Akihiro Ishibazawa

Optical Coherence Tomography Angiography in Diabetic Retinopathy: A Prospective Pilot Study.

PURPOSE To evaluate how optical coherence tomography (OCT) angiography depicts clinical fundus findings in patients with diabetic retinopathy (DR). DESIGN Prospective study evaluating imaging technology. METHODS Forty-seven eyes of 25 patients with DR were scanned using a high-speed 840-nm-wavelength spectral-domain optical coherence tomography instrument (RTVue XR Avanti; Optovue, Inc, Fremont, California, USA). Blood flow was detected using the split-spectrum amplitude-decorrelation angiography algorithm. Fluorescein angiography (FA) images were also obtained in all eyes and the ability to visualize microaneurysms, retinal nonperfused areas, and neovascularization was compared with that of the en face OCT angiograms. RESULTS In 42 eyes, microaneurysms detected by FA near the macula appeared as focally dilated saccular or fusiform capillaries on OCT angiograms of the superficial and/or deep capillary plexus. Retinal nonperfused areas visualized by FA appeared as lesions with no or sparse capillaries on OCT angiograms. Area measurement of retinal nonperfusion near the macula in 7 eyes revealed a difference between the extent of nonperfused areas in superficial and deep plexuses. In 4 eyes, the vascular structures of neovascularization at the optic disc were clearly visualized on OCT angiograms. Decreases and re-increases of flow in new vessels were quantified in an eye treated with anti-vascular endothelial growth factor. CONCLUSIONS OCT angiography can clearly visualize microaneurysms and retinal nonperfused areas and enables closer observation of each layer of the retinal capillaries. Quantitative information on new vessels can also be obtained. OCT angiography may be clinically useful to evaluate the microvascular status and therapeutic effect of treatments for DR.

Relationship Between Choroidal Thickness and Choroidal Circulation in Healthy Young Subjects

PURPOSE To investigate the relationship between the choroidal thickness and choroidal blood flow in healthy young subjects. DESIGN Retrospective, cross-sectional study. METHODS We examined 25 eyes of 25 healthy young Japanese subjects. The subfoveal choroidal thickness was measured by enhanced depth imaging optical coherence tomography (EDI-OCT). The total choroidal blood flow and subfoveal choroidal blood flow were evaluated by pulsatile ocular blood flow using Langham OBF computerized tonometry and the choroidal blood flow using laser Doppler flowmetry. The refractive error, intraocular pressure, and axial length were also measured. RESULTS The mean refractive error was -3.4 ± 3.1 diopters, mean intraocular pressure 15.3 ± 1.7 mm Hg, and axial length 25.4 ± 2.0 mm. The subfoveal choroidal thickness was correlated positively (r = 0.785, P < .01) with the refractive error and negatively (r = -0.735, P < .001) with the axial length. No significant correlation was found between the subfoveal choroidal thickness and the pulsatile ocular blood flow or choroidal blood flow. CONCLUSION Our results suggested that there were no significant correlations between the subfoveal choroidal thickness and the total choroidal blood flow and the subfoveal choroidal blood flow in healthy young subjects; however, decreased subfoveal choroidal thickness was associated with decreased refractive error and axial length.

Central corneal thickness measurements with Fourier-domain optical coherence tomography versus ultrasonic pachymetry and rotating Scheimpflug camera.

Purpose: To compare the accuracy and repeatability of Fourier-domain optical coherence tomography (FD-OCT) with ultrasonic pachymetry (USP) and a rotating Scheimpflug camera for measuring the central corneal thickness (CCT). Methods: The CCT was measured in 30 subjects (30 normal corneas) by the same examiner using RTVue-100 FD-OCT with an anterior segment adaptor, Pentacam rotating Scheimpflug camera, and SP-2000 USP. Two examiners obtained one FD-OCT measurement from 10 eyes of 5 subjects to assess interexaminer reproducibility. Results: The mean CCT (±SD) measured by FD-OCT, USP, and the Pentacam were 530 ± 33, 544 ± 34, and 552 ± 35 μm, respectively. Significant correlations were found between FD-OCT and USP (r = 0.97; P < 0.0001), FD-OCT and Pentacam (r = 0.97; P < 0.0001), and USP and Pentacam (r = 0.96; P < 0.0001). Pairwise comparisons showed that the FD-OCT CCT measurement was significantly thinner than those of the other 2 methods (P < 0.001 for all comparisons). Regarding intraexaminer repeatability, the intraclass correlation coefficients ranged between 0.97 and 0.98. There was high repeatability of the CCT measurements with all methods. FD-OCT also had high interexaminer reproducibility (intraclass correlation coefficient = 0.98). Conclusions: RTVue-100 FD-OCT may be a useful alternative for measuring the CCT; however, it significantly underestimates the CCT compared with the USP and the Pentacam with slight differences. Although highly correlated, the measurements are not directly interchangeable in clinical practice.

Effects of shear stress on the gene expressions of endothelial nitric oxide synthase, endothelin-1, and thrombomodulin in human retinal microvascular endothelial cells.

PURPOSE Physiological shear stress is higher in the retinal microcirculatory network than in other organs. The effects of laminar shear stress on gene expression in human retinal microvascular endothelial cells (HRMECs) was investigated. METHODS Cultured HRMECs on glass plates were exposed to a laminar shear stress of 0, 1.5, 6, 15, 30, 60, or 100 dyne/cm(2) for 24 hours and to 60 dyne/cm(2) for 0, 1, 3, 6, 12, 24, or 48 hours. The mRNA expressions of endothelial nitric oxide synthase (eNOS), endothelin-1 (ET-1), and thrombomodulin (TM) in the HRMECs were evaluated using real-time reverse transcription polymerase chain reaction. RESULTS The HRMECs elongated and aligned parallel with the flow direction based on the shear stress and exposure times. The expression of eNOS mRNA gradually increased and became saturated at 60 dyne/cm(2); ET-1 mRNA expression increased at 1.5 dyne/cm(2) but decreased below that of the static control at shear stresses of 30 dyne/cm(2) or more. TM mRNA expression in response to shear stress increased linearly from 0 to 100 dyne/cm(2). A shear stress of 60 dyne/cm(2) for 6 hours or more promoted eNOS and TM mRNA expression but suppressed ET-1 mRNA expression in HRMECs. CONCLUSIONS Long-term exposure to a physiological shear stress in the retinal arterioles up-regulated eNOS and TM mRNA expressions and downregulated ET-1 mRNA expression in HRMECs. These results suggest that shear stress may be associated with the vasoregulatory and antithrombotic properties of retinal vessels under physiological conditions present during retinal circulation.

Radial Peripapillary Capillary Network Visualized Using Wide-Field Montage Optical Coherence Tomography Angiography

PURPOSE We quantitatively analyzed the features of a radial peripapillary capillary (RPC) network visualized using wide-field montage optical coherence tomography (OCT) angiography in healthy human eyes. METHODS Twenty eyes of 20 healthy subjects were recruited. En face 3 × 3-mm OCT angiograms of multiple locations in the posterior pole were acquired using the RTVue XR Avanti, and wide-field montage images of the RPC were created. To evaluate the RPC density, the montage images were binarized and skeletonized. The correlation between the RPC density and the retinal nerve fiber layer (RNFL) thickness measured by an OCT circle scan was investigated. RESULTS The RPC at the temporal retina was detected as far as 7.6 ± 0.7 mm from the edge of the optic disc but not around the perifoveal area within 0.9 ± 0.1 mm of the fovea. Capillary-free zones beside the first branches of the arterioles were significantly (P < 0.0001) narrower than those beside the second ones. The RPC densities at 0.5, 2.5, and 5 mm from the optic disc edge were 13.6 ± 0.8, 11.9 ± 0.9, and 10.4 ± 0.9 mm-1. The RPC density also was correlated significantly (r = 0.64, P < 0.0001) with the RNFL thickness, with the greatest density in the inferotemporal region. CONCLUSIONS Montage OCT angiograms can visualize expansion of the RPC network. The RPC is present in the superficial peripapillary retina in proportion to the RNFL thickness, supporting the idea that the RPC may be the vascular network primarily responsible for RNFL nourishment.

Characteristics of Retinal Neovascularization in Proliferative Diabetic Retinopathy Imaged by Optical Coherence Tomography Angiography

Purpose To characterize the morphology of neovascularization at the disc (NVD) and neovascularization elsewhere (NVE) in treatment-naïve or previously treated proliferative diabetic retinopathy (PDR) patients using optical coherence tomography (OCT) angiography. Methods En face OCT angiograms of NVD/NVE in 40 eyes of 33 patients with PDR were acquired using RTVue XR Avanti OCT. The morphology of NVD/NVE on OCT angiograms was evaluated, and the activity was determined by biomicroscopy and fluorescein angiography (FA). In 12 eyes that were treated or treatment-naïve, changes in the morphology and vessel area of NVD/NVE before and after panretinal photocoagulation (PRP) were investigated. Results Twenty eyes had treatment-naïve PDR, whereas 20 eyes were previously treated with PRP. All treatment-naïve NVD/NVE had remarkable (i.e., active) leakage in early-phase FA. Ninety-five percent of treatment-naïve NVD/NVE observed by OCT angiography had exuberant vascular proliferation (EVP), identified as irregular proliferation of fine (smaller-caliber) new vessels; whereas, the presence of EVP in previously treated eyes (13/20) was significantly less than in treatment-naïve eyes (65% vs. 95%, P = 0.043). The remaining seven treated eyes had pruned NVD/NVE without EVP, observed as fibrotic changes or faint (inactive) leakage in FA. The vessel areas of NVD/NVE significantly decreased following PRP (n = 12, P = 0.019), and NVD/NVE morphology showed pruning and decreased EVP. Conclusions Exuberant vascular proliferation on OCT angiograms should be considered as an active sign of neovascularization; therefore, morphologic evaluation of neovascularization using OCT angiography may be useful to estimate the activity of each neovascularization in eyes with PDR.

Dilation of porcine retinal arterioles to cilostazol: roles of eNOS phosphorylation via cAMP/protein kinase A and AMP-activated protein kinase and potassium channels.

PURPOSE Cilostazol, a selective inhibitor of phosphodiesterase 3, has antiplatelet aggregation and peripheral vasodilation effects. We examined the effects of cilostazol on the retinal microvascular diameter to determine its dependence on the endothelium and/or smooth muscle to reveal the signaling mechanisms involved in this vasomotor activity. METHODS Porcine retinal arterioles were isolated, cannulated, and pressurized without flow in vitro. Video microscopic techniques recorded the diametric responses to cilostazol. RESULTS The retinal arterioles dilated in response to cilostazol in a dose-dependent (100 pM-10 μM) manner; the dilation decreased by 60% after endothelial removal. The nitric oxide (NO) synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), inhibited cilostazol-induced vasodilation comparable to denudation. Inhibition of soluble guanylyl cyclase and blockade of protein kinase A (PKA) were comparable to L-NAME. Compound C, an AMP-activated protein kinase (AMPK) inhibitor, partially inhibited cilostazol-induced vasodilation, which exhibited a weaker inhibitory effect on cilostazol-induced vasodilation than blockade of PKA. The large-conductance Ca²⁺-activated K channel (BK(Ca) channel) blocker, iberiotoxin, also inhibited cilostazol-induced vasodilation. The residual vasodilation decreased further with co-administration of L-NAME and iberiotoxin. CONCLUSIONS Cilostazol elicits endothelium-dependent and -independent dilation of the retinal arterioles mediated by NO release and BK(Ca) channel activation, respectively. Endothelial nitric oxide synthase (eNOS) phosphorylation via the cAMP/PKA and AMPK pathways and consequent activation of the soluble guanylyl cyclase/cyclic guanosine monophosphate pathway might play an important role in cilostazol-induced vasodilation of the retinal arterioles.

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.

Wound healing process after corneal stromal thinning observed with anterior segment optical coherence tomography.

Purpose: The aim of this study was to observe the wound healing process after corneal stromal thinning by using anterior segment optical coherence tomography (AS-OCT) and a slit lamp. Methods: Four patients with corneal stromal thinning (2 patients: corneal iron foreign bodies; 2 patients: keratitis) were included. Serial AS-OCT and slit-lamp examinations were used to follow up the progress of these patients. The thicknesses of the whole cornea and the corneal stroma were measured with AS-OCT and compared with the findings observed during the slit-lamp examination. Results: AS-OCT showed that epithelial hypertrophy and hyperplasia initially occurred in the area of the corneal stromal thinning; subsequently, scar tissue formed in the area with an improvement in the thickness of the corneal stroma. This wound healing process was observed in all 4 patients. The scar tissue initially appeared opaque on slit-lamp examination and was characterized by a high signal produced on AS-OCT, which was different from the normal corneal stroma. The scar tissue gradually appeared clear on slit-lamp examination; however, the high signal on AS-OCT remained. Conclusions: AS-OCT can be used to detect the wound healing process of corneal stromal thinning.

Transforming Growth Factor-β Signaling Cascade Induced by Mechanical Stimulation of Fluid Shear Stress in Cultured Corneal Epithelial Cells.

Purpose Because blinking is regarded as mechanical stimulation of fluid shear stress on the corneal epithelial cells, we investigated the effects of fluid shear stress on cultured human corneal epithelial cells (HCECs). Methods The HCECs were exposed to shear stress (0, 1.2, 12 dyne/cm2) with the parallel-plate type of flow chamber. Wound healing, cellular proliferation, growth factor expression, TGF-β1 concentration in the culture supernatant, and phosphorylation of SMAD2 were investigated. Results Monolayers of HCECs exposed to shear stress had delayed wound healing and decreased proliferation compared with those of the static control (0 dyne/cm2). With increasing shear stress, TGF-β1 expression and phosphorylation of SMAD2 increased significantly, but the levels of total TGF-β1 in the culture supernatant decreased significantly. Delayed wound healing, decreased proliferation, and phosphorylation of the SMAD2 by shear stress were canceled out with a TGF-β receptor inhibitor. Conclusions Fluid shear stress on the HCECs affected TGF-β signaling, which was associated with delayed wound healing. Mechanical stress by blinking might involve TGF-β signaling, and activation of TGF-β might be a key factor in wound healing of the corneal epithelium. Further studies should investigate the molecular mechanism of shear stress-induced activation of TGF-β.