Ocular perfusion pressure and glaucoma: clinical trial and epidemiologic findings

[Ocular hypotensive effect of systemic beta-blockers in patients with primary glaucoma and arterial hypertension]

AIM

to evaluate the ocular hypotensive efficacy of systemic beta-blockers in primary glaucoma patients suffering from arterial hypertension (AH).

MATERIAL AND METHODS

The study included 29 patients with POAG (58 eyes) aged from 47 to 83 years. Patients with stage I-III POAG received instillations of prostaglandin analogs and carbonic anhydrase inhibitors. All POAG patients also suffered from arterial hypertension and were prescribed selective beta-blockers (metoprolol, bisoprolol, or nebivalol) as monotherapy or as part of combination therapy (if the target arterial pressure had not been achieved under the initial treatment). After the start of oral beta-blockers therapy, the patients were re-examined at 2 and 4 weeks, 3 months, 6 months, and 1 year.

RESULTS

A clinically significant reduction of IOP in the most seriously affected eye - by 3.3 mmHg (p<0.05), or 14% - occurred four weeks after the start of selective beta-blockers. Over three months of combination therapy, IOP in the 'worst' eye decreased by 4.4 mmHg (18.5%). At 1 year, IOP in the 'worst' eye was 6.2 mmHg (26%) lower than at baseline (p<0.05).

CONCLUSION

Aged and senile patients with primary glaucoma usually suffer from polypathy (on average, they have 6.3±0.6 concurrent somatic diseases). To reduce the risk of polypharmacy and the frequency of side effects in the treatment of POAG and AH patients, it is advised that the treatment includes oral selective beta-blockers able to provide target levels of arterial pressure and IOP. In this study, oral beta-blockers in POAG and AH patients enabled IOP reduction as great as 18.5%-26% of baseline values over a 1-year follow-up period.

Presence and Risk Factors for Glaucoma in Patients with Diabetes

Diabetes mellitus represents a growing international public health issue with a near quadrupling in its worldwide prevalence since 1980. Though it has many known microvascular complications, vision loss from diabetic retinopathy is one of the most devastating for affected individuals. In addition, there is increasing evidence to suggest that diabetic patients have a greater risk for glaucoma as well. Though the pathophysiology of glaucoma is not completely understood, both diabetes and glaucoma appear to share some common risk factors and pathophysiologic similarities with studies also reporting that the presence of diabetes and elevated fasting glucose levels are associated with elevated intraocular pressure-the primary risk factor for glaucomatous optic neuropathy. While no study has completely addressed the possibility of detection bias, most recent epidemiologic evidence suggests that diabetic populations are likely enriched with glaucoma patients. As the association between diabetes and glaucoma becomes better defined, routine evaluation for glaucoma in diabetic patients, particularly in the telemedicine setting, may become a reasonable consideration to reduce the risk of vision loss in these patients.

Relationship between systemic hypertension, perfusion pressure and glaucoma: a comparative study in an adult Indian population

AIMS

To study the relationship between blood pressure (BP), intraocular pressure (IOP), mean ocular perfusion pressure (MOPP) and primary open angle glaucoma (POAG) in patients with hypertension and compare it to a control group of normotensives.

DESIGN

Cross-sectional observational study.

MATERIALS AND METHODS

A total of 108 subjects with primary hypertension and 100 age-matched controls without hypertension were enrolled for the study. IOP measurement using Noncontact Tonometer and dilated fundus evaluation using + 90 D lens were done for all cases. Single recording of BP was taken. Gonioscopy, Humphrey's central visual fields, optical coherence tomography and pachymetry were done for all subjects with IOP > 21 mm Hg or C: D ratio ≥ 0.5 or asymmetry of > 0.2.

STATISTICAL ANALYSIS

Univariate and multivariate multinomial regression models were used to determine the association between covariates and risk of glaucoma or glaucoma suspect.

RESULTS

There was no difference in the glaucoma status between subjects with and without hypertension. Subjects on antihypertensive medications were 1΍ times more likely to have suspicious glaucoma (odds ratio [OR] =1.56] and nearly twice as likely to have POAG (OR = 1.85). In addition, we found a 31% and 12% reduction in risk of having POAG (95% confidence interval [CI] =13-45%, P = 0.001) and glaucoma suspect (95% CI = 2-21%, P = 0.03) respectively with every 1 mm Hg increment in MOPP.

CONCLUSION

Subjects on antihypertensive medications are more likely to have either glaucoma or glaucoma suspect, and higher ocular perfusion pressure offers relative protection from glaucomatous damage.

Changes in choroidal thickness after intraocular pressure reduction following trabeculectomy

PURPOSE

To evaluate the changes of peripapillary and subfoveal choroidal thickness (CT) after trabeculectomy.

METHODS

Prospective longitudinal study included 37 eyes with open-angle glaucoma. The subfoveal and peripapillary CT was measured using enhanced depth imaging spectral domain optical coherence tomography before trabeculectomy and 1 week, 3 and 6 months postoperatively. The associations between changes in the CT, intraocular pressure (IOP) and axial length were analysed.

RESULTS

The medium subfoveal CT (IQR) increased from 182 (97) μm at baseline to 267 (107) μm 1 week, 213 (97) μm 3 months and 207 (91) μm 6 months postoperatively (p < 0.001). The peripapillary CT increased in all four quadrants at all follow-ups (p < 0.05). The subfoveal and peripapillary choroidal thickening correlated with the magnitude of IOP reduction (p < 0.05) and axial length shortening (p < 0.01) during whole follow-up period. There was a peripapillary CT increase of 2.9 μm per mmHg of IOP reduction (p < 0.001, CI 1.5-4.4) and 4.8 μm per mm of baseline axial length (p = 0.049, CI 0.03-9.6) 1 week postoperatively after adjustment for baseline IOP. Six months postoperatively, the decrease in axial length was the only factor associated with peripapillary choroidal thickening (p = 0.031; regression coefficient: 73.29 μm/mm, CI 7.1-139.5).

CONCLUSION

Intraocular pressure (IOP) reduction after trabeculectomy caused the increase in subfoveal and peripapillary CT for at least 6 months postoperatively correlating with greater IOP reduction and axial length shortening. In the long term, the decrease in axial eye length, but not IOP, was the only factor to be associated with peripapillary choroidal thickening.

Twenty-four-hour intraocular pressure and ocular perfusion pressure characteristics in newly diagnosed patients with normal tension glaucoma

PurposeTo determine the mean 24-h intraocular pressure (IOP) and mean ocular perfusion pressure (MOPP) characteristics of newly diagnosed, previously untreated, Caucasian, normal tension glaucoma (NTG) patients and to identify relationships between these features and visual field (VF) loss at diagnosis.MethodsConsecutive newly diagnosed NTG patients underwent 24-h habitual IOP and blood pressure (BP) monitoring. Parameters from pooled measurements obtained in the sitting (0800-2200 hours) and supine (1200-0600 hours) positions were compared and associations were sought with VF mean deviation (MD) and pattern standard deviation (PSD).ResultsSixty-two Caucasian NTG patients (24 men and 38 women) successfully completed circadian IOP and BP monitoring. In habitual position, 8 subjects (12.9%) exhibited a diurnal acrophase, 42 subjects (67.7%) demonstrated a nocturnal acrophase, one subject (1.6%) showed a flat rhythm and 11 patients (17.7%) revealed a biphasic/polyphasic rhythm. Nighttime MOPP values (supine position) were significantly greater than diurnal values (sitting position); (P<0.001). No association could be demonstrated between glaucomatous damage, as indicated by VF parameters, and either mean habitual 24-h IOP (P=0.20 and P=0.12 for MD and PSD, respectively), or habitual 24-h MOPP (P=0.96 and 0.29, for MD and PSD, respectively).ConclusionsIn this cohort of Caucasian NTG patients, most patients exhibited a nocturnal IOP acrophase when evaluated in a habitual position. No association was found between 24-h IOP or MOPP and VF damage.

Understanding Glaucomatous Optic Neuropathy: The Synergy Between Clinical Observation and Investigation

Glaucoma is a complex disorder of aging defined by the death of retinal ganglion cells and remodeling of connective tissues at the optic nerve head. Intraocular pressure-induced axonal injury at the optic nerve head leads to apoptosis. Loss of retinal ganglion cells follows a slowly progressive sequence. Clinical features of the disease have suggested and corroborated pathological events. The death of retinal ganglion cells causes secondary loss of neurons in the brain, but only as a by-product of injury to the retinal ganglion cells. Although therapy to lower intraocular pressure is moderately effective, new treatments are being developed to alter the remodeling of ocular connective tissue, to interrupt the injury signal from axon to soma, and to upregulate a variety of survival mechanisms.

Clinical Factors Associated with Lamina Cribrosa Thickness in Patients with Glaucoma, as Measured with Swept Source Optical Coherence Tomography

Purpose

To investigate the influence of various risk factors on thinning of the lamina cribrosa (LC), as measured with swept-source optical coherence tomography (SS-OCT; Topcon).

Methods

This retrospective study comprised 150 eyes of 150 patients: 22 normal subjects, 28 preperimetric glaucoma (PPG) patients, and 100 open-angle glaucoma patients. Average LC thickness was determined in a 3 x 3 mm cube scan of the optic disc, over which a 4 x 4 grid of 16 points was superimposed (interpoint distance: 175 μm), centered on the circular Bruch’s membrane opening. The borders of the LC were defined as the visible limits of the LC pores. The correlation of LC thickness with Humphrey field analyzer-measured mean deviation (MD; SITA standard 24–2), circumpapillary retinal nerve fiber layer thickness (cpRNFLT), the vertical cup-to-disc (C/D) ratio, and tissue mean blur rate (MBR) was determined with Spearman's rank correlation coefficient. The relationship of LC thickness with age, axial length, intraocular pressure (IOP), MD, the vertical C/D ratio, central corneal thickness (CCT), and tissue MBR was determined with multiple regression analysis. Average LC thickness and the correlation between LC thickness and MD were compared in patients with the glaucomatous enlargement (GE) optic disc type and those with non-GE disc types, as classified with Nicolela’s method.

Results

We found that average LC thickness in the 16 grid points was significantly associated with overall LC thickness (r = 0.77, P < 0.001). The measurement time for this area was 12.4 ± 2.4 minutes. Average LC thickness in this area had a correlation coefficient of 0.57 with cpRNFLT (P < 0.001) and 0.46 (P < 0.001) with MD. Average LC thickness differed significantly between the groups (normal: 268 ± 23 μm, PPG: 248 ± 13 μm, OAG: 233 ± 20 μm). Multiple regression analysis showed that MD (β = 0.29, P = 0.013), vertical C/D ratio (β = -0.25, P = 0.020) and tissue MBR (β = 0.20, P = 0.034) were independent variables significantly affecting LC thickness, but age, axial length, IOP, and CCT were not. LC thickness was significantly lower in the GE patients (233.9 ± 17.3 μm) than the non-GE patients (243.6 ± 19.5 μm, P = 0.040). The correlation coefficient between MD and LC thickness was 0.58 (P < 0.001) in the GE patients and 0.39 (P = 0.013) in the non-GE patients.

Conclusion

Cupping formation and tissue blood flow were independently correlated to LC thinning. Glaucoma patients with the GE disc type, who predominantly have large cupping, had lower LC thickness even with similar glaucoma severity.

Ocular perfusion pressure and ophthalmic artery flow in patients with normal tension glaucoma

Background

Vascular insufficiency has been reported to be a cause of normal tension glaucoma (NTG). The aim of this study was to compare ocular perfusion pressure (OPP) and ophthalmic artery flow (OAF) between patients with NTG and those without glaucoma.

Methods

We considered one eye each from 31 NTG and 15 non-glaucoma control patients. Blood pressure and intraocular pressure (IOP) were measured in the sitting position, for calculation of OPP. Humphrey visual field (HVF) assessment was then carried out on NTG patients. All patients then underwent Transcranial Doppler ultrasound measurements of OAF parameters, including mean flow velocity (MFV), end diastolic velocity (EDV), peak systolic velocity (PSV) and resistive index (RI). We looked at differences in OPP and OAF parameters between the two groups, and their correlations in NTG patients. T-tests, χ², ANOVA and Pearson Correlation tests were performed, with p < 0.05 considered statistically significant.

Results

There were no statistically significant differences in OPP between the NTG and control groups (60.5+/-8.7 mmHg and 62.9+/-10.2 mmHg respectively, p = 0.393), and also no statistically significant differences in MFV, EDV, PSV and RI (all p > 0.05). In the NTG group, there were positive correlations between OPP and both MFV (r = 0.416, p = 0.020) and EDV (r = 0.369, p = 0.041). There were no statistically significant correlations between HVF mean deviation and OPP or OAF parameters (all p > 0.05).

Conclusion

There is no difference in OPP and OAF parameters between patients with NTG and non-glaucoma controls, suggesting that vascular insufficiency or dysregulation by themselves may not account for the pathogenesis of NTG.

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.

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.

The Association between Primary Open-Angle Glaucoma and Blood Pressure: Two Aspects of Hypertension and Hypotension

Glaucoma is the second leading cause of blindness worldwide. Although the mechanism of the development of primary open-angle glaucoma (POAG) is not fully understood, elevated intraocular pressure (IOP) is considered the most important risk factor. Several vascular factors have also been identified as risk factors and can lead to hypoperfusion of the optic nerve head and thus may play an important role in the pathogenesis and progression of POAG. The results of the present study suggest that both high and low blood pressure (BP) are associated with an increased risk of POAG based on a comprehensive literature review. Elevated BP is associated with elevated IOP, leading to increased risk of glaucoma, but excessive BP lowering in glaucoma patients may cause a drop in ocular perfusion pressure (OPP) and subsequent ischemic injury. The relationship between IOP, OPP, and BP suggests that the relationship between BP and glaucoma progression is U-shaped.

Changes in intraocular pressure during surgery in the lateral decubitus position under sevoflurane and propofol anesthesia

Intraocular pressure (IOP) has been shown to change with body position. Several studies have shown that the lateral decubitus position (LDP) is associated with a significant increase in IOP in the dependent eye. However, whether anesthetic agents alter IOP in the LDP remains unclear. This study investigated the effect of sevoflurane and propofol anesthesia on IOP in the LDP. A total of 28 patients undergoing surgery in the LDP were included. Patients were randomly allocated to sevoflurane or propofol groups. IOP in both eyes was recorded and compared between groups at five time points: after anesthesia induction, after endotracheal intubation, at 5 min and 1 h after a positional change to the LDP, and 5 min after returning to the supine position. In the sevoflurane group, IOP was significantly increased in both dependent and non-dependent eyes 1 h after changing to the LDP. In the propofol group, IOP decreased in both dependent and non-dependent eyes after tracheal intubation, but did not increase after changing to the LDP. The number of patients in whom IOP increased to ≥28 mmHg was greater in the sevoflurane group than in the propofol group. Propofol may be better than sevoflurane for the maintenance of anesthesia in the LDP. Monitoring of IOP in the LDP might help avoid ophthalmic complications.

New directions in the treatment of normal tension glaucoma

Glaucoma is a progressive optic neuropathy that causes characteristic changes of the optic nerve and visual field in relation to intraocular pressure (IOP). It is now known that glaucoma can occur at statistically normal IOPs and prevalence studies have shown that normal tension glaucoma (NTG) is more common than previously thought. While IOP is believed to be the predominant risk factor in primary open angle glaucoma (POAG), IOP-independent risk factors, such as vascular dysregulation, are believed to play an important part in the pathogenesis of NTG. Though certain distinguishing phenotypic features of NTG have been reported, such as an increased frequency of disc hemorrhages, acquired pits of the optic nerve and characteristic patterns of disc cupping and visual field loss, there is much overlap of the clinical findings in NTG with POAG, suggesting that NTG is likely part of a continuum of open angle glaucomas. However, IOP modification is still the mainstay of treatment in NTG. As in traditional POAG, reduction of IOP can be achieved with the use of medications, laser trabeculoplasty or surgery. Studies now show that the choice of medication may also be important in determining the outcomes of these patients. Though it is likely that future treatment of NTG will involve modification of both IOP and IOP-independent risk factors, current efforts to develop IOP-independent neuroprotective treatments have not yet proven to be effective in humans.

Effect of subconjunctival glucose on retinal ganglion cell survival in experimental retinal ischaemia and contrast sensitivity in human glaucoma

PURPOSE

This study aims to evaluate the effect of subconjunctival glucose on the retinal ganglion cells (RGCs) in experimental retinal ischaemia and contrast sensitivity in humans with primary open-angle glaucoma (POAG).

METHODS

First, we measured the intravitreal concentration of glucose at various time points after a subconjunctival injection of 100 μl of 50% glucose to Sprague-Dawley rats. Next, treatment and control groups received 50% subconjunctival glucose and iso-osmotic (8%) saline, respectively, 1 h prior to a unilateral ischaemic retinal injury; 7 days later, the damage profiles were compared using RGC and axon counts. Subsequently, we conducted a double-blind, crossover, pilot clinical study in seven eyes of five pseudophakic subjects with severe POAG. Subjects received either 0.3 mL of 50% glucose subconjunctivally or iso-osmotic (8%) saline, then vice versa after a 2-3 week 'wash-out' period; change in contrast sensitivity from baseline was the primary outcome.

RESULTS

Subconjunctival glucose preserved approximately 60% of Brn3a-positive RGCs in all retinal zones compared with an 80% loss in control retinas, and rescued approximately 40% of the axonal loss. In the human trial, the contrast sensitivity at 12 cycles/degree was 0.24 log units greater than baseline (95% confidence interval 0.12-0.36; P < 0.001).

CONCLUSIONS

Subconjunctival glucose partially protects RGC somata and axons against an ischaemic insult and temporarily recovers contrast sensitivity in patients with severe POAG. Although an unlikely therapeutic strategy for POAG, the findings motivate further bioenergetic-based research in glaucoma and other optic nerve and retinal diseases, where energy failure may be part of the pathogenesis.

Dementia is associated with open-angle glaucoma: a population-based study

PURPOSE

Previous epidemiologic studies that focused on the association between open-angle glaucoma (OAG) and dementia showed inconsistent results. In the present study, we explored the association between OAG and dementia in an ethnic Chinese (i.e., Taiwanese) population using a population-based data set.

METHODS

We retrieved data on study subjects for this case-control study from the Longitudinal Health Insurance Database 2000. We identified 7770 patients who had a diagnosis of dementia as cases, and 7770 subjects matched in terms of sex and age, which were randomly extracted as controls. A conditional logistic regression conditioned on age group, sex, and index year was used to assess the association of dementia with previously diagnosed OAG among the sampled patients.

RESULTS

Of 15,540 patients, 1.70% had prior OAG, including 2.02% of the dementia group and 1.38% of the controls. After adjusting for patient socioeconomic characteristics and comorbid medical disorders, dementia patients were more likely to have had prior OAG than controls (odds ratio (OR): 1.44; 95% confidence interval (CI): 1.12-1.85; P<0.01). In addition, female dementia patients were more likely to have had prior OAG than controls (OR: 1.93; 95% CI: 1.35-2.77; P<0.001), whereas no statistical difference in prior OAG between male dementia patients and controls was found.

CONCLUSIONS

Female dementia patients were associated with a higher proportion of prior OAG than were the controls.

The African Descent and Glaucoma Evaluation Study (ADAGES): predictors of visual field damage in glaucoma suspects

PURPOSE

To evaluate racial differences in the development of visual field (VF) damage in glaucoma suspects.

DESIGN

Prospective, observational cohort study.

METHODS

Six hundred thirty-six eyes from 357 glaucoma suspects with normal VF at baseline were included from the multicenter African Descent and Glaucoma Evaluation Study (ADAGES). Racial differences in the development of VF damage were examined using multivariable Cox proportional hazard models.

RESULTS

Thirty one of 122 African-descent participants (25.4%) and 47 of 235 European-descent participants (20.0%) developed VF damage (P = .078). In multivariable analysis, worse baseline VF mean deviation, higher mean arterial pressure during follow-up, and a race ∗ mean intraocular pressure (IOP) interaction term were significantly associated with the development of VF damage, suggesting that racial differences in the risk of VF damage varied by IOP. At higher mean IOP levels, race was predictive of the development of VF damage even after adjusting for potentially confounding factors. At mean IOPs during follow-up of 22, 24, and 26 mm Hg, multivariable hazard ratios (95% confidence intervals) for the development of VF damage in African-descent compared to European-descent subjects were 2.03 (1.15-3.57), 2.71 (1.39-5.29), and 3.61 (1.61-8.08), respectively. However, at lower mean IOP levels (below 22 mm Hg) during follow-up, African descent was not predictive of the development of VF damage.

CONCLUSION

In this cohort of glaucoma suspects with similar access to treatment, multivariate analysis revealed that at higher mean IOP during follow-up, individuals of African descent were more likely to develop VF damage than individuals of European descent.

T-helper1/T-helper2 cytokine imbalance in the iris of patients with glaucoma

The mechanistic study of glaucoma pathogenesis has shifted to seeking to understand the effects of immune responses on retinal ganglion cell damage and protection. Cytokines mediate the biological effects of the immune system, and our previous study revealed an imbalance of T-helper (Th) 1-derived and Th2-derived cytokines in the serum of patients with glaucoma. In this study, we collected irises from normal individuals and patients with primary open-angle closure (POAG) or chronic angle-closure glaucoma (CACG). We used real-time polymerase chain reaction (PCR) to measure the expression of Th1 (interleukin (IL)-2, interferon-gamma (IFN-γ)), Th2 (IL-4, IL-6, IL-10), and Th3 (transforming growth factor-beta (TGF-β)) cytokines. We then performed immunohistochemical staining to characterize the localization of the upregulated cytokines in iris cryosections. We observed an upward trend in the expression of IL-2 and IFN-γ and a downward trend in IL-6 expression in the iris of POAG and CACG patients. Expression of TGF-β also increased. Immunohistochemistry revealed that IL-2 expression in POAG and CACG patients was localized in the anterior surface of the blood vessel wall in the stroma of the iris, in the cytoplasm of some cells, in the anterior epithelium, and in the posterior pigment epithelium. These findings indicate that immune status differed between the iris tissues of POAG and CACG patients and those of normal individuals. A T-helper cytokine imbalance may modulate the immune microenvironment in glaucomatous eyes and thus influence optic neuropathy.

Pharmacotherapy of glaucoma

Glaucoma is a group of diseases involving the optic nerve and associated structures, which is characterized by progressive visual field loss and typical changes of the optic nerve head (ONH). The only known treatment of the disease is reduction of intraocular pressure (IOP), which has been shown to reduce glaucoma progression in a variety of large-scale clinical trials. Nowadays, a relatively wide array of topical antiglaucoma drugs is available, including prostaglandin analogues, carbonic anhydrase inhibitors, beta-receptor antagonists, adrenergic agonists, and parasympathomimetics. In clinical routine, this allows for individualized treatment taking risk factors, efficacy, and safety into account. A major challenge is related to adherence to therapy. Sustained release devices may help minimize this problem but are not yet available for clinical routine use. Another hope arises from non-IOP-related treatment concepts. In recent years, much knowledge has been gained regarding the molecular mechanisms that underlie the disease process in glaucoma. This also strengthens the hope that glaucoma therapy beyond IOP lowering will become available. Implementing this concept with clinical trials remains, however, a challenge.

Comparison of the effects of bimatoprost and a fixed combination of latanoprost and timolol on 24-hour blood and ocular perfusion pressures: the results of a randomized trial

BACKGROUND

To compare the effect of bimatoprost and the fixed combination latanoprost-timolol (LTFC) on 24-hour systolic (SBP) and diastolic (DBP) blood pressure and on 24-hour ocular perfusion pressure (OPP).

METHODS

200 patients with glaucoma or ocular hypertension, controlled on the unfixed combination of latanoprost and timolol or eligible for dual therapy being not being fully controlled on monotherapy were enrolled in a randomized, double-masked, placebo-controlled, multicentre clinical trial. They were randomized to LTFC (8 a.m.) or bimatoprost (8 p.m.) and received 24-hour IOP curve at baseline, 6 and 12 weeks (supine and sitting position IOPs were recorded at 8 p.m., midnight, 5 a.m., 8a.m., noon and 4 p.m.). Holter 24-hour blood pressure curve was obtained between weeks 2 and 12. SBP, DBP, OPP were calculated and compared with ANOVA. Rates of diastolic OPP (DPP)≤50, ≤40, ≤30 mmHg in the 2 groups were calculated and compared using Fisher's test.

RESULTS

Mean baseline SBP and DBP were 136.5±18.3 vs 134.2±20.1 mmHg (p=0.1) and 79.1±10.2 vs 78.2±10.1 mmHg (p=0.4) in the bimatoprost and LTFC groups respectively. Holter SBP was significantly higher for bimatoprost (135.1 mmHg vs 128.1 mmHg, p=0.04), while no statistically significant difference in DBP was found. DPP was similar in the 2 groups, and proportions of patients with at least one value of the 24-hour curve≤50, ≤40, ≤30 mmHg were 94%, 86%, 41% respectively.

CONCLUSIONS

Bimatoprost and LTFC had similar DBPs and OPPs; SBP was significantly lower with LTFC. In this study, the percentage of "dippers" was considerably higher than the one described in previous studies on the role of perfusion pressure in glaucoma.

TRIAL REGISTRATION

NCT02154217, May 21, 2014.

Correlation of optic nerve microcirculation with papillomacular bundle structure in treatment naive normal tension glaucoma

Purpose. To assess the association between optic nerve head (ONH) microcirculation, central papillomacular bundle (CPB) structure, and visual function in eyes with treatment naive normal tension glaucoma (NTG). Methods. This study included 40 eyes of 40 patients with NTG and 20 eyes of 20 normal patients. We used laser speckle flowgraphy (LSFG) to measure mean blur rate (MBR) in all eyes and calculated the ratio of MBR in the horizontal quadrants of tissue area ONH (temporal/nasal ratio of MBR in the tissue area: T/N MT). Clinical findings also included retinal nerve fiber layer thickness (RNFLT) and ganglion cell complex thickness (GCCT) in the CPB and macular areas, best-corrected visual acuity (BCVA), mean deviation (MD), and refractive error. Results. T/N MT was correlated with both BCVA and MD. The OCT parameters most highly correlated with T/N MT were macular RNFLT and mid-CPB RNFLT. Furthermore, T/N MT, mid-CPB RNFLT, and macular RNFLT were higher in NTG than in normal eyes. A discrimination analysis revealed that T/N MT and refractive error were independent factors indicating NTG. Conclusions. Our results suggest that T/N MT is a candidate biomarker of NTG. Furthermore, T/N MT reflects visual function, including acuity and sensitivity, and CPB structure.

Metabolic syndrome as a risk factor in normal-tension glaucoma

PURPOSE

To determine whether normal-tension glaucoma (NTG) is associated with metabolic syndrome and to evaluate which components of metabolic syndrome are related to NTG.

METHODS

This study included 18240 participants who underwent health check-ups including fundus photography and intraocular pressure measurements. For NTG diagnosis, all participants with findings suggestive of glaucoma completed a further glaucoma evaluation, including applanation tonometry, gonioscopy and standard automated perimetry. The National Cholesterol Education Program Adult Treatment Panel III guideline was used to characterize metabolic syndrome.

RESULTS

Of the 18240 participants, 3635 (19.9%) had metabolic syndrome and 300 (1.6%) were diagnosed with NTG. The prevalence of NTG was 1.5% in subjects without metabolic syndrome and 2.1% in subjects with metabolic syndrome. The presence of metabolic syndrome was not significantly associated with NTG (p = 0.067). There were significant associations of NTG with hypertension and impaired glucose tolerance (IGT) among the individual components of metabolic syndrome (OR, 1.53; 95% CI, 1.20-1.94; p = 0.001 and OR, 1.47; 95% CI, 1.12-1.94; p = 0.006). NTG was positively associated with the number of metabolic syndrome components (OR, 1.10; p = 0.040). Multivariable analysis showed the prevalence of NTG to be significantly higher in participants aged between 50 and 70 years relative to those aged 40 to 50 years, male gender, participants with higher baseline intraocular pressure, hypertension and IGT.

CONCLUSIONS

Of the metabolic syndrome components, hypertension and IGT contributed to an increased risk of NTG. These findings suggest that metabolic syndrome components may play a role in the pathogenesis of NTG.

Correlation between structure/function and optic disc microcirculation in myopic glaucoma, measured with laser speckle flowgraphy

Background

It is difficult to identify glaucoma in myopic eyes because the configuration of the optic disc varies; yet it is important clinically. Here, we used laser speckle flowgraphy (LSFG) to measure mean blur rate (MBR), representing optic disc microcirculation, and assessed its ability to identify glaucoma in eyes with myopic optic discs.

Methods

129 eyes (normal disc: 21 eyes; myopic disc: 108 eyes) were enrolled. The eyes were classified as normal or mildly, moderately, or severely glaucomatous with standard automated perimetry (SAP). We determined the relationship between optic nerve head (ONH) MBR, measured with LSFG, mean deviation (MD), measured with SAP, and circumpapillary retinal nerve fiber layer thickness (cpRNFLT), measured with optical coherence tomography (OCT).

Results

ONH MBR and cpRNFLT decreased significantly with the severity of glaucoma. MBR was significantly correlated with cpRNFLT and MD (r =0.65 and r =0.63, respectively). A multiple regression analysis revealed that MBR and cpRNFLT were independent factors indicating glaucoma severity. A logistic regression analysis revealed that MBR and cpRNFLT were also independent factors indicating the presence of glaucoma. In a receiver operating characteristic (ROC) analysis, MBR and cpRNFLT could both differentiate between normal and glaucomatous eyes (MBR area under the ROC curve: 0.86, with a cut-off score of 24.0 AU).

Conclusion

These results suggest that in addition to cpRNFLT, non-invasive and objective LSFG measurements of MBR may enable the identification of glaucoma and the classification of its severity in eyes with myopic optic discs.

Effects of head elevation on intraocular pressure in healthy subjects: raising bed head vs using multiple pillows

PURPOSE

To evaluate the effects of different methods of head elevation on intraocular pressure (IOP) in healthy young subjects.

METHODS

Twenty-four healthy young Korean subjects were included in this prospective observational study. The IOP measurements were taken with the subjects in the sitting position and in the supine positions with the head flat and 30° up using two different methods: (1) raising the bed head and (2) using multiple pillows. IOP was measured using Tonopen AVIA in both eyes 10 min after assuming each position in a randomized sequence. The Wilcoxon signed-rank test was used to compare the IOP by changing the methods of head elevation.

RESULTS

Mean IOP of both eyes when sitting was lower than that measured in the supine position with head flat (P=0.001). Compared with that measured in the supine position with head flat, the mean IOP was lower when measured in the supine position with the head kept 30 ° up by bed head elevation (P=0.001), whereas the mean IOP was not significantly different when measured in the supine position with the head elevated using multiple pillows (right eye, P=0.061; left eye, P=0.089).

CONCLUSION

In normal subjects, IOP was lower when measured in the supine position with the head kept up by the bed head elevation compared with that measured when lying flat. However, such head-up position-induced IOP reduction was not found when the head was kept up using multiple pillows. These findings suggest that elevating the head using multiple pillows may not help to reduce IOP in the supine posture.

The association of blood pressure and primary open-angle glaucoma: a meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis of the association between blood pressure levels and hypertension with primary open-angle glaucoma and intraocular pressure endpoints.

DESIGN

Systematic review with quantitative meta-analysis.

METHODS

Studies were identified by searching the PubMed and EMBASE databases. Inverse-variance weighted random-effects models were used to summarize relative risks. Subgroup analyses and meta-regression were used to explore potential sources of heterogeneity across studies.

RESULTS

Sixty observational studies were included. The pooled relative risk for primary open-angle glaucoma comparing patients with hypertension to those without hypertension was 1.16 (95% CI = 1.05-1.28), with modest heterogeneity across studies (I(2) 34.5%). Virtually all studies reported a positive association between blood pressure and intraocular pressure (IOP). The pooled average increase in IOP associated with a 10 mm Hg increase in systolic blood pressure was 0.26 mm Hg (95% CI 0.23-0.28, I(2) 30.7%), and the average increase associated with a 5 mm Hg increase in diastolic blood pressure was 0.17 mm Hg (95% CI 0.11-0.23, I(2) 90.5%).

CONCLUSIONS

In this meta-analysis, hypertension was associated with increased intraocular pressure. The association between hypertension and primary open-angle glaucoma was stronger in cross-sectional compared with case-control and longitudinal studies. Our findings support a role of increased blood pressure in elevated intraocular pressure and possibly in the development of glaucoma.

Optic nerve head blood flow response to reduced ocular perfusion pressure by alteration of either the blood pressure or intraocular pressure

PURPOSE

To test the hypothesis that blood flow autoregulation in the optic nerve head has less reserve to maintain normal blood flow in the face of blood pressure-induced ocular perfusion pressure decrease than a similar magnitude intraocular pressure-induced ocular perfusion pressure decrease.

MATERIALS AND METHODS

Twelve normal non-human primates were anesthetized by continuous intravenous infusion of pentobarbital. Optic nerve blood flow was monitored by laser speckle flowgraphy. In the first group of animals (n = 6), the experimental eye intraocular pressure was maintained at 10 mmHg using a saline reservoir connected to the anterior chamber. The blood pressure was gradually reduced by a slow injection of pentobarbital. In the second group (n = 6), the intraocular pressure was slowly increased from 10 mmHg to 50 mmHg by raising the reservoir. In both experimental groups, optic nerve head blood flow was measured continuously. The blood pressure and intraocular pressure were simultaneously recorded in all experiments.

RESULTS

The optic nerve head blood flow showed significant difference between the two groups (p = 0.021, repeat measures analysis of variance). It declined significantly more in the blood pressure group compared to the intraocular pressure group when the ocular perfusion pressure was reduced to 35 mmHg (p < 0.045) and below. There was also a significant interaction between blood flow changes and the ocular perfusion pressure treatment (p = 0.004, adjusted Greenhouse & Geisser univariate test), indicating the gradually enlarged blood flow difference between the two groups was due to the ocular perfusion pressure decrease.

CONCLUSIONS

The results show that optic nerve head blood flow is more susceptible to an ocular perfusion pressure decrease induced by lowering the blood pressure compared with that induced by increasing the intraocular pressure. This blood flow autoregulation capacity vulnerability to low blood pressure may provide experimental evidence related to the hemodynamic pathophysiology in glaucoma.

Ocular pulse amplitude and Doppler waveform analysis in glaucoma patients

PURPOSE

To determine the correlation between ocular blood flow velocities and ocular pulse amplitude (OPA) in glaucoma patients using colour Doppler imaging (CDI) waveform analysis.

METHOD

A prospective, observer-masked, case-control study was performed. OPA and blood flow variables from central retinal artery and vein (CRA, CRV), nasal and temporal short posterior ciliary arteries (NPCA, TPCA) and ophthalmic artery (OA) were obtained through dynamic contour tonometry and CDI, respectively. Univariate and multiple regression analyses were performed to explore the correlations between OPA and retrobulbar CDI waveform and systemic cardiovascular parameters (blood pressure, blood pressure amplitude, mean ocular perfusion pressure and peripheral pulse).

RESULTS

One hundred and ninety-two patients were included [healthy controls: 55; primary open-angle glaucoma (POAG): 74; normal-tension glaucoma (NTG): 63]. OPA was statistically different between groups (Healthy: 3.17 ± 1.2 mmHg; NTG: 2.58 ± 1.2 mmHg; POAG: 2.60 ± 1.1 mmHg; p < 0.01), but not between the glaucoma groups (p = 0.60). Multiple regression models to explain OPA variance were made for each cohort (healthy: p < 0.001, r = 0.605; NTG: p = 0.003, r = 0.372; POAG: p < 0.001, r = 0.412). OPA was independently associated with retrobulbar CDI parameters in the healthy subjects and POAG patients (healthy CRV resistance index: β = 3.37, CI: 0.16-6.59; healthy NPCA mean systolic/diastolic velocity ratio: β = 1.34, CI: 0.52-2.15; POAG TPCA mean systolic velocity: β = 0.14, CI 0.05-0.23). OPA in the NTG group was associated with diastolic blood pressure and pulse rate (β = -0.04, CI: -0.06 to -0.01; β = -0.04, CI: -0.06 to -0.001, respectively).

CONCLUSIONS

Vascular-related models provide a better explanation to OPA variance in healthy individuals than in glaucoma patients. The variables that influence OPA seem to be different in healthy, POAG and NTG patients.

Ocular perfusion pressure in glaucoma

This review article discusses the relationship between ocular perfusion pressure and glaucoma, including its definition, factors that influence its calculation and epidemiological studies investigating the influence of ocular perfusion pressure on the prevalence, incidence and progression of glaucoma. We also list the possible mechanisms behind this association, and discuss whether it is secondary to changes in intraocular pressure, blood pressure or both. Finally, we describe the circadian variation of ocular perfusion pressure and the effects of systemic and topical medications on it. We believe that the balance between IOP and BP, influenced by the autoregulatory capacity of the eye, is part of what determines whether an individual will develop optic nerve damage. However, prospective, longitudinal studies are needed to better define the role of ocular perfusion pressure in the development and progression of glaucoma.

Vascular tone pathway polymorphisms in relation to primary open-angle glaucoma

AIMS

Vascular perfusion may be impaired in primary open-angle glaucoma (POAG); thus, we evaluated a panel of markers in vascular tone-regulating genes in relation to POAG.

METHODS

We used Illumina 660W-Quad array genotype data and pooled P-values from 3108 POAG cases and 3430 controls from the combined National Eye Institute Glaucoma Human Genetics Collaboration consortium and Glaucoma Genes and Environment studies. Using information from previous literature and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, we compiled single-nucleotide polymorphisms (SNPs) in 186 vascular tone-regulating genes. We used the 'Pathway Analysis by Randomization Incorporating Structure' analysis software, which performed 1000 permutations to compare the overall pathway and selected genes with comparable randomly generated pathways and genes in their association with POAG.

RESULTS

The vascular tone pathway was not associated with POAG overall or POAG subtypes, defined by the type of visual field loss (early paracentral loss (n=224 cases) or only peripheral loss (n=993 cases)) (permuted P≥0.20). In gene-based analyses, eight were associated with POAG overall at permuted P<0.001: PRKAA1, CAV1, ITPR3, EDNRB, GNB2, DNM2, HFE, and MYL9. Notably, six of these eight (the first six listed) code for factors involved in the endothelial nitric oxide synthase activity, and three of these six (CAV1, ITPR3, and EDNRB) were also associated with early paracentral loss at P<0.001, whereas none of the six genes reached P<0.001 for peripheral loss only.

DISCUSSION

Although the assembled vascular tone SNP set was not associated with POAG, genes that code for local factors involved in setting vascular tone were associated with POAG.

Regulation of intraocular pressure by soluble and membrane guanylate cyclases and their role in glaucoma

Glaucoma is a progressive optic neuropathy characterized by visual field defects that ultimately lead to irreversible blindness (Alward, 2000; Anderson et al., 2006). By the year 2020, an estimated 80 million people will have glaucoma, 11 million of which will be bilaterally blind. Primary open-angle glaucoma (POAG) is the most common type of glaucoma. Elevated intraocular pressure (IOP) is currently the only risk factor amenable to treatment. How IOP is regulated and can be modulated remains a topic of active investigation. Available therapies, mostly geared toward lowering IOP, offer incomplete protection, and POAG often goes undetected until irreparable damage has been done, highlighting the need for novel therapeutic approaches, drug targets, and biomarkers (Heijl et al., 2002; Quigley, 2011). In this review, the role of soluble (nitric oxide (NO)-activated) and membrane-bound, natriuretic peptide (NP)-activated guanylate cyclases that generate the secondary signaling molecule cyclic guanosine monophosphate (cGMP) in the regulation of IOP and in the pathophysiology of POAG will be discussed.

Association of the optic disc structure with the use of antihypertensive medications: the thessaloniki eye study

PURPOSE

To investigate the association of antihypertensive medications with optic disc structure by blood pressure (BP) level, in nonglaucoma subjects.

DESIGN

Cross-sectional, population-based study.

METHODS

A subset of Thessaloniki Eye Study participants was included in this study. Subjects were interviewed for medical history and underwent extensive ophthalmic examination, BP measurement, and optic disc imaging with the Heidelberg retinal tomograph. Subjects treated for hypertension were grouped in the following groups: (1) angiotensin-converting enzyme inhibitors and/or angiotensin-receptor blockers; (2) beta blockers and/or calcium-channel blockers; (3) diuretics alone or combined with others; and (4) other combinations. Cup size and cup-to-disc (C/D) ratio in the above groups were compared with the untreated group, using regression models. Analyses were rerun for subjects with systolic BP (SBP)<140 mm Hg, SBP≥140 mm Hg, diastolic BP (DBP)<90 mm Hg, and DBP≥90 mm Hg.

RESULTS

Among 232 subjects, 131 were receiving antihypertensive medications. In subjects with DBP<90 mm Hg, all medications groups were associated with larger cup size and higher C/D ratio compared with the untreated group. Results were similar in subjects with SBP<140 mm Hg, with the exception of the beta blockers and/or calcium-channel blockers group. None of the medications groups were associated with the Heidelberg retinal tomograph parameters in those with DBP≥90 mm Hg or SBP≥140 mm Hg.

CONCLUSIONS

All classes of antihypertensive medications were associated with larger cup size and higher C/D ratio in subjects with either DBP<90 mm Hg or SBP<140 mm Hg. These results suggest that there is no specific medication-related effect on optic disc structure, and the associations found are mediated through the hypotensive effect of antihypertensive medications.

The role of epigenetics in the fibrotic processes associated with glaucoma

Glaucoma is an optic neuropathy that affects 60 million people worldwide. The main risk factor for glaucoma is increased intraocular pressure (IOP), this is currently the only target for treatment of glaucoma. However, some patients show disease progression despite well-controlled IOP. Another possible therapeutic target is the extracellular matrix (ECM) changes in glaucoma. There is an accumulation of ECM in the lamina cribrosa (LC) and trabecular meshwork (TM) and upregulation of profibrotic factors such as transforming growth factor β (TGFβ), collagen1α1 (COL1A1), and α-smooth muscle actin (αSMA). One method of regulating fibrosis is through epigenetics; the study of heritable changes in gene function caused by mechanisms other than changes in the underlying DNA sequence. Epigenetic mechanisms have been shown to drive renal and pulmonary fibrosis by upregulating profibrotic factors. Hypoxia alters epigenetic mechanisms through regulating the cell's response and there is a hypoxic environment in the LC and TM in glaucoma. This review looks at the role that hypoxia plays in inducing aberrant epigenetic mechanisms and the role these mechanisms play in inducing fibrosis. Evidence suggests that a hypoxic environment in glaucoma may induce aberrant epigenetic mechanisms that contribute to disease fibrosis. These may prove to be relevant therapeutic targets in glaucoma.

Association between risk factors and glaucomatous damage in untreated primary open-angle glaucoma

PURPOSE

To analyze an association between the presumed risk factors for glaucoma and the actual extent of glaucomatous damage in untreated primary open-angle glaucoma.

PATIENTS AND METHODS

In 50 untreated open-angle glaucoma patients, we analyzed an association between the level of glaucomatous damage and presumed glaucoma risk factors: mean untreated intraocular pressure (IOP) and short-term IOP variability, ocular pulse amplitude, corneal thickness, acral and corneal temperature, retinal arterial diameter and retinal venous diameter, choroidal blood flow (laser Doppler flowmetry flow, velocity, volume), heart rate, and ocular perfusion pressure. Morphologic damage (mean retinal nerve fiber layer thickness, measured by ocular coherence tomography) and functional damage (visual field mean defect) were evaluated separately in 2 forward-stepwise multiple regression models.

RESULTS

The mean retinal nerve fiber layer thickness was significantly (P<0.05) associated with IOP (r=-0.35), retinal arterial diameter (r=0.36), and choroidal blood flow (r=0.30); mean defect was associated with ocular perfusion pressure (r=-0.30), laser Doppler flowmetry volume (r=-0.33), and IOP variability (0.36).

CONCLUSIONS

Despite small differences between the morphologic and functional glaucomatous damage, IOP and perfusion parameters seem to contribute, at least in part, independently to both.

Static blood flow autoregulation in the optic nerve head in normal and experimental glaucoma

PURPOSE

To characterize the static blood flow autoregulation in the optic nerve head (ONH), and to investigate its role in hemodynamic changes in experimental glaucoma (EG).

METHODS

Unilateral elevation of intraocular pressure (IOP) was induced in 15 adult rhesus macaques by laser treatment to the trabecular meshwork. Prior to and after laser treatment, retinal nerve fiber layer thickness (RNFLT) was assessed, biweekly, by spectral-domain optical coherence tomography. Optic nerve head static autoregulation was assessed by determining the percentage blood flow (BF) change after the IOP was acutely increased from 10 to 30, 40, or 50 mm Hg manometrically, utilizing a laser speckle flowgraphy device.

RESULTS

Postlaser IOP (measured during average 7.7 ± 2.6 months) was 20.2 ± 5.9 mm Hg in EG eyes and 12.3 ± 2.6 mm Hg in control eyes (P < 0.0001). Retinal nerve fiber layer thickness was reduced by 33 ± 22% of the baseline values (P < 0.001) on average in EG eyes and by 0.4 ± 2.3% in control eyes (P > 0.05). The ONH BF remained at a constant level within a range of ocular perfusion pressure (OPP), 41 mm Hg and above. The autoregulation curves, created by all 723 tests in control and 352 tests in EG, were not significantly different (P = 0.71).

CONCLUSIONS

Optic nerve head BF in normal nonhuman primate (NHP) eyes is effectively regulated within a range of OPP approximately 41 mm Hg and above. Chronic IOP elevation causes no remarkable change to the static autoregulation within the ONH of EG eyes.

Glucose-induced temporary visual recovery in primary open-angle glaucoma: a double-blind, randomized study

PURPOSE

To investigate the effect of topical glucose on visual parameters in individuals with primary open-angle glaucoma (POAG).

DESIGN

Double-blind, randomized, crossover study.

PARTICIPANTS

Nondiabetic pseudophakic patients with definite POAG were recruited; 29 eyes of 16 individuals participated in study 1. A follow-up study (study 2) included 14 eyes of 7 individuals.

INTERVENTION

Eyes were randomly allocated to receive 50% glucose or saline eye drops every 5 minutes for 60 minutes.

MAIN OUTCOME MEASURES

The contrast sensitivity and best-corrected logarithm of the minimum angle of resolution (logMAR).

RESULTS

The 50% glucose reached the vitreous in pseudophakic but not phakic individuals. Glucose significantly improved the mean contrast sensitivity at 12 cycles/degree compared with 0.9% saline by 0.26 log units (95% confidence interval [CI], 0.13-0.38; P < 0.001) and 0.40 log units (95% CI, 0.17-0.60; P < 0.001) in the follow-up study. The intraocular pressure, refraction, and central corneal thickness were not affected by glucose; age was not a significant predictor of the response.

CONCLUSIONS

Topical glucose temporarily improves psychophysical visual parameters in some individuals with POAG, suggesting that neuronal energy substrate delivery to the vitreous reservoir may recover function of "sick" retinal neurons.

Optic nerve head blood flow autoregulation during changes in arterial blood pressure in healthy young subjects

AIM

In the present study the response of optic nerve head blood flow to an increase in ocular perfusion pressure during isometric exercise was studied. Based on our previous studies we hypothesized that subjects with an abnormal blood flow response, defined as a decrease in blood flow of more than 10% during or after isometric exercise, could be identified.

METHODS

A total of 40 healthy subjects were included in this study. Three periods of isometric exercise were scheduled, each consisting of 2 minutes of handgripping. Optic nerve head blood flow was measured continuously before, during and after handgripping using laser Doppler flowmetry. Blood pressure was measured non-invasively in one-minute intervals. Intraocular pressure was measured at the beginning and the end of the measurements and ocular perfusion pressure was calculated as 2/3*mean arterial pressure -intraocular pressure.

RESULTS

Isometric exercise was associated with an increase in ocular perfusion pressure during all handgripping periods (p < 0.001). By contrast no change in optic nerve head blood flow was seen. However, in a subgroup of three subjects blood flow showed a consistent decrease of more than 10% during isometric exercise although their blood pressure values increased. In addition, three other subjects showed a consistent decline of blood flow of more than 10% during the recovery periods.

CONCLUSION

Our data confirm previous results indicating that optic nerve head blood flow is autoregulated during an increase in perfusion pressure. In addition, we observed a subgroup of 6 subjects (15%) that showed an abnormal response, which is in keeping with our previous data. The mechanisms underlying this abnormal response remain to be shown.

Regulation of optic nerve head blood flow during combined changes in intraocular pressure and arterial blood pressure

In the choroid, there is evidence that blood flow does not only depend on ocular perfusion pressure (OPP), but also on absolute mean arterial pressure (MAP) and intraocular pressure (IOP). The present study included 40 healthy subjects to investigate whether such behavior is also found in the optic nerve head (ONH). The ONH blood flow (ONHBF) was studied using laser Doppler flowmetry during a separate increase in IOP and MAP as well as during a combined elevation. Mean arterial pressure was increased by isometric exercise and IOP by the suction method. During both, the change in ONHBF was less pronounced than the change in OPP indicating autoregulation. Correlation analysis was performed for the combined experiments after pooling all data according to IOP and MAP values. A correlation between ONHBF and MAP was found at IOPs 25 mm Hg (P<0.001), but not at IOPs>25 mm Hg (P=0.79). Optic nerve head blood flow and IOP were significantly correlated (P<0.001), and ONHBF was only slightly dependent on MAP. The data of the present study indicate a complex regulation of ONHBF during combined changes in MAP and IOP. Our results may be compatible with myogenic mechanisms underlying autoregulation, and indicate better ONHBF regulation during an increase in MAP than during an increase in IOP.

Role of nitric oxide in optic nerve head blood flow regulation during an experimental increase in intraocular pressure in healthy humans

The present study set out to investigate whether nitric oxide, a potent vasodilator, is involved in the regulatory processes in optic nerve head blood flow during an experimental increase in intraocular pressure (IOP). The study was conducted in a randomized, double-masked, placebo-controlled, three way cross-over design. 12 healthy subjects were scheduled to receive either L-NMMA (an unspecific nitric oxide synthase inhibitor), phenylephrine (an α-adrenoceptor agonist) or placebo on three different study days. Optic nerve head blood flow was measured using laser Doppler flowmetry and IOP was increased stepwise with a suction cup. Mean arterial pressure (MAP) and IOP were measured non-invasively and ocular perfusion pressure (OPP) was calculated as OPP = 2/3 MAP-IOP. Administration of L-NMMA and phenylephrine significantly increased MAP and therefore OPP at rest (p < 0.01). L-NMMA significantly reduced baseline blood flow in the optic nerve head (p < 0.01). Application of the suction cup induced a significant increase in IOP and a decrease in OPP (p < 0.01). During the stepwise increase in IOP, some autoregulatory potential was observed until OPP decreased approximately -30% below baseline. None of the administered substances had an effect on this autoregulatory behavior (p = 0.49). The results of the present study confirm that the human optic nerve head shows some regulatory capacity during a decrease in OPP. Nitric oxide is involved in the regulation of basal vascular tone in the optic nerve head but does not seem to be involved in the regulatory mechanisms during an acute increase in IOP in young healthy subjects.

Lack of spontaneous venous pulsation: possible risk indicator in normal tension glaucoma?

PURPOSE

Recently, the absence of spontaneous venous pulsation (SVP) has been suggested as a vascular risk factor for primary open-angle glaucoma (POAG). As the mechanism behind this phenomenon is still unknown, the authors have studied this vascular component using colour Doppler imaging (CDI).

METHODS

A total of 236 patients were divided into three diagnostic groups: healthy controls (81), POAG (86) and normal tension glaucoma (NTG; 69). All subjects were submitted to CDI studies of the retrobulbar circulation, intraocular pressure measurements and assessment of SVP existence. Mann-Whitney, chi-square contingency tables and Spearman correlations were used to explore differences and correlations between variables in the diagnostic groups.

RESULTS

Eighty-two percent of healthy controls had SVP (66/81), while a smaller numbers were registered in both glaucoma groups: POAG - 50% (43/86); NTG - 51% (35/69). In NTG patients, but not in POAG patients, the prevalence of the SVP phenomenon decreases with increased glaucoma damage (p = 0.04; p = 0.55, respectively). Overall glaucoma patients from both groups had lower central retinal vein (CRV) velocities than the healthy controls (p < 0.05). NTG patients with SVP had less severe visual field defects (mean defect -6.92 versus -11.1, p < 0.05), higher [correction added after online publication 21 September 2012; the word 'higher' has been inserted to replace the word 'lower'] peak systolic and mean flow velocities in the central retinal artery (p < 0.01; p < 0.05, respectively) as well as higher [correction added after online publication 21 September 2012; the word higher has been inserted to replace the word lower] maximal velocities and RI of the CRV (p < 0.02; p < 0.05, respectively).

CONCLUSIONS

Glaucoma patients have a decrease in CRV velocities. SVP is less prevalent in glaucoma patients than in healthy individuals. This phenomenon apparently reflects different hemodynamic patterns in the central retinal vessels. This variable may be of particular importance in NTG patients, where it may be associated with more advanced functional damage.

Association of open-angle glaucoma with perfusion pressure status in the Thessaloniki Eye Study

PURPOSE

To investigate the association of open-angle glaucoma (OAG), primary open-angle glaucoma (POAG), and pseudoexfoliative glaucoma (PEXG) with ocular perfusion pressure status (ocular perfusion pressure with or without antihypertensive treatment).

DESIGN

Cross-sectional, population-based study.

METHODS

A total of 2554 randomly selected, ≥ 60-year old subjects participated in the Thessaloniki Eye Study. Only clinic-visit participants (n = 2261), who had uniformly collected data, were included in the analyses. A logistic regression model was run for OAG in all clinic-visit participants; covariates included age, sex, diastolic ocular perfusion pressure, antihypertensive treatment, intraocular pressure (IOP), IOP-lowering treatment, pseudoexfoliation, and vascular factors identified as risk factors for glaucoma in a previous analysis. Similar logistic regression models were run separately for POAG and PEXG. In addition, logistic regression models were run for OAG, POAG, and PEXG in subjects with and without antihypertensive treatment. Also, logistic regression models were run to assess the role of systolic ocular perfusion pressure in OAG, POAG, and PEXG.

RESULTS

Among clinic-visits, 1212 subjects (53.7%) were using antihypertensive treatment. An association of borderline significance was found between low diastolic ocular perfusion pressure and POAG (OR = 0.84 per 10 mm Hg, 95% CI = 0.70-1.01, P = .059). The effect of antihypertensive treatment on POAG was not statistically significant (OR = 1.20, 95% CI = 0.75-1.91, P = .45). In subgroup analyses, diastolic ocular perfusion pressure was significantly associated with POAG in subjects using antihypertensive treatment (OR = 0.78 per 10 mm Hg, 95% CI = 0.62-0.97, P = .028). No association was found between diastolic ocular perfusion pressure and PEXG, regardless of the use of antihypertensive treatment. No associations were found between systolic ocular perfusion pressure and OAG, POAG, or PEXG, regardless of the use of antihypertensive treatment.

CONCLUSIONS

Low diastolic ocular perfusion pressure may be associated with increased risk for POAG. This association was confirmed in subjects treated for systemic hypertension in subgroup analysis. This may support the hypothesis that the concept of ocular perfusion pressure status may be more relevant to glaucoma pathogenesis than ocular perfusion pressure alone.

Impact of arterial hypertension on the eye

Systemic hypertension has been linked to a wide range of major eye diseases. High arterial blood pressure (BP) decreases choroidal circulatory flow, increases intraocular pressure, and is associated with retinal microvascular abnormalities and prevalence of retinal vein occlusion (RVO) and retinopathy. This review offers a comprehensive overview of ocular diseases associated with hypertension and emphasizes their importance as predictors to future cardiovascular events. It also gives evidence-based clinical data for the therapeutic approach of eye disease in hypertensive patients.

Clinical trials for glaucoma neuroprotection are not impossible

PURPOSE OF REVIEW

To discuss issues that affect development of new glaucoma treatments known as neuroprotection.

RECENT FINDINGS

There are barriers to neuroprotection trials for glaucoma.

SUMMARY

With design features discussed in the review, neuroprotection trials can be effectively carried out.

Soluble guanylate cyclase α1-deficient mice: a novel murine model for primary open angle glaucoma

Primary open angle glaucoma (POAG) is a leading cause of blindness worldwide. The molecular signaling involved in the pathogenesis of POAG remains unknown. Here, we report that mice lacking the α1 subunit of the nitric oxide receptor soluble guanylate cyclase represent a novel and translatable animal model of POAG, characterized by thinning of the retinal nerve fiber layer and loss of optic nerve axons in the context of an open iridocorneal angle. The optic neuropathy associated with soluble guanylate cyclase α1-deficiency was accompanied by modestly increased intraocular pressure and retinal vascular dysfunction. Moreover, data from a candidate gene association study suggests that a variant in the locus containing the genes encoding for the α1 and β1 subunits of soluble guanylate cyclase is associated with POAG in patients presenting with initial paracentral vision loss, a disease subtype thought to be associated with vascular dysregulation. These findings provide new insights into the pathogenesis and genetics of POAG and suggest new therapeutic strategies for POAG.