Seigo Nakabayashi

Autoregulation of retinal blood flow in response to decreased ocular perfusion pressure in cats: comparison of the effects of increased intraocular pressure and systemic hypotension.

PURPOSE To investigate the regulatory mechanisms responsible for autoregulation of retinal blood flow (RBF) during periods of decreased ocular perfusion pressure (OPP). METHODS The effects of acute reductions in OPP on RBF were assessed using laser Doppler velocimetry in cats. The OPP decreased from 90 to 40 mm Hg by increasing the IOP (elevated IOP) or by decreasing the systemic blood pressure via exsanguination (systemic hypotension). The contributions of nitric oxide (NO), adenosine, and/or N-methyl-D-aspartic acid (NMDA) in regulation of the retinal arteriolar hemodynamics during decreased OPP was determined at 120 minutes after intravitreal injection of various inhibitors or PBS. RESULTS Following PBS injection, the flow velocity decreased in proportion to the decrease in OPP; however, the retinal arteriolar diameter gradually increased. Consequently, the RBF was maintained near baseline levels when the OPP exceeded 70 mm Hg but decreased significantly (P < 0.01) when the OPP fell to less than or equal to 60 mm Hg due to elevated IOP or systemic hypotension. Adenosine receptor blocker 8-(p-sulfophenyl)theophylline, significantly (P < 0.01) enhanced decreases in RBF induced by elevated IOP and systemic hypotension at OPP from 80 to 40 mm Hg, whereas NO synthase inhibitor N(G)-nitro-L-arginine-methyl ester and NMDA receptor antagonist DL-2-amino-5-phosphonopentanoic acid only significantly (P < 0.01) enhanced reductions in RBF induced by elevated IOP. CONCLUSIONS These results indicate that adenosine contributes to autoregulation of RBF during systemic hypotension, whereas adenosine, NO, and NMDA receptors autoregulate the RBF after elevated IOP. Different vasoregulatory factors might contribute to autoregulation of RBF after decreases in OPP induced by elevated IOP and systemic hypotension.

Acute hyperglycemia-induced endothelial dysfunction in retinal arterioles in cats.

PURPOSE To investigate the effects of acute hyperglycemia on retinal microcirculation and endothelial function in cats and removal of superoxide to prevent retinal endothelial dysfunction from hyperglycemia. METHODS Hyperglycemia was induced by intravenous injection of 25% glucose to maintain the plasma glucose concentration at 30 mM. Laser Doppler velocimetry was used to measure the vessel diameter (D) and blood velocity (V) simultaneously and calculated retinal blood flow (RBF) in second-order retinal arterioles in cats. Intravitreous, endothelial-dependent vasodilator bradykinin (BK) and endothelium-independent vasodilator sodium nitroprusside (SNP) were administered into the vitreous cavity to evaluate endothelial function in the retinal arterioles. To control osmolality, 25% mannitol was administered the same way. Systemic hyperoxia was induced to noninvasively examine endothelial function during hyperglycemia. To determine the effect of the superoxide on the hyperglycemia-induced changes in the retinal circulation, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) was administered in drinking water for 14 days before the experiment. RESULTS The D, V, and RBF increased with acute hyperglycemia and mannitol compared with baseline. BK-induced increases in D, V, and RBF significantly declined, whereas SNP-induced increases were unattenuated during acute hyperglycemia. Return of the decreased RBF to baseline after cessation of systemic hyperoxia was significantly (P < 0.05) inhibited by acute hyperglycemia. TEMPOL significantly (P < 0.05) prevented a decrease in the BK-induced increase in RBF during hyperglycemia. CONCLUSIONS The results suggest that acute hyperglycemia increases RBF via increased osmolality and may cause retinal endothelial dysfunction partially via increased oxidative stress. Systemic hyperoxia can be used to noninvasively evaluate retinal endothelial function during hyperglycemia.

Retinal arteriolar responses to acute severe elevation in systemic blood pressure in cats: role of endothelium-derived factors.

The purpose of this study was to investigate the roles of endothelium-derived factors in the retinal arteriolar responses to acute severe elevation in systemic blood pressure (BP) in cats. Acute elevation of mean arterial BP by 60% for 5 min was achieved by inflating a balloon-tipped catheter in the descending aorta. The retinal arteriolar diameter, flow velocity, wall shear rate (WSR) and blood flow (RBF) changes during BP elevation were assessed with laser Doppler velocimetry 2 h after intravitreal injections of nitric oxide (NO) synthase inhibitor l-NAME, cyclooxygenase inhibitor indomethacin, endothelin-1 receptor antagonists (BQ-123 for type A and BQ-788 for type B), or Rho kinase inhibitor fasudil. BP elevation caused a marked increase in retinal arteriolar flow velocity and WSR with slight vasoconstriction, resulting in an increase in RBF. The increases in velocity, WSR and RBF, but not diameter, were correlated with the increase in ocular perfusion pressure. With l-NAME or indomethacin, the increase in RBF upon BP elevation was significantly attenuated due to enhanced retinal arteriolar vasoconstriction. In contrast, BQ-123 and fasudil potentiated the increased RBF. BQ-788 had no effect on arteriolar diameter and hemodynamics. Our data suggest that acute elevation of BP by 60% leads to an increase in RBF due to the release of NO and prostanoids probably through a shear stress-induced vasodilation mechanism. The release of endothelin-1 and Rho kinase activation help to limit RBF augmentation by counteracting the vasodilation. It appears that the retinal endothelium, by releasing vasoactive substances, contributes to RBF regulation during acute severe elevation of systemic blood pressure.

Association Between Diabetic Retinopathy and Flow-Mediated Vasodilation in Type 2 DM

Objective: Retinal endothelial dysfunction is a key in the etiogenesis of diabetic retinopathy (DR), in patients with type 2 diabetes mellitus (DM). Brachial artery flow-mediated vasodilation (FMD) is a marker of endothelial function associated with production of endogenous nitric oxide. Using FMD, we investigated the relationship between macrovascular function and DR. Methods: We studied 74 patients with type 2 DM, including non-DR (NDR) (n = 30); mild nonproliferative DR (NPDR) (n = 16); moderate NPDR (n = 10); severe NPDR (n = 10); and proliferative DR (PDR) (n = 8); and 21 age-matched controls. We measured FMD in each group. Retinal blood flow and pulsatility ratios were measured using laser Doppler velocimetry. Results: FMD decreased significantly in patients with DM compared with healthy control subjects. No significant differences were found in FMD among the NDR, mild NPDR, and moderate NPDR groups. FMD decreased significantly in the severe NPDR and PDR groups compared with the NDR group. FMD was significantly and negatively correlated with duration of DM and pulsatility ratio. Conclusion: Systemic endothelial dysfunction appears to be associated with DR and vascular abnormalities in patients with type 2 DM.

Role of Glial Cells in Regulating Retinal Blood Flow During Flicker-Induced Hyperemia in Cats.

PURPOSE To investigate how glial cells participate in retinal circulation during flicker stimulation in cats. METHODS Using laser Doppler velocimetry, we measured the vessel diameter and blood velocity simultaneously and calculated the retinal blood flow (RBF) in feline first-order retinal arterioles. Twenty-four hours after intravitreal injections of L-2-aminoadipic acid (LAA), a gliotoxic compound, and the solvent of 0.01 N hydrochloric acid as a control, we examined the changes in RBF in response to 16-Hz flicker stimulation for 3 minutes. We also measured the changes in RBF 2 hours after intravitreal injection of Nω-propyl-L-arginine (L-NPA), a selective neuronal nitric oxide synthase inhibitor, in LAA-treated eyes. To evaluate the effects of LAA on retinal neuronal function, ERGs were monitored. Immunohistochemical examinations were performed. RESULTS In LAA-treated eyes, histologic changes selectively occurred in retinal glial cells. There were no significant reductions in amplitude or elongation of implicit time in ERG after LAA injections compared with controls. In control eyes, the RBF gradually increased and reached the maximal level (53.5% ± 2.5% increase from baseline) after 2 to 3 minutes of flicker stimulation. In LAA-treated eyes, the increases in RBF during flicker stimulation were attenuated significantly compared with controls. In LAA-treated eyes 2 hours after injection of L-NPA, flicker-evoked increases in RBF decreased significantly compared with LAA-treated eyes. CONCLUSIONS The current results suggested that increases in RBF in response to flicker stimulation were regulated partly by retinal glial cells.

Impaired systemic vascular endothelial function in patients with branch retinal vein occlusion.

Purpose: To evaluate systemic endothelial function in patients with branch retinal vein occlusion (BRVO). Methods: Twenty-seven patients with BRVO (BRVO group, 8 men, 19 women; mean age, 65.4 ± 1.3), 10 patients with systemic hypertension and no other systemic or ocular disease (hypertension group, 6 men, 4 women; mean age, 70.4 ± 2.2), and 10 healthy volunteers (healthy group, 3 men, 7 women; mean age, 63.8 ± 2.1) were enrolled. We excluded patients with diabetes mellitus and current smokers. Using high-resolution ultrasonographic imaging, we evaluated the brachial artery (mm) to evaluate the flow-mediated vasodilation (FMD) by measuring the diameter of the brachial artery during reperfusion after arterial occlusion. Results: There were no significant differences among the three groups in age (p = 0.98), sex (p = 0.21), or the baseline diameter of the brachial artery (p = 0.11). The group-averaged FMD value decreased significantly in the BRVO group (4.6 ± 0.4%) compared to the hypertension group (8.0 ± 0.8%, p < 0.01) and the healthy group (6.9 ± 0.6%, p < 0.05). Multiple logistic regression analysis identified lower FMD as an independent risk factor for BRVO. Conclusions: The results suggested that BRVO is associated with generalized endothelial dysfunction and that impaired systemic endothelial function may be associated with BRVO.

Evaluation of Retinal Circulation Using Segmental-Scanning Doppler Optical Coherence Tomography in Anesthetized Cats

PURPOSE To study retinal blood flow (RBF) measurement reproducibility using segmental-scanning Doppler optical coherence tomography (DOCT) in vitro in glass capillaries and in vivo in anesthetized cats. METHODS As a preliminary study, the flow rates of human blood through glass capillaries were changed by using an infusion pump and measured at 13 preset velocities by DOCT. For in vivo measurement, the cats were anesthetized using sevoflurane. The flow in the parent vessel was compared with the sum of the flow values in the two daughter vessels. The RBF was measured using two different instruments: bidirectional laser Doppler velocimetry (LDV) and DOCT. The reproducibility of the measurements was assessed by calculating the coefficients of variation (CVs) for repeated measurements of RBF at the superior retinal arterioles and venules. RESULTS In vitro, the flow velocities measured by DOCT agreed well with the preset velocities. In vivo, the flow in the parent vessel agreed with the sum of the flow values in the two daughter vessels. In addition, there were no significant differences in the mean averaged CVs of the RBF in both the arterioles and venules between LDV and DOCT. CONCLUSIONS The newly developed segmental-scanning DOCT revealed the accuracy of the measurement in in vitro glass capillaries and reproducibility of the measurements of blood velocity in both the retinal arterioles and venules in anesthetized cats.

Autologous Transplantation of a Free Tenon's Graft for Repairing Excessive Bleb Leakage after Trabeculectomy: A Case Report

Purpose: To report a case of autologous transplantation of a free Tenons graft to repair excessive bleb leakage after trabeculectomy. Case Report: A 39-year-old Japanese woman presented with severe hypotony in her left eye. She had undergone trabeculectomy with mitomycin C 14 years ago. Slit-lamp examination showed an ischemic and ruptured bleb, excessive bleb leakage, and an extremely shallow anterior chamber. A large scleral defect was vaguely observed through the bleb conjunctiva. The hypotony was attributed to excessive bleb leakage. A surgical revision was required. First, the avascular bleb conjunctiva and the melted scleral flap were excised. A scleral defect was observed. Thick fibrotic tissue, i.e., the autologous Tenons graft, was separated from the underlying sclera, cut to the desired size to cover the defect, and sutured to the sclera with 10-0 nylon sutures. Irrigation with balanced salt solution through the paracentesis confirmed deepening of the anterior chamber with no bleb leakage. In the current case, a layer of amniotic membrane was applied to cover the largely exposed sclera. Two weeks postoperatively, the surgical site was totally re-epithelialized with no aqueous leakage. Three months postoperatively, vascularization into the surgical site was observed. The intraocular pressure remained within normal levels without recurrent bleb leakage. Conclusions: Autologous transplantation of a free Tenons graft successfully repaired excessive bleb leakage through a scleral defect after trabeculectomy. This technique is easier, safer, and may be more cost effective for repairing excessive bleb leakage after trabeculectomy than conventional management techniques.

Glial Endothelin-1 Regulates Retinal Blood Flow During Hyperoxia in Cats

Purpose To investigate the role of endothelin-1 (ET-1) in retinal glial cells in regulating retinal blood flow (RBF) during hyperoxia in cats. Methods We measured the vessel diameter (D), blood velocity (V), and blood flow (F) simultaneously in first-order retinal arterioles using a laser Doppler velocimetry system. The animals were under general anesthesia during hyperoxia (100% oxygen) for 10 minutes 24 hours after intravitreal injection of L-2-aminoadipic acid (LAA), a gliotoxic compound, or diluted hydrochloric acid (0.01 N) used as the vehicle control. We also measured the changes in the RBF after intravitreal injection of BQ-123, a specific ET type A receptor antagonist, in LAA-treated eyes. To examine if endothelin-converting enzyme-1 (ECE-1), as an ET-1-generating enzyme located in retinal glial cells, immunohistochemical examinations with costaining of antiglial fibrillary acidic protein (GFAP) antibody and anti-ECE-1 antibody were performed in whole-mount retinas. Results During hyperoxia, the decreases in D, V, and F in response to hyperoxia were attenuated significantly (P < 0.01 for all comparisons) in the LAA-treated eyes compared with the vehicle control (LAA, D, -8.5 ± 1.5%; V, -13.8 ± 1.5%; F, -27.8 ± 3.0% versus vehicle control, D, -16.8 ± 1.3%; V, -26.3 ± 2.0%; F, -48.9 ± 2.4%). In LAA-treated eyes, intravitreal injections of BQ-123 did not change the rate of hyperoxia-induced RBF compared to LAA-treated eyes. The anti-ECE-1 antibody was costained with anti-GFAP antibody in the whole-mount retinas. Conclusions The current findings suggest that retinal glial ET-1 may play an important role in regulating RBF during hyperoxia in cats.

A low meat diet increases the risk of open-angle glaucoma in women—The results of population-based, cross-sectional study in Japan

Background Studies identifying modifiable lifestyle risk factors related to open-angle glaucoma (OAG) are limited, especially from Asian countries. This study aimed to identify lifestyle risk factors for OAG in a Japanese population. Methods and findings This population-based, cross-sectional study recruited Japanese participants aged 40 years or older from January 2013 to March 2015. We took fundus photographs for OAG screening, determined lifestyle and health characteristics through a questionnaire and performed physical examinations. The participants who had suspect findings in the fundus photographs were sent for a detailed ophthalmic examination to diagnose OAG. Lifestyle and heath characteristics were statistically compared between the OAG and non-OAG participants. A total of 1583 participants were included in the study, of which 42 had OAG and 1541 did not have OAG. The number of days per week that the female participants consumed meat (mean±SD; OAG: 1.7±1.2 days, non-OAG: 2.7±1.5 days) was negatively associated with OAG (OR = 0.61; 95% CI: 0.43–0.88; p = 0.007). Higher intraocular pressure was positively associated with OAG in men (OR = 1.20; 95% CI: 1.05–1.38, p = 0.009). No significant difference between participants with and without OAG was observed for a range of other lifestyle factors and health criteria including self-report of diabetes, number of family living together, body mass index, blood pressure, pulse rate, coffee drinking, tea drinking, alcohol drinking, number of fruits consumed per day and days of fish consumption per week. Conclusions A higher weekly consumption of meat appears to be negatively associated with OAG in Japanese women. Increasing the dietary intake of meat can contribute to reducing the risk of developing OAG.