evidence for active progressive remodeling as a mechanism

The purpose of this review is to examine the literature in an attempt to elucidate a biomechanical basis for glaucomatous cupping. In particular, this work focuses on the role of biomechanics in driving connective tissue remodeling in the progression of laminar morphology from a normal state to that of an excavated glaucomatous state. While there are multiple contributing factors to the pathogenesis of glaucoma, we focus on laminar extracellular matrix (ECM) remodeling in glaucoma and the feedback mechanisms and signals that may guide progressive laminar cupping. We review the literature on the potential mechanisms of glaucomatous changes in the laminar ECM at the anatomic, structural, cellular and subcellular levels in the context of the biomechanical paradigm of glaucomatous onset and progression. Several conclusions can be drawn from this review. First, extensive remodeling of the lamina cribrosa ECM occurs in primary open angle glaucoma. Second, there is surprisingly little evidence to support acute mechanical damage to the lamina as the principal mechanism of cupping. Third, ONH astrocytes and lamina cribrosa cells can sense their mechanical environment and respond to mechanical stimuli by remodeling the ECM. Fourth, there is evidence suggesting that chronic remodeling of the lamina results in a progressive posterior migration of the laminar insertion into the canal wall, which eventually results in the posterior lamina inserting into the pia mater. Finally, modeling studies suggest that laminar remodeling may be a biomechanical feedback mechanism through which cells modify their environment in an attempt to return to a homeostatic mechanical environment. It is plausible that biomechanics-driven connective tissue remodeling is a mechanism in the progression of laminar morphology from a normal state to that of a cupped, excavated glaucomatous state.

Prevalence of normal tension glaucoma in obstructive sleep apnea syndrome patients

PURPOSE

To explore the prevalence of normal tension glaucoma (NTG) among patients with obstructive sleep apnea syndrome (OSAS) and to examine OSAS as a risk factor of NTG.

PATIENTS AND METHODS

Fifty-one consecutive white patients with OSAS were compared with 40 healthy subjects. All the study subjects underwent blood gas analysis, polysomnography, oxyhemoglobin saturation, and an ophthalmologic examination including visual field, visually evoked potential (VEP), and pattern electroretinography (PERG) and disc analysis with the Heidelberg Retina Tomograph II.

RESULTS

Three of 51 OSAS patients (5.9%) had NTG. No patient in the control group had OSAS or NTG. The severity of OSAS correlated with intraocular pressure, the mean deviation of the visual field, the cup/disk ratio and the mean of the retinal nerve fiber layer thickness (P<0.01 to 0.001). Apnea hypopnea index and intraocular pressure were significantly greater in OSAS patients with abnormal VEP and PERG, compared to those with normal PERG and VEP.

CONCLUSIONS

The present study suggests that the prevalence of NTG in our OSAS patients is higher than expected in a white population of the same age and that OSAS may be an important risk factor for NTG. Our data underline the importance of taking an accurate sleep history from patients with NTG and referring patients with sleep disturbance for polysomnography.

Prevalence of serum autoantibodies and paraproteins in patients with glaucoma

PURPOSE

To investigate the possible link between normal tension glaucoma (NTG) and autoimmunity.

METHODS

We studied the serum of 95 patients: 31 with NTG, 32 with primary open-angle glaucoma (POAG), and 32 age- and sex-matched controls. Blood was drawn from each patient and serum was examined for the presence of antinuclear antigens (ANA), autoantibodies to extractable nuclear antigens (ENA), anti-double-strand DNA, serum protein electrophoresis, and immunoglobulin (IgG, IgA, and IgM) levels.

RESULTS

In the NTG group, the relative risks for ANA and ENA positivity were 2.5 and 4.4 times, respectively, that of the control group. There was a statistically significant difference between IgA levels in the NTG and control group (P=0.024), but there was no statistically significant difference between both groups regarding IgM or IgG levels. In the POAG group, the relative risks for ANA and ENA positivity were 0.77 and 2.9 times, respectively, that of the control group. The relative risk for detection of paraprotein in the POAG group was 0.97 times that of the control group. Also, there was a statistically significant difference between IgA levels in the POAG and control group (P=0.011), but there was no statistically significant difference between both groups regarding IgM or IgG.

CONCLUSION

These results support the hypothesis that humoral immune mechanisms may have a role in the pathogenesis of NTG.

Nitric oxide synthase in retina and optic nerve head of rat with increased intraocular pressure and effect of timolol

We investigated the expression of nitric oxide synthase (NOS) isoforms -1, -2 and -3 in the retina and optic nerve head (ONH) in an experimental rat model of elevated intraocular pressure (IOP) before and after treatment with timolol, to assess whether its neuroprotective action is associated with the activity of these enzymes. Episcleral vein cauterization in unilateral eyes of Wistar rats was performed to produce elevated IOP. Histological sections of retina and ONH from animals with normal IOP, with elevated IOP, and elevated IOP treated with timolol, were studied by immunohistochemistry with antibodies to NOS-1, NOS-2, and NOS-3. In the control rats, NOS-1 was localized to photoreceptor inner segments, amacrine cells and bipolar cells in the retina, and in astrocytes, pericytes and vascular nitrergic terminals in the ONH. NOS-3 immunostaining localized to the endothelial cells. The rats with elevated IOP showed increased expression of NOS-1 in the plexiform layers of the retina and reactive astrocytes in the ONH. These cells also showed NOS-2 positivity. The rats treated with timolol showed reduced expression of NOS-1 in the retina and ONH. NOS-2 was only detected in a few groups of astrocytes in the ONH. NOS-3 was unchanged in both elevated IOP and timolol-treated groups. These results show that excessive levels of NO synthesized by the NOS-1 and -2 isoforms, considered neurotoxic, might contribute to the progressive lesions of retinal ganglion cell axons. Their reduction after treatment suggests a possible neuroprotective effect of timolol in neurons exposed to excessive amounts of NO.

Vasospasm in Glaucoma: Clinical and Laboratory Aspects

During the last decade, the presumed etiology of glaucoma has moved from a pure pressure concept to a combined mechanical and vascular theory. Evidence of a localized vascular insufficiency leading to perfusion deficits of ocular structures, including the optic nerve head, the retina, the choroid, and the retrobulbar vessels, is now clear. This article evaluates the role of vasospasm as the primary cause of such a vascular failure. The role of both ocular and systemic vasospasms and their clinical correlations are discussed. At a cellular level, the function of the modulating role of the vascular endothelium is reviewed. Evidence of abnormalities of the vascular endothelium and its vasoactive peptides as a conduit for vasospasm is mounting. Herein lies exciting prospects for potential pharmacologic targets in future glaucoma management.

A Sick Eye in a Sick Body? Systemic Findings in Patients with Primary Open-angle Glaucoma

Despite intense research, the pathogenesis of primary open-angle glaucoma (POAG) is still not completely understood. There is ample evidence for a pathophysiological role of elevated intraocular pressure; however, several systemic factors may influence onset and progression of the disease. Systemic peculiarities found in POAG include alterations of the cardiovascular system, autonomic nervous system, immune system, as well as endocrinological, psychological, and sleep disturbances. An association between POAG and other neurodegenerative diseases, such as Alzheimer disease and Parkinson disease, has also been described. Furthermore, the diagnosis of glaucoma can affect the patient's quality of life. By highlighting the systemic alterations found in POAG, this review attempts to bring glaucoma into a broader medical context.

Coincidence of normal tension glaucoma, progressive sensorineural hearing loss, and elevated antiphosphatidylserine antibodies

BACKGROUND

Recently, in patients with normal tension glaucoma (NTG) elevated levels of antiphosphatidylserine antibodies (APSA), a subgroup of antiphospholipid antibodies (APLA) were found. Progressive sensorineural hearing loss (PSHL) is associated with autoimmune diseases and also the presence of APLA.

METHODS

To investigate a possible association between NTG and PSHL, 34 patients (age range 31-81 years) with NTG were evaluated for evidence of audiovestibular disorders. Besides ophthalmological standard examinations (slit lamp, IOP, funduscopy, perimetry) scanning laser tomography and polarimetry were performed. From all patients' audiograms, stapedial thresholds and otoacoustic emissions were obtained. The serological testing of patients and controls (40 healthy blood donors older than 50 years) concerned IgG and IgM levels of antibodies against phosphatidylserine (APSA) and beta2 glycoprotein.

RESULTS

23 of 34 NTG patients had hearing loss (PSHL n = 11; presbyacusis n = 12). The NTG patients had significantly higher APSA levels than controls. Elevated APSA concentrations were significantly more frequent in patients with NTG and hearing loss compared with NTG patients with normacusis.

CONCLUSIONS

These findings show that NTG and hearing loss have a high coincidence. The elevated APSA levels may indicate an association with similar systemic autoimmune processes.

The phenotype of normal tension glaucoma patients with and without OPA1 polymorphisms

AIM

Polymorphisms in OPA1, the gene responsible for autosomal dominant optic atrophy, were recently found to be strongly associated with normal tension glaucoma (NTG). The aim of this study was to determine whether OPA1 polymorphisms affect the phenotype of NTG patients.

METHODS

A retrospective analysis was performed of 108 well characterised NTG patients who had been genotyped for OPA1 variations, and who had previously undergone automated perimetry and Heidelberg retina tomography (HRT). 25 NTG patients had the at-risk OPA1 genotype (IVS 8 +4 C/T; +32 T/C) and 83 NTG patients did not. Differences between groups were sought in a wide range of structural, psychophysical, and demographic factors. These included sex, age at diagnosis, family history of glaucoma, history of ischaemic risk factors and vasospasm, laterality of glaucoma, presenting and highest diurnal intraocular pressure (IOP), initial cup-disc (CD) ratio, baseline visual field global indices, and optic disc parameters as measured by HRT. For a subgroup of patients with at least 5 years of follow up and 10 visual field tests, pointwise linear regression analysis (PROGRESSOR for Windows software) was applied to the visual field series.

RESULTS

There was no significant difference in the two groups with respect to sex, age at diagnosis, family history of glaucoma, history of ischaemic risk factors and vasospasm, or laterality of glaucoma. The comparison of IOP, CD ratio and visual field global indices, MD and CPSD in the two groups showed no significant difference. There were no differences in the mean values for any of the HRT parameters analysed. For the subgroup of patients with at least 5 years of follow up, there was also no significant difference in the number of patients with progressing locations, the mean number of progressing locations per subject, the mean slope of the progressing locations or the mean slope for whole visual field.

CONCLUSIONS

The absence of phenotypic differences in normal tension glaucoma patients with and without the OPA1 polymorphisms IVS 8 +4 C/T; +32 T/C suggest that these OPA1 polymorphisms do not underlie any major phenotypic diversity in these patients.

Plasma vascular endothelial growth factor, soluble VEGF receptor FLT-1, and von Willebrand factor in glaucoma

AIM

To investigate plasma indices of vascular permeability (vascular endothelial growth factor, VEGF-also an index of angiogenesis, as well as the soluble receptor for VEGF, sFlt-1) and endothelial damage/dysfunction (von Willebrand factor, vWf) in glaucoma.

METHODS

Citrated plasma was assayed for VEGF, sFlt-1, and vWf (all ELISA) in a cross sectional study of 50 patients (20 male; mean age 63.9 years, SD 10.5) with glaucoma: 26 had normal tension glaucoma (NTG) and 24 had primary open angle glaucoma (POAG), who were compared with 26 healthy controls (mean age 73.4 years, SD 9.2).

RESULTS

Median (interquartile range, IQR) levels of VEGF were significantly elevated in patients with NTG and POAG compared to healthy controls (Kruskal-Wallis test, p<0.001). Similarly, mean (SD) vWF levels were abnormal in NTG and POAG compared to healthy controls (one way ANOVA, p<0.001). Median levels of sFlt-1 were significantly lower in patients with NTG and POAG, when compared to healthy controls (Kruskal-Wallis test, p<0.001; p<0.05 with Tukey's post hoc test for controls v POAG). There were no significant differences in VEGF, sFlt-1 or vWf levels between the NTG and POAG groups (Tukey's test, all p=NS). In both NTG and POAG groups, there was a significant correlation between VEGF and sFlt-1 (Spearman, NTG: r=0.6517, p=0.001; POAG: r=0.6017, p=0.008). There were no significant correlations between VEGF and sFlt-1, or with vWf among the controls.

CONCLUSIONS

The pathogenesis of optic nerve damage in both NTG and POAG may be associated with abnormal vascular permeability and endothelial damage/dysfunction, as indicated by abnormal plasma VEGF and vWf levels in these patients.

The impact of ocular blood flow in glaucoma

Two principal theories for the pathogenesis of glaucomatous optic neuropathy (GON) have been described--a mechanical and a vascular theory. Both have been defended by various research groups over the past 150 years. According to the mechanical theory, increased intraocular pressure (IOP) causes stretching of the laminar beams and damage to retinal ganglion cell axons. The vascular theory of glaucoma considers GON as a consequence of insufficient blood supply due to either increased IOP or other risk factors reducing ocular blood flow (OBF). A number of conditions such as congenital glaucoma, angle-closure glaucoma or secondary glaucomas clearly show that increased IOP is sufficient to lead to GON. However, a number of observations such as the existence of normal-tension glaucoma cannot be satisfactorily explained by a pressure theory alone. Indeed, the vast majority of published studies dealing with blood flow report a reduced ocular perfusion in glaucoma patients compared with normal subjects. The fact that the reduction of OBF often precedes the damage and blood flow can also be reduced in other parts of the body of glaucoma patients, indicate that the hemodynamic alterations may at least partially be primary. The major cause of this reduction is not atherosclerosis, but rather a vascular dysregulation, leading to both low perfusion pressure and insufficient autoregulation. This in turn may lead to unstable ocular perfusion and thereby to ischemia and reperfusion damage. This review discusses the potential role of OBF in glaucoma and how a disturbance of OBF could increase the optic nerve's sensitivity to IOP.

Blood flow in the optic nerve head and factors that may influence it

In the recent past there has been great interest in the blood supply of the optic nerve head (ONH), how to evaluate ONH blood flow, and what factors influence it, in health and disease. This is because evidence has progressively accumulated that there is vascular insufficiency in the ONH in both anterior ischemic optic neuropathy (AION) and glaucomatous optic neuropathy (GON)-two major causes of blindness or of seriously impaired vision in man. For the management and prevention of visual loss in these two disorders, a proper understanding of the factors that influence the blood flow in the ONH is essential. The objective of this paper is, therefore, to review and discuss all these factors. The various factors that influence the vascular resistance, mean blood pressure and intraocular pressure are discussed, to create a better basic understanding of the ONH blood flow, which may help us toward a logical strategy for prevention and management of ischemic disorders of the ONH.

Three Common Assumptions About Ocular Blood Flow and Glaucoma

Although substantial indirect evidence exists to link altered ocular blood flow to glaucoma, it must be remembered that the validity of investigations in this area depends on acceptance of three basic assumptions: 1) ischemia directly causes or increases the susceptibility of the optic nerve to glaucomatous damage; 2) optic nerve vascular anatomy and physiology allows identification of the critical vascular beds in optic nerve disease; and 3) current measurement techniques provide the ability to monitor important vascular beds. The hypotheses underlying these assumptions are examined.

Normal tension glaucoma and primary open angle glaucoma associated with increased platelet aggregation

On purpose of the present study was to evaluate platelet aggregation and fibrinolytic systems in patients with normal tension glaucoma (NTG) or primary open angle glaucoma (POAG). For platelet aggregation, we photoelectrophotometrically investigated adenosine diphosphate (ADP) or collagen-induced platelet aggregation in consecutively selected patients with glaucoma (22 patients with NTG and 13 patients with POAG) and 42 glaucoma free control subjects with normal ocular findings. The aggregation patterns of the patients' platelets reacted abnormally to ADP 1 microM or collagen 0.5 microg/ml as evidenced by secondary aggregation were compared with those of control subjects. For blood coagulative and fibrinolytic systems, we measured prothrombin time, activated partial thromboplastin time, fibrinogen, thrombin-antithrombin III complex (TAT), alpha2 plasmin inhibitor-plasmin complex. Seventeen of 22 patients (77%) with NTG and 5 of 13 patients (38%) with POAG showed abnormal secondary aggregation. A significant difference was observed between the two groups. No control subjects showed abnormal secondary aggregation. In the fibrinolytic test, all the parameters examined showed within normal ranges, although the log10(TAT) value was higher in NTG than in POAG. Results of the present study suggested that increased platelet aggregation as defined by ADP or collagen induced abnormal secondary aggregation in vitro is frequently associated with glaucoma patients and this tendency is more apparent in NTG than that in POAG.

Optic nerve head structure in glaucoma: astrocytes as mediators of axonal damage

Increased intraocular pressure (IOP) is recognised as the principal risk factor for the development of glaucomatous cupping of the optic disc. The hypothesis that it disrupts the function of retinal ganglion cell axons by increasing mechanical forces on the lamina cribrosa of the optic nerve head has received considerable experimental support. However, many patients with glaucoma will have progressive cupping even though the IOPs remain within the normal range, suggesting that mechanical compression is unlikely to be the sole cause of optic nerve damage. Clinical studies have emphasised the role of other factors, such as optic nerve head ischaemia, in generating optic disc cupping. One of the outstanding problems in understanding optic nerve head dysfunction in glaucoma has been the elucidation of the pathways that could integrate the effects of IOP and ischaemia to generate the characteristic changes seen. This review considers the role that optic nerve head astrocytes might play in the initiation of axon damage, based on the hypothesis that these cells are sensitive to mechanical or ischaemic factors and are important for the maintenance of retinal ganglion physiology. It discusses their role in the remodelling of the structure of the lamina cribrosa and the effect that this might have on axon function. Recent evidence has shown that the modulation of astrocyte activity, for example by the reduction of the production of nitric oxide, may prevent retinal ganglion cell death in ocular hypertension. The possibility that astrocyte-axon interactions are important in the development of glaucomatous optic neuropathy suggests new avenues of therapeutic intervention, not related to the control of IOP, that would prevent retinal ganglion cell death in glaucoma.

Optic nerve blood flow in glaucoma

Vascular disorders of the anterior optic nerve, historically, have been described as potential etiologic factors in the development of glaucomatous optic neuropathy. During the past several decades, clinical and experimental evidence of the involvement of vascular aberrations as a potential causative factor or associated risk factor have increased. However, the direct evidence that optic nerve ischemia contributes to glaucomatous optic neuropathy remains limited. Several questions about our current knowledge arise. Can ischemia alone or in combination with other factors cause glaucomatous optic neuropathy? Does our current knowledge of the vascular anatomy and physiology of the optic nerve allow us to understand vascular changes observed in individuals with glaucoma? Can we rely on current measurement techniques to assess and monitor the vascular beds of the optic nerve? This article summarizes the complex nature of the microcirculation in the anterior optic nerve, discusses the possible contribution of vascular factors in the development of glaucoma optic neuropathy, and examines the measurement techniques used in current studies.

The role of age and cardiovascular disease in glaucomatous optic neuropathy

The role of systemic cardiovascular disorders in glaucomatous optic neuropathy was studied experimentally in rhesus monkeys and clinically in humans. These studies suggest that, in the multifactorial phenomenon of glaucomatous optic neuropathy, among other risk factors, age, cardiovascular disease and nocturnal arterial hypotension may play an important role in the development and progression of glaucomatous optic neuropathy in many cases, independent of intraocular pressure. In glaucomatous optic neuropathy, age may be an indirect index of cardiovascular disease rather than an independent factor per se. Nocturnal arterial hypotension, particularly among hypertensive patients taking oral hypotensive medication, may be an important risk factor. Because 24-hour ambulatory blood pressure monitoring is becoming popular among ophthalmic researchers, multiple confounding factors in ambulatory blood pressure monitoring in patients with optic nerve head ischemic disorders that can produce misleading information are discussed.

A comparison of ocular blood flow in untreated primary open-angle glaucoma and ocular hypertension

PURPOSE

To compare ocular blood flow in untreated primary open-angle glaucoma and ocular hypertension using scanning laser Doppler flowmetry and pulsatile ocular blood flow.

METHOD

Fourteen ocular hypertensive subjects and 10 patients with primary open-angle glaucoma were matched for intraocular pressure, mean arterial blood pressure, and age. They had scanning laser Doppler flowmetry images taken centered on the optic disk. Pulsatile ocular blood flow readings were performed in sitting, standing, and supine positions. No subjects were receiving topical antiglaucoma treatment, systemic beta-blockers, calcium antagonists, or nitrates at the time of measurement.

RESULTS

Laser Doppler flowmetry results showed a significant reduction in blood velocity, volume, and flow at the lamina cribrosa and the temporal neuroretinal rim in glaucoma compared to ocular hypertension (P < .05). No difference was found between the groups at the nasal neuroretinal rim or the nasal juxtapapillary retina. There was a significant increase in minimum velocity (P = .03) at the temporal juxtapapillary retina in glaucoma compared to ocular hypertension. The ocular pulse amplitude, pulse volume, and pulsatile ocular blood flow were significantly lower (P < .05) in the glaucoma group compared to ocular hypertension in sitting and standing positions.

CONCLUSION

Having controlled for factors known to affect perfusion pressure, we found evidence of reduced ocular blood flow in primary open-angle glaucoma compared with ocular hypertension. Our findings indicate a reduction in choroidal and short posterior ciliary artery circulation in primary open-angle glaucoma. Whether these changes in blood flow are a cause or a consequence of glaucomatous optic atrophy is still unknown.

Pulsatile ocular blood flow investigation in asymmetric normal tension glaucoma and normal subjects

AIMS

This study was designed to investigate pulsatile ocular blood flow (POBF) in normal tension glaucoma (NTG) patients and in normal controls. NTG patients with unilateral field loss were evaluated to compare POBF values between eyes with and without field loss.

METHODS

POBF measurements from more than 1500 subjects were collected during a period of 6 months from six optometric centres. Subjects with systemic vascular diseases (such as systemic hypertension and diabetes), ophthalmic diseases, a positive family history of glaucoma, and those individuals receiving treatment with systemic beta blockers were excluded on the basis of a questionnaire. For comparison, 95 NTG patients with unilateral field loss, selected from 403 consecutive patients with NTG, underwent POBF testing. For each individual age, sex, intraocular pressure, refraction, and pulse rate were entered into a database.

RESULTS

Data from 777 subjects were included in the analysis. POBF measurements of patients and subjects were compared allowing for differences in age, sex, intraocular pressure, refraction, and pulse rate. POBF was significantly lower in eyes of NTG patients with and without field loss (p < 0.001 and p = 0.01 respectively). Eyes of NTG patients with field loss showed significantly lower POBF than the contralateral eyes with normal field (p < 0.001).

CONCLUSIONS

POBF was significantly lower in eyes of NTG patients with and without field loss than in normal subjects, suggesting that differences in ocular blood perfusion are relevant to the development of NTG and are detectable from the early stage of the disease. Furthermore, the finding of lower POBF in NTG eyes with field loss than in the contralateral eyes with normal field suggests that haemodynamic differences between fellow eyes contribute to determine the side of onset of the disease.