Alterations of retinal capillary blood flow in preclinical retinopathy in subjects with type 2 diabetes

Association of OCT and OCT angiography measures with the development and worsening of diabetic retinopathy in type 2 diabetes

OBJECTIVE

To assess if optical coherence tomography (OCT) and OCT angiography (OCTA) measures are associated with the development and worsening of diabetic retinopathy (DR) over four years.

METHODS

280 participants with type 2 diabetes underwent ultra-wide field fundus photography, OCT and OCTA. OCT-derived macular thickness measures, retinal nerve fibre layer and ganglion cell-inner plexiform layer thickness and OCTA-derived foveal avascular zone area, perimeter, circularity, vessel density (VD) and macular perfusion (MP) were examined in relation to the development and worsening of DR over four years.

RESULTS

After four years, 206 eyes of 219 participants were eligible for analysis. 27 of the 161 eyes (16.7%) with no DR at baseline developed new DR, which was associated with a higher baseline HbA1c and longer diabetes duration. Of the 45 eyes with non-proliferative DR (NPDR) at baseline, 17 (37.7%) showed DR progression. Baseline VD (12.90 vs. 14.90 mm/mm2, p = 0.032) and MP (31.79% vs. 36.96%, p = 0.043) were significantly lower in progressors compared to non-progressors. Progression of DR was inversely related to VD ((hazard ratio [HR] = 0.825) and to MP (HR = 0.936). The area under the receiver operating characteristic curves for VD was AUC = 0.643, with 77.4% sensitivity and 41.8% specificity for a cut-off of 15.85 mm/mm2 and for MP it was AUC = 0.635, with 77.4% sensitivity and 25.5% specificity for a cut-off of 40.8%.

CONCLUSIONS

OCTA metrics have utility in predicting progression rather than the development of DR in individuals with type 2 diabetes.

Retinal and choroidal microvascular characterization and density changes in different stages of diabetic retinopathy eyes

Background

The purpose of this study was to evaluate the changes in fundus vascular density and micromorphological structure of all vascular plexuses during the different stages of diabetic retinopathy (DR), and the correlation between fundus blood flow and the DR severity.

Methods

This observational cross-sectional study was conducted of 50 eyes with different stages of DR, 25 diabetes mellitus (DM) patients without clinical signs of DR and 41 healthy eyes. The foveal avascular zone (FAZ), vessel density of superficial capillary plexus (SCP), and deep retinal capillary plexus (DCP) were acquired by RTVue XR Avanti OCTA device. The perfusion density (PD), skeleton vessel density (SVD) was manually calculated using ImageJ. The area under receiver operating characteristic (ROC) curve was used to determine the diagnostic value of OCTA parameters in distinguishing DR and healthy eyes.

Results

The choroidal VD were significantly higher in the healthy group than in the DM without DR, NPDR, and PDR groups (p < 0.001). The mean retinal parafovea VD, PD, and retinal SVD were higher in healthy and DM without DR eyes compared with NPDR and DR eyes in all vascular layers (p < 0.001). The parafoveal VD of SCP, and DCP decreased, and FAZ area increased with the exacerbation of DR. The OCTA parameters, including FAZ area, parafovea VD, PD, and SVD in all vascular layers showed significant correlation with DR severity (all p < 0.001). ROC curves of OCTA parameters (FAZ area, retinal parafovea VD, retinal PD, and SVD in all vascular layers) for had high sensitivity and specificity in distinguishing DR versus healthy eyes.

Conclusion

The choroidal parafovea VD, retinal parafovea VD, retinal PD, and SVD in the two plexuses decreased, and retinal FAZ area increased significantly with worsening DR. VD, PD, and SVD might be potential early biomarkers indicating the progression of DR before appearance of clinically PDR in patients with DM. In this study, OCTA parameters had high sensitivity and specificity in distinguishing DR and healthy eyes.

Association between neurodegeneration and macular perfusion in the progression of diabetic retinopathy. A 3-year longitudinal study

Objective and purpose: To explore the relation between retinal neurodegenerative changes and vessel closure (VC) in individuals with non-proliferative diabetic retinopathy (NPDR) in a follow-up period of 3 years.

DESIGN

3-year prospective longitudinal study with four annual visits.

PARTICIPANTS

74 individuals with type 2 diabetes, NPDR and ETDRS grades from 10 to 47, one eye/person. An age-matched healthy control population of 84 eyes was used as control group.

METHODS

Participants were annually examined by color fundus photography (CFP), spectral domain-optical coherence tomography (SD-OCT) and OCT-Angiography (OCTA). Vessel closure was assessed by OCTA vessel density maps. SD-OCT segmentations was performed to access central retinal thickness (CRT) and retinal neurodegeneration considered as thinning of the ganglion cell plus inner plexiform layer (GCL+IPL).

RESULTS

Type 2 diabetic individuals presented significantly higher CRT (p=0.001), GCL+IPL thinning (p=0.042), and decreased vessel density at the superficial capillary plexus (p<0.001) and full retina (p=0.001). When looking at changes occurring over the 3-year period of follow up (Table 2), there were statistically significant decreases in GCL+IPL thickness (-0.438 µm/year; p=0.038), foveal avascular zone circularity (-0.009; p=0.047), and vessel density, in superficial capillary plexus (-0.172 mm-1/year; p<0.001), deep capillary plexus (-0.350 mm-1/year; p<0.001) and full retina (-0.182 mm-1/year; p<0.001). A statistically significant association was identified between GCL+IPL thinning and decrease in deep capillary plexus vessel density (β = 0.196 [95% CI 0.037, 0.355], z = 2.410, p = 0.016), after controlling for age, gender, diabetes duration, hemoglobin A1c level, and CRT.

CONCLUSIONS

Retinal neurodegenerative changes show a steady progression during a 3-year period of follow-up in eyes with NPDR and appear to be directly associated with progression in decreased vessel density including vascular closure through preferential involvement of the deep capillary plexus. Our findings provide evidence that retinal neuropathy is linked with microvascular changes occurring in diabetic patients.

Comparison of Different Metrics for the Identification of Vascular Changes in Diabetic Retinopathy Using OCTA

Retinal vessel metrics identifying microvascular changes such as vessel closure (VC) have shown potential clinical value by identifying eyes with diabetic retinopathy (DR) at different severity levels and at increased risk for disease progression to more severe stages. We compare the performance of 11 different metrics, which include 2 metrics supplied by the manufacturer, based on OCTA for identification of VC in different Early Treatment for Diabetic Retinopathy Study (ETDRS) severity groups. OCTA en-face slabs from 84 healthy eyes (70 ± 4.8 years) and 78 eyes of diabetic individuals (67 ± 7.5 years) were processed using different methods that include abnormal intercapillary spaces (AIS), vessel density (VD), and nine metrics extracted from the en-face slab. The best separation between the eyes with DR and the control group was obtained in the superficial capillary plexus (SCP), with the full retina (FR) also performing well. In the SCP, the metrics that show better performance were the AIS and the VD with a value of area under curve (AUC) equal to 0.89 [95% CI 0.84-0.94] and 0.85 [95% CI 0.79-0.91], respectively, indicating that the VD metric supported by the manufacturer is satisfactory. The values of these metrics on the different ETDRS groups show a progressive increase in VC, which is correlated with disease severity.

Characterization of Risk Profiles for Diabetic Retinopathy Progression

Diabetic retinopathy (DR) is a frequent complication of diabetes and, through its vision-threatening complications, i.e., macular edema and proliferative retinopathy, may lead to blindness. It is, therefore, of major relevance to identify the presence of retinopathy in diabetic patients and, when present, to identify the eyes that have the greatest risk of progression and greatest potential to benefit from treatment. In the present paper, we suggest the development of a simple to use alternative to the Early Treatment Diabetic Retinopathy Study (ETDRS) grading system, establishing disease severity as a necessary step to further evaluate and categorize the different risk factors involved in the progression of diabetic retinopathy. It needs to be validated against the ETDRS classification and, ideally, should be able to be performed automatically using data directly from the examination equipment without the influence of subjective individual interpretation. We performed the characterization of 105 eyes from 105 patients previously classified by ETDRS level by a Reading Centre using a set of rules generated by a decision tree having as possible inputs a set of metrics automatically extracted from Swept-source Optical Coherence Tomography (SS-OCTA) and Spectral Domain- OCT (SD-OCT) measured at different localizations of the retina. When the most relevant metrics were used to derive the rules to perform the organization of the full pathological dataset, taking into account the different ETDRS grades, a global accuracy equal to 0.8 was obtained. In summary, it is now possible to envision an automated classification of DR progression using noninvasive methods of examination, OCT, and SS-OCTA. Using this classification to establish the severity grade of DR, at the time of the ophthalmological examination, it is then possible to identify the risk of progression in severity and the development of vision-threatening complications based on the predominant phenotype.

Optical Coherence Tomography Angiography Metrics Monitor Severity Progression of Diabetic Retinopathy-3-Year Longitudinal Study

To examine retinal vessel closure metrics and neurodegenerative changes occurring in the initial stages of nonproliferative diabetic retinopathy (NPDR) and severity progression in a three-year period. Methods: Three-year prospective longitudinal observational cohort of individuals with type 2 diabetes (T2D), one eye per person, using spectral domain-optical coherence tomography (SD-OCT) and OCT-Angiography (OCTA). Eyes were examined four times with one-year intervals. OCTA vessel density maps of the retina were used to quantify vessel closure. Thickness of the ganglion cell + inner plexiform layer (GCL + IPL) was examined to identify retinal neurodegenerative changes. Diabetic retinopathy ETDRS classification was performed using the seven-field ETDRS protocol. Results: A total of 78 eyes/patients, aged 52 to 80 years, with T2D and ETDRS grades from 10 to 47 were followed for 3 years with annual examinations. A progressive increase in retinal vessel closure was observed. Vessel density (VD) showed higher decreases with retinopathy worsening demonstrated by step-changes in ETDRS severity scale (p < 0.001). No clear correlation was observed between neurodegenerative changes and retinopathy progression. Conclusions: Retinal vessel closure in NPDR correlates with DR severity progression. Our findings provide supporting evidence that OCTA metrics of vessel closure may be used as a surrogate for DR severity progression.

Topical Treatment With Brimonidine and Somatostatin Causes Retinal Vascular Dilation in Patients With Early Diabetic Retinopathy From the EUROCONDOR

Purpose

Structural retinal microvascular changes have been identified as risk markers of diabetic retinopathy (DR). In order to estimate the retinal response of neuroprotective eye drops, we aimed to evaluate the effect of topical retinal neuroprotection on retinal microvascular changes in early DR.

Methods

Patients with type 2 diabetes with no or early DR were randomized 1:1:1 to topical treatment with placebo, brimonidine, or somatostatin in a 96-week prospective, phase II to III, European multicenter trial. Retinal vascular calibers were measured semiautomatically in digital fundus images by certified graders at baseline and follow-up and summarized as central retinal arteriolar and venular equivalent (CRAE and CRVE).

Results

Of 449 patients originally included, 297 completed the study with gradable retinal images. Median age and duration of diabetes was 64.5 and 9.9 years, and 65.7% were male. At baseline, Early Treatment Diabetic Retinopathy Study levels were 10 (no DR, 42.8%), 20 (minimal DR, 28.3%), and 35 (mild DR, 29.0%), and CRAE and CRVE did not differ between groups. As opposed to patients with no or minimal DR at baseline, patients with mild DR in the active groups developed a larger retinal arteriolar (brimonidine: +6.2 μm, P = 0.006; somatostatin: +7.2 μm, P = 0.006) and venular (brimonidine: +13.9 μm, P = 0.01; somatostatin: +14.3 μm, P = 0.0001) caliber in contrast to those in the placebo group.

Conclusions

Topical treatment with brimonidine and somatostatin causes retinal arteriolar and venular dilation in patients with type 2 diabetes and preexisting early DR. Upcoming studies should elaborate on the potential of these findings in arresting early DR.

Importance of Considering the Middle Capillary Plexus on OCT Angiography in Diabetic Retinopathy

Purpose

To quantify microvasculature changes in the superficial (SCP), middle (MCP), and deep capillary plexuses (DCP) in diabetic retinopathy (DR).

Methods

Retrospective cross-sectional study at a tertiary academic referral center, in which 26 controls (44 eyes), 27 diabetic subjects without retinopathy (44 eyes), 32 subjects with nonproliferative retinopathy (52 eyes), and 27 subjects with proliferative retinopathy (40 eyes) were imaged with optical coherence tomography angiography (OCTA). Outcome measures included parafoveal vessel density (VD), percentage area of nonperfusion (PAN), and adjusted flow index (AFI) at the different plexuses.

Results

MCP VD and MCP AFI decreased with worsening DR, while PAN increased, mirroring changes within the DCP. The fitted regression line for MCP and DCP AFI were significantly different than the SCP, while DCP PAN differed from SCP PAN with disease progression. Higher SCP AFI and PAN were different in eyes with diabetes without retinopathy compared with controls. Unexpectedly, sex was found to independently influence MCP VD and AFI with worsening disease.

Conclusions

OCTA parameters in the MCP and DCP displayed parallel changes with DR progression, different from the SCP, emphasizing the importance of physiologic considerations in the retinal capillaries. Thus, segmentation protocols that include the MCP within the SCP may be confounded. A difference in DCP PAN with worsening DR was unmasked relative to a prior study that included the MCP with SCP. We confirm that SCP AFI and PAN may serve as early indicators of microvascular changes in DR and identify an interaction between sex and the MCP deserving further study.

Impact of dipeptidyl-peptidase 4 inhibitors on cardiovascular diseases

Dipeptidyl peptidase 4 (DPP-4) inhibitor is a novel group of medicine employed in type 2 diabetes mellitus (T2DM),which improves meal stimulated insulin secretion by protecting glucagon-like peptide-1 (GLP-1) and glucose dependent insulinotropic polypeptide (GIP) from enzymatic degradation. Cardiovascular diseases are serious complications and leading causes of mortality among individuals with diabetes mellitus. Glycemic control per se seems to fail in preventing the progression of diabetic cardiovascular complications. DPP-4 has the capability to inactivate not only incretins, but also a series of cytokines, chemokines, and neuropeptides involved in inflammation, immunity, and vascular function. Pre-clinical studies suggested that DPP-4 inhibitors may have potential cardiovascular protective effects in addition to their antidiabetic actions. In recent years, a number of clinical trials have been conducted to evaluate the effect of different DPP-4 inhibitors on the cardiovascular system. We herein review the available clinical studies in cardiovascular effects played by each DPP-4 inhibitor and discuss the prospective application of DPP-4 inhibitors on cardiovascular diseases.

Acetagastrodin effects on retinal oscillatory potentials in patients during the early stages of diabetes

AIMS

To investigate the protective effect of acetagastrodin on visual electrophysiology in patients with early-stage diabetes.

METHODS

A prospective, randomized, controlled, double-blind trial was conducted. Subjects who were randomly assigned to either the treatment group or the control group were orally administered acetagastrodin or placebo, respectively, for 6 months. The quantity, mean amplitude and mean latency of oscillatory potentials (OPs) wavelets at baseline and 6 months were measured on electroretinogram (ERG), in all subjects.

RESULTS

A total of 92 right eyes in 92 patients with type 2 diabetes, who were diagnosed for the first time, were enrolled. Each group consisted of 46 cases (46 eyes). There was no significant difference in baseline characteristic between treatment and control groups at baseline, but quantity in treatment group was more than that in control group at 6 months (P = 0.001). The mean amplitude of OPs was reduced in the control group 6 months later compared with treatment group (P = 0.001). As to mean latency of OPs, statistical difference was also detectable between the treatment group and control group 6 months later (P < 0.001). No statistical differences were found in hemoglobin between both groups at 6 months (P > 0.05).

CONCLUSIONS

Electrophysiological changes would go on worsening even hemoglobin was under control during the initial stage of diabetes. Acetagastrodin treatment may be an effective treatment to protect retinal neurons against such functional impairment during the early stages of diabetes.

Higher glucose level and systemic oxidative stress decrease the mean velocity index of the retinal artery during flickering light stimulation in type 1 diabetes

Aim

To determine whether higher glucose level and systemic oxidative stress decrease mean velocity (MV) index of the central retinal artery (CRA) during flickering light stimulation in type 1 diabetes (T1D).

Methods

The study was performed in the period from 2008 to 2015 at the University Eye Clinic in Ljubljana. 41 patients with T1D and 37 participants without diabetes were included. MV in the CRA was measured using Doppler ultrasound diagnostics in basal conditions and during 8 Hz flickering light irritation. The plasma levels of glucose, fructosamine, 8-hydroxy-2'-deoxyguanosine (8-OHdG), triglycerides, cholesterol, and low-density lipoprotein (LDL) were measured.

Results

Patients with T1D had significantly higher levels of blood glucose (P < 0.001), fructosamine (P < 0.001), and 8-OHdG (P < 0.001), but there were no significant differences in triglycerides (P = 0.108), cholesterol (P = 0.531), and LDL (P = 0.645) between the groups. Patients with T1D also had a significantly lower MV index in the CRA (1.11 ± 0.15 vs 1.24 ± 0.23; P = 0.010). In the T1D group, a significant negative correlation was found between the level of glucose (r = −0.58; P < 0.001), fructosamine (r = −0.46; P = 0.003), 8-OHdG (r = −0.48; P = 0.002) and the MV index in the CRA. At the same time, in this group fructosamine and 8-OHdG levels had a separate effect on the MV index (adjusted R² = 0.38, P < 0.001).

Conclusion

Higher glucose levels, the medium-term glucose level, and systemic oxidative stress could importantly reduce retinal vasodilatation during flickering light irritation in patients with T1D.

Retinal blood flow is increased in type 1 diabetes mellitus patients with advanced stages of retinopathy

BACKGROUND

Diabetic retinopathy (DRP) is a common microvascular complication seen in patients with type 1 diabetes mellitus (T1DM). The effects of T1DM and concomitant (proliferative) DRP on retinal blood flow are currently unclear. Therefore, we measured retinal vascular blood flow in T1DM patients with and without DRP and non-diabetic controls. We further assessed the acute effects of panretinal photocoagulation on retinal microvascular bloodflow in eight patients with diabetes.

METHODS

Thirty-three T1DM patients with proliferative DRP, previously treated with panretinal photocoagulation (pDRP), 11 T1DM patients with untreated non-proliferative retinopathy (npDRP) and 32 T1DM patients without DRP (nDRP) were compared with 44 non-diabetic gender-matched controls. Using scanning laser Doppler flowmetry (HRF, Heidelberg) blood flow in the retinal microvasculature was measured temporal and nasal of the optic disc and averaged into one flow value per eye. The right eye was used as a default for further analyses. Eight patients with novel proliferative retinopathy (4 T1DM and 4 with type 2 diabetes) were measured before and several months after photocoagulation. Between-group differences in retinal blood flow were assessed using ANOVA corrected for multiple comparisons (Bonferroni).

RESULTS

Retinal blood flow was higher in the treated pDRP compared with the nDRP group and controls (all P Bonferroni < 0.01). Furthermore, there was a positive linear trend for blood flow with lowest blood flow in the control group and highest in the pDRP group (P-for-trend < 0.01). In the eight patients with novel proliferative retinopathy, blood flow did not significantly change before and after panretinal photocoagulation (P > 0.05). Using regression analysis, no variables were found as predictors of retinal blood flow.

CONCLUSIONS

In comparison with controls and nDRP patients, retinal blood flow significantly increased in the pDRP group, which previously underwent photocoagulation treatment, but not in the npDRP patients. These changes may be a consequence of a failing vascular autoregulation in advanced diabetic retinopathy.

Neuroretinal dysfunction with intact blood-retinal barrier and absent vasculopathy in type 1 diabetes

It is unknown whether independent neural damage may occur in the pre-/absent vascular diabetic retinopathy (DR). To exclude vasculopathy, it is important to measure the integrity of the blood-retinal barrier (BRB). This cross-sectional study addressed this problem in type 1 diabetic patients with normal ocular fundus and absent breakdown of the BRB (confirmed with vitreous fluorometry). These were compared with a group with disrupted BRB (with normal fundus or initial DR) and normal controls. Multifocal electroretinography and chromatic/achromatic contrast sensitivity were measured in these 42 patients with preserved visual acuity. Amplitudes of neurophysiological responses (multifocal electroretinogram) were decreased in all eccentricity rings in both clinical groups, when compared with controls, with sensitivity >78% for a specificity level of 90%. Implicit time changes were also found in the absence of initial DR. Impaired contrast sensitivity along chromatic axes was also observed, and achromatic thresholds were also different between controls and both clinical groups. The pattern of changes in the group without baseline BRB permeability alterations, as probed by psychophysical and electrophysiological measurements, does thereby confirm independent damage mechanisms. We conclude that retinal neuronal changes can be diagnosed in type 1 diabetes, independently of the breakdown of the BRB and onset of vasculopathy.

Phenotypes and biomarkers of diabetic retinopathy

Diabetic retinopathy (DR) remains a major cause of blindness as the prevalence of diabetes is expected to approximately double globally between 2000 and 2030. DR progresses over time at different rates in different individuals with only a limited number developing significant vision loss due to the two major vision-threatening complications, clinically significant macular edema and proliferative retinopathy. Good metabolic control is important to prevent and delay progression, but whereas some patients escape vision loss even with poor control, others develop vision loss despite good metabolic control. Our research group has been able to identify three different DR phenotypes characterized by different dominant retinal alterations and different risks of progression to vision-threatening complications. Microaneurysm turnover has been validated as a prognostic biomarker of development of clinically significant macular edema, whereas subclinical macular edema identified by OCT and mfERG appear to be also good candidates as organ-specific biomarkers of DR. Hemoglobin A1c remains the only confirmed systemic prognostic biomarker of DR progression. The availability of biomarkers of DR progression and the identification of different phenotypes of DR with different risks for development of vision-threatening complications offers new perspectives for understanding DR and for its personalized management.

Retinal Microcirculation in Type 1 Diabetic Patients With and Without Peripheral Sensory Neuropathy

In patients with diabetes mellitus (DM), early retinal microvascular alterations can be observed even before the clinical diagnosis of diabetic retinopathy. This study aimed to investigate morphological and functional changes in retinal microvascular blood flow in type 1 diabetic patients with and without peripheral neuropathy (PNP) as compared to nondiabetic controls. Retinal microvascular blood flow (RBF) was assessed using scanning laser Doppler flowmetry (Heidelberg Retina Flowmeter, Heidelberg Engineering, Germany) before and after stimulation with flicker light. PNP was assessed using the neuropathy disability score (NDS) and by the evaluation of the vibration perception threshold (VPT). A total of 41 subjects were recruited for study participation and were stratified to 3 different groups according to their metabolic and neurological status: 14 nondiabetic subjects without PNP, 14 diabetic patients without PNP, and 13 diabetic patients with PNP. All subjects were free from diabetic retinopathy as assessed by fundoscopy. In diabetic patients with PNP, baseline and stimulated RBF was higher compared with diabetic patients without PNP and the nondiabetic control group. No difference with regard to RBF could be observed between the nondiabetic control subjects and patients with type 1 DM without PNP. No difference in the arterial WLR could be observed between the 3 groups. A linear correlation was found for VPT and RBF (r = .38, P < .001) and for NDS and RBF (r = .44, P < .0001). In our study population of patients with type 1 diabetes, PNP was associated with functional but not morphological changes in RBF.

The influence of retinal blood flow on open-angle glaucoma in patients with and without diabetes

PURPOSE

To evaluate the impact of retinal blood flow on optic nerve head (ONH) morphology in patients with open-angle glaucoma (OAG) with and without diabetes mellitus (DM).

METHODS

A total of 66 patients with OAG (14 with DM, 52 without DM) were assessed at baseline and 3-year follow-up for retinal capillary blood flow using confocal scanning laser Doppler and ocular structure using Heidelberg retinal tomography and optical coherence tomography.

RESULTS

Change in retinal tissue with zero blood flow in the superior and inferior retina was found to have a strong correlation with ONH changes in diabetic patients (r≥0.90, p≤0.03); however, no relation was found in the nondiabetic cohort. There were also significant changes in inferior mean flow that strongly correlated with changes in cup area (r = 0.97, p = 0.0029), cup/disc area ratio (r = 0.96, p = 0.0070), linear cup/disc ratio (r = 0.93, p = 0.0172), rim area (r = -0.97, p = 0.0036), and rim volume (r = -0.95, p = 0.0084) in diabetic patients only, while changes in the superior mean flow were only significantly associated with cup area (r = -0.30, p = 0.0498), cup volume (r = -0.36, p = 0.0178), and rim volume (r = 0.35, p = 0.0193) in nondiabetic patients.

CONCLUSIONS

In this cohort of patients with OAG, changes in retinal capillary blood flow correlated more strongly with changes in ONH morphology in patients with DM than in those without DM. These data suggest that changes in retinal blood flow may play a larger role in glaucomatous ONH progression in patients with OAG with DM.

Barriers to the management of Diabetes Mellitus - is there a future role for Laser Doppler Flowmetry?

Diabetes Mellitus (DM) is a chronic disease that carries a significant disease burden in Australia and worldwide. The aim of this paper is to identify current barriers in the management of diabetes, ascertain whether there is a benefit from early detection and determine whether LDF has the potential to reduce the disease burden of DM by reviewing the literature relating to its current uses and development. In this literature review search terms included; laser Doppler flowmetry, diabetes mellitus, barriers to management, uses, future, applications, vasomotion, subcutaneous, cost. Databases used included Google Scholar, Scopus, Science Direct and Medline. Publications from the Australian government and textbooks were also utilised. Articles reviewed had access to the full text and were in English.

Disruption of the retinal parafoveal capillary network in type 2 diabetes before the onset of diabetic retinopathy

PURPOSE

To establish, using adaptive optics scanning laser ophthalmoscopy (AOSLO), that the retinal parafoveal capillary network is altered before the onset of diabetic retinopathy in adult patients with type 2 diabetes.

METHODS

AOSLO videos were acquired in the parafoveal region of one eye from control subjects and from patients with type 2 diabetes and no retinopathy. Detailed images of the parafoveal capillary network were generated with custom motion contrast enhancement algorithms. The combination of AOSLO images and videos enabled the simultaneous assessment of several features of the parafoveal capillary network. Arteriovenous (AV) channels were identified by finding the least tortuous capillary channels connecting terminal arterioles to postcapillary venules. Measures of capillary dropout and capillary hemodynamics were also quantified.

RESULTS

The average tortuosity of AV channels was 26% higher in patients with type 2 diabetes when compared with controls, even though there were no signs of diabetic retinopathy in any of the eyes that were assessed (P < 0.05). In addition, the metrics of capillary dropout showed small changes (between 3% and 7%), leukocyte speed 14% lower, and pulsatility 25% higher, but none of these differences was statistically significant.

CONCLUSIONS

It is often difficult to find consistent changes in the retinal microvasculature due to large intersubject variability. However, with a novel application of AOSLO imaging, it is possible to visualize parafoveal capillaries and identify AV channels noninvasively. AV channels are disrupted in type 2 diabetes, even before the onset of diabetic retinopathy.

Prophylactic Intravitreal Bevacizumab for Diabetic Macular Edema (thickening) after Cataract Surgery: Prospective Randomized Study

Purpose

TO determine the role of intravitreal bevacizumab injected at the time of cataract surgery on postoperative increase of retinal thickness in patients with diabetic retinopathy.

Methods

Patients were randomized to a standardized procedure of phacoemulsification with intraocular lens implantation alone (control group; 30 eyes) or to receive 1.25 mg intravitreal bevacizumab at the end of surgery (IVB group; 31 eyes). Efficacy measures included best-corrected visual acuity (BCVA) testing, optical coherence tomography (OCT), and ophthalmoscopic examination at each postoperative visit during a 6-month follow-up.

Results

There were no significant differences in central macular thickness, BCVA, or systemic condition between the control and IVB groups at baseline. One month after surgery, the control group showed a significant increase in central macular thickness, whereas the bevacizumab group did not show an increase. After 6 months, there was no significant difference in macular thickness and postoperative visual acuity between the 2 groups.

Conclusions

Intravitreal administration of 1.25 mg bevacizumab at the time of cataract surgery is effective just for the short term and 6-month results are the same as the control group.

[Not Available]

The aim of the study was to determine whether the Heidelberg Retinal Flowmeter (HRF), a confocal scanning laser Doppler flowmeter, can measure choroidal blood flow in pig eyes.

An HRF was used to obtain flow maps from in vitro pig eyes under a range of perfusion flow rates (0 – 500 µL/min) under conditions in which only the choroid was perfused. In some cases choroidal blood flow was also measured simultaneously using a conventional fiberoptic based Laser Doppler Perfusion Monitor (LDPM) which used the same laser wavelength (780 nm). The relationship between perfusion flow, HRF measured flow and LDPM measured flow was determined. HRF flow maps were also obtained in vivo as a function of focal plane setting through the retina and choroid.

Across the range of perfusion flow rates through the isolated eyes there was a poor correlation with HRF measured choroidal flow and perfusion flow. In contrast, there was a strong linear relationship between perfusion flow and LDPM measured blood flow. Both in vitro and in vivo, no choroidal vessels could be visualised in the HRF flow maps, even when the focal plane was in the choroid.

The HRF is unable to measure choroidal blood flow in pig eyes. This is not due to an inability of the 780 nm laser to penetrate into the choroid or due to red blood cell velocities in the choroid being higher than the measurement range of the instrument.

Regulation of retinal blood flow in health and disease

Optimal retinal neuronal cell function requires an appropriate, tightly regulated environment, provided by cellular barriers, which separate functional compartments, maintain their homeostasis, and control metabolic substrate transport. Correctly regulated hemodynamics and delivery of oxygen and metabolic substrates, as well as intact blood-retinal barriers are necessary requirements for the maintenance of retinal structure and function. Retinal blood flow is autoregulated by the interaction of myogenic and metabolic mechanisms through the release of vasoactive substances by the vascular endothelium and retinal tissue surrounding the arteriolar wall. Autoregulation is achieved by adaptation of the vascular tone of the resistance vessels (arterioles, capillaries) to changes in the perfusion pressure or metabolic needs of the tissue. This adaptation occurs through the interaction of multiple mechanisms affecting the arteriolar smooth muscle cells and capillary pericytes. Mechanical stretch and increases in arteriolar transmural pressure induce the endothelial cells to release contracting factors affecting the tone of arteriolar smooth muscle cells and pericytes. Close interaction between nitric oxide (NO), lactate, arachidonic acid metabolites, released by the neuronal and glial cells during neural activity and energy-generating reactions of the retina strive to optimize blood flow according to the metabolic needs of the tissue. NO, which plays a central role in neurovascular coupling, may exert its effect, by modulating glial cell function involved in such vasomotor responses. During the evolution of ischemic microangiopathies, impairment of structure and function of the retinal neural tissue and endothelium affect the interaction of these metabolic pathways, leading to a disturbed blood flow regulation. The resulting ischemia, tissue hypoxia and alterations in the blood barrier trigger the formation of macular edema and neovascularization. Hypoxia-related VEGF expression correlates with the formation of neovessels. The relief from hypoxia results in arteriolar constriction, decreases the hydrostatic pressure in the capillaries and venules, and relieves endothelial stretching. The reestablished oxygenation of the inner retina downregulates VEGF expression and thus inhibits neovascularization and macular edema. Correct control of the multiple pathways, such as retinal blood flow, tissue oxygenation and metabolic substrate support, aiming at restoring retinal cell metabolic interactions, may be effective in preventing damage occurring during the evolution of ischemic microangiopathies.

Real-time spectral domain Doppler optical coherence tomography and investigation of human retinal vessel autoregulation

Investigation of the autoregulatory mechanism of human retinal perfusion is conducted with a real-time spectral domain Doppler optical coherence tomography (SDOCT) system. Volumetric, time-sequential, and Doppler flow imaging are performed in the inferior arcade region on normal healthy subjects breathing normal room air and 100% oxygen. The real-time Doppler SDOCT system displays fully processed, high-resolution [512 (axial) x 1000 (lateral) pixels] B scans at 17 frames/sec in volumetric and time-sequential imaging modes, and also displays fully processed overlaid color Doppler flow images comprising 512 (axial) x 500 (lateral) pixels at 6 frames/sec. Data acquired following 5 min of 100% oxygen inhalation is compared with that acquired 5 min postinhalation for four healthy subjects. The average vessel constriction across the population is -16+/-26% after oxygen inhalation with a dilation of 36+/-54% after a return to room air. The flow decreases by -6+/-20% in response to oxygen and in turn increases by 21+/-28% as flow returns to normal in response to room air. These trends are in agreement with those previously reported using laser Doppler velocimetry to study retinal vessel autoregulation. Doppler flow repeatability data are presented to address the high standard deviations in the measurements.

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.

Nonproliferative retinopathy in diabetes type 2. Initial stages and characterization of phenotypes

This review addresses the initial stages of nonproliferative diabetic retinopathy in diabetes type 2. The natural history of the initial lesions occurring in the diabetic retina has particular relevance for our understanding and management of diabetic retinal disease, one of the major causes of vision loss in the western world. Diabetic retinal lesions are still reversible at this stage opening entirely new opportunities for effective intervention. Four main alterations characterize these early stages of diabetic retinopathy: microaneurysms/hemorrhages, alteration of the blood-retinal barrier, capillary closure and alterations in the neuronal and glial cells of the retina. These alterations may be monitored by red-dot counting on eye fundus images and by fluorescein leakage and retinal thickness measurements. A combination of these methods through multimodal macula mapping has contributed by identifying three different phenotypes of diabetic retinopathy. They show different types and rates of progression which suggest the involvement of different susceptibility genes. The identification of different phenotypes opens the door for genotype characterization, different management strategies targeted treatments.