Endothelial dysfunction in glaucoma

Lipid peroxidation: pathophysiological and pharmacological implications in the eye

Oxygen-derived free radicals such as hydroxyl and hydroperoxyl species have been shown to oxidize phospholipids and other membrane lipid components leading to lipid peroxidation. In the eye, lipid peroxidation has been reported to play an important role in degenerative ocular diseases (age-related macular degeneration, cataract, glaucoma, diabetic retinopathy). Indeed, ocular tissues are prone to damage from reactive oxygen species due to stress from constant exposure of the eye to sunlight, atmospheric oxygen and environmental chemicals. Furthermore, free radical catalyzed peroxidation of long chain polyunsaturated acids (LCPUFAs) such as arachidonic acid and docosahexaenoic acid leads to generation of LCPUFA metabolites including isoprostanes and neuroprostanes that may further exert pharmacological/toxicological actions in ocular tissues. Evidence from literature supports the presence of endogenous defense mechanisms against reactive oxygen species in the eye, thereby presenting new avenues for the prevention and treatment of ocular degeneration. Hydrogen peroxide (H2O2) and synthetic peroxides can exert pharmacological and toxicological effects on tissues of the anterior uvea of several mammalian species. There is evidence suggesting that the retina, especially retinal ganglion cells can exhibit unique characteristics of antioxidant defense mechanisms. In the posterior segment of the eye, H2O2 and synthetic peroxides produce an inhibitory action on glutamate release (using [(3)H]-D-aspartate as a marker), in vitro and on the endogenous glutamate and glycine concentrations in vivo. In addition to peroxides, isoprostanes can elicit both excitatory and inhibitory effects on norepinephrine (NE) release from sympathetic nerves in isolated mammalian iris ciliary bodies. Whereas isoprostanes attenuate dopamine release from mammalian neural retina, in vitro, these novel arachidonic acid metabolites exhibit a biphasic regulatory effect on glutamate release from retina and can regulate amino acid neurotransmitter metabolism without inducing cell death in the retina. Furthermore, there appears to be an inhibitory role for neuroprostanes in the release of excitatory amino acid neurotransmitters in mammalian retina. The ability of peroxides and metabolites of LCPUFA to alter the integrity of neurotransmitter pools provides new potential target sites and pathways for the treatment of degenerative ocular diseases.

Role of endothelium in vasomotor responses to endothelin system and protein kinase C activation in porcine retinal arterioles

PURPOSE

Endothelial cells synthesize vasodilator nitric oxide (NO) and vasoconstrictor endothelin-1 (ET-1) from NO synthase (eNOS) and endothelin-converting enzyme-1 (ECE-1), respectively. Protein kinase C (PKC) and Rho kinase (ROCK) are major signaling molecules mediating vasoconstriction. Although endothelial cells express eNOS, ECE-1, endothelin B (ET(B)) receptors, PKC, and ROCK, their influences on ET-1-induced vasoconstriction remain elusive. We studied whether these endothelial signaling molecules modulate retinal arteriolar constriction to ET-1.

METHODS

Porcine retinal arterioles were isolated and pressurized for vasomotor study, under conditions with intact or denuded endothelium, using videomicroscopic techniques.

RESULTS

Retinal arterioles developed similar resting tone (≈45% of maximum diameter) with or without endothelium. Endothelial denudation attenuated vasoconstriction to ET-1 precursor, big ET-1, by almost equal to 50%, but did not affect vasoconstrictions to ET-1, ET(B) agonist sarafotoxin S6c, or PKC activator phorbol-12, 13-dibutyrate (PDBu). The ROCK inhibitor H-1152 caused vasodilation, and abolished vasoconstrictions to ET-1 and PDBu independent of endothelium. With L-type voltage-operated calcium channel (L-VOCC) blocker nifedipine, PDBu-induced vasoconstriction was abolished and converted to NO-mediated vasodilation in the presence of endothelium. The ET-1-induced vasoconstriction was unaffected by NO released from endothelium during flow elevation.

CONCLUSIONS

Endothelial and smooth muscle ECE-1 contribute equally to synthesis of vasoactive ET-1 in retinal arterioles, with nominal role of endothelial ETB receptors in vasoconstriction to ET-1. The PKC activation leads to endothelium-dependent NO-mediated vasodilation when smooth muscle contraction is ablated by L-VOCC blockade. Endothelial cells and NO appear to have modest roles in modulating ROCK-dependent vasoconstriction, and are insufficient to counteract smooth muscle contractions to ET-1 and PKC activation.

Nutritional, lifestyle and environmental factors in ocular hypertension and primary open-angle glaucoma: an exploratory case-control study

PURPOSE

To evaluate known and potential risk factors, including nutritional, lifestyle and environmental factors, differentiating patients with high-tension primary open-angle glaucoma (POAG) from control subjects with ocular hypertension (OHT).

METHODS

In 2006-2007, 111 French ophthalmologists prospectively enrolled 339 cases of POAG and 339 age-matched controls with OHT. After a clinical examination with assessment of ocular risk factors, the ophthalmologist filled, during face-to-face interview, a detailed questionnaire developed by nutritionists and epidemiologist on lifestyle and environmental risk factors, including socio-demographic variables, dietary habits related to omega-3 fatty acids intake, smoking and alcohol drinking and professional exposure to pesticides and other chemicals. Associations of POAG with risk factors were estimated using conditional logistic regression, with adjustment for age, gender and duration of disease.

RESULTS

In the final multivariate model, by comparison with OHT, POAG was significantly associated with more frequent use of pesticides during the professional life [OR = 2.65, 95% confidence interval (CI): 1.04-6.78, p = 0.04] and with low consumption of fatty fish (OR = 2.14, 95% CI: 1.10-4.17, p = 0.02) and walnuts (OR = 2.02, 95% CI: 1.18-3.47, p = 0.01). POAG was also associated with higher frequency of heavy smoking (40 pack-years or more, OR = 3.93, 95% CI: 1.12-13.80, p = 0.03) but not with moderate (20-40 pack-years) and light smoking (<20 pack-years).

CONCLUSIONS

These exploratory observations suggest a protective effect of omega-3 fatty acids and a deleterious effect of heavy smoking and professional exposure to pesticides in POAG. This will need to be confirmed in future studies.

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.

Color Doppler imaging analysis of retrobulbar blood flow velocities in primary open-angle glaucomatous eyes: a meta-analysis

Background

To analyze the diagnostic value of color Doppler imaging (CDI) of blood flow in the retrobulbar vessels of eyes with primary open-angle glaucoma (POAG).

Methods

Pertinent publications were retrieved from the Cochrane Central Register of Controlled Trials, PubMed and the ISI Web of Knowledge up to October 2012. Changes in peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive index (RI) of the ophthalmic artery (OA), central retinal artery (CRA) and short posterior ciliary artery (SPCA) of POAG eyes and normal controls were evaluated by CDI. Subgroup analyses were conducted according to whether patients received IOP-lowering drugs treatment and were defined as treated and untreated.

Results

PSV and EDV were statistically significantly reduced in the OA of POAG eyes (P = 0.0002; P<0.00001; respectively), with significant heterogeneity (P_{heterogeneity}<0.00001, I² = 94%; P_{heterogeneity}<0.00001, I² = 85%; respectively). Similar results were demonstrated for the CRA (P<0.00001; respectively) and SPCA (P = 0.005; P<0.00001; respectively), with significant heterogeneities for both the CRA (P_{heterogeneity}<0.00001, I² = 81%; P_{heterogeneity}<0.00001, I² = 98%; respectively) and the SPCA (P_{heterogeneity}<0.00001, I² = 96%; P_{heterogeneity}<0.00001, I² = 93%; respectively). Significant increases in RI were found in all retrobulbar vessels (P<0.00001; respectively), with significant heterogeneities (P_{heterogeneity}<0.00001, I² = 95%; P_{heterogeneity}<0.00001, I² = 94%; P_{heterogeneity}<0.00001, I² = 97%; respectively).

Conclusions

This meta-analysis suggests that CDI is a potential diagnostic tool for POAG.

Retinal Oxygen Saturation and Metabolism: How does it Pertain to Glaucoma? An Update on the Application of Retinal Oximetry in Glaucoma

Purpose

To discuss the techniques and mechanisms of retinal oximetry with a focus on utilization of retinal oximetry in the assessment of retinal oxygen saturation in glaucoma.

Methods

We reviewed recent literature found by searching combinations of the following search terms: glaucoma, retinal oximetry, ocular blood flow, retinal blood flow, oxygen saturation. We also reviewed pertinent references from articles found in this search.

Results

Retinal oximetry offers the potential for directly assessing oxygen saturation in retinal tissue. This capability can contribute to the knowledge of ocular blood flow and its role in the pathogenesis of glaucoma.

Conclusions

Recent research has shown that retinal oximetry could become an important clinical tool in glaucoma. However, more research is needed to validate the reliability and reproducibility of retinal oximetry, and to fully deduce its clinical role in ocular diseases.

Imaging of retinal ganglion cells in glaucoma: pitfalls and challenges

Imaging has gained a key role in modern glaucoma management. Traditionally, interest was directed toward the appearance of the optic nerve head and the retinal nerve fiber layer. With the improvement of the resolution of optical coherence tomography, the ganglion cell complex has also become routinely accessible in the clinic. Further advances have been made in understanding the structure-function relationship in glaucoma. Nevertheless, direct imaging of the retinal ganglion cells in glaucoma would be advantageous. With the currently used techniques, this goal cannot be achieved, because the transversal resolution is limited by aberrations of the eye. The use of adaptive optics has significantly improved transversal resolution, and the imaging of several cell types including cones and astrocytes has become possible. Imaging of retinal ganglion cells, however, still remains a problem, because of the transparency of these cells. However, the visualization of retinal ganglion cells and their dendrites has been achieved in animal models. Furthermore, attempts have been made to visualize the apoptosis of retinal ganglion cells in vivo. Implementation of these techniques in clinical practice will probably improve glaucoma care and facilitate the development of neuroprotective strategies.

Retinal oximetry

ABSTRACT.:

PURPOSE

Malfunction of retinal blood flow or oxygenation is believed to be involved in various diseases. Among them are retinal vessel occlusions, diabetic retinopathy and glaucoma. Reliable, non-invasive technology for retinal oxygen measurements has been scarce and most of the knowledge on retinal oxygenation comes from animal studies. This thesis describes human retinal oximetry, performed with novel retinal oximetry technology. The thesis describes studies on retinal vessel oxygen saturation in (1) light and dark in healthy volunteers, (2) central retinal vein occlusion, (3) branch retinal vein occlusion, (4) central retinal artery occlusion, (5) diabetic retinopathy, (6) patients undergoing glaucoma surgery and (7) patients taking glaucoma medication.

METHODS

The retinal oximeter (Oxymap ehf., Reykjavik, Iceland) is based on a fundus camera. An attached image splitter allows the simultaneous capture of four images of the same area of the fundus. Two images are used for further analysis, one acquired with 586 nm light and one with 605 nm light. Light absorbance of retinal vessels is sensitive to oxygen saturation at 605 nm but not at 586 nm. Measurement of reflected light at these wavelengths allows estimation of oxygen saturation in the main retinal vessels. This is performed with custom-made analysis software.

RESULTS

LIGHT AND DARK: After 30 min in the dark, oxygen saturation in retinal arterioles of healthy volunteers was 92 ± 4% (mean ± SD, n = 15). After 5 min in 80 cd/m(2) light, the arteriolar saturation was 89 ± 5%. The decrease was statistically significant (p = 0.008). The corresponding values for retinal venules were 60 ± 5% in the dark and 55 ± 10% in the light (p = 0.020). Similar results were found after alternating 5 min periods of darkness and light. In a second experiment (n = 19), a significant decrease in retinal vessel oxygen saturation was found in 100 cd/m(2) light compared with darkness but 1 and 10 cd/m(2) light had no significant effect. CENTRAL RETINAL VEIN OCCLUSION: In patients with central retinal vein occlusion, the mean saturation in affected retinal venules was 49 ± 12%, while the mean value for venules in the fellow eye was 65 ± 6% (mean ± SD, p = 0.003, n = 8). The retinal arteriolar saturation was the same in affected (99 ± 3%) and the unaffected (99 ± 6%) eyes. The venous oxygen saturation showed much variation between affected eyes. BRANCH RETINAL VEIN OCCLUSION: Median oxygen saturation in venules affected by branch retinal vein occlusion was 59% (range, 12-93%, n = 22), while it was 63% (23-80%) in unaffected venules in the affected eye and 55% (39-80%) in venules in the fellow eye. The difference was not statistically significant (p > 0.05). There was a significant difference between affected arterioles (median 101%; range, 89-115%) and unaffected arterioles (95%, 85-104%) in the affected eye (p < 0.05, n = 18). CENTRAL RETINAL ARTERY OCCLUSION: In a patient with a day's history of central retinal artery occlusion due to temporal arteritis, the mean arteriolar saturation was 71 ± 9% and 63 ± 9% in the venules. One month later, after treatment with prednisolone, the mean arteriolar saturation was 100 ± 4% and the venous saturation 54 ± 5%. DIABETIC RETINOPATHY: When compared with healthy volunteers (n = 31), patients with all categories of diabetic retinopathy had on average 7-10 percentage points higher saturation in retinal arterioles (p < 0.05 for all categories, n = 6-8 in each category). In venules, the saturation was 8-12 percentage points higher (p < 0.05 for all categories). GLAUCOMA SURGERY: Oxygen saturation in retinal arterioles increased by 2 percentage points on average (p = 0.046, n = 19) with surgery, which lowered intraocular pressure from 23 ± 7 mmHg (mean ± SD) to 10 ± 4 mmHg (p < 0.0001). No other significant changes were found (p ≥ 0.35). DORZOLAMIDE: A significant reduction of 3 percentage points was found in arterioles (p < 0.01) and venules (p < 0.05) when patients with glaucoma or ocular hypertension changed from dorzolamide-timolol combination eye drops to timolol alone (n = 6). No change was found in patients, who started on timolol and switched to the combination therapy (p > 0.05, n = 7).

CONCLUSIONS

Dual wavelength oximetry can be used to non-invasively measure retinal vessel oxygen saturation in health and disease. The results indicate that retinal vessel oxygen saturation is (1) increased in the dark, (2) lower in venules affected by central retinal vein occlusions, (3) variable in branch retinal vein occlusion, (4) lower in retinal arterioles in central retinal artery occlusion, (5) increased in diabetic retinopathy, (6-7) mildly affected by glaucoma surgery or dorzolamide.

Association between heart rate variability and systemic endothelin-1 concentration in normal-tension glaucoma

PURPOSE

To investigate the association between heart rate variability (HRV) and the plasma level of endothelin-1 (ET-1) in normal-tension glaucoma (NTG).

MATERIALS AND METHODS

Twenty-four patients with NTG were enrolled. Subjects with systemic diseases were excluded. All patients underwent a complete ophthalmic examination and were referred to the rheumatology department, where HRV assessment was performed. Patients were divided into two groups according to the standard deviation of normal-normal intervals (SDNN). The low heart rate variability (LHV) group consisted of patients with SDNN values in the bottom half of range of values, and the high heart rate variability (HHV) group consisted of those with SDNN values in the upper half of the range. Blood samples were assayed for ET-1 concentrations, which were compared between the LHV and HHV groups. The relationships between the ET-1 level and HRV parameters were analyzed.

RESULTS

The LHV group showed significantly lower ET-1 levels compared with the HHV group (0.57 ± 1.09 versus 2.21 ± 3.56 pg/ml, respectively; p = 0.04). Among the HRV parameters, the SDNN and total power were significantly associated with the systemic level of ET-1 (ρ = 0.729, p < 0.001; ρ = 0.713, p < 0.001, respectively).

CONCLUSIONS

After excluding patients with systemic diseases, the plasma ET-1 level was associated with HRV parameters in patients with NTG. These observations suggest that the relationship between autonomic dysfunction and autoregulation may play a role in the pathogenesis of NTG.

In vivo laser scanning confocal microscopy of the cornea in patients with silicone oil tamponade after vitreoretinal surgery

PURPOSE

To evaluate the morphological changes in the cornea by in vivo laser scanning confocal microscopy (LSCM) in a large case series with silicone oil endotamponade after vitreoretinal surgery and to explore the value of LSCM in the early detection of silicone keratopathy (SK).

METHODS

Ninety-nine patients (99 eyes) with silicone oil endotamponade after vitreoretinal surgery were included in the current study. Slit-lamp examination and measurement of intraocular pressure (IOP) were performed first. Then the central corneas of the subjects' eyes were examined by in vivo LSCM. The analysis of images of each corneal layer was performed and the endothelial cellular density (ECD), endothelial cellular area (ECA), coefficient of variation of cell size (CoV), and percentage of hexagonal cells (PHC) were measured. Moreover, the total size of stromal deposits was measured, and the correlation between the size of deposits and the parameters of endothelial cells was analyzed.

RESULTS

Clinically recognizable abnormalities involving the cornea were identified in only 12 eyes (12.1%) under slit-lamp biomicroscopy, whereas in vivo LSCM revealed morphological abnormalities in 40 eyes (40.4%). The manifestations of endothelial lesions varied from decreased cellular density, increased polymegathism and pleomorphism to hyperreflective silicone oil membrane or droplets adhering to the endothelium. Moreover, hyperreflective deposits with various shapes could be identified in both posterior and anterior stroma, along with the infiltration of Langerhans cells beneath the epithelium. The average ECD and PHC of eyes with corneal abnormalities were significantly lower than those of normal corneas, whereas the average ECA and CoV were significantly larger (all Ps < 0.001). The patients with corneal abnormalities were significantly older than those others (P = 0.003). The rate of pseudophakic and aphakic eyes having corneal abnormalities was significantly higher than that of phakic eyes (P = 0.045). Interestingly, the total size of stromal deposits had a significant negative correlation with ECD and PHC but a significant positive correlation with ECA and CoV (all Ps < 0.001). Further correlation analysis performed in groups divided according to the lens status showed similar results and even stronger correlations in aphakic and pseudophakic eyes, whereas no statistically significant correlations were found in phakic eyes.

CONCLUSIONS

In vivo LSCM was a useful tool in the early detection of corneal abnormalities caused by silicone oil injection, including varying corneal endothelium lesions and stromal abnormalities. Pseudophakic or aphakic eyes, as well as those of older patients, should receive more attention because they are more inclined to develop silicone keratopathy.

Ocular perfusion pressure and ocular blood flow in glaucoma

Glaucoma is a progressive optic neuropathy of unknown origin. It has been hypothesized that a vascular component is involved in glaucoma pathophysiology. This hypothesis has gained support from studies showing that reduced ocular perfusion pressure is a risk factor for the disease. The exact nature of the involvement is, however, still a matter of debate. Based on recent evidence we propose a model including primary and secondary insults in glaucoma. The primary insult appears to happen at the optic nerve head. Increased intraocular pressure and ischemia at the post-laminar optic nerve head affects retinal ganglion cell axons. Modulating factors are the biomechanical properties of the tissues and cerebrospinal fluid pressure. After this primary insult retinal ganglion cells function at a reduced energy level and are sensitive to secondary insults. These secondary insults may happen if ocular perfusion pressure falls below the lower limit of autoregulation or if neurovascular coupling fails. Evidence for both faulty autoregulation and reduced hyperemic response to neuronal stimulation has been provided in glaucoma patients. The mechanisms appear to involve vascular endothelial dysfunction and impaired astrocyte-vessel signaling. A more detailed understanding of these pathways is required to direct neuroprotective strategies via the neurovascular pathway.

Retinal vascular geometry and glaucoma: the Singapore Malay Eye Study

PURPOSE

To determine the associations of geometric measurements (tortuosity, branching angle, and fractal dimension) of retinal vessels with glaucoma.

DESIGN

Population-based, cross-sectional study.

PARTICIPANTS

Persons aged 40 to 80 years who participated in the Singapore Malay Eye Study (n=3280; 78.7% response rate).

METHODS

Quantitative retinal vascular parameters (tortuosity, branching angle, and fractal dimension) were measured from digital retinal fundus photographs using a computer-assisted program following a standardized grading protocol. Glaucoma was diagnosed according to the International Society of Geographic and Epidemiological Ophthalmology classification system.

MAIN OUTCOME MEASURES

The associations among retinal vascular parameters with glaucoma, the main glaucoma subtype primary open-angle glaucoma (POAG), and ocular hypertension (OHT).

RESULTS

A total of 123 persons (4.4% of the 2789 participants) had glaucoma in the final analysis, 87 (70.7%) of whom were diagnosed with POAG. After adjusting for age, sex, body mass index, diabetes, hypertension, smoking, axial length, and intraocular pressure (IOP), decreased retinal arteriolar tortuosity (odds ratio [OR], 1.73; 95% confidence interval [CI], 1.38-2.18, comparing lowest vs. highest quartiles), decreased retinal venular tortuosity (OR, 1.59; 95% CI, 1.29-1.97), and narrower retinal venular branching angle (OR, 1.22; 95% CI, 1.00-1.48) were associated with glaucoma. Similar associations were found between these retinal vascular parameters and POAG. Decreased retinal vascular fractal dimension was associated with OHT (OR 1.37; 95% CI, 1.04-1.82).

CONCLUSIONS

Certain features of retinal vascular geometry are associated with glaucomatous optic neuropathy independently of vascular risk factors and IOP.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Response of retinal blood flow to systemic hyperoxia as measured with dual-beam bidirectional Doppler Fourier-domain optical coherence tomography

PURPOSE

There is a long-standing interest in the study of retinal blood flow in humans. In the recent years techniques have been established to measure retinal perfusion based on optical coherence tomography (OCT). In the present study we used a technique called dual-beam bidirectional Doppler Fourier-domain optical coherence tomography (FD-OCT) to characterize the effects of 100% oxygen breathing on retinal blood flow. These data were compared to data obtained with a laser Doppler velocimeter (LDV).

METHODS

10 healthy subjects were studied on 2 study days. On one study day the effect of 100% oxygen breathing on retinal blood velocities was studied using dual-beam bidirectional Doppler FD-OCT. On the second study day the effect of 100% oxygen breathing on retinal blood velocities was assessed by laser Doppler velocimetry (LDV). Retinal vessel diameters were measured on both study days using a commercially available Dynamic Vessel Analyzer. Retinal blood flow was calculated based on retinal vessel diameters and red blood cell velocity.

RESULTS

As expected, breathing of pure oxygen induced a pronounced reduction in retinal vessel diameters, retinal blood velocities and retinal blood flow on both study days (p<0.001). Blood velocity data correlated well between the two methods applied under both baseline as well as under hyperoxic conditions (r = 0.98 and r = 0.75, respectively). Data as obtained with OCT were, however, slightly higher.

CONCLUSION

A good correlation was found between red blood cell velocity as measured with dual-beam bidirectional Doppler FD-OCT and red blood cell velocity assessed by the laser Doppler method. Dual-beam bidirectional Doppler FD-OCT is a promising approach for studying retinal blood velocities in vivo.

Analysis of systemic endothelin-1, matrix metalloproteinase-9, macrophage chemoattractant protein-1, and high-sensitivity C-reactive protein in normal-tension glaucoma

PURPOSE

To investigate the roles of vascular dysregulation and inflammation in normal-tension glaucoma (NTG), we determined the plasma levels of endothelin-1 (ET-1), matrix metalloproteinase-9 (MMP-9), macrophage chemoattractant protein-1 (MCP-1), and high-sensitivity C-reactive protein (hs-CRP).

MATERIALS AND METHODS

Forty-five patients with NTG and age-matched 35 healthy controls were enrolled in this study. Blood samples from all subjects were assayed for ET-1, MMP-9, MCP-1, and hs-CRP concentrations and other systemic factors.

RESULTS

There were no significant differences in hemoglobin, hematocrit, RBC count, WBC count, platelet count, fasting glucose, HbA1c, total cholesterol, triglyceride, LDL, and HDL between the NTG and control groups. The systemic levels of ET-1 and MCP-1 were significantly higher in the NTG group than in the control group (p = 0.05 and 0.02, respectively). The MMP-9 and hs-CRP levels were not significantly different between the NTG and control groups.

CONCLUSIONS

After excluding patients with cardiovascular and other systemic diseases, plasma ET-1 and MCP-1 levels were elevated in patients with NTG. The MMP-9 and hs-CRP levels were not significantly different in NTG. Increased ET-1 and MCP-1 levels suggest that ischemia/inflammation may play a role in the pathogenesis of NTG.

Relationship among visual field, blood flow, and neural structure measurements in glaucoma

PURPOSE

To determine the relationship among visual field, neural structural, and blood flow measurements in glaucoma.

METHODS

Case-control study. Forty-seven eyes of 42 patients with perimetric glaucoma were age-matched with 27 normal eyes of 27 patients. All patients underwent Doppler Fourier-domain optical coherence tomography to measure retinal blood flow and standard glaucoma evaluation with visual field testing and quantitative structural imaging. Linear regression analysis was performed to analyze the relationship among visual field, blood flow, and structure, after all variables were converted to logarithmic decibel scale.

RESULTS

Retinal blood flow was reduced in glaucoma eyes compared to normal eyes (P < 0.001). Visual field loss was correlated with both reduced retinal blood flow and structural loss of rim area and retinal nerve fiber layer (RNFL). There was no correlation or paradoxical correlation between blood flow and structure. Multivariate regression analysis revealed that reduced blood flow and structural loss are independent predictors of visual field loss. Each dB decrease in blood flow was associated with at least 1.62 dB loss in mean deviation (P ≤ 0.001), whereas each dB decrease in rim area and RNFL was associated with 1.15 dB and 2.56 dB loss in mean deviation, respectively (P ≤ 0.03).

CONCLUSIONS

There is a close link between reduced retinal blood flow and visual field loss in glaucoma that is largely independent of structural loss. Further studies are needed to elucidate the causes of the vascular dysfunction and potential avenues for therapeutic intervention. Blood flow measurement may be useful as an independent assessment of glaucoma severity.

Endothelin-1 plasma levels and vascular endothelial dysfunction in primary open angle glaucoma

AIMS

To assess the relationship between endothelial dysfunction, endothelin 1 (ET-1) plasma levels and subclinical inflammation in primary open angle glaucoma (POAG) patients.

MAIN METHODS

We enrolled 40 POAG patients with progressive visual field damage, although well controlled intraocular pressure (IOP) and compared to age and sex matched healthxy subjects. Each patient underwent an ophthalmological examination, a standard achromatic perimetry (SAP), blood sampling to assess ET-1 plasma levels, an objective assessment of cellularity within the anterior chamber (FLARE) and measurement of flow mediated dilation (FMD) with high resolution 2-dimensional ultrasonographic imaging of the brachial artery.

KEY FINDINGS

At baseline, POAG patients, compared to healthy controls, showed an increase of ET-1 plasma levels: 2.83 ± 0.28 pg/ml vs. 1.75 ± 0.25 pg/ml (p<0.001), lower FMD values 4.46 ± 1.28% vs. 13.18 ± 2.80% (p<0.001) and increased FLARE values 9.98 ± 0.97 photons/ms vs. 5.87 ± 0.64 photons/ms (p<0.001). A follow up after 1 year revealed a further increase of ET-1 plasma levels (to 3.68 ± 0.60; p<0.001) and decrease of FMD (3.52 ± 1.28; p>0.001).

SIGNIFICANCE

The increase of ET-1 in POAG patients is related to vascular dysfunction (r=0.942; p=0.001) and vascular dysfunction is related to sub-clinical intraocular inflammation (r=0.968; p=0.001). Thus ET-1 and vascular dysfunction related to sub-clinical inflammation may play a key role in determining a progressive visual field damage in POAG patients who present a well-controlled IOP.

Correlation of optic disc morphology and ocular perfusion parameters in patients with primary open angle glaucoma

PURPOSE

Little information is available about the relationship between glaucomatous visual field defects, morphological changes of the optic disc and ocular blood flow. In this study, ocular blood flow parameters were correlated with parameters of optic nerve head (ONH) morphology and visual field performance in a cross-sectional study.

METHODS

A total of 103 patients with primary open angle glaucoma were included. Choroidal and ONH blood flow was assessed using laser Doppler flowmetry. Retinal blood velocities and retinal vessel diameters were measured with laser Doppler velocimetry and a Retinal Vessel Analyzer, respectively. To evaluate the ONH morphology, fundus photographs were taken and confocal laser scanning tomography was performed.

RESULTS

Among all measured ocular hemodynamic parameters, the ONH blood flow was most strongly correlated to structural parameters of ONH damage and visual field loss. Reduced retinal vessel diameters were only slightly correlated with the degree of glaucomatous damage.

CONCLUSION

Reduced blood flow in the ONH was associated with increasing amount of visual field defect and morphological changes of the ONH. Retinal vessel diameters were only marginally associated with glaucomatous optic nerve damage. Based on retinal vessel diameter determination alone, it is not possible to assess whether reduced retinal blood flow is causative or secondary in glaucoma.

Identification of the muscarinic acetylcholine receptor subtype mediating cholinergic vasodilation in murine retinal arterioles

PURPOSE

To identify the muscarinic acetylcholine receptor subtype that mediates cholinergic vasodilation in murine retinal arterioles.

METHODS

Muscarinic receptor gene expression was determined in murine retinal arterioles using real-time PCR. To assess the functional relevance of muscarinic receptors for mediating vascular responses, retinal vascular preparations from muscarinic receptor-deficient mice were studied in vitro. Changes in luminal arteriole diameter in response to muscarinic and nonmuscarinic vasoactive substances were measured by video microscopy.

RESULTS

Only mRNA for the M(3) receptor was detected in retinal arterioles. Thus, M(3) receptor-deficient mice (M3R(-/-)) and respective wild-type controls were used for functional studies. Acetylcholine concentration-dependently dilated retinal arterioles from wild-type mice. In contrast, vasodilation to acetylcholine was almost completely abolished in retinal arterioles from M3R(-/-) mice, whereas responses to the nitric oxide (NO) donor nitroprusside were retained. Carbachol, an acetylcholinesterase-resistant analog of acetylcholine, also evoked dilation in retinal arterioles from wild-type, but not from M3R(-/-), mice. Vasodilation responses from wild-type mice to acetylcholine were negligible after incubation with the non-subtype-selective muscarinic receptor blocker atropine or the NO synthase inhibitor N(ω)-nitro-L-arginine methyl ester, and were even reversed to contraction after endothelial damage with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate.

CONCLUSIONS

These findings provide evidence that endothelial M(3) receptors mediate cholinergic vasodilation in murine retinal arterioles via activation of NO synthase.

The association of ocular blood flow with haemorheological parameters in primary open-angle and exfoliative glaucoma

PURPOSE

To evaluate the ocular blood flow velocities and haemorheological parameters in patients with primary open-angle glaucoma (POAG), exfoliative glaucoma (XFG) and exfoliation syndrome (XFS) and to compare their results with those of healthy controls.

METHODS

Twenty-five patients with POAG (group 1), 25 patients with XFG (group 2), 25 patients with XFS (group 3) and 25 healthy controls (group 4) were included in the study. Ocular blood flow velocities of ophthalmic artery (OA), central retinal artery (CRA) and short posterior ciliary arteries (SPCAs) were measured using colour Doppler imaging (CDI). Haemorheological parameters (erythrocyte elongation and aggregation index, aggregation amplitude, aggregation half-life, plasma viscosity, haematocrit) were measured in venous blood samples of all patients.

RESULTS

The peak systolic velocity (PSV) and end-diastolic velocity (EDV) values were lower and resistive indices (RI) were higher for the OA, CRA and SPCA of glaucomatous (groups 1 and 2) patients compared with those of controls (group 4) (PSV: OA, 40.4 ± 11.3 versus 52.6 ± 12.8 cm/second, p < 0.001; CRA, 12.9 ± 2.9 versus 15.3 ± 4.2 cm/second, p = 0.02; SPCA, 21.7 ± 6.6 versus 26.6 ± 8.3 cm/second, p = 0.013) (EDV: OA, 10.3 ± 4.3 versus 14.2 ± 5.1 cm/second, p < 0.001; CRA, 3.7 ± 1.1 versus 4.5 ± 1.3 cm/second, p = 0.025; SPCA, 5.2 ± 1.8 versus 7.7 ± 3.2 cm/second, p = 0.001) (RI: OA, 0.75 ± 0.05 versus 0.66 ± 0.07, p < 0.001; CRA, 0.73 ± 0.08 versus 0.68 ± 0.10, p = 0.223; SPCA, 0.70 ± 0.10 versus 0.63 ± 0.11, p = 0.004). There were no statistically significant differences between the haemorheological parameters of glaucomatous and non-glaucomatous patients. The reduction in ocular blood flow velocities in groups 1, 2 and 3 were not associated with changes in haemorheological parameters.

CONCLUSION

Our results suggest that impairment of the retrobulbar blood flow in POAG and XFG is not associated with alterations in haemorheological parameters.

Endothelin-1 and nitric oxide levels in patients with glaucoma

AIMS

To investigate the levels of endothelin-1 (ET-1) and nitric oxide (NO) in the aqueous humor and plasma of human eyes with different types of glaucoma: primary open-angle glaucoma (POAG) and chronic closed-angle glaucoma (CCAG).

METHODS

Patients were classified into 3 groups: group I comprised 35 patients with POAG, group II comprised 25 patients with CCAG, and 30 patients with senile cataract (group III) were used as a control group. Aqueous humor and corresponding plasma were analyzed for ET-1 and NO concentrations by enzyme-linked immunosorbent assay. A Bonferroni correction for multiple comparisons was performed.

RESULTS

There was no significant difference in plasma levels of either ET-1 or NO metabolites between the groups studied. ET-1 and NO were significantly elevated in the aqueous humor of patients with CCAG and POAG compared to the corresponding value in patients with cataract (p < 0.001). ET-1 and NO concentrations in the aqueous humor were more marked in CCAG than in POAG. NO levels were correlated with ET-1 in the aqueous humor of patients with glaucoma (p < 0.001).

CONCLUSIONS

Increased concentrations of ET-1 and NO in aqueous humor may be useful with POAG and CCAG. In addition, ET-1 and NO may have useful metabolite levels in the aqueous humor of POAG and CCAG patients as a result of glaucoma damage and may not be a cause of it.

Ocular findings in patients with systemic sclerosis

OBJECTIVE

To evaluate the frequency and characteristics of ocular manifestations in outpatients with systemic sclerosis.

METHODS

In this cross-sectional study, 45 patients with systemic sclerosis were enrolled. Data regarding demographics, disease duration and subtype, age at diagnosis, nailfold capillaroscopic pattern and autoantibody profile were collected, and a full ophthalmic examination was conducted. Parametric (Student's t-test) and nonparametric (Mann-Whitney U test) tests were used to compare continuous variables. Fisher's exact test was used to compare categorical data. P values < 0.05 were considered significant.

RESULTS

Twenty-three subjects (51.1%) had eyelid skin changes; 22 (48.9%) had keratoconjunctivitis sicca, 19 (42.2%) had cataracts, 13 (28.9%) had retinal microvascular abnormalities and 6 (13.3%) had glaucoma. Eyelid skin changes were more frequent in patients with the diffuse subtype of systemic sclerosis and were associated with a younger age and an earlier age at diagnosis. Cataracts were presumed to be age-related and secondary to corticosteroid treatment. There was no association between demographic, clinical or serological data and keratoconjunctivitis sicca. The retinal microvascular abnormalities were indistinguishable from those related to systemic hypertension and were associated with an older age and a severe capillaroscopic pattern.

CONCLUSIONS

Eyelid skin abnormalities and keratoconjunctivitis sicca were the most common ocular findings related to systemic sclerosis. Some demographic and clinical data were associated with some ophthalmic features and not with others, showing that the ocular manifestations of systemic sclerosis are characterized by heterogeneity and reflect the differences in the implicated pathophysiological mechanisms.

Influence of gender and menopausal status on peripheral and choroidal circulation

PURPOSE

To evaluate the influence of menopausal status and age on peripheral and ocular circulation assessed by means of continuous laser Doppler flowmetry (LDF).

METHODS

Fifty-three healthy participants were recruited randomly. Twenty-six men and 27 women were divided into two age groups. Choroidal blood flow was measured by LDF and peripheral circulation was measured at the fingertips (digit IV) using the Perimed PeriFlux (Järfälla, Sweden) laser Doppler System 5000. Independent t-test and two-way analysis of variance (anova) were performed.

RESULTS

Group distribution was: male/female = 14/16 for the younger group and 12/11 for the older group. Average age across groups was 31.3 ± 6.8/28.4 ± 7.0 years and 66.3 ± 8.3/61.5 ± 3.6 years, respectively. Finger and choroidal LDF flow values were significantly different between the two female age groups (p < 0.001 and p = 0.03, respectively). In men this was not the case (p = 0.85 and p = 0.56, respectively). anova interaction p-value for the factors 'age group' and 'gender' for finger LDF flow was p = 0.012, and for choroidal LDF flow p = 0.049, demonstrating significant gender differences with ageing.

CONCLUSION

  Menopausal status in women has significant influence on both choroidal and peripheral blood flow; the opposite behaviour occurs with ageing.

Openers of small conductance calcium-activated potassium channels selectively enhance NO-mediated bradykinin vasodilatation in porcine retinal arterioles

BACKGROUND AND PURPOSE

Small (SK(Ca) or K(Ca)2) and intermediate (IK(Ca) or K(Ca)3.1) conductance calcium-activated potassium channels are involved in regulation of vascular tone and blood pressure. The present study investigated whether NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) and CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), which are selective openers of SK(Ca) and IK(Ca) channels and of SK(Ca)2 and SK(Ca)3 channels, respectively, enhance endothelium-dependent vasodilatation in porcine retinal arterioles.

EXPERIMENTAL APPROACH

In porcine retinal arterioles, SK(Ca)3 and IK(Ca) protein localization was examined by immunolabelling. Endothelial cell calcium was measured by fluorescence imaging. For functional studies, arterioles with internal diameters of 116 +/- 2 microm (n = 276) were mounted in microvascular myographs for isometric tension recordings.

KEY RESULTS

SK(Ca)3 and IK(Ca) protein was localized in the endothelium. Bradykinin, but not NS309 or CyPPA increased endothelial cell calcium. Pre-incubation with NS309 or CyPPA enhanced bradykinin relaxation without changing endothelial cell calcium. This enhanced relaxation was abolished by blocking SK(Ca) channels with apamin. In the presence of NS309 or CyPPA, mainly inhibition of NO synthase with asymmetric dimethylarginine, but also inhibition of cyclooxygenase with indomethacin, reduced bradykinin relaxation. Bradykinin relaxation was completely abolished by NO synthase and cyclooxygenase inhibition together with a NO scavenger, oxyhaemoglobin.

CONCLUSIONS AND IMPLICATIONS

In porcine retinal arterioles, bradykinin increases endothelial cell calcium leading to activation of SK(Ca) and IK(Ca) channels. Without altering endothelial cell calcium, NS309 and CyPPA open SK(Ca) channels that enhance NO-mediated bradykinin relaxations. These results imply that opening SK(Ca) channels improves endothelium-dependent relaxation and makes this channel a potential target for treatments aimed at restoring retinal blood flow.

Systemic high-sensitivity C-reactive protein level in pseudoexfoliation syndrome and pseudoexfoliation glaucoma

PURPOSE

To evaluate the systemic high sensitivity C-reactive protein (hsCRP) levels in patients with pseudoexfoliation syndrome (XFS) and pseudoexfoliation glaucoma (XFG).

MATERIALS AND METHODS

We prospectively examined 31 patients with XFS, 26 with XFG, and 25 controls. To the study patients with the exclusion of serious hypertension that do not have any cardiovascular and cerebrovascular disease and that diagnosed as XFS and XFG have been included. Each patient passed through a detailed blood sampling including hsCRP, biochemistry, and lipid profile. Plasma C-reactive protein (CRP) levels were measured with nephelometric method by using Beckman IMMAGE hsCRP reagent.

RESULTS

Each group had similar demographic parameters including age, sex, body mass index, heart rate, and blood pressure. When we compared with controls, there was no statistically significant difference in the hsCRP and biochemistry results between the 3 groups. When all patients with pseudoexfoliation (PEX) compared with controls there was no difference.

CONCLUSIONS

Our findings indicated no difference in the hsCRP level between XFS, XFG, and controls. This study suggests that CRP is not a predictive marker of inflammation and peripheral endothelial dysfunction in XFS, which is accepted as a systemic disorder.

The complex interaction between ocular perfusion pressure and ocular blood flow - relevance for glaucoma

Glaucoma is an optic neuropathy of unknown origin. The most important risk factor for the disease is an increased intraocular pressure (IOP). Reducing IOP is associated with reduced progression in glaucoma. Several recent large scale trials have indicated that low ocular perfusion pressure (OPP) is a risk factor for the incidence, prevalence and progression of the disease. This is a strong indicator that vascular factors are involved in the pathogenesis of the disease, a hypothesis that was formulated 150 years ago. The relation between OPP and blood flow to the posterior pole of the eye is, however, complex, because of a phenomenon called autoregulation. Autoregulatory processes attempt to keep blood flow constant despite changes in OPP. Although autoregulation has been observed in many experiments in the ocular vasculature the mechanisms underlying the vasodilator and vasoconstrictor responses in face of changes in OPP remain largely unknown. There is, however, recent evidence that the human choroid regulates its blood flow better during changes in blood pressure induced by isometric exercise than during changes in IOP induced by a suction cup. This may have consequences for our understanding of glaucoma, because it indicates that blood flow regulation is strongly dependent not only on OPP, but also on the level of IOP itself. Indeed there is data indicating that reduction of IOP by pharmacological intervention improves optic nerve head blood flow regulation independently of an ocular vasodilator effect.

Oxidative stress markers in patients with primary open-angle glaucoma

PURPOSE

To investigate the levels of antioxidant enzymes catalase (CAT), glutathione peroxidase (GPO), superoxide dismutase (SOD), and malondialdehyde (MDA) in human eyes with primary open-angle glaucoma (POAG) and to correlate their concentrations with severity of glaucoma.

DESIGN

A prospective cases control study.

PATIENTS AND METHODS

Thirty patients with primary open-angle glaucoma and twenty-five patients with senile cataracts of matched age and gender were included in the study prospectively. Aqueous humor samples were obtained by paracentesis at the time of elective surgery for glaucomatous and cataractous patients. Aqueous humor were analyzed for CAT, GPO, SOD, and MDA status.

RESULTS

GPO, SOD, and MDA enzyme levels revealed a high significant increase in aqueous humor of POAG patients with respect to the comparative group of cataract patients (P < 0.001). No significant difference in the activity of CAT enzyme in aqueous humor of POAG and cataract patient (P = 0.201). Significant correlation was found between the MDA enzyme level and severe visual field loss (P < 0.001) in POAG patients.

CONCLUSION

Increased levels of aqueous humor GPO, SOD, and MDA may be associated with POAG. In addition, they may be useful antioxidant enzyme levels in aqueous humor of POAG patients as a result of glaucoma disease and not a cause.

Metabolic vulnerability disposes retinal ganglion cell axons to dysfunction in a model of glaucomatous degeneration

We tested the hypothesis that glaucoma disrupts electrophysiological conduction properties and axon function in optic nerve as a function of intraocular pressure (IOP) levels and age in the DBA/2J mouse model of glaucoma. The amplitude and the integral of electrical signals evoked along the axons decreased considerably by 6 months of age as a function of increasing IOP levels. At young ages, raised IOP was directly associated with increased vulnerability to metabolic challenge. Changes in the physiological function of the optic nerves were accentuated with aging, leading to loss of compound action potential in an entire population of fibers: small, slow conducting axons. This loss was accompanied with loss of small fiber axon counts and declining metabolic reserve by demonstrating IOP-dependent ATP decrease in mouse optic nerves. These data shed light on a novel potential mechanism of glaucoma pathology whereby increased IOP and declining metabolic capacity lead to axon liability and eventually dysfunction and loss.

Ocular blood flow and oxygen delivery to the retina in primary open-angle glaucoma patients: the addition of dorzolamide to timolol monotherapy

PURPOSE

To assess the effects of adding dorzolamide to timolol monotherapy on ocular haemodynamics and retinal oxygen saturation in patients with primary open-angle glaucoma (POAG).

METHODS

Twenty-four patients (12 healthy, 12 with POAG) were treated with dorzolamide/timolol combination (DT) versus timolol maleate 0.5% twice daily in a randomized, crossover, double-blind study conducted over a period of 18 months. Patients received each treatment for 8 months then crossed over to the other treatment after a 1-month washout and second baseline. Goldmann applanation tonometry, Heidelberg retinal flowmetry (HRF), colour Doppler imaging (CDI) and retinal photographic oximetry were performed at each visit.

RESULTS

DT significantly reduced intraocular pressure (IOP) in both glaucomatous [right eye (OD) -13.15%, left eye (OS) -14.43%; p < 0.036] and non-glaucomatous (OD -12.4%, OS -13.88%; p < 0.039) patients compared to timolol after 8 months of treatment. DT significantly reduced the number of zero blood flow pixels in the superior (-39.72%; p < 0.014) and inferior (-51.44%; p < 0.008) retina in the non-glaucomatous group and inferior retina in the glaucomatous group (-55.38%, p < 0.006). The continuation of timolol monotherapy from baseline did not change (p < 0.05) any measured parameter and neither treatment had a significant effect (p < 0.05) on retinal oximetry or CDI parameters.

CONCLUSION

The addition of dorzolamide to timolol monotherapy decreases IOP and increases retinal blood flow in the superficial retinal vasculature in both glaucomatous and healthy patients following 8 months of treatment. The combination of increased retinal blood flow with consistent oxygen saturation may potentially increase oxygen delivery to the retina.

Reduced endothelial progenitor cells and brachial artery flow-mediated dilation as evidence of endothelial dysfunction in ocular hypertension and primary open-angle glaucoma

PURPOSE

This study aimed to assess vascular endothelial function in patients with ocular hypertension (OHT) or primary open-angle glaucoma (POAG) by measuring: (a) endothelium-dependent flow-mediated vasodilation (FMD) of the brachial artery, and (b) circulating endothelial progenitor cells, which are believed to support the integrity of the vascular endothelium.

METHODS

We enrolled 25 patients with OHT, 23 with POAG and 26 control subjects, all of whom were aged < 65 years and had no medical history of cardiovascular disease or cardiovascular risk factors. All subjects underwent a complete ophthalmological examination, biochemistry study, assessment of cardiovascular parameters, brachial artery ultrasound assessment of endothelium-dependent FMD, generic circulating progenitor cell (CPC) and circulating endothelial progenitor cell (EPC) count with the use of flow cytometry.

RESULTS

Flow-mediated vasodilation values differed significantly in OHT (4.5 +/- 1.1%; p = 0.021) and POAG (4.0 +/- 0.9%; p = 0.003) patients compared with controls (7.7 +/- 0.8%). The CD34(+) KDR(+) EPC count was markedly lower in OHT (28.0 +/- 5.0; p < 0.001) and POAG (24.3 +/- 3.4; p < 0.001) patients compared with controls (73.1 +/- 8.1). Neither FMD not EPCs differed significantly between OHT and POAG patients. No significant differences in CPC count or cardiovascular parameters were found among OHT or POAG patients and controls. The levels of CD34(+) KDR(+) EPCs were directly correlated (p = 0.043) with FMD, and inversely correlated (p = 0.032) with baseline intraocular pressure in OHT and POAG patients.

CONCLUSIONS

Both OHT and POAG patients without cardiovascular risk factors have previously unreported severely reduced circulating EPCs and reduced FMD, both of which are indicators of endothelial dysfunction and increased risk of cardiovascular events.

Ocular hemodynamic effects of nitrovasodilators in healthy subjects

Nitric oxide (NO) plays a key role in the regulation of ocular blood flow and may be an interesting therapeutic target in ocular ischemic disease. In the present study, we hypothesized that NO-releasing drugs may increase blood flow to the head of the optic nerve and also in the choroid. The study employed a randomized, placebo-controlled, double blind, four-way crossover design. On separate study days, 12 healthy subjects received infusions of nitroglycerin, isosorbide dinitrate, sodium nitroprusside, or placebo. All three study drugs reduced the mean arterial pressure (MAP) and ocular perfusion pressure (OPP) (P < 0.001). None of the administered drugs increased the ocular hemodynamic variables. By contrast, vascular resistance decreased dose dependently during administration of the study drugs (P < 0.001). These results indicate that systemic administration of NO-donor drugs is associated with a decrease in vascular resistance in the ocular vasculature. However, because these drugs also reduce blood pressure, they do not improve perfusion to the posterior eye pole.

Correlation between local stress and strain and lamina cribrosa connective tissue volume fraction in normal monkey eyes

PURPOSE

To investigate the biomechanical response to IOP elevation of normal monkey eyes using eye-specific, three-dimensional (3-D) finite element (FE) models of the ONH that incorporate lamina cribrosa (LC) microarchitectural information.

METHODS

A serial sectioning and episcopic imaging technique was used to reconstruct the ONH and peripapillary sclera of four pairs of eyes fixed at 10 mm Hg. FE models were generated with local LC material properties representing the connective tissue volume fraction (CTVF) and predominant LC beam orientation and used to simulate an increase in IOP from 10 to 45 mm Hg. An LC material stiffness constant was varied to assess its influence on biomechanical response.

RESULTS

Strains and stresses within contralateral eyes were remarkably similar in both magnitude and distribution. Strain correlated inversely, and nonlinearly, with CTVF (median, r (2) = 0.73), with tensile strains largest in the temporal region. Stress correlated linearly with CTVF (median r(2) = 0.63), with the central and superior regions bearing the highest stresses. Net average LC displacement was either posterior or anterior, depending on whether the laminar material properties were compliant or stiff.

CONCLUSIONS

The results show that contralateral eyes exhibit similar mechanical behavior and suggest that local mechanical stress and strain within the LC are correlate highly with local laminar CTVF. These simulations emphasize the importance of developing both high-resolution imaging of the LC microarchitecture and next-generation, deep-scanning OCT techniques to clarify the relationships between IOP-related LC displacement and CTVF-related stress and strain in the LC. Such imaging may predict sites of IOP-related damage in glaucoma.