Impaired retinal artery blood flow in IDDM patients before clinical manifestations of diabetic retinopathy

Retinal and Choroidal Phenotypes Across Novel Subtypes of Type 2 Diabetes Mellitus

PURPOSE

To investigate longitudinal changes in choroidal thickness (CT) and ganglion cell-inner plexiform layer thickness (GC-IPLT) across distinct phenotypes of type 2 diabetes mellitus (T2DM) patients.

DESIGN

Prospective cohort study.

METHODS

T2DM patients were categorized into 5 groups (SAID, SIDD, SIRD, MOD, and MARD) using K-means clustering based on β-cell function and insulin resistance. Swept-source optical coherence tomography measured baseline and 4-year follow-up CT and GC-IPLT. Linear mixed-effects models assessed absolute and relative changes in CT and GC-IPLT across subtypes.

RESULTS

Over a median 4.11-year follow-up, CT and GC-IPLT decreased significantly across all groups. Choroidal thinning rates were most pronounced in SIDD (-6.5 ± 0.53 µm/year and -3.5 ± 0.24%/year) and SAID (-6.27 ± 0.8 µm/year and -3.19 ± 0.37%/year), while MARD showed the slowest thinning rates (-3.63 ± 0.34 µm/year and -1.98 ± 0.25%/year). SIRD exhibited the greatest GC-IPLT loss (-0.66 ± 0.05 µm/year and -0.91 ± 0.07%/year), with the least in SIDD (-0.36 ± 0.05 µm/year and -0.49 ± 0.07%/year), all statistically significant (all P < 0.001). Adjusted for confounding variables, SIDD and SAID groups showed faster CT thinning than MARD [-2.57 µm/year (95% CI: -4.16 to -0.97; P = 0.002) and -2.89 µm/year (95% CI: -4.12 to -1.66; P < 0.001), respectively]. GC-IPLT thinning was notably accelerated in SIRD versus MARD, but slowed in SIDD relative to MARD [differences of -0.16 µm/year (95% CI: -0.3 to -0.03; P = 0.015) and 0.15 µm/year (95% CI: 0.03 to 0.27; P = 0.015), respectively].

CONCLUSIONS

Microvascular damage in the choroid is associated with SIDD patients, whereas early signs of retinal neurodegeneration are evident in SIRD patients. All these changes may precede the onset of DR.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Doppler ultrasound-based evaluation of hemodynamic changes in the ophthalmic artery and central retinal artery in patients with type 1 diabetes mellitus without retinopathy and with mild non-proliferative retinopathy

Aim

Determination of blood flow parameters in the ophthalmic artery and central retinal artery using Doppler ultrasound in patients with type 1 diabetes mellitus without fundus signs of diabetic retinopathy and with mild non-proliferative retinopathy.

Material and methods

To eliminate the impact of other systemic factors on vascular flow, the study enrolled a total of 80 patients with type 1 diabetes mellitus, aged between 18 and 45 years. The study participants did not have any diabetic complications or other systemic or ocular comorbidities. The control group comprised 81 healthy individuals within a similar age range. Color Doppler ultrasound examinations of the ophthalmic artery and central retinal artery were performed to evaluate selected blood flow parameters including peak systolic velocity, end-diastolic velocity, and resistance index.

Results

Patients with type 1 diabetes mellitus exhibited statistically significant decrease in both systolic and end-diastolic velocities in the central retinal artery, accompanied by an elevation in resistance index, compared to the control group. The study revealed differences in blood flow parameters between the patients without fundus changes and those exhibiting mild non-proliferative retinopathy. Specifically, patients with retinopathy showed a significant decrease in both systolic velocity and end-diastolic velocity in the central retinal artery. No differences were observed for the same parameters in the ophthalmic artery. When analyzing the patients' blood flow parameters in relation to the degree of diabetes control, as determined by glycated hemoglobin levels, a statistically significant reduction in systolic velocity was identified in both the ophthalmic and central retinal arteries in the group with poorly controlled diabetes.

Conclusions

Examination of the orbital vessels using Doppler ultrasound in patients with type 1 diabetes mellitus holds promise as an effective method for early detection of vascular abnormalities.

Rates of Choroidal and Neurodegenerative Changes Over Time in Diabetic Patients Without Retinopathy: A 3-Year Prospective Study

PURPOSE

To evaluate the longitudinal changes of retinal neurodegeneration and choroidal thickness in diabetic patients with and without diabetic retinopathy (DR).

DESIGN

Prospective observational cohort study.

METHODS

This prospective observational cohort study recruited type 2 diabetic patients from a community registry in Guangzhou. All participants underwent annual ocular examinations via swept-source optical coherence tomography that obtained choroid thickness (CT), retinal thickness (RT), and ganglion cell-inner plexiform layer (GC-IPL) thickness. The changes in GC-IPL, CT, and RT between patients who developed incident DR (IDR) or remained non-DR (NDR) were compared during a 3-year follow-up.

RESULTS

Among 924 patients, 159 (17.2%) patients developed IDR within the 3-year follow-up. A reduction in GC-IPL, RT, and CT was observed in NDR and IDR; however, CT thinning in patients with IDR was significantly accelerated, with an average CT reduction of -6.98 (95% CI: -8.26, -5.71) μm/y in patients with IDR and -3.98 (95% CI: -4.60, -3.36) μm/y in NDR patients (P < .001). Reductions in average GC-IPL thickness over 3 years were -0.97 (95% CI: -1.24, -0.70) μm/y in patients with IDR and -0.76 (95% CI: -0.82, -0.70) μm/y in NDR patients (P = .025). After adjusting for confounding factors, the average CT and GC-IPL thinning were significantly faster in patients with IDR compared with those who remained NDR by 2.09 μm/y (95% CI: 1.01, 3.16; P = .004) and -0.29 μm/y (95% CI: -0.49, -0.09; P = .004), respectively. The RT in the IDR group increased, whereas the RT in the NDR group decreased over time, with the adjusted difference of 2.09 μm/y (95% CI: 1.01, 3.16; P < .001) for central field RT.

CONCLUSIONS

The rate of retinal neurodegeneration and CT thinning were significantly different between the eyes that developed IDR and remained NDR during the 3-year follow-up, but both groups observed thickness reduction. This indicates that GC-IPL and CTs may decrease before the clinical manifestations of DR.

Anomalies in neurovascular coupling during early diabetes: A review

Diabetic retinopathy is the most feared complication for those with diabetes. Although visible vascular pathology traditionally defines the management of this condition, it is now recognised that a range of cellular changes occur in the retina from an early stage of diabetes. One of the most significant functional changes that occurs in those with diabetes is a loss of vasoregulation in response to changes in neural activity. There are several retinal cell types that are critical for mediating so-called neurovascular coupling, including Müller cells, microglia and pericytes. Although there is a great deal of evidence that suggests that Müller cells are integral to regulating the vasculature, they only modulate part of the vascular tree, highlighting the complexity of vasoregulation within the retina. Recent studies suggest that retinal immune cells, microglia, play an important role in mediating vasoconstriction. Importantly, retinal microglia contact both the vasculature and neural synapses and induce vasoconstriction in response to neurally expressed chemokines such as fractalkine. This microglial-dependent regulation occurs via the vasomediator angiotensinogen. Diabetes alters the way microglia regulate the retinal vasculature, by increasing angiotensinogen expression, causing capillary vasoconstriction and contributing to a loss of vascular reactivity to physiological signals. This article summarises recent studies showing changes in vascular regulation during diabetes, the potential mechanisms by which this occurs and the significance of these early changes to the progression of diabetic retinopathy.

Diagnostic and predictive value of resistive / pulsatility indices of ophthalmic artery and common carotid artery for the development of diabetic retinopathy

Background

Ophthalmic artery resistive index (OA RI) was a controversial parameter to show hemodynamic changes due to diabetic retinopathy (DRP).

Purpose

To investigate the diagnostic and predictive value of resistive and pulsatility index (RI and PI, respectively) of OA and common carotid artery (CCA) for the development of DRP.

Material and Methods

A total of 60 patients with diabetes mellitus (DM) type 2 (study group) and 30 healthy participants (control group) were evaluated between January and June 2021 by Doppler ultrasonography (DUS). RI and PI values were compared between groups with a Student’s t-test. Cutoff value, sensitivity, and specificity were calculated for the significant variables with receiver operating characteristic (ROC) analysis.

Results

In total, there were 20 (22.2%) patients with DM without DRP (DMwoRP), 20 (22.2%) patients in the non-proliferative diabetic retinopathy group (NPDRP), and 20 (22.2%) patients in the proliferative diabetic retinopathy group (PDRP). The mean of CCA RI and OA RI in the PDRP group was significantly higher than in the other three groups ( P < 0.001). The mean of CCA RI and OA RI was significantly higher in the PDRP group than in the NPDRP group, and in the NPDRP group compared to the DMwoRP group. CCA RI and OA RI showed a significantly high correlation (r = 0.849; P < 0.001). Sensitivity was 95% and specificity was 100% for the diagnosis of PDRP for the 0.82 cutoff value of OA RI (AUR = 0.999, 95% confidence interval for AUC = 0.997–0.1000; P < 0.001).

Conclusion

The OA RI accurately reflects DRP-induced orbital blood flow changes and is a predictive index for DRP prognosis.

Candesartan Normalizes Changes in Retinal Blood Flow and p22phox in the Diabetic Rat Retina

Angiotensin II has been implicated in the progression of diabetic retinopathy, which is characterized by altered microvasculature, oxidative stress, and neuronal dysfunction. The signaling induced by angiotensin II can occur not only via receptor-mediated calcium release that causes vascular constriction, but also through a pathway whereby angiotensin II activates NADPH oxidase to elicit the formation of reactive oxygen species (ROS). In the current study, we administered the angiotensin II receptor antagonist candesartan (or vehicle, in untreated animals) in a rat model of type 1 diabetes in which hyperglycemia was induced by injection of streptozotocin (STZ). Eight weeks after the STZ injection, untreated diabetic rats were found to have a significant increase in tissue levels of angiotensin converting enzyme (ACE; p < 0.05) compared to non-diabetic controls, a 33% decrease in retinal blood flow rate (p < 0.001), and a dramatic increase in p22phox (a subunit of the NADPH oxidase). The decrease in retinal blood flow, and the increases in retinal ACE and p22phox in the diabetic rats, were all significantly attenuated (p < 0.05) by the administration of candesartan in drinking water within one week. Neither STZ nor candesartan induced any changes in tissue levels of superoxide dismutase (SOD-1), 4-hydroxynonenal (4-HNE), or nitrotyrosine. We conclude that one additional benefit of candesartan (and other angiotensin II antagonists) may be to normalize retinal blood flow, which may have clinical benefits in diabetic retinopathy.

Doppler Indices of the Ophthalmic Artery in Pregnant Women With Pregestational Diabetes Mellitus With and Without Retinopathy

OBJECTIVES

To evaluate ophthalmic Doppler velocimetry patterns in pregnant women with pregestational diabetes mellitus with and without retinopathy in comparison to pregnant women without gestational intercurrences.

METHODS

This cross-sectional observational study analyzed Doppler indices of the ophthalmic arteries, including the resistive index (RI), pulsatility index, peak systolic velocity, second peak systolic velocity, peak ratio, and end-diastolic velocity (EDV), in 3 groups of pregnant women: diabetic with retinopathy (n = 12); diabetic without retinopathy (n = 85); and nondiabetic controls (n = 122). The Kruskal-Wallis test was used for the statistical analysis with a probability of 95%.

RESULTS

The mean gestational ages ± SDs of pregnant women with and without retinopathy and nondiabetic controls were 29.1 ± 2.2, 29.7 ± 2.7, and 31 ± 1.0 weeks, respectively, with no significant differences between the groups (P > .099). The mean RI in the group with retinopathy was significantly higher (P = .030) than in the control group, but it did not significantly differ compared to the group without retinopathy (P = .204). The RI in the control group did not differ from that in the group without retinopathy (P = .079). The EDV was significantly lower in the group with retinopathy (P = .015) in relation to the control group, but there were no differences compared to the group without retinopathy (P = .217).

CONCLUSIONS

Pregnant women with pregestational diabetes mellitus and retinopathy had increased vascular impedance in the ophthalmic artery together with a reduction in the EDV, which was probably related to ischemia, thrombosis, and neovascularization of retinal vessels.

Role of Arginase in Selective Impairment of Endothelium-Dependent Nitric Oxide Synthase-Mediated Dilation of Retinal Arterioles during Early Diabetes

Purpose

Retinal vasomotor activity can be regulated by two major endothelial enzymes, nitric oxide synthase (NOS) and cyclooxygenase (COX). The vascular arginase also consumes a NOS substrate and thus impedes NOS-mediated vasodilation. Diabetes mellitus exhibits vascular complications in the retina with elevated oxidative stress and compromised NOS-mediated vasodilation. However, the underlying molecular mechanisms remain unclear, and the effect of diabetes on COX-mediated vasodilation is unknown. Herein, we examined the relative impact of diabetes on retinal arteriolar dilations to COX and NOS activation and the roles of arginase and superoxide in diabetes-induced vasomotor dysfunction.

Methods

Retinal arterioles were isolated from streptozocin-induced diabetic pigs (2 weeks of hyperglycemia, 433 ± 27 mg/dL) or age-matched control pigs (97 ± 4 mg/dL). The vasodilations to bradykinin (NOS activator) and histamine (NOS/COX activator) were examined in vitro.

Results

Retinal arteriolar dilations to histamine and bradykinin were significantly reduced after 2 weeks of diabetes. The NOS inhibitor N^G-nitro-L-arginine methyl ester (L-NAME) attenuated the dilations of control vessels, but not diabetic vessels, to histamine. In the presence of L-NAME and COX inhibitor indomethacin, histamine-induced dilations of control and diabetic vessels were reduced similarly. Treatment of diabetic vessels with arginase inhibitor nor-NOHA, but not superoxide dismutase mimetic TEMPOL, preserved both histamine- and bradykinin-induced dilations in an L-NAME-sensitive manner.

Conclusions

Arginase, rather than superoxide, impairs endothelium-dependent NOS-mediated dilation of retinal arterioles during diabetes, whereas vasodilation mediated by COX remains intact. Blockade of vascular arginase may improve endothelial function of retinal arterioles during early onset of diabetes.

Longitudinal follow-up study of the retrobulbar and intrarenal hemodynamics in patients with T2DM

OBJECTIVE

The primary aim of this study is to examine the hemodynamics of retrobulbar and intrarenal in the changes of early stage of type 2 diabetes mellitus (T2DM) patients from 2000 to 2015 and to assess incidence associated with diabetic kidney disease (DKD) and diabetic retinopathy (DR).

METHOD

Our study contained 60 subjects newly diagnosed of T2DM were divided into 2 groups base on the mean resistive index (RI) (≤0.7 and >0.7) of hemodynamic and to compare between-group differences of the early changes in hemodynamics of retrobulbar and intrarenal and also to conclude the incidences of diabetic kidney disease (DKD) and diabetic retinopathy (DR)subsequently with a long follow-up duration(2000-2015). First, to compare the mean RI of central retinal artery (CRA) between 2 groups. Second, to compare the mean RI of intrarenal hemodynamics in the bilateral interlobular renal arteries, renal function parameters (blood urea nitrogen (BUN), creatinine (Cr), blood glucose parameters (glycosylated hemoglobinA1c (HbA1c), fasting plasma glucose (FBG), and 2-hour postprandial blood glucose (2hPBG)), glomerular filtration rate (GFR), albumin excretion rate (AER), and urine albumin-to-creatinine ratio (UACR) between 2 groups.

RESULTS

First part of our follow-up studies was to compare hemodynamic RI index of retrobulbar in years of 2000 and 2015, both renal function and blood glucose parameters were fund significantly enhanced in subject group RIs ≤0.7. Incidence of DKD and DR was notably lower in group RIs ≤0.7 than group RIs > 0.7, difference was statistically significant (P < .05). Incidence of HbA1c ≤7% was higher in group RIs ≤0.7 than group RIs >0.7, but difference was not statistically significant (P > .05). Incidence of proliferative diabetic retinopathy (PDR) was notably lower in group RIs ≤0.7 than group RIs >0.7, but the difference was not statistically significant (P > .05). Second part of our follow-up studies was to compare hemodynamic RI index of interlobular renal in years of 2000 and 2015, both renal function and blood glucose parameters were fund significantly enhanced in subject group RIs ≤0.7. Compared data of various incidences from first part of study were coherent with second part. (Incidence of DKD and DR was notably lower in group RIs ≤0.7 than group RIs >0.7, difference was statistically significant (P < .05). Incidence of HbA1c ≤7% was higher in group RIs ≤0.7 than group RIs >0.7, but difference was not statistically significant (P > .05). Incidence of PDR was notably lower in group RIs ≤0.7 than group RIs >0.7, but the difference was not statistically significant (P > .05).

CONCLUSIONS

RIs of retrobulbar and interlobular renal which would serve as a good predictors for the hemodynamics changes in retrobulbar and intrarenal would assess incidence of DKD and DR during the preclinical stage in long-term range excluding renal function and HbA1c in T2DM patients.

Human vitreous in proliferative diabetic retinopathy: Characterization and translational implications

Diabetic retinopathy (DR) is one of the leading causes of visual impairment in the working-age population. DR is a progressive eye disease caused by long-term accumulation of hyperglycaemia-mediated pathological alterations in the retina of diabetic patients. DR begins with asymptomatic retinal abnormalities and may progress to advanced-stage proliferative diabetic retinopathy (PDR), characterized by neovascularization or preretinal/vitreous haemorrhages. The vitreous, a transparent gel that fills the posterior cavity of the eye, plays a vital role in maintaining ocular function. Structural and molecular alterations of the vitreous, observed during DR progression, are consequences of metabolic and functional modifications of the retinal tissue. Thus, vitreal alterations reflect the pathological events occurring at the vitreoretinal interface. These events are caused by hypoxic, oxidative, inflammatory, neurodegenerative, and leukostatic conditions that occur during diabetes. Conversely, PDR vitreous can exert pathological effects on the diabetic retina, resulting in activation of a vicious cycle that contributes to disease progression. In this review, we recapitulate the major pathological features of DR/PDR, and focus on the structural and molecular changes that characterize the vitreal structure and composition during DR and progression to PDR. In PDR, vitreous represents a reservoir of pathological signalling molecules. Therefore, in this review we discuss how studying the biological activity of the vitreous in different in vitro, ex vivo, and in vivo experimental models can provide insights into the pathogenesis of PDR. In addition, the vitreous from PDR patients can represent a novel tool to obtain preclinical experimental evidences for the development and characterization of new therapeutic drug candidates for PDR therapy.

Retinal oxygen extraction in individuals with type 1 diabetes with no or mild diabetic retinopathy

AIMS/HYPOTHESIS

The aim of this study was to compare retinal oxygen extraction in individuals with diabetes with no or mild non-proliferative diabetic retinopathy and healthy age- and sex-matched volunteers.

METHODS

A total of 24 participants with type 1 diabetes and 24 healthy age- and sex-matched volunteers were included in this cross-sectional study. Retinal oxygen extraction was measured by combining total retinal blood flow measurements using a custom-built bi-directional Doppler optical coherence tomography system with measurements of oxygen saturation using spectroscopic reflectometry. Based on previously published mathematical modelling, the oxygen content in retinal vessels and total retinal oxygen extraction were calculated.

RESULTS

Total retinal blood flow was higher in diabetic participants (46.4 ± 7.4 μl/min) than in healthy volunteers (40.4 ± 5.3 μl/min, p = 0.002 between groups). Oxygen content in retinal arteries was comparable between the two groups, but oxygen content in retinal veins was higher in participants with diabetes (0.15 ± 0.02 ml O₂/ml) compared with healthy control participants (0.13 ± 0.02 ml O₂/ml, p < 0.001). As such, the arteriovenous oxygen difference and total retinal oxygen extraction were reduced in participants with diabetes compared with healthy volunteers (total retinal oxygen extraction 1.40 ± 0.44 vs 1.70 ± 0.47 μl O₂/min, respectively, p = 0.03).

CONCLUSIONS/INTERPRETATION

Our data indicate early retinal hypoxia in individuals with type 1 diabetes with no or mild diabetic retinopathy as compared with healthy control individuals. Further studies are required to fully understand the potential of the technique in risk stratification and treatment monitoring.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01843114.

Application of Arterial Spin Labelling in the Assessment of Ocular Tissues

Arterial spin labelling (ASL) is a noninvasive magnetic resonance imaging (MRI) modality, capable of measuring blood perfusion without the use of a contrast agent. While ASL implementation for imaging the brain and monitoring cerebral blood flow has been reviewed in depth, the technique is yet to be widely used for ocular tissue imaging. The human retina is a very thin but highly stratified structure and it is also situated close to the surface of the body which is not ideal for MR imaging. Hence, the application of MR imaging and ASL in particular has been very challenging for ocular tissues and retina. That is despite the fact that almost all of retinal pathologies are accompanied by blood perfusion irregularities. In this review article, we have focused on the technical aspects of the ASL and their implications for its optimum adaptation for retinal blood perfusion monitoring. Retinal blood perfusion has been assessed through qualitative or invasive quantitative methods but the prospect of imaging flow using ASL would increase monitoring and assessment of retinal pathologies. The review provides details of ASL application in human ocular blood flow assessment.

Preserved Pressure Autoregulation but Disturbed Cyclo-Oxygenase and Nitric Oxide Effects on Retinal Arterioles during Acute Hypoxia in Diabetic Patients without Retinopathy

BACKGROUND

Acute hypoxia induces retinal vasodilatation, which depends on cyclooxygenase (COX) products and nitric oxide (NO) in vitro. However, it is unknown whether these mechanisms are active in diabetic patients and may contribute to the development of diabetic retinopathy.

METHODS

The Dynamic Vessel Analyzer was used to study the diameter regulation in retinal vessels during hypoxia in type 1 diabetic patients without retinopathy. The influence of NO and COX synthesis inhibition on the diameter of larger retinal vessels was studied during hypoxia, during isometric exercise and during flicker stimulation.

RESULTS

Increased arterial blood pressure during L-NMMA infusion and isometric exercise were paralleled by constriction of the retinal arterioles suggesting normal pressure autoregulation. Hypoxia significantly reduced the diameter responses during isometric exercise and during flicker stimulation as compared to normal persons.

CONCLUSION

The findings support that changes in metabolic autoregulation develop before changes in pressure autoregulation in diabetic patients.

Retrobulbar blood flow changes in eyes with diabetic retinopathy: a 10-year follow-up study

Purpose

We sought to assess long-term changes in the flow parameters of retrobulbar vessels in diabetic patients.

Methods

The retrobulbar circulation of 138 eyes was evaluated between 1994 and 1995 and 36 eyes were reevaluated between 2004 and 2008 (study group). They were divided into four groups: eyes of diabetic patients without diabetic retinopathy (DR), eyes with nonproliferative DR, eyes with proliferative DR, and eyes of nondiabetic patients (controls). Color Doppler imaging was used to assess the flow velocities in the major retrobulbar vessels. The resistive index (RI) was calculated and compared among the groups and between the two time periods.

Results

RI values of the central retinal artery and posterior ciliary artery had increased in the two non-DR groups and in the nonproliferative DR group, with a surprising decrease measured in eyes with proliferative DR (P= nonsignificant [NS]). Combining the nonproliferative DR and proliferative DR groups resulted in a milder increase of the RI of the posterior ciliary artery (P= NS) and the central retinal artery (P=0.02) in the DR group compared to the other groups.

Conclusion

Our results demonstrate that an increase of the resistance in the retrobulbar vessels, as a part of DR, can lessen over time and may even be reversed.

Color Doppler imaging of the retrobulbar vessels in diabetic retinopathy

Diabetes is a metabolic disease characterized by elevated blood glucose level due to impaired insulin secretion and activity. Chronic hyperglycemia leads to functional disorders of numerous organs and to their damage. Vascular lesions belong to the most common late complications of diabetes. Microangiopathic lesions can be found in the eyeball, kidneys and nervous system. Macroangiopathy is associated with coronary and peripheral vessels. Diabetic retinopathy is the most common microangiopathic complication characterized by closure of slight retinal blood vessels and their permeability. Despite intensive research, the pathomechanism that leads to the development and progression of diabetic retinopathy is not fully understood. The examinations used in assessing diabetic retinopathy usually involve imaging of the vessels in the eyeball and the retina. Therefore, the examinations include: fluorescein angiography, optical coherence tomography of the retina, B-mode ultrasound imaging, perimetry and digital retinal photography. There are many papers that discuss the correlations between retrobulbar circulation alterations and progression of diabetic retinopathy based on Doppler sonography. Color Doppler imaging is a non-invasive method enabling measurements of blood flow velocities in small vessels of the eyeball. The most frequently assessed vessels include: the ophthalmic artery, which is the first branch of the internal carotid artery, as well as the central retinal vein and artery, and the posterior ciliary arteries. The analysis of hemodynamic alterations in the retrobulbar vessels may deliver important information concerning circulation in diabetes and help to answer the question whether there is a relation between the progression of diabetic retinopathy and the changes observed in blood flow in the vessels of the eyeball. This paper presents the overview of literature regarding studies on blood flow in the vessels of the eyeball in patients with diabetic retinopathy.

Imaging evidence of diabetic choroidopathy in vivo: angiographic pathoanatomy and choroidal-enhanced depth imaging

Purpose

To describe the pathoanatomy of diabetic choroidopathy (DC) in pre-diagnosed diabetic retinopathy (DR) cases and to provide angiographic and optical evidence for DC using indocyanine green angiography (ICGA) and enhanced depth imaging spectral-domain optical coherence tomography (EDI SD-OCT).

Methods

A retrospective analysis of 80 eyes from 40 DR patients was conducted. In Group One, choroidal vascular abnormalities were evaluated by comparing angiographic findings from simultaneous ICGA with those from fundus fluorescein angiography (FFA). In Group Two, EDI SD-OCT was used to evaluate the subfoveal choroidal thickness (SFCT) and define the choroid boundary in order to acquire the bilateral and symmetric choroidal area (CA). Data were then analyzed by Image Pro Plus 6.0.

Results

In Group One, choroidal abnormalities that were evident using ICGA but not FFA included early hypofluorescent spots in 47 eyes (75.81%), late hyperfluorescent spots in 37 eyes (59.68%), and late choroidal non-perfusion regions in 32 eyes (51.61%). In particular, a significant difference between proliferative DR (PDR) in 17 of 23 eyes (73.91%) and non-PDR in 16 of 39 eyes (41.03%) was observed in late choroidal non-perfusion regions. Eighteen of 31 eyes (58.06%) also exhibited “inverted inflow phenomena.” In Group Two, both the SFCT and CA of eyes with diabetic macular edema and serous macular detachment were significantly greater than those in the other eyes. The CA in panretinal photocoagulation (PRP) treated cases was also greater than that in non-PRP treated cases.

Conclusions

Early hypofluorescent spots, late choroidal non-perfusion regions, inverted inflow phenomena, higher SFCT, and larger CA are qualitative and quantitative indexes for DC. Moreover, the late choroidal non-perfusion region is a risk factor for DC with DR. Our study suggests that the supplemental use of ICGA and EDI SD-OCT with FFA is a better choice for DR patients.

Calculation of central retinal artery diameters from non-invasive ocular haemodynamic measurements in type 1 diabetes patients

PURPOSE

The aim of the study was to compare the diameter of the central retinal artery (CRA) between patients with diabetes mellitus and healthy subjects in vivo. CRA diameters were calculated from retinal haemodynamic parameters measured with noninvasive measurement techniques.

METHODS

Sixteen patients with type 1 diabetes with no or mild diabetic retinopathy and 16 age-matched healthy controls were included in this study. Total retinal blood flow was assessed by combining bidirectional laser Doppler velocimetry in all veins entering the optic disc with measurements of retinal vessel diameters using a Dynamic Vessel Analyser. Blood flow velocity in the CRA was measured with colour Doppler imaging (CDI). The diameter of the CRA in the optic nerve was then calculated for each subject using the individual ocular haemodynamic data.

RESULTS

Calculated CRA diameters were significantly larger in patients with diabetes (180 ± 13 μm) compared with healthy controls (166 ± 10 μm, p = 0.001). No significant differences were found in retinal blood flow, retinal artery or vein diameters or mean flow velocity of the CRA.

CONCLUSION

The data of the present study show increased calculated CRA diameter in patients with type 1 diabetes with no or mild retinopathy. Blood flow velocity measurements in retrobulbar vessels using CDI need to be interpreted with caution in terms of retinal blood flow, because no information about vessel diameters is obtained by this technique.

Measurement of retinal blood flow rate in diabetic rats: disparity between techniques due to redistribution of flow

PURPOSE

Reports of altered retinal blood flow in experimental models of type I diabetes have provided contrasting results, which leads to some confusion as to whether flow is increased or decreased. The purpose of our study was to evaluate early diabetes-induced changes in retinal blood flow in diabetic rats, using two distinctly different methods.

METHODS

Diabetes was induced by injection of streptozotocin (STZ), and retinal blood flow rate was measured under anesthesia by a microsphere infusion technique, or by an index of flow based on the mean circulation time between arterioles and venules. Measurements in STZ rats were compared to age-matched nondiabetic controls. In addition, the retinal distribution of fluorescently-labeled red blood cells (RBCs) was viewed by confocal microscopy in excised flat mounts.

RESULTS

Retinal blood flow rate was found to decrease by approximately 33% in the STZ rats compared to controls (P < 0.001) as assessed by the microsphere technique. However, in striking contrast, the mean circulation time through the retina was found to be almost 3× faster in the STZ rats (P < 0.01). This contradiction could be explained by flow redistribution through the superficial vessels of the diabetic retina, with this possibility supported by our observation of significantly fewer RBCs flowing through the deeper capillaries.

CONCLUSIONS

We conclude that retinal blood flow rate is reduced significantly in the diabetic rat, with a substantial decrease of flow through the capillaries due to shunting of blood through the superficial layer, allowing rapid transit from arterioles to venules.

Temporal development of retinal arteriolar endothelial dysfunction in porcine type 1 diabetes

PURPOSE

Although hyperglycemia is implicated in retinal vascular dysfunction associated with the development of diabetic retinopathy, the temporal influence of hyperglycemia on retinal arteriolar reactivity remains unclear. Development of a large animal model of diabetes relevant to the human retina for evaluation of vascular function is also lacking. Herein, we examined nitric oxide (NO)-mediated dilation and endothelin-1 (ET-1)-induced constriction in retinal arterioles at various time periods in a porcine model of type 1 diabetes.

METHODS

Retinal arterioles were isolated from streptozocin-induced diabetic pigs (2, 6, and 12 weeks of hyperglycemia, 427 ± 23 mg/dL) and age-matched control pigs (73 ± 4 mg/dL), and then cannulated and pressurized for vasoreactivity study using videomicroscopic techniques.

RESULTS

Retinal arterioles isolated from control and diabetic pigs developed comparable levels of myogenic tone. The endothelium-dependent NO-mediated vasodilations to bradykinin and stepwise increases in luminal flow were significantly reduced within 2 weeks of hyperglycemia. The inhibitory effect was comparable following 6 and 12 weeks of hyperglycemia. However, the endothelium-independent vasodilation to sodium nitroprusside was unaffected. Constriction of retinal arterioles to ET-1 was unaltered at all time periods of hyperglycemia.

CONCLUSIONS

Our findings provide the first direct evidence for selective impairment of endothelium-dependent NO-mediated dilation of retinal arterioles within 2 weeks of hyperglycemia in a pig model of diabetes. By contrast, the ability of arteriolar smooth muscle to dilate to NO donor or contract to ET-1 was unaffected throughout the study period. This endothelial vasodilator dysfunction during early diabetes may contribute to development of retinopathy with chronic hyperglycemia.

Evaluation of resistive index by color Doppler imaging of orbital arteries in type II diabetes mellitus patients with microalbuminuria

OBJECTIVE

Resistive index (RI) is an indirect measurement of blood flow resistance that can be used to evaluate vascular damage in ophthalmologic diseases. The purpose of this study was to evaluate the association between RI values of orbital arteries by using the color Doppler imaging (CDI) in type II diabetes mellitus (DM) patients with microalbuminuria.

PATIENTS AND METHODS

We evaluated 91 type II DM patients with microalbuminuria and 27 healthy subjects. The DM patients with microalbuminuria were grouped into two: group 1 consisted of patients with retinopathy (n = 51) and group 2 consisted of patients without retinopathy (n = 40). Healthy subjects constituted group 3 (n = 27). The mean RI values of ophthalmic artery (OA), central retinal artery (CRA), and posterior ciliary artery (PCA) were measured using CDI.

RESULTS

Compared to diabetic group 2, group 1 had significantly higher mean RIs of OA, CRA, PCA, and HbA1c levels (p < 0.001 for all). Besides, there were no statistical differences in mean RIs of OA, CRA, and PCA between the control group and group 2 (p = 1.0; p = 0.44; p = 0.67, respectively). Mean RIs of OA and PCA were significantly correlated with age in group 1 (r = 0.549, p < 0.001; r = 0.407, p = 0.003, respectively). Mean RI of CRA was significantly correlated with the duration of diabetes and age in group 1 (r = 0.296, p = 0.035; r = 0.486, p < 0.001, respectively).

CONCLUSION

Our study indicates that RI might be a useful marker for early diagnosis and follow-up of diabetic retinopathy, and orbital RI assessment would be beneficial for diabetic patients with retinopathy.

Correlation between the resistive index values of renal and orbital arteries

BACKGROUND

Resistive index (RI) is an indirect measurement of blood flow resistance that can be used to evaluate vascular damage.

AIMS

The purpose of this study is to evaluate the association between RI values of orbital and intrarenal arteries by means of Doppler ultrasonography (US).

METHODS

We evaluated 103 diabetic patients. As a control group, 30 subjects were examined. The patients were divided into two groups. Group 1 consisted of patients with urinary albumin excretion (UAE) <300 mg/day and estimated glomerular filtration rate (eGFR) levels >90 ml/min (n = 50); Group 2 had a UAE >300 mg/day and/or eGFR levels between 89 and 60 ml/min (n = 53). The association between RI values obtained with Doppler US of the ophthalmic artery, central retinal artery, posterior ciliary artery and intrarenal arteries were calculated.

RESULTS

Both orbital and intrarenal arterial RI values in Group 1 and Group 2 were higher than the control group (p = 0.001); furthermore, values were higher in Group 2 than in Group 1 (p = 0.0004/0.029/0.036, p = 0.016, respectively). A positive correlation was found between orbital and intrarenal arterial RI values in Group 2 (r = 0.475, 0.285, 0.363, p < 0.01, respectively).

CONCLUSION

Both orbital and renal arterial RI values were shown to be higher than the control group. Further, a trend towards higher RI values was observed with renal disease. RI may be useful as one of the markers for early diagnosis and follow-up of diabetic nephropathy and retinopathy.

Blue flash ERG PhNR changes associated with poor long-term glycemic control in adolescents with type 1 diabetes

PURPOSE

To investigate the relationship between long-term glycemic control and photopic negative response (PhNR) changes in the blue flash ERG in adolescents with type 1 diabetes (T1D) without diabetic retinopathy (DR).

METHODS

After light adaptation, ERG responses to 1.60 cd·s/m(2) blue (420 nm) flashes (blue flash ERG) and 3.0 cd·s/m(2) white flashes (LA 3.0 ERG) were recorded in 22 patients (age range, 12 to 19 years) and 28 age-similar control subjects. The primary outcome measure was the amplitude of the PhNR. Secondary outcome measures were the amplitude and implicit time of the a-wave and b-wave. Multiple regression analyses were conducted with glycated hemoglobin (HbA(1c)) values and the time since diagnosis of T1D as covariates.

RESULTS

Blue flash ERG PhNR amplitudes were reduced (P = 0.005) in patients compared with control subjects. Multiple regression analysis demonstrated that a 1-unit increase in HbA(1c) was associated with a 15% decrease in the blue flash ERG PhNR amplitude (r = 0.61, P = 0.003). Compared with controls blue flash ERG a-waves (P = 0.03) and b-waves (P = 0.02) were delayed in patients but were not significantly associated with HbA(1c) or time since diagnosis of T1D. None of the ERG measures in the LA 3.0 ERG were significantly different in patients compared with controls.

CONCLUSIONS

Poorer long-term glycemic control is associated with worsening inner retinal dysfunction involving short-wavelength cone pathways of adolescents with T1D and no clinically visible DR. Future studies are warranted to determine whether changes in the blue flash ERG PhNR are a predictive marker of subclinical DR.

Pilot study for the evaluation of morphological and functional changes in retinal blood flow in patients with insulin resistance and/or type 2 diabetes mellitus

BACKGROUND

The aim of this study was to investigate early morphological and functional pathology in the retinal micro-circulation in patients with insulin resistance and/or type 2 diabetes mellitus (T2DM).

METHODS

Fifty-four subjects, without features of retinopathy under ophthalmological investigation, were recruited for study participation and were classified into three study groups according to their metabolic staging: (1) Group C comprised nondiabetic, insulin-sensitive subjects with a BMI <28 kg/m(2); (2) Group IR comprised nondiabetic, insulin-resistant, obese subjects with a BMI ≥28 kg/m(2); and (3) Group DM comprised patients with manifested T2DM. Retinal microvascular blood flow was assessed using scanning laser doppler flowmetry (Heidelberg Retina Flowmeter) before and after flicker light stimulation (10 Hz; Photo Stimulater 750).

RESULTS

No significant difference was observed in retinal blood flow (RBF) among the three groups, neither at baseline nor after stimulating the retina with flicker light. The arterial wall-to-lumen ratio (WLR) tended to be smaller in Group DM compared with Group C, and was significantly lower when comparing Group IR with Group C. When the subjects were grouped according to their insulin resistance, a steady decline in RBF and WLR could be observed with increasing insulin resistance.

CONCLUSIONS

In conclusion, laser scanner flowmetry of the retina was found to detect very early changes in microvascular blood flow. Development of insulin resistance seems to be an important component in the deterioration of RBF.

Ophthalmodynamometric pressure in eyes with proliferative diabetic retinopathy measured during pars plana vitrectomy

PURPOSE

To measure ophthalmodynamometric pressure (ODP) during vitrectomy in patients with proliferative diabetic retinopathy (PDR).

DESIGN

Prospective, interventional, consecutive case series.

METHODS

This study included 75 eyes of 75 patients undergoing vitrectomy for PDR. After core vitrectomy, the intraocular pressure was gradually raised using a vented-gas forced-infusion system (VGFI), and the optic nerve head was continuously monitored through a planoconvex contact lens. When the central retinal artery or its branches on the optic nerve head showed pulsations, the pressure was recorded as ODP. Diastolic blood pressure (DBP) and systolic blood pressure (SBP) were measured at the time of ODP measurement. Multiple regression analysis was performed to investigate the relationship between ODP and various explanatory variables: DBP, SBP, age, gender, body mass index, presence of hypertension, serum hemoglobin A1c, serum total cholesterol, fasting plasma glucose, presence of rubeosis iridis, and severity of PDR.

RESULTS

ODP was 63.6 ± 11.5 mm Hg (range 15.5-84.4 mm Hg). The ODP significantly correlated with DBP (r=0.570, P<.0001) and the mean arterial blood pressure (r=0.522, P<.0001), but not with SBP (r=0.121, P=.303). Multiple regression analysis revealed that ODP had a significant correlation with DBP (P<.0001), presence of rubeosis iridis (P<.0001), and severity of PDR (P=.046).

CONCLUSIONS

We measured ODP using VGFI during vitrectomy in patients with PDR. The ODP was significantly associated with DBP. The ODP was lower in patients with rubeosis iridis and severe PDR.

Modulation of retinal blood flow by kinin B₁ receptor in Streptozotocin-diabetic rats

The vasoactive kinin B₁ receptor (B₁R) is overexpressed in the retina of diabetic rats in response to hyperglycemia and oxidative stress. The aim of the present study was to determine whether B₁R could contribute to the early retinal blood flow changes occurring in diabetes. Male Wistar rats were rendered diabetic with a single i.p. injection of Streptozotocin (STZ) and studied 4 days or 6 weeks after diabetes induction. The presence of B₁R in the retina was confirmed by Western blot. The impact of oral administration of the B₁R selective antagonist SSR240612 (10mg/kg) was measured on alteration of retinal perfusion in awake diabetic rats by quantitative autoradiography. Data showed that B₁R was upregulated in the STZ-diabetic retina at 4 days and 6 weeks. Retinal blood flow was not altered in 4-day diabetic rats compared with age-matched controls but was significantly decreased following SSR240612 treatment. In 6-week diabetic rats, retinal blood flow was markedly reduced compared to control rats and SSR240612 did not further decrease the blood flow. These results suggest that B₁R is upregulated in STZ-diabetic retina and has a protective compensatory role on retinal microcirculation at 4 days but not at 6 weeks following diabetes induction.

Retinal blood flow in type 1 diabetic patients with no or mild diabetic retinopathy during euglycemic clamp

OBJECTIVE

To compare total retinal blood flow in diabetic patients with no or mild nonproliferative diabetic retinopathy and healthy control subjects and to investigate in patients whether there is a difference between retinal blood flow before morning insulin and under normoglycemic conditions using a glucose clamp.

RESEARCH DESIGN AND METHODS

Twenty patients with type 1 diabetes with no or mild diabetic retinopathy were included in this open parallel-group study, and 20 healthy age- and sex-matched subjects were included as control subjects. Retinal blood flow was assessed by combining velocity measurements using laser Doppler velocimetry and diameter measurements using a commercially available dynamic vessel analyzer. Measurements were performed before and during a euglycemic clamp.

RESULTS

Total retinal blood flow was higher in diabetic patients (53 +/- 16 microl/min) than in healthy subjects (43 +/- 16 microl/min; P = 0.034 between groups). When plasma glucose in diabetic patients was reduced from 9.3 +/- 1.7 to 5.3 +/- 0.5 mmol/l (P < 0.001) retinal blood flow decreased to 49 +/- 15 microl/min (P = 0.0003 vs. baseline). Total retinal blood flow during the glucose clamp was not significantly different from blood flow in normal control subjects (P = 0.161).

CONCLUSIONS

Type 1 diabetic patients with no or only mild diabetic retinopathy have increased retinal blood flow before their morning insulin dosage. Blood flow is reduced toward normal during euglycemic conditions. Retinal blood flow may fluctuate significantly with fluctuating plasma glucose levels, which may contribute to the microvascular changes seen in diabetic retinopathy.

The renin-angiotensin system in retinal health and disease: Its influence on neurons, glia and the vasculature

Renin-Angiotensin System is classically recognized for its role in the control of systemic blood pressure. However, the retina is recognized to have all the components necessary for angiotensin II formation, suggestive of a role for Angiotensin II in the retina that is independent of the systemic circulation. The most well described effects of Angiotensin II are on the retinal vasculature, with roles in vasoconstriction and angiogenesis. However, it is now emerging that Angiotensin II has roles in modulation of retinal function, possibly in regulating GABAergic amacrine cells. In addition, Angiotensin II is likely to have effects on glia. Angiotensin II has also been implicated in retinal vascular diseases such as Retinopathy of Prematurity and diabetic retinopathty, and more recently actions in choroidal neovascularizaiton and glaucoma have also emerged. The mechanisms by which Angiotensin II promotes angiogensis in retinal vascular diseases is indicative of the complexity of the RAS and the variety of cell types that it effects. Indeed, these diseases are not purely characterized by direct effects of Angiotensin II on the vasculature. In retinopathy of prematurity, for example, blockade of AT1 receptors prevents pathological angiogenesis, but also promotes revascularization of avascular regions of the retina. The primary site of action of Angiotensin II in this disease may be on retinal glia, rather than the vasculature. Indeed, blockade of AT1 receptors prevents glial loss and promotes the re-establishment of normal vessel growth. Blockade of RAS as a treatment for preventing the incidence and progression of diabetic retinopathy has also emerged based on a series of studies in animal models showing that blockade of the RAS prevents the development of a variety of vascular and neuronal deficits in this disease. Importantly these effects may be independent of actions on systemic blood pressure. This has culminated recently with the completion of several large multi-centre clinical trials that showed that blockade of the RAS may be of benefit in some at risk patients with diabetes. With the emergence of novel compounds targeting different aspects of the RAS even more effective ways of blocking the RAS may be possible in the future.

Effect of candesartan on prevention (DIRECT-Prevent 1) and progression (DIRECT-Protect 1) of retinopathy in type 1 diabetes: randomised, placebo-controlled trials

BACKGROUND

Results of previous studies suggest that renin-angiotensin system blockers might reduce the burden of diabetic retinopathy. We therefore designed the DIabetic REtinopathy Candesartan Trials (DIRECT) Programme to assess whether candesartan could reduce the incidence and progression of retinopathy in type 1 diabetes.

METHODS

Two randomised, double-blind, parallel-design, placebo-controlled trials were done in 309 centres worldwide. Participants with normotensive, normoalbuminuric type 1 diabetes without retinopathy were recruited to the DIRECT-Prevent 1 trial and those with existing retinopathy were recruited to DIRECT-Protect 1, and were assigned to candesartan 16 mg once a day or matching placebo. After 1 month, the dose was doubled to 32 mg. Investigators and participants were unaware of the treatment allocation status. The primary endpoints were incidence and progression of retinopathy and were defined as at least a two-step and at least a three-step increase on the Early Treatment Diabetic Retinopathy Study (ETDRS) scale, respectively. These trials are registered with ClinicalTrials.gov, numbers NCT00252733 for DIRECT-Prevent 1 and NCT00252720 for DIRECT-Protect 1.

FINDINGS

1421 participants (aged 18-50 years) were randomly assigned to candesartan (n=711) or to placebo (n=710) in DIRECT-Prevent 1, and 1905 (aged 18-55 years) to candesartan (n=951) or to placebo (n=954) in DIRECT-Protect 1. Incidence of retinopathy was seen in 178 (25%) participants in the candesartan group versus 217 (31%) in the placebo group. Progression of retinopathy occurred in 127 (13%) participants in the candesartan group versus 124 (13%) in the placebo group. Hazard ratio (HR for candesartan vs placebo) was 0.82 (95% CI 0.67-1.00, p=0.0508) for incidence of retinopathy and 1.02 (0.80-1.31, p=0.85) for progression of retinopathy. The post-hoc outcome of at least a three-step increase for incidence yielded an HR of 0.65 (0.48-0.87, p=0.0034), which was attenuated but still significant after adjustment for baseline characteristics (0.71, 0.53-0.95, p=0.046). Final ETDRS level was more likely to have improved with candesartan treatment in both DIRECT-Prevent 1 (odds 1.16, 95% CI 1.05-1.30, p=0.0048) and DIRECT-Protect 1 (1.12, 95% CI 1.01-1.25, p=0.0264). Adverse events did not differ between the treatment groups.

INTERPRETATION

Although candesartan reduces the incidence of retinopathy, we did not see a beneficial effect on retinopathy progression.

Ocular blood flow in diabetes and age-related macular degeneration

The 2 leading causes of blindness in adults in the industrialized nations, diabetic retinopathy and age-related macular degeneration, have been investigated thoroughly with respect to their pathogenesis. In recent years, it has been discovered that dysfunctional ocular microcirculation appears to play a part in the development of both diseases. In diabetic retinopathy, it has been shown that the disease is associated with early retinal vascular dysregulation. In the later states of the disease, retinal tissue hypoxia is a major trigger of sight-threatening neovascularization. In age-related macular degeneration, there is increasing evidence that reduced blood flow in the choroid is associated with the development and progression of the disease. Knowledge of the pathophysiological vascular states underlying these diseases is essential for the assessment and development of future therapies.

Doppler ultrasonography imaging of hemodynamic alteration of retrobulbar circulation in type 1 diabetic children and adolescents without retinopathy

AIM

We aimed to investigate the retrobulbar blood circulation using Colour Doppler Imaging (CDI) in type 1 diabetic children and adolescents who had no diabetic retinopathy and to compare the results with their healthy peers.

METHODS

Forty-nine patients with type 1 diabetes mellitus with no retinopathy on fundoscopic examination were included in the study. Forty-nine healthy children were defined as the control group. Central retinal artery (CRA), ophthalmic artery (OA) and posterior ciliary artery (PCA) were examined with Doppler US bilaterally. Peak systolic velocity (PSV), end diastolic velocity (EDV) and resistive indices (RI) for each artery were recorded.

RESULTS

Blood flow velocity of the OA was significantly different in diabetic patients (p<0.05). EDV of the OA was significantly higher (p=0.011) and RI was significantly lower (p=0.027) in patients with diabetes duration of longer than 5 years. RI of the CRA was significantly higher in patients who had higher microalbuminuria levels (p=0.016).

CONCLUSION

EDV of the OA increases and RI of the OA decreases in diabetes duration longer 5 years. Raised AER increases RI of the CRA. These findings may be the initial changes in the arterial circulation before vascular rigidity develops.

Retinal haemodynamics in individuals with well-controlled type 1 diabetes

AIMS/HYPOTHESIS

Abnormalities in retinal haemodynamics have been reported in patients with type 1 diabetes in advance of clinical retinopathy. These abnormalities could therefore be useful as early markers or surrogate endpoints for studying the microangiopathy. Since the DCCT, the increased focus on good glycaemic control is changing the natural history of diabetic retinopathy. Based on this, the aim of this study was to investigate whether patients with type 1 diabetes treated entirely or mostly in the post-DCCT era and tested in the absence of confounding factors show retinal haemodynamic abnormalities.

METHODS

We measured retinal haemodynamics by laser Doppler flowmetry in 33 type 1 diabetic individuals with no or minimal retinopathy (age 30+/-7 years, duration of diabetes 8.8+/-4.6 years, 9% showing microaneurysms), and 31 age- and sex-matched non-diabetic controls. The study participants were not taking vasoactive medications, and blood glucose at the time of haemodynamic measurements was required to be between 3.8 and 11.1 mmol/l.

RESULTS

HbA1c was 7.5+/-1.2% and blood glucose 7.7+/-2.8 mmol/l in these type 1 diabetic individuals, indicating relatively good glycaemic control. Retinal blood speed, arterial diameter and blood flow were not different between the diabetic individuals and the matched controls.

CONCLUSIONS/INTERPRETATION

Type 1 diabetic patients with no or minimal retinopathy who maintain relatively good glycaemic control do not show abnormalities of the retinal circulation at steady state, even after several years of diabetes. In such patients it may be necessary to test the vascular response to challenges to uncover any subtle abnormalities of the retinal vessels.

Ozagrel attenuates early streptozotocin-induced constriction of arterioles in the mouse retina

Retinal blood flow in human diabetics has been reported to follow a biphasic time course in which an initial period of reduced flow and ischemia is often followed by a hyperemic and angiogenic phase in which flow can exceed normal levels. The purpose of the present study is to investigate the mechanisms of the initial decrease in flow, since early interventions could provide the most effective treatment strategies. C57BL/6 mice were injected with streptozotocin (STZ) at 12 weeks of age and remained hyperglycemic until data were gathered 4 or 8 weeks later. Experimental measurements included retinal arteriolar red blood cell velocity and arteriolar diameters, with the diameters measured prior to and following an intravenous injection of the thromboxane synthase inhibitor ozagrel (100 mg/kg). Arterioles leading out of the optic disk constricted significantly at 4 weeks post-STZ (p<0.001) compared to age-matched controls, but not at 8 weeks post-STZ. Calculations of retinal blood flow indicated a 45% decrease at 4 weeks post-STZ, but only a 26% decrease by 8 weeks. Not all arterioles constricted equally in response to STZ; the most substantial constrictions were present in arterioles that were more closely arranged with countercurrent venules leading back into the optic disk. Injection of ozagrel provided significant dilation of constricted retinal arterioles. In addition, the pattern of dilation was consistent with the sites of the most severe constriction, i.e., ozagrel-induced dilation in the STZ mice occurred to the greatest extent in the arterioles more closely paired with the venules draining the microvascular bed. In summary, STZ induces a biphasic alteration in retinal blood flow in mice, in which thromboxane contributes to the initial reduction in blood flow at 4 weeks. Moreover, the thromboxane-induced arteriolar constriction is dependent on the proximity of the retinal arterioles to countercurrent venules.

Retinal arteriolar hemodynamic response to an acute hyperglycemic provocation in early and sight-threatening diabetic retinopathy

The aim was to quantify the magnitude of retinal arteriolar vascular reactivity to a hyperglycemic provocation in diabetic patients stratified by severity of retinopathy and in age-matched controls. The sample comprised 20 non-diabetic controls (Group 1), 19 patients with no clinically visible DR (Group 2), 18 patients with mild-to-moderate non-proliferative DR (Group 3) and 18 patients with diabetic macular edema (Group 4). Retinal hemodynamic measurements using the Canon Laser Blood Flowmeter (CLBF-100) were acquired before and 1 h after drinking a standardized oral glucose load drink. The magnitude of the retinal vascular response, as well as max:min velocity ratio and wall shear rate (WSR), was calculated and compared across groups. A significant change in blood glucose level was observed for all groups (p<0.05). The change in blood glucose elevation was significantly less in Group 1 compared to the other groups. No significant change in arteriolar diameter, blood velocity, blood flow, max:min velocity ratio and WSR was found in patients with diabetes and in age-matched subjects without diabetes. The results of this study indicate that retinal arteriolar blood flow is unaffected by acute elevation of blood glucose using an oral glucose load drink in patients with diabetes and in age-matched controls. This lack of a blood flow response to acute hyperglycemia in patients with early sight-threatening DR may be explained by a loss of retinal vascular reactivity.

Retinal hemodynamics in early diabetic macular edema

The objective of this study was to establish the baseline retinal hemodynamic characteristics of stratified groups of diabetic patients at increasing risk for the development of diabetic macular edema (DME). Group 1 had 50 control subjects, group 2 had 56 diabetic patients without clinically visible retinopathy, group 3 had 54 diabetic patients with microaneurysms and/or hard exudates within two disc diameters of the fovea in the absence of clinically manifest DME, and group 4 had 40 patients with clinically manifest DME. Retinal hemodynamics (diameter, velocity, maximum-to-minimum velocity ratio, and flow) were assessed. Intraocular pressure, blood pressure, and relevant systemic markers of diabetes control and complications were also undertaken. The maximum-to-minimum velocity ratio was elevated with increasing risk of clinically significant DME (P < 0.0001). No significant differences were found between the groups with respect to diameter, velocity, or flow. The maximum-to-minimum velocity ratio was correlated to age, duration of diabetes, blood pressure, pulse rate, intraocular pressure, and serum potassium levels. In conclusion, the maximum-to-minimum velocity ratio was significantly increased with increasing risk of development of DME. Retinal arteriolar hemodynamics were positively correlated to age, duration of diabetes, and blood pressure. These findings suggest a reduction in the compliance (i.e., an increase of vascular rigidity) of the arteriolar circulation with increasing risk of DME.

Plasma levels of adiponectin and soluble thrombomodulin in hypothyroid patients with normal thyroid function following levothyroxine replacement therapy

Hypothyroidism is associated with increased morbidity from cardiovascular disease, and adiponectin (ApN) is a newly-identified adipocytokine, which is expressed in human adipose cells and may have a protective effect against the development of coronary artery disease. The aim of the study was to evaluate the involvement of ApN secretion in hypothyroid patients with normal thyroid function following levothyroxine (L-T(4)) replacement therapy, and to associate plasma ApN levels with intima-media thickness (IMT) in the common carotid artery (CCA), an indicator of early atherosclerosis, and cardiovascular parameters including soluble thrombomodulin (sTM), a plasma endothelial injury marker. The CCA IMT and plasma levels of ApN and sTM were measured in 52 hypothyroid patients and in age-, sex- and body mass index (BMI)-matched normal control subjects. Thirty-six of the hypothyroid patients were further monitored for changes in these markers during 1 year in a euthyroid state induced by L-T(4) replacement therapy. Although the basal CCA IMT was significantly higher in hypothyroid patients [0.633 +/- 0.018 mm (mean +/- S.E.)] than in control subjects (0.552 +/- 0.022 mm, P < 0.005), both groups had similar baseline ApN and sTM levels [10.23 +/- 0.76 vs. 10.10 +/- 0.93 microg/ml: NS; and 2.58 +/- 0.14 vs. 2.68 +/- 0.20 ng/ml: NS, respectively]. Simple regression analysis revealed that plasma ApN was significantly correlated in a positive manner with age (r = 0.339, P = 0.015), HDL-cholesterol (r = 0.295, P = 0.048), and sTM (r = 0.490, P = 0.0005), but not with CCA IMT (r = 0.059, P = 0.742). In multivariate analysis, the plasma ApN level was significantly associated with that of sTM (r = 0.546, P = 0.0001) and with serum high-density lipoprotein (HDL)-cholesterol levels (r = 0.291, P = 0.029) in hypothyroid patients. During 1 year of L-T(4) replacement therapy, hypothyroid patients showed a significant decrease in CCA IMT, to 0.553 +/- 0.016 mm (P < 0.0001), a level comparable to normal controls, but no significant change in ApN (from 10.79 +/- 1.07 to 10.6 9+/- 1.14 microg/ml, NS) or sTM (from 2.59 +/- 0.15 to 2.74 +/- 0.18 ng/ml, NS). Hence, we provide evidence that ApN and sTM might not contribute to enhanced atherosclerosis, as reflected by increased CCA IMT in hypothyroid patients. However, this is the first report to demonstrate a positive and significant association of sTM with ApN. These data support the hypothesis that sTM is one of the determinant of ApN and thus suggest the presence of an sTM-associated regulatory mechanism for ApN secretion in hypothyroid patients.

Correlation between capillary blood flow of retina estimated by SLDF and circulatory parameters of retrobulbar blood vessels estimated by CDI in diabetic patients

BACKGROUND

The aim of this study was to investigate the correlation between the recordings of scanning laser Doppler flowmetry (SLDF) of the retina and the recordings of color Doppler imaging (CDI) of the retrobulbar circulatory parameters in diabetic patients without diabetic retinopathy.

METHODS

Twenty-three diabetic patients without diabetic retinopathy were evaluated using SLDF for the apparent retinal circulation and using CDI for the apparent retrobulbar circulation in the central retinal artery, the central retinal vein and the short posterior ciliary artery. The circulatory parameters estimated in the retinal tissue using SLDF were velocity, volume and flow. The Circulatory parameters that were recorded using the CDI method were peak systolic velocity (PSV), end-diastolic velocity (EDV), mean velocity (MV), pulsatility (PI) and resistivity index (RI). We obtained the correlation coefficients between parameters of SLDF and CDI. Multiple regression analysis was performed with "flow" parameter of SLDF recordings as a dependent variable and all estimated CDI parameters as independent variables. Multiple linear regression was also performed, including the "flow" parameter of SLDF recordings as a dependent variable and PI of the CDI parameters of all the measured blood vessels as independent variables.

RESULTS

The "velocity" parameter of SLDF was significantly correlated with the PI in the central retinal artery (P=0.02), PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery, as recorded by CDI (P=0.003; P=0.02; P=0.002; P=0.01). The "volume" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.03; P=0.03) and the PSV in the short posterior ciliary artery (P=0.03), as recorded by CDI. The "flow" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery (P=0.003; P=0.03; P=0.002; P=0.01) as measured by CDI. The multiple regression analysis was statistically non-significant (P=0.86). The multiple linear regression analysis indicated that from among the PI of the evaluated blood vessels, the PI of the short posterior ciliary artery was the most significant predictor of the "flow" parameter of SLDF (P=0.01).

CONCLUSION

This study suggests a positive correlation between the recordings of SLDF of the retinal tissue and the retrobulbar circulatory parameters of the CDI in diabetic patients without diabetic retinopathy.

Ocular Blood Flow Velocity Determined by Color Doppler Imaging in Diabetic Retinopathy

PURPOSE

To measure and investigate changes of blood flow velocity by color Doppler imaging in the ophthalmic artery (OA), central retinal artery (CRA) and short posterior ciliary arteries (PCA) in diabetic retinopathy (DR) and to compare the results with those in healthy control subjects.

METHODS

In this investigation we included 44 eyes of 44 diabetic patients with different stages of DR forming group NPDR (11 eyes with mild and 11 eyes with moderate nonproliferative DR) and group SNPDR/PDR (19 eyes with severe nonproliferative and 3 eyes with proliferative DR) and 22 eyes of 22 healthy age- and sex-matched subjects forming control group HC. With color Doppler imaging we measured the peak systolic velocity (PSV, cm/s) and end-diastolic velocity (EDV, cm/s) of blood flow in the OA, CRA and PCA. The resistance index of each vessel was then calculated. Statistical analysis comparing the results of groups NPDR, SNPDR/PDR and HC was carried out. Statistical significance was set at p < 0.05.

RESULTS

There was a statistically significant increase in PSV in the OA in group SNPDR/PDR compared with group HC (35.71 +/- 6.90 vs. 31.45 +/- 4.32 cm/s; mean +/- SD). There was a statistically significant decrease in PSV in the CRA in group NPDR compared with group HC (8.50 +/- 1.62 vs. 10.61 +/- 1.75 cm/s; mean +/- SD) and in group SNPDR/PDR compared with group HC (7.34 +/- 1.78 vs. 10.61 +/- 1.75 cm/s; mean +/- SD), also there was a statistically significant decrease in EDV in group SNPDR/PDR compared with group HC (2.05 +/- 0.53 vs. 3.00 +/- 0.81 cm/s; mean +/- SD). A statistically significant decrease in EDV in the PCA in group SNPDR/PDR compared with group HC (2.95 +/- 1.04 vs. 3.95 +/- 0.98 cm/s; mean +/- SD) was found, also there was a statistically significant increase in the resistance index in group SNPDR/PDR compared with group NPDR (0.72 +/- 0.05 vs. 0.67 +/- 0.07; mean +/- SD) and in group SNPDR/PDR compared with group HC (0.72 +/- 0.05 vs. 0.67 +/- 0.05; mean +/- SD).

CONCLUSIONS

In this investigation, color Doppler imaging was used to determine significant changes of blood flow velocity in the OA, CRA and PCA in DR compared with healthy control subjects and the changes of blood flow velocity become further significant considering the progression of DR. This points to the presence of circulatory changes in the OA, CRA and PCA in diabetic patients with DR.

Retinal vessel diameters and the incidence of gross proteinuria and renal insufficiency in people with type 1 diabetes

Early retinal vessel caliber changes may predict risk of diabetic nephropathy. We examined the association of retinal vessel diameters and the incidence of gross proteinuria and renal insufficiency in a population-based cohort of people with type 1 diabetes (n = 557). Baseline retinal photographs were digitized, and diameters of individual retinal vessels were measured and summarized. Incident cases of gross proteinuria and renal insufficiency were identified over a 16-year period. Larger retinal venular diameter was associated with higher cumulative incidence of gross proteinuria (18.6, 25.4, 37.7, and 50.4%, comparing increasing venular diameter quartiles) and renal insufficiency (10.7, 15.5, 23.2, and 32.8%). After adjusting for age, sex, duration of diabetes, HbA(1c) levels, baseline retinopathy levels, and other factors, larger retinal venular diameter was associated with an increased risk of gross proteinuria (RR 1.53, 95% CI 1.19-1.97, comparing 4th vs. 1st to 3rd quartiles of venular diameter) and renal insufficiency (1.51, 1.05-2.17). Retinal arteriolar diameter was not associated with either gross proteinuria or renal insufficiency. We conclude that in individuals with type 1 diabetes, larger retinal venular diameter is independently associated with the long-term incidence of gross proteinuria and renal insufficiency and may provide additional predictive information regarding risk of nephropathy.

Decrease in carotid intima-media thickness in hypothyroid patients after normalization of thyroid function

OBJECTIVE

This case-control study was carried out to assess whether levothyroxine (L-T4) replacement might cause regression of the enhanced atherosclerosis seen in hypothyroid patients.

PATIENTS AND METHODS

Intima-media thickness (IMT) in the common carotid artery (CCA) was measured from digitalized still images taken during scanning by high-resolution ultrasonography as an indicator of early atherosclerosis. Thirty-five hypothyroid patients were examined for their CCA IMT before and 1 year after normalization of thyroid function by L-T4 replacement. As control, 35 healthy subjects were enrolled from among the participants in a local health-check programme conducted at the Osaka City University Hospital.

RESULTS

Basal CCA IMT was significantly higher in hypothyroid patients [0.635 +/- 0.018 (mean +/- SE) mm] than in control subjects (0.559 +/- 0.021 mm, P < 0.005). After 1 year of euthyroidism, 34 out of 35 patients showed a significant decrease of CCA IMT, to 0.552 +/- 0.015 mm (P < 0.0001), a level comparable to normal controls. CCA IMT change was closely associated with basal levels of total cholesterol (r = -0.472, P= 0.0031), low-density lipoprotein (LDL) cholesterol (r = -0.441, P= 0.0076) and the total/HDL cholesterol ratio (r =-0.435, P= 0.0057), but not with any of the other variables measured except for age (r = -0.353, P= 0.0296).

CONCLUSIONS

This study demonstrated that L-T4 treatment might have the potential to reverse the progression of atherosclerosis in hypothyroid patients. Furthermore, it suggests that increased levels of LDL cholesterol and the total/HDL cholesterol ratio have an important role in the increased common carotid intima-media thickness in hypothyroid patients.

ecNOS gene polymorphism is associated with endothelium-dependent vasodilation in Type 2 diabetes

The association between endothelial constitutive nitric oxide synthase (ecNOS) gene polymorphism and vascular endothelial function has not been clarified. We investigated the impact of ecNOS gene polymorphism on endothelial function in 95 patients with Type 2 diabetes (ecNOS genotype: 4b/b, n = 62; 4b/a, n = 30; 4a/a, n = 3). Flow-mediated (endothelium dependent, FMD) and nitroglycerin-induced (endothelium independent, NTG) vasodilations of the right brachial artery were studied using a phase-locked echotracking system. There were no significant differences in clinical characteristics among the ecNOS genotypes. The FMD was significantly lower in the patients with ecNOS4a allele than in those without ecNOS4a allele (P < 0.05). Multiple regression analysis showed that ecNOS4a allele and mean blood pressure were significant independent determinants for reduced FMD in all patients (R(2) = 0.122, P = 0.0025). The ecNOS4a allele was an independent determinant for reduced FMD in smokers but not in nonsmokers. These results suggest that ecNOS4a allele is a genetic risk factor for endothelial dysfunction in diabetic patients, especially in smokers.

Increased stiffness in common carotid artery in hyperthyroid Graves' disease patients

The present study was undertaken to assess the effect of hyperthyroidism on stiffness in the common carotid artery (CCA) in patients with Graves' disease (GD) and elucidate the mechanism by which arterial stiffness is increased in hyperthyroidism. The arterial stiffness index beta (stiffness beta) was evaluated in the CCA using an ultrasonic phase-locked echo-tracking system. Stiffness beta was defined as the logarithm of the ratio of systolic to diastolic blood pressure divided by the fractional diameter increase during the cardiac cycle and thus established as a measure of arterial stiffness uninfluenced by the change in blood pressure. Seventy euthyroid GD patients were measured for CCA stiffness beta to determine its relationship to retinal blood flow and plasma levels of vascular injury markers. To investigate the effect of hyperthyroidism, 27 GD patients were measured for changes during antithyroid drug (ATD) therapy in stiffness beta and in hemodynamic parameters, retinal blood flow and plasma vascular injury markers. In euthyroid GD patients, stiffness beta in the CCA showed a significant and positive correlation with systolic blood pressure and pulse pressure, but not with peripheral blood flow in the central retinal artery. ATD therapy significantly reduced stiffness beta from 5.23 +/- 2.10 to 4.36 +/- 1.48. The fractional reduction of stiffness beta during ATD therapy correlated significantly with reductions in pulse pressure and retinal blood flow, but not with the reductions in systolic and mean blood pressure, or any of the plasma injury markers. In summary, the significant increase in stiffness beta in the hyperthyroid state may reflect the harmful effect of hyperthyroidism on the arterial wall, which may in turn result from increased stroke volume.

Choroidal circulation in diabetic patients

PURPOSE

To evaluate choroidal circulatory changes in diabetic patients with and without background diabetic retinopathy (BDR) by measuring the retrobulbar circulation with colour Doppler imaging (CDI).

METHODS

CDI was used to measure circulatory parameters of the PCA (posterior ciliary artery), CRA (central retinal artery), OA (ophthalmic artery) and the respective veins in 73 diabetic patients and 22 controls in a sitting posture. Among the diabetic patients, 38 patients were without diabetic retinopathy (NDR) and 35 had BDR. A non-parametric Kruskal-Wallis test with a Dunn correction was used for data analysis.

RESULTS

End-diastolic velocity (EDV) in the PCA was decreased (2.55+/-0.80 cm/s) and resistivity index (RI) in the PCA was increased (0.70+/-0.08) in BDR patients compared with the control patients' EDV (3.23+/-1.08 cm/s, p = 0.01) and RI (0.62+/-0.06, p = 0.0003). RI in the CRA was significantly higher in the BDR group (0.74+/-0.09) than in the control group (0.68+/-0.08, p = 0.006). RI in the OA was significantly higher in the BDR group (0.87+/-0.06) compared both with the NDR group (0.83+/-0.07) and with the control group (0.81+/-0.06; p = 0.007, p = 0.004). NDR patients had a significantly higher RI in the PCA (0.67+/-0.08) than control patients (0.62+/-0.06, p = 0.01, while the CRA RI (0.71+/-0.09) did not show significant differences from the control group (0.69+/-0.08, p = 0.32). Decreased EDV in the CRA was detected in NDR patients (2.16+/-0.76 cm/s) compared with the controls (2.72+/-0.92 cm/s, p = 0.007).

CONCLUSION

The results from this study suggest that not only the retinal but also the choroidal circulation is affected in NDR and BDR patients.

The pathogenesis of edema in diabetic maculopathy

Diabetic maculopathy is characterized by the accumulation of extracellular fluid in Henle's layer and the inner nuclear layer of the retina. The localization of the edema is likely to be due, in part, to the relative barrier properties of the inner and outer plexiform layers. The origin of the extracellular fluid is from the intravascular compartment. Although changes to retinal blood flow may partly explain the extravasation of fluid, the most important mechanism is breakdown of the blood retinal barriers. Both the inner blood retinal barrier formed by the retinal capillary endothelial cell tight junctions and the outer barrier formed by the retinal pigment epithelial cell tight junctions can be affected. The mechanism of breakdown of the blood retinal barriers is likely to be changes to the tight junction proteins including occludin and ZO-1. The biochemical messenger inducing these changes may be vascular endothelial growth factor. The origin of this or other cofactors may be the retinal glial cells. The underlying biochemical stimulus to the production of vascular endothelial growth factor is chronic hyperglycaemia, but it is uncertain by what pathway this is effected.