The chronic stress risk phenotype mirrored in the human retina as a neurodegenerative condition

The brain is the key organ that orchestrates the stress response which translates to the retina. The retina is an extension of the brain and retinal symptoms in subjects with neurodegenerative diseases substantiated the eye as a window to the brain. The retina is used in this study to determine whether chronic stress reflects neurodegenerative signs indicative of neurodegenerative conditions. A 3-year prospective cohort (n = 333; aged 46 ± 9 years) was stratified into stress-phenotype cases (n = 212) and controls (n = 121) by applying the Malan stress-phenotype index. Neurodegenerative risk markers included ischemia (astrocytic S100 calcium-binding protein B/S100B); 24h blood pressure, proteomics; inflammation (tumor-necrosis-factor-α/TNF-α); neuronal damage (neuron-specific-enolase); anti-apoptosis of retinal-ganglion-cells (beta-nerve-growth-factor), astrocytic activity (glial-fibrillary-acidic-protein); hematocrit (viscosity) and retinal follow-up data [vessels; stress-optic-neuropathy]. Stress-optic-neuropathy risk was calculated from two indices: a newly derived diastolic-ocular-perfusion-pressure cut-point ≥68 mmHg relating to the stress-phenotype; combined with an established cup-to-disc ratio cut-point ≥0.3. Higher stress-optic-neuropathy (39% vs. 17%) and hypertension (73% vs. 16%) prevalence was observed in the stress-phenotype cases vs. controls. Elevated diastolic-ocular-perfusion-pressure, indicating hypoperfusion, was related to arterial narrowing and trend for ischemia increases in the stress-phenotype. Ischemia in the stress-phenotype at baseline, follow-up and 3-yr changes was related to consistent inflammation (TNF-α and cytokine-interleukin-17-receptor-A), neuron-specific-enolase increases, consistent apoptosis (chitinase 3-like-1, low beta-nerve-growth-factor), glial-fibrillary-acidic-protein decreases, elevated viscosity, vein widening as risk marker of endothelial dysfunction in the blood-retinal-barrier, lower vein count, and elevated stress-optic-neuropathy. The stress-phenotype and related neurodegenerative signs of ongoing brain ischemia, apoptosis and endothelial dysfunction compromised blood-retinal-barrier permeability and optic nerve integrity. In fact, the stress-phenotype could identify persons at high risk of neurodegeneration to indicate a neurodegenerative condition.

In-vivo assessment of retinal vessel diameters and observer variability in mice: A methodological approach

Background

Central retinal arteriolar (CRAE) and venular (CRVE) diameter equivalents are predictive for cardiovascular and all-cause mortality in humans. The aim of this study was to investigate the inter- and intraobserver variability for the assessment of CRAE and CRVE in mice using fluorescein contrast enhancement as compared to crude analysis.

Methods

Three high quality images with (F) and without fluorescein (NF) of eight mice (type C57BL) were recorded and analysed by two independent experienced investigators to investigate interobserver variability. In addition, one investigator analysed 20 F and 20 NF images twice to investigate intraobserver variability. The time course of CRAE and CRVE vessel responses after fluorescein injection were recorded in one mouse every 30 seconds for 15 minutes.

Results

The interobserver variability was lower in F images compared to NF images for CRAE (r = 0.99, p < 0.001 vs. r = 0.65, p = 0.083) and CRVE (r = 0.99, p < 0.001 vs. r = 0.79, p = 0.019). Intraobserver variability for CRAE (r = 0.99, p < 0.001 vs. r = 0.48, p = 0.032) and CRVE (r = 0.98, p < 0.001 vs. r = 0.86, p < 0.001) were lower in F compared to NF images. Fluorescein injection induced vascular staining mimicking vessel dilation (+14%) followed by a long-lasting stable staining phase well suited for precise measurements.

Conclusions

Measurement variability can be optimized by use of fluorescein as contrast enhancement in mice. Standardization for time of image acquisition after fluorescein injection is advisable. Translation of static retinal vessel analysis into a rodent model has the potential to bridge the research gap between proof of concept studies in animals and clinical studies in humans.

Retinal vessel diameters and function in cardiovascular risk and disease

In the last two decades evidence has gradually accumulated suggesting that the eye may be a unique window for cardiovascular risk stratification based on the assessment of subclinical damage of retinal microvascular structure and function. This can be facilitated by non-invasive analysis of static retinal vessel diameters and dynamic recording of flicker light-induced and endothelial function-related dilation of both retinal arterioles and venules. Recent new findings have made retinal microvascular biomarkers strong candidates for clinical implementation as reliable risk predictors. Beyond a review of the current evidence and state of research, the article aims to discuss the methodological benefits and pitfalls and to identify research gaps and future directions. Above all, the potential use for screening and treatment monitoring of cardiovascular disease risk are highlighted. The article provides fundamental comprehension of retinal vessel imaging by explaining anatomical and physiological essentials of the retinal microcirculation leading to a detailed description of the methodological approach. This allows for better understanding of the underlying retinal microvascular pathology associated with the prevalence and development of cardiovascular disease. A body of new evidence is presented on the clinical validity and predictive value of retinal vessel diameters and function for incidence cardiovascular disease and outcome. Findings in children indicate the potential for utility in childhood cardiovascular disease prevention, and the efficacy of exercise interventions highlight the treatment sensitivity of retinal microvascular biomarkers. Finally, coming from the availability of normative data, solutions for diagnostic challenges are discussed and conceptual steps towards clinical implementation are put into perspective.

Optic disc blood perfusion and oxygenation in glaucoma

Purpose

To investigate the haemoglobin concentration and oxygenation in the optic disc in glaucoma patients vs. controls.

Methods

Thirty-one eyes of primary open angle glaucoma patients (mean age: 64.9 ± 2.1 years) and 31 eyes of 31 healthy controls (65.5 ± 2.0 years) were included. Perimetry, optical coherence tomography (OCT), and OCT angiography were performed. Multispectral imaging was used to record the optic disc reflectance at wavelengths 522 nm, 548 nm, 555 nm, 586 nm, and 610 nm, and haemoglobin concentration and oxygenation (SO₂) were calculated from these measures. This was done in the rest and under stimulation of neuronal activity by flicker light.

Results

The haemoglobin concentration was significantly lower (p < 0.001) in the rim (40.0 ± 6.3) and the excavation (35.7 ± 8.0) of the glaucoma patients’ discs than in controls (45.7 ± 7.5). SO₂ was not different in general, but lower in a subgroup of 18 glaucoma patients with ischaemic disc rims than in non-ischaemic ones (median 26.8%, interquartile range (IQR): 29.5% vs. 51.9%, IQR 32.0%, p = 0.02) as well as in controls (41.0%, IQR 30.6%, p = 0.01). Flicker light stimulation significantly increased the haemoglobin concentration in the controls (+ 1.3 ± 3.6, p = 0.048) as well as in the rim of glaucoma discs (+ 2.6 ± 5.0, p = 0.006) and SO₂ in the controls only (+ 15.4 ± 23.6%, p = 0.001). The haemoglobin concentration was significantly correlated with the perimetric mean defect, retinal nerve fibre layer (RNFL) thickness and para-papillary perfusion density.

Conclusions

The optic disc haemoglobin concentration and oxygenation are quantifiable from multispectral imaging and reduced in glaucoma. The correlation of haemoglobin concentration with perfusion density, RNFL thickness and visual field loss indicates its implication in glaucoma pathology.

Modulation of Human Intraocular Pressure Using a Pneumatic System

Purpose

To technically validate a novel pneumatically based system and method for modulation of intraocular pressure (IOP) and to test its application in the human eye. Special attention was paid to the applicability of the pneumatically driven balloon, which realizes the modulation of the IOP through its contact with the conjunctiva.

Methods

A force sensor as key component of a customized measurement setup was used to check the applied pressure through the balloon. The IOP of 10 healthy subjects (4 female, 6 male, aged 28.8 ± 6.64 years) was modulated and increased linearly to at least 40 mmHg. At this point, the pressure inside the balloon was kept constant for 2 minutes, with IOP measurements taken every 40 seconds using a rebound tonometer.

Results

The technical setup led to an IOP decrease of 0.71 mmHg within 2 minutes at an operating point of 40 mmHg. For all subjects, the IOP could be increased up to 42.8 ± 3.6 mmHg, whereby a mean pressure decrease of 2.4 mmHg/min was determined, which seems to be caused mainly by physiological processes.

Conclusions

With the new pneumatically based setup, a targeted modulation in terms of level and constancy of the IOP can be realized.

Translational Relevance

Additional and, compared with the technique according to Löw, a more precise and more constant methodology for the modulation of the IOP, can significantly simplify the determination of retinal vessel pressures for clinical application. It is suitable for practical questions concerning an enhanced retinal venous pressure.

Normative data and standard operating procedures for static and dynamic retinal vessel analysis as biomarker for cardiovascular risk

Retinal vessel phenotype is predictive for cardiovascular outcome. This cross-sectional population-based study aimed to quantify normative data and standard operating procedures for static and dynamic retinal vessel analysis. We analysed central retinal arteriolar (CRAE) and venular (CRVE) diameter equivalents, as well as retinal endothelial function, measured by flicker light‐induced maximal arteriolar (aFID) and venular (vFID) dilatation. Measurements were performed in 277 healthy individuals aged 20 to 82 years of the COmPLETE study. The mean range from the youngest compared to the oldest decade was 196 ± 13 to 166 ± 17 µm for CRAE, 220 ± 15 to 199 ± 16 µm for CRVE, 3.74 ± 2.17 to 3.79 ± 2.43% for aFID and 4.64 ± 1.85 to 3.86 ± 1.56% for vFID. Lower CRAE [estimate (95% CI): − 0.52 (− 0.61 to − 0.43)], CRVE [− 0.33 (− 0.43 to − 0.24)] and vFID [− 0.01 (− 0.26 to − 0.00)], but not aFID, were significantly associated with older age. Interestingly, higher blood pressure was associated with narrower CRAE [− 0.82 (− 1.00 to − 0.63)] but higher aFID [0.05 (0.03 to 0.07)]. Likewise, narrower CRAE were associated with a higher predicted aFID [− 0.02 (− 0.37 to − 0.01)]. We recommend use of defined standardized operating procedures and cardiovascular risk stratification based on normative data to allow for clinical implementation of retinal vessel analysis in a personalized medicine approach.

Delayed retinal vein recovery responses indicate both non-adaptation to stress as well as increased risk for stroke: the SABPA study

OBJECTIVES

Low or high sympatho-adrenal-medullary axis (SAM) and hypothalamic-pituitary-adrenal axis (HPA) dysregulation reflect chronic stress. Retinal vessel dynamics may relate to SAM, HPA activity and stroke risk. Our objectives were therefore to assess the relationships between retinal vessel, SAM and HPA responses, and to determine stroke risk.

METHODS

A prospective bi-ethnic gender cohort (n = 275, 45 ± 9 years) was included. Urine/serum/saliva samples for SAM [norepinephrine:creatinine ratio (u-NE)] and HPA [adrenocorticotrophic hormone (ACTH), cortisol] were obtained at baseline, three-year follow up and upon flicker light-induced provocation. Diastolic ocular perfusion pressure was measured as a marker of hypo-perfusion. Retinal arterial narrowing and venous widening calibres were quantified from digital images in the mydriatic eye. A validated stress and stroke risk score was applied.

RESULTS

An interaction term was fitted for venous dilation in u-NE tertiles (p ≤ 0.05) and not in u-NE median/quartiles/quintiles. Independent of race or gender, tertile 1 (low u-NE) had a 112% increase in u-NE, decreases in cortisol, and no changes in ACTH over three years (positive feedback). Tertile 3 (high u-NE) contradictorily had decreases in u-NE and cortisol, and increases in ACTH (negative feedback). In tertile 1, reduced arterial dilation, and faster arterial vasoconstriction and narrowing were related to higher SAM activity and hypo-perfusion (p ≤ 0.05), whereas delayed venous dilation, recovery and widening were related to cortisol hypo-secretion (p ≤ 0.05). In tertile 1, delayed venous recovery responses predicted stress and stroke risk [odds ratio 4.8 (1.2-19.6); p = 0.03]. These associations were not found in u-NE tertiles 2 and 3.

CONCLUSIONS

In response to low norepinephrine, a reflex increase in SAM activity occurred, enhancing arterial vasoconstriction and hypo-perfusion. Concomitant HPA dysregulation attenuated retinal vein vasoactivity and tone, reflecting delayed vein recovery responses and non-adaptation to stress. These constrained vein recovery responses are indicative of increased chronic stress and stroke risk.

New Frontiers in Noninvasive Analysis of Retinal Wall-to-Lumen Ratio by Retinal Vessel Wall Analysis

Purpose

To compare measurement of wall-to-lumen ratio (WLR) by means of high-resolution adaptive optics imaging (AO) with intuitive to use retinal vessel wall (VW) analysis (VWA). Moreover, to validate the techniques by comparing WLR of healthy young (HY) with healthy older patients.

Methods

Ten retinal VW images of 13 HY (24 ± 2 years) and 16 healthy older (60 ± 8 years) were obtained with AO and VWA. The average of five measurements of VW, retinal vessel lumen and WLR of a single vessel from AO and VWA were calculated and compared.

Results

WLR of AO and VWA images showed high correlations, r = 0.75, t(27) = 5.98, P < .001, but differed systematically (WLR: VWA, 40 ± 7% and AO, 35 ± 9%; P < .001). Comparable patterns were found for VW and vessel lumen. HY showed significantly lower WLR (AO, 31 ± 8% and VWA, 36 ± 8%) compared with healthy older (AO, 39 ± 9% [P = .012]; VWA, 42 ± 5% [P = .013]).

Conclusions

Assessment of WLR by VWA showed a good correlation with laborious analysis of the microstructure by high-resolution AO. Measurement of WLR in different age groups indicated good validity. Deviations in VW, vessel lumen, and WLR between AO and VWA can be explained by systematic differences in image scale and resolution. Future studies are needed to investigate the clinical relevance of microvascular WLR assessment by retinal VWA and its prognostic value.

Translational Relevance

Additional assessment of retinal WLR by use of digital VWA to evaluate microstructural remodeling may prove to be a valuable extension to the current use of retinal vessel diameters as biomarkers of cardiovascular risk.

Retinal vessel caliber and caliber responses in true normotensive black and white adults: The African-PREDICT study

PURPOSE

Globally, a detrimental shift in cardiovascular disease risk factors and a higher mortality level are reported in some black populations. The retinal microvasculature provides early insight into the pathogenesis of systemic vascular diseases, but it is unclear whether retinal vessel calibers and acute retinal vessel functional responses differ between young healthy black and white adults.

METHODS

We included 112 black and 143 white healthy normotensive adults (20-30 years). Retinal vessel calibers (central retinal artery and vein equivalent (CRAE and CRVE)) were calculated from retinal images and vessel caliber responses to flicker light induced provocation (FLIP) were determined. Additionally, ambulatory blood pressure (BP), anthropometry and blood samples were collected.

RESULTS

The groups displayed similar 24 h BP profiles and anthropometry (all p > .24). Black participants demonstrated a smaller CRAE (158 ± 11 vs. 164 ± 11 MU, p < .001) compared to the white group, whereas CRVE was similar (p = .57). In response to FLIP, artery maximal dilation was greater in the black vs. white group (5.6 ± 2.1 vs. 3.3 ± 1.8%; p < .001).

CONCLUSIONS

Already at a young age, healthy black adults showed narrower retinal arteries relative to the white population. Follow-up studies are underway to show if this will be related to increased risk for hypertension development. The reason for the larger vessel dilation responses to FLIP in the black population is unclear and warrants further investigation.

Retinal Endothelial Function, Physical Fitness and Cardiovascular Risk: A Diagnostic Challenge

INTRODUCTION

Dynamic retinal vessel analysis (DVA) is a new non-invasive method to quantify microvascular endothelial dysfunction by flicker light-induced dilatation (FID). FID has been shown to be impaired in type 2 diabetes as well as heart failure. The aim of the study was to analyze FID in healthy active versus healthy sedentary and cardiovascular (CV) risk patients in addition to corresponding static vessel diameters.

METHODS

Thirty-one healthy active (HA, mean age 60 ± 8 years), 33 healthy sedentary individuals (HS, 59 ± 7 years) and 76 sedentary patients with increased CV risk (SR, 58 ± 6 years) were included in this cross-sectional study. Group differences in CV risk factors and cardiorespiratory fitness, maximal arteriolar (ADmax) and venular (VDmax) dilatation as well as the arteriolar (AFarea) and venular (VFarea) area under the flicker curve were analyzed. The central retinal arteriolar and venular diameters were used to calculate the arteriolar-to-venular diameter ratio (AVR).

RESULTS

HS [ADmax = 3.5 (2.1)%; AFarea = 48.2 (31.9)%∗s] showed higher FID compared to SR [ADmax = 2.7 (1.8)%, p = 0.021; AFarea = 34.5 (26.5)%∗s, p = 0.006] and HA [AFarea = 32.8 (23.1)%∗s, p = 0.029]. HA and SR did not significantly differ. HA had a higher AVR (0.87 ± 0.05) compared to HS (0.83 ± 0.04, p < 0.001) with further deterioration in SR (0.79 ± 0.05, p < 0.001). Interestingly, 28 participants had impaired FID but normal AVR and 43 participants had normal FID but impaired AVR.

DISCUSSION

FID can differentiate between sedentary low and high risk individuals. However, FID in healthy active persons (HA) seemed impaired with a concomitant higher AVR. We postulate that lower FID in HA may be explained by predilatated arterioles and a reduced dilatation reserve. We recommend combination of FID with analysis of retinal vessel diameters to differentiate functional non-responders from manifest microvascular endothelial dysfunction and, thereby, improve microvascular risk stratification in a personalized medicine approach.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: NCT02796976 (https://clinicaltrials.gov/ ct2/show/NCT02796976).

Non-invasive evaluation of neurovascular coupling in the murine retina by dynamic retinal vessel analysis

Background

Impairment of neurovascular coupling (NVC) was recently reported in the context of subarachnoid hemorrhage and may correlate with disease severity and outcome. However, previous techniques to evaluate NVC required invasive procedures. Retinal vessels may represent an alternative option for non-invasive assessment of NVC.

Methods

A prototype of an adapted retinal vessel analyzer was used to assess retinal vessel diameter in mice. Dynamic vessel analysis (DVA) included an application of monochromatic flicker light impulses in predefined frequencies for evaluating NVC. All retinae were harvested after DVA and electroretinograms were performed.

Results

A total of 104 retinal scans were conducted in 21 male mice (90 scans). Quantitative arterial recordings were feasible only in a minority of animals, showing an emphasized reaction to flicker light impulses (8 mice; 14 scans). A characteristic venous response to flicker light, however, could observed in the majority of animals. Repeated measurements resulted in a significant decrease of baseline venous diameter (7 mice; 7 scans, p < 0.05). Ex-vivo electroretinograms, performed after in-vivo DVA, demonstrated a significant reduction of transretinal signaling in animals with repeated DVA (n = 6, p < 0.001).

Conclusions

To the best of our knowledge, this is the first non-invasive study assessing murine retinal vessel response to flicker light with characteristic changes in NVC. The imaging system can be used for basic research and enables the investigation of retinal vessel dimension and function in control mice and genetically modified animals.

Blood Pressure Effects on Retinal Vessel Diameter and Flicker Response: A 1.5-Year Follow-Up

PURPOSE

The study examined the influence of individual blood pressure changes overtime on retinal vessel diameter and the latter's response to flicker light.

METHODS

The diameter of a retinal arterial and venous segment was measured continuously on-line with a Dynamic Vessel Analyzer in 20 patients twice (mean interval between examinations of 24 months). Eleven patients had no cardiovascular disease. Nine patients had arterial hypertension and were untreated at the time of the first measurement; at the time of the second measurement they were undergoing various antihypertensive therapies. Each test consisted of a 50-s baseline plus three 20-s periods of flicker stimulation followed by an 80-s period of observation. During the examinations the blood pressure was measured at 1-minute intervals.

RESULTS

In the hypertension group changes in the mean arterial blood pressure (MAP) correlated significantly with changes in the arterial baseline diameter (y = -0.1 - 0.37x, r =0.74, p (increase) <0.03). A comparison of the two measurements showed no such relationship in the group of cardiovascularly healthy subjects. The venous baseline and the arterial and venous flicker response did not change significantly in either group between the two measurements and showed no relationship to blood pressure changes.

CONCLUSIONS

In hypertensive subjects, long-term therapy-related changes in blood pressure induced a change in the arterial baseline by approximately +3.7 microm/-10 mmHg MAP. An influence of lowering MAP to the arterial flicker response could not be detected.

Retinal Vessel Reaction to Short-Term IOP Elevation in Ocular Hypertensive and Glaucoma Patients

PURPOSE

Regulation of ocular blood flow might be impaired in glaucoma patients. We compared the reaction of retinal vessels to a short-term increase of intraocular pressure (IOP), using a retinal vessel analyzer (RVA), in normal volunteers, ocular hypertensive patients (OH) and primary open angle glaucoma patients (POAG).

METHODS

Ten healthy subjects (56+/-8 years, IOP 13.7+/-1.6 mmHg), 10 OH patients (55+/-12 years, IOD 23.4+/-4.1 mmHg) and 11 POAG patients (60+/-11 years, IOP 23.3+/-1.95 mmHg) were evaluated. Arterial and venous retinal vessel diameter was measured continuously before, during and after raising IOP to suprasystolic values by the suction cup method, described as ocular oscillo-dynamography.

RESULTS

The change in vessel diameter after the IOP rise differed in its temporal sequence and in absolute values depending on the group examined. In the retinal branch veins the reduction of vessel diameter during the IOP rise was significantly different in POAG (0%+/-6.7) and volunteers (-6.7%+/-8.5; p = 0.06) and in POAG and OH (-6.7%+/-7.0; p = 0.04). At 70-130 sec after IOP increase a dilatation occurred, again differing significantly in POAG (+5.8%+/-3.9) and volunteers (+9.7%+/-4.3; p = 0.03). Systemic blood pressure did not show any significant differences between groups or during the course of the examination.

DISCUSSION

At short-term rise in IOP leads to less retinal vessel reaction in POAG patients than in volunteers and OH. This might be due to impaired autoregulation to ocular perfusion changes in POAG patients.

Vasoconstriction and Impairment of Neurovascular Coupling after Subarachnoid Hemorrhage: a Descriptive Analysis of Retinal Changes

Impaired cerebral autoregulation and neurovascular coupling (NVC) contribute to delayed cerebral ischemia after subarachnoid hemorrhage (SAH). Retinal vessel analysis (RVA) allows non-invasive assessment of vessel dimension and NVC hereby demonstrating a predictive value in the context of various neurovascular diseases. Using RVA as a translational approach, we aimed to assess the retinal vessels in patients with SAH. RVA was performed prospectively in 24 patients with acute SAH (group A: day 5-14), in 11 patients 3 months after ictus (group B: day 90 ± 35), and in 35 age-matched healthy controls (group C). Data was acquired using a Retinal Vessel Analyzer (Imedos Systems UG, Jena) for examination of retinal vessel dimension and NVC using flicker-light excitation. Diameter of retinal vessels-central retinal arteriolar and venular equivalent-was significantly reduced in the acute phase (p < 0.001) with gradual improvement in group B (p < 0.05). Arterial NVC of group A was significantly impaired with diminished dilatation (p < 0.001) and reduced area under the curve (p < 0.01) when compared to group C. Group B showed persistent prolonged latency of arterial dilation (p < 0.05). Venous NVC was significantly delayed after SAH compared to group C (A p < 0.001; B p < 0.05). To our knowledge, this is the first clinical study to document retinal vasoconstriction and impairment of NVC in patients with SAH. Using non-invasive RVA as a translational approach, characteristic patterns of compromise were detected for the arterial and venous compartment of the neurovascular unit in a time-dependent fashion. Recruitment will continue to facilitate a correlation analysis with clinical course and outcome.

Chronic depression symptoms and salivary NOx are associated with retinal vascular dysregulation: The SABPA study

BACKGROUND

Depression has been associated with impaired nitric oxide (NO)-mediated vasodilation and vascular dysregulation (VD). Whether depression and NO levels will disturb retinal haemodynamics is not clear.

OBJECTIVES AND METHODS

Associations between the retinal vasculature, diastolic ocular perfusion pressure (DOPP) as measure of hypoperfusion, NO metabolites (NOx) and depression symptoms were assessed. Chronic VD risk markers [depression symptoms (Patient Health Questionnaire/PHQ-9 ≥ 10) and 24 h pulse pressure] were determined in a bi-ethnic cohort (n = 313; 48.6 ± 9 years; 53.9% men). At 3 year follow-up, retinal vessel calibre and retinopathy signs were quantified from digital images. Salivary NOx was obtained pre- and post-flicker light-induced provocation (FLIP). DOPP was defined as diastolic blood pressure minus intraocular pressure.

RESULTS

Chronic VD risk was evident in Blacks opposed to acute risk in Whites (P < 0.05). At follow-up, retinopathy (Blacks 60.4%/Whites 39.6%), lower pre-FLIP (μM) and higher post-FLIP NOx (changes from baseline, %), arteriolar narrowing and wider venular calibre values were evident in Blacks compared to Whites, independent of confounders. A wider venular calibre, an index of stroke risk, was associated with chronic depression symptoms [cut point 248 MU: Area under the curve 0.61 (95% CI: 0.51, 0.72); 71% sensitivity; 55% specificity] as well as with hypoperfusion in the Blacks. In this group, arteriolar narrowing was associated with hypoperfusion; and attenuated arteriolar dilation with increased post-FLIP NOx responses.

CONCLUSIONS

Chronic depression symptoms may alter NO regulation and facilitate VD. NO-mediated vasoconstriction presumably impeded perfusion, retinal haemodynamics and -remodelling; potentiating stroke risk in Blacks.

Insulin is a key determinant of elevated retinal arteriolar flicker response in insulin-resistant individuals

AIMS/HYPOTHESIS

Insulin may link metabolic disorders to retinal microvascular pathology. The aim of the present study was to investigate the impact of early insulin resistance on retinal microcirculation.

METHODS

Retinal diameter responses to flicker-light stimulation were investigated in 81 clinically healthy participants (32 ± 6 years [mean ± SD], 59% women) who were recruited according to their BMI. All participants underwent an OGTT and euglycaemic-hyperinsulinaemic clamp (40 mU/m(2) · min(-1) insulin dose). After stratification by low and high insulin sensitivity based on a clamp-derived glucose disposal rate of ≤ or >4.9 mg/kg body mass, respectively, baseline retinal diameters and their relative changes to flicker stimulation were compared while controlling for mean arterial pressure, BMI and sex.

RESULTS

The arterial vasodilator response at the end of flicker stimulation (p = 0.044) and the area under the arterial reaction curve during flicker stimulation (p = 0.015) were significantly higher in individuals with low vs high insulin sensitivity. Vasodilatory responses of retinal veins to flicker stimulation and baseline retinal diameters did not differ between insulin-sensitive and insulin-resistant participants (p > 0.05). In a stepwise linear regression analysis, fasting insulin remained the only predictor of the arterial vasodilator response to flicker-light (p < 0.01). Waist circumference also contributed, although to a lesser extent, to the arterial vasodilator response (p = 0.023).

CONCLUSIONS/INTERPRETATION

Insulin sensitivity is an important determinant of retinal microvascular function. We propose that the elevated arterial flicker response in insulin-resistant states is a result of higher circulating insulin levels.

Local endothelial dysfunction does not affect global endothelial function

Abstract. Background: The purpose of this study was to evaluate two alternative non-invasive techniques for assessment of endothelial function in adults with special focus on their ability to monitor acute changes. Patients and methods: Twenty-five clinically healthy men (mean age 24 ± 2 years) underwent endothelial function measurements twice in fasting state and twice after experimental induction of transient endothelial dysfunction by oral application of 0.1g/kg L-methionine and by ingestion of 500 ml whipped cream (30 % fat), respectively. Microvascular vasodilator responses to flickering-light by retinal vessel analysis and vascular responses to inhaled salbutamol by pulse wave analysis were assessed at each occasion. Ultrasound based flow-mediated dilation (FMD) was used as reference method. Results: Transient endothelial dysfunction in response to acute hyperlipidaemia and hyperhomocysteinaemia was verified by blunted brachial responses to hyperaemia. Retinal vessel analysis demonstrated significantly impaired flicker-responses of retinal vessels to both challenges depending on the vessel type. Pulse wave analysis did not show any significant changes in salbutamol responses. Reproducibility of retinal vessel analysis was comparable to FMD and slightly better than pulse wave analysis. Conclusions: Acute changes in endothelial function can be monitored by retinal vessel analysis with comparable reproducibility as FMD. Salbutamol based pulse wave analysis is currently unsuited to detect endothelial dysfunction in serial measurements.

Trabeculectomy Improves Vessel Response Measured by Dynamic Vessel Analysis (DVA) in Glaucoma Patients

PURPOSE

To determine the effects of surgical IOP reduction (trabeculectomy) on retinal blood flow parameters in glaucoma patients using Dynamic Vessel Analysis (DVA).

METHODS

26 eyes of 26 patients with progressive primary open-angle glaucoma (POAG) despite maximal topical therapy were examined before and after trabeculectomy. The responses of the retinal vessels to flickering light provocation were measured with DVA the day before surgery and 4 to 6 weeks after trabeculectomy. Between 3 and 4 weeks before surgery all local therapies were stopped and a systemic therapy with acetazolamide and conservative free topic steroidal eye drops was started.

RESULTS

In 19 patients (73%), an inadequate response to the flicker stimulation was measured preoperatively. In these patients, the maximum dilation of arteries and veins was reduced significantly as compared to healthy eyes. In this group, the maximum dilation of the arteries following the flicker provocation improved from 1.4% before to 3.8% following trabeculectomy (p<0.01). In retinal veins, this parameter increased from 3.1% to 4.6% (p<0.05). In the 7 patients whose arterial and venous reactions to flickering light provocation preoperatively did not differ from healthy eyes, there was no significant change after surgery. The initial baseline values of arteries and veins (MU) did not deviate significantly in both groups.

CONCLUSION

POAG patients with progressive disease and impaired vascular regulation profit from IOP lowering trabeculectomy concerning vascular reactivity and dilative reserve, indicating a possible improvement of retinal perfusion following effective IOP control. Future studies with long-term follow-up must determine the clinical importance of these findings for the treatment of glaucoma patients.

Influence of latanoprost on retinal microcirculation in glaucoma

Purpose :

To test whether latanoprost has an influence on ocular haemodynamics, considering the general reputation of prostaglandins which is frequently associated with vasoconstriction. The effect of latanoprost on the retinal blood supply of treatment-naïve glaucoma patients was tested.

Materials and Methodology :

13 patients (7 male, 6 female) who had just recently been diagnosed with primary open-angle glaucoma (POAG) were treated with latanoprost (0.005%). The average age of our study group was 63.8 years (+/- 2.9 years).

The drug’s effect on retinal autoregulation was assessed by flicker test using the Dynamic Vessel Analyzer (DVA). Examinations took place before initializing treatment, after 4 weeks and once again after 4 to 6 months.

Results :

In our group of POAG patients, the IOP under treatment was significantly reduced about 25%. No intraindividual differences in systemic blood pressure and heart rate were observed. In DVA measurements of glaucoma patients, the maximum flicker dilation of the arteries was significantly lower than reported for healthy volunteers. Beyond that, POAG patients did not show significant differences in vessel diameters, peak amplitudes as well as maximum dilations of retinal arteries and veins before and under treatment with latanoprost (0.005%).

Conclusion :

Latanoprost markedly lowered the IOP but it did not exert a significant effect on retinal haemodynamics. There was neither a tendency towards vasoconstriction nor towards vasodilation. Sustaining reperfusion damage after topical latanoprost therapy thus seems to be highly unlikely. Further studies must show if sole IOP lowering or a dual positive effect – IOP lowering and improvement of retinal vessel autoregulation – have a more positive impact on the long term follow-up of glaucoma patients.

Measurement of the total retinal blood flow using dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes

We present a system capable of measuring the total retinal blood flow using a combination of dual beam Fourier-domain Doppler optical coherence tomography with orthogonal detection planes and a fundus camera-based retinal vessel analyzer. Our results show a high degree of conformity of venous and arterial flows, which corroborates the validity of the measurements. In accordance with Murray's law, the log-log regression coefficient between vessel diameter and blood flow was found to be ~3. The blood's velocity scaled linearly with the vessel diameter at higher diameters (> 60 µm), but showed a clear divergence from the linear dependence at lower diameters. Good agreement with literature data and the large range and high measurement sensitivity point to a high potential for further investigations.

Measurement of retinal blood flow in the rat by combining Doppler Fourier-domain optical coherence tomography with fundus imaging

A wide variety of ocular diseases are associated with abnormalities in ocular circulation. As such, there is considerable interest in techniques for quantifying retinal blood flow, among which Doppler optical coherence tomography (OCT) may be the most promising. We present an approach to measure retinal blood flow in the rat using a new optical system that combines the measurement of blood flow velocities via Doppler Fourier-domain optical coherence tomography and the measurement of vessel diameters using a fundus camera-based technique. Relying on fundus images for extraction of retinal vessel diameters instead of OCT images improves the reliability of the technique. The system was operated with an 841-nm superluminescent diode and a charge-coupled device camera that could be operated at a line rate of 20 kHz. We show that the system is capable of quantifying the response of 100% oxygen breathing on the retinal blood flow. In six rats, we observed a decrease in retinal vessel diameters of 13.2% and a decrease in retinal blood velocity of 42.6%, leading to a decrease in retinal blood flow of 56.7%. Furthermore, in four rats, the response of retinal blood flow during stimulation with diffuse flicker light was assessed. Retinal vessel diameter and blood velocity increased by 3.4% and 28.1%, respectively, leading to a relative increase in blood flow of 36.2%. The presented technique shows much promise to quantify early changes in retinal blood flow during provocation with various stimuli in rodent models of ocular diseases in rats.

Does increased blood pressure rather than aging influence retinal pulse wave velocity?

PURPOSE

It was demonstrated previously that retinal pulse wave velocity (rPWV) as a measure of retinal arterial stiffness is increased in aged anamnestically healthy volunteers compared with young healthy subjects. Using novel methodology of rPWV assessment this finding was confirmed and investigated whether it might relate to the increased blood pressure usually accompanying the aging process, rather than to the aging itself.

METHODS

A total of 12 young 25.5-year-old (24.0-28.8) [median(1st quartile-3rd quartile)] and 12 senior 68.5-year-old (63.8-71.8) anamnestically healthy volunteers; and 12 senior 63.0-year-old (60.8-65.0) validated healthy volunteers and 12 young 33.0-year-old (29.5-35.0) hypertensive patients were examined. Time-dependent alterations of vessel diameter were assessed by the Dynamic Vessel Analyzer in a retinal artery of each subject. The data were filtered and processed using mathematical signal analysis and rPWVs were calculated.

RESULTS

rPWV amounted to 1200 (990-1470) RU (relative units)/s in the hypertensive group and to 1040 (700-2230) RU/s in anamnestically healthy seniors. These differed significantly from rPWVs in young healthy group (410 [280-500] RU/s) and in validated healthy seniors (400 [320-510] RU/s). rPWV associated with age and mean arterial pressure (MAP) in the pooled cohort excluded validated healthy seniors. In a regression model these associations remain when alternately adjusted for MAP and age. When including validated healthy seniors in the pooled cohort only association with MAP remains.

CONCLUSIONS

Both aging (with not excluded cardiovascular risk factors) and mild hypertension are associated with elevated rPWV. rPWV increases to a similar extent both in young mildly hypertensive subjects and in aged anamnestically healthy persons. Healthy aging is not associated with increased rPWV.

Novel non-contact retina camera for the rat and its application to dynamic retinal vessel analysis

We present a novel non-invasive and non-contact system for reflex-free retinal imaging and dynamic retinal vessel analysis in the rat. Theoretical analysis was performed prior to development of the new optical design, taking into account the optical properties of the rat eye and its specific illumination and imaging requirements. A novel optical model of the rat eye was developed for use with standard optical design software, facilitating both sequential and non-sequential modes. A retinal camera for the rat was constructed using standard optical and mechanical components. The addition of a customized illumination unit and existing standard software enabled dynamic vessel analysis. Seven-minute in-vivo vessel diameter recordings performed on 9 Brown-Norway rats showed stable readings. On average, the coefficient of variation was (1.1 ± 0.19) % for the arteries and (0.6 ± 0.08) % for the veins. The slope of the linear regression analysis was (0.56 ± 0.26) % for the arteries and (0.15 ± 0.27) % for the veins. In conclusion, the device can be used in basic studies of retinal vessel behavior.

Retinal venous oxygen saturation increases by flicker light stimulation

PURPOSE

Luminance flicker stimulation of the photoreceptors is known to increase retinal blood flow. Elevated blood velocity was determined using laser Doppler velocimetry, and increased vascular diameters during flicker were observed by measurements with a retinal vessel analyzer. Oxygen supply may be the target of the regulation of retinal blood flow. Thus, the oxygen saturation (SO(2)) in retinal arterioles and venules was investigated along with their diameters.

METHODS

Dual-wavelength (548 nm and 610 nm) fundus images were taken in 19 healthy volunteers (mean age, 26 ± 2.5 years) before (baseline) and during luminance flicker stimulation (12.5 Hz; modulation depth, 1:25). Retinal vessel SO(2) (dual-wavelength optical oximetry) and diameters (central retinal arterial and venous equivalents [CRAE and CRVE]) were determined.

RESULTS

CRAEs and CRVEs of 193 ± 20 μm and 228 ± 20 μm at baseline increased statistically significant to a maximum of 202 ± 19 μm (P < 0.0005) and 242 ± 17 μm (P < 0.0005), respectively, under flicker stimulation. Although the arterial SO(2) remained unchanged at 98%-99%, an increase of the venous saturation from 60% ± 5.7% to 64% ± 5.9% (P < 0.0005) was found.

CONCLUSIONS

In agreement with earlier investigations, the vessel dilation found here indicates an elevation of retinal blood flow by luminance flicker stimulation. This increase of the flow should meet the enhanced metabolic need of the neural retina under a physiological stimulus. The augmentation of venous oxygenation may indicate a higher capillary oxygen concentration, necessary to provide a sufficient diffusion rate of oxygen from the capillaries to the inner retinal tissue.

Use of the retinal vessel analyzer in ocular blood flow research

The present article describes a standard instrument for the continuous online determination of retinal vessel diameters, the commercially available retinal vessel analyzer. This report is intended to provide informed guidelines for measuring ocular blood flow with this system. The report describes the principles underlying the method and the instruments currently available, and discusses clinical protocol and the specific parameters measured by the system. Unresolved questions and the possible limitations of the technique are also discussed.

Pulse wave velocity in retinal arteries of healthy volunteers

BACKGROUND/AIMS

Measurement of pulse wave velocity (PWV) in large vessels has been used extensively in clinical practice as an indirect measure of arterial stiffness and an indicator of cardiovascular risk factors. Arterial stiffness increases with age and in coronary artery disease. An in vivo clinical method to characterise arterial stiffness of the central microcirculation was developed.

METHODS

Time-dependent alterations of retinal vessel diameter were examined by the dynamic vessel analyzer in a randomly chosen eye of 10 young (26.0 (23.5, 27.0) years old (median (1st quartile, 3rd quartile)) and 10 old (67.0 (61.3, 69.5)) years old) healthy volunteers. Two segments of a retinal artery were measured simultaneously. The distance between the segments was measured using retinal photographs. The data were filtered and analysed using signal analysis methods in order to calculate PWV in the assessed retinal artery (rPWV).

RESULTS

rPWV differed significantly between young (21.5 (17.9, 4.6) mm/s) and old (243.8 (186.1, 347.7) mm/s) volunteers: (p=0.0001, Mann-Whitney test with Bonferroni correction).

CONCLUSIONS

This study demonstrates a higher rPWV in elderly people than in young people. Therefore this new parameter resembles large artery PWV. This suggests that dynamic in vivo imaging of the central microcirculation enables the measurement of local microvascular stiffness with a commercially available medical device.

Flicker light-induced retinal vasodilation in diabetes and diabetic retinopathy

OBJECTIVE

Flicker light-induced retinal vasodilation may reflect endothelial function in the retinal circulation. We investigated flicker light-induced vasodilation in individuals with diabetes and diabetic retinopathy.

RESEARCH DESIGN AND METHODS

Participants consisted of 224 individuals with diabetes and 103 nondiabetic control subjects. Flicker light-induced retinal vasodilation (percentage increase over baseline diameter) was measured using the Dynamic Vessel Analyzer. Diabetic retinopathy was graded from retinal photographs.

RESULTS

Mean +/- SD age was 56.5 +/- 11.8 years for those with diabetes and 48.0 +/- 16.3 years for control subjects. Mean arteriolar and venular dilation after flicker light stimulation were reduced in participants with diabetes compared with those in control subjects (1.43 +/- 2.10 vs. 3.46 +/- 2.36%, P < 0.001 for arteriolar and 2.83 +/- 2.10 vs. 3.98 +/- 1.84%, P < 0.001 for venular dilation). After adjustment for age, sex, diabetes duration, fasting glucose, cholesterol and triglyceride levels, current smoking status, systolic blood pressure, and use of antihypertensive and lipid-lowering medications, participants with reduced flicker light-induced vasodilation were more likely to have diabetes (odds ratio 19.7 [95% CI 6.5-59.1], P < 0.001 and 8.14 [3.1-21.4], P < 0.001, comparing lowest vs. highest tertile of arteriolar and venular dilation, respectively). Diabetic participants with reduced flicker light-induced vasodilation were more likely to have diabetic retinopathy (2.2 [1.2-4.0], P = 0.01 for arteriolar dilation and 2.5 [1.3-4.5], P = 0.004 for venular dilation).

CONCLUSIONS

Reduced retinal vasodilation after flicker light stimulation is independently associated with diabetes status and, in individuals with diabetes, with diabetic retinopathy. Our findings may therefore support endothelial dysfunction as a pathophysiological mechanism underlying diabetes and its microvascular manifestations.

Abnormal retinal autoregulation is detected by provoked stimulation with flicker light in well-controlled patients with type 1 diabetes without retinopathy

AIMS

Investigation of retinal vasodilation under flickering light is considered a dynamic analysis in contrast to the static analysis of retinal vessel equivalents (mean retinal vessel diameter). We investigated whether dynamic analysis apart from the static one in type 1 diabetic patients without diabetic retinopathy with well-controlled diabetes could lead to additional information regarding retinal autoregulation.

METHODS

18 normotensive type 1 diabetic patients without retinopathy and 19 healthy subjects were included. Diameter of retinal vessels was measured with Dynamic Vessel Analyzer. Changes in vasodilation are expressed as percent change over baseline values.

RESULTS

HbA(1c) was 7.5+/-1.0% in diabetic patients. In arteries, the response to flicker was diminished in diabetic patients compared to healthy volunteers (p<0.023). In patients flicker stimulation increased arterial diameter by +2.7% in contrast to +4.4% in controls. Venous vessel diameter increased by +3.1% in diabetic individuals and by +5.3% in the control group (p<0.002). There were no differences in static analysis between both groups.

CONCLUSIONS

Diabetic patients without retinopathy with relatively good glycemic control show reduced retinal vasodilation after flicker indicating dysfunction in retinal autoregulation. The use of provocation test in conjunction with static analysis could lead to additional information regarding abnormal retinal autoregulation.

Correlation of light-flicker-induced retinal vasodilation and retinal vascular caliber measurements in diabetes

PURPOSE

Subtle changes in retinal vascular caliber have been shown to predict diabetic retinopathy and other diabetic complications. This study was undertaken to investigate whether retinal vascular caliber correlates with light-flicker-induced retinal vasodilation, a measure of endothelial function.

METHODS

The participants were 224 persons with diabetes (85 type 1 and 139 type 2) and 103 persons without diabetes (controls). Flicker-induced retinal vasodilation (percentage increase over baseline diameter) was measured with a vessel analyzer. Retinal vascular caliber was measured from digital retinal photographs according to a standardized, validated protocol. Data from both right and left eyes were used and modeled with generalized estimating equations to account for correlation between eyes.

RESULTS

In persons with diabetes, after adjustment for age and sex, reduced flicker-induced vasodilation was associated with wider retinal vascular caliber. Eyes with the lowest tertiles of flicker-induced arteriolar dilation had wider arteriolar caliber (5.40 mum; 95% confidence interval [CI], 1.76-9.05) and eyes with the lowest tertiles of flicker-induced venular dilation had corresponding wider venular caliber (12.4 mum; 95% CI, 6.48-18.2), respectively, than eyes with the highest tertile of vasodilation. These associations persisted after further adjusting for diabetes duration, systolic blood pressure, fasting glucose, lipids, body mass index, current smoking, and presence of diabetic retinopathy. No associations were evident in persons without diabetes.

CONCLUSIONS

Changes in retinal vascular caliber (wider arterioles and venules) are associated with impaired flicker-induced vasodilation in persons with diabetes. Determining whether endothelial dysfunction explains the link between retinal vascular caliber and risks of diabetic microvascular complications calls for further study.

Dorzolamide Influences the Autoregulation of Major Retinal Vessels Caused by Artificial Intraocular Pressure Elevation in Patients with POAG: A Clinical Study

PURPOSE

The study investigated whether dorzolamide influences the autoregulatory behavior of major retinal arterioles in glaucoma patients via a moderate perfusion pressure reduction.

METHODS

The study included one eye each of 12 untreated patients with a primary open-angle glaucoma (POAG) (age 60.8 +/- 8.3, IOP 22.3 +/- 6.5 mmHg). Changes in the diameter of a retinal artery segment before (120 s), during (100 s), and after (380 s) artificial IOP elevation to 38 mmHg for 100 s were recorded continuously by means of a Retinal Vessel Analyzer. The measurement was repeated after 4-week treatment with dorzolamide eye drops t.i.d.

RESULTS

Ocular perfusion pressure (mmHg) was reduced by the intraocular pressure (IOP) elevation from 58 (+/- 10) to 41 (+/- 11) in the pretreatment examination and from 60 (+/- 8) to 40 (+/- 8) posttreatment (differences between the examinations n.s.). Before IOP elevation, the arterial diameter was found to be +1.7 +/- 3.5% greater in the posttreated eyes than in the pretreated eyes (p < 0.02). During IOP elevation, the arterial diameter decreased by -1.8% +/- 3.8 in the pretreated eyes, whereas dilatation by +1.4% +/- 2.5 was observed in the posttreated eyes (p = 0.02). At the end of the observation period following IOP elevation, the vessel diameter in the pretreated eyes had increased by +1.8% +/- 4.2, whereas in the posttreated eyes it had decreased by -1.7% +/- 3.0. On average, dorzolamide reduced IOP by -5.6 mmHg (p = 0.001).

CONCLUSIONS

The arterial diameter dilatation during IOP elevation in dorzolamide-treated eyes could be an accelerated counter-regulation on the induced elevated IOP and could constitute an additional therapeutic effect.

Diabetic patients with retinopathy show increased retinal venous oxygen saturation

BACKGROUND

Longstanding diabetes mellitus results in a disturbed microcirculation. A new imaging oximeter was used to investigate the effect of this disturbance on retinal vessel oxygen saturation.

METHODS

The haemoglobin oxygen saturation was measured in the retinal arterioles and venules of 41 diabetic patients (65 +/- 12.3 years) with mild non-proliferative through proliferative diabetic retinopathy (DR). Twelve individuals (61.3 +/- 6.2 years, mean +/- standard deviation) without systemic or ocular disease were investigated as controls. Measurements were taken by an imaging oximeter (oxygen module by Imedos GmbH, Jena). This technique is based on the proportionality of the oxygen saturation and ratio of the optical density of the vessel at two wavelengths (548 nm and 610 nm).

RESULTS

Whereas there were no significant differences in the arterial oxygen saturation between controls and diabetic retinopathy at any stage, the venous oxygen saturation increased in diabetic patients with the severity of the retinopathy: controls 63 +/- 5%, mild non-proliferative DR 69 +/- 7%, moderate non-proliferative DR 70 +/- 5%, severe non-proliferative DR, 75 +/- 5%, and proliferative DR 75 +/- 8%.

CONCLUSIONS

The increase of retinal vessel oxygen saturation in diabetic retinopathy points to a diabetic microvascular alteration. This may be due to occlusions and obliterations in the capillary bead and the formation of arterio-venous shunt vessels. On the other hand, hyperglycaemia-induced endothelial dysfunction, with subsequent suppression of the endothelial NO-synthase and disturbance of the vascular auto-regulation, may contribute to retinal tissue hypoxia.

[Temporal oscillations of retinal vessel diameter in healthy volunteers of different age]

PURPOSE

We investigated whether temporal oscillations of the retinal vessel diameter, as measured with the dynamic vessel analyzer (DVA), undergo age-related changes.

METHODS

Vessel diameters of retinal arterial and venous segments were examined with the DVA in 28 medically healthy volunteers divided into two age groups of 14 persons each: young subjects (21-32 years) and seniors (52-70 years). Continuous temporal records of vessel diameter were mathematically evaluated and divided into high-frequency (period <1.5 s) and low-frequency (period > or =1.5 s) oscillations.

RESULTS

The phase difference between temporal arterial and venous vessel diameter records was higher in the young group [0.6 (0.1, 3.3)] s [median (1st quartile, 3rd quartile)] compared with the seniors [0.1 (-0.4, 0.3) s]. There was a difference in the periodicity in veins between the groups and, in seniors, between the arteries and the veins.

CONCLUSIONS

High-frequency oscillations of vessel diameter correspond to the heartbeat. These were expressed more in seniors. Low-frequency oscillations were well expressed in young subjects. Our results show significant age-related alterations in retinal vessel regulation.

Retinal vessel response to flicker light in children and adolescents with type 1 diabetes mellitus and overweight or obesity

It was the goal of the trial to assess cardiovascular risk factors in children and adolescents with type 1 diabetes mellitus or overweight/obesity. All children and adolescents (n=77 [n=45 patients with diabetes mellitus, n=32 patients with overweight/obesity]) admitted to our hospital during the period from 01/07 to 31/08/2006 were included in the trial. Socio-demographic and laboratory data (age, sex, diabetes duration, BMI, BMI-SDS, HbA1c, fasting blood glucose, oGTT in patients with overweight/obesity, lipids, CRP, TSH, creatinine, and microalbuminuria) were assessed. The diameter of a retinal arterial and a venous segment was measured continuously on-line with a Dynamic Vessel Analyzer, carotid intima-media thickness (IMT) was measured, and 24-h-blood pressure monitoring was applied.

RESULTS

Flicker light stimulation induces a comparable arterial dilatation in patients with type 1 diabetes and overweight/obesity. Univariate ANOVA in patients with type 1 diabetes shows an influence of diastolic blood pressure on arterial dilatation. Other factors such as BMI, age, diabetes duration, smoking, sex, HbA1c and insulin dose/kg had no effect.

CONCLUSIONS

In children and adolescents with diabetes or overweight/obesity retinal vascular alterations seem to be more sensitive and already present before the occurrence of classic cardiovascular markers.

[Influence of two different cameras on the spectrometric measurement of oxygen saturation]

OBJECTIVES

Oxygen saturation in retinal vessels can be measured by spectrometry. However, there are no studies on the influence of different camera chips on these measurements. The presented study reports the effect of two different camera chips ("1-CCD" vs. "3-CCD") on the spectrometric measurements in the same patients.

METHODS

61 eyes of 61 patients were included in this study. The study was approved by the local ethics commission. Patients were separated in 3 groups: the first group contained healthy volunteers, the second group patients with diabetes mellitus but without previous laser treatment, the third group included patients with diabetes mellitus and previous laser coagulation treatment. The oxygen saturation was calculated from the difference between wavelengths on and right next to the retinal vessel. This methodology uses the different absorption spectra of oxy- and deoxyhaemoglobin.

RESULTS

All 3 groups demonstrated valid outcomes of the retinal oxygen saturation in arterial and venous vessels. No significant differences we found in the arterial-venous oxygen difference between the two different camera chips (group 1 p = 0.063, group 2 p = 0.204, group 3 p = 0.059).

CONCLUSION

As no significant differences could be found between the two camera chips, the less expensive system should be used if the spectrometric measurement of oxygen saturation is added to an analysis system already established on the market.

Retinal vessel oximetry-calibration, compensation for vessel diameter and fundus pigmentation, and reproducibility

The purpose of this study was to measure the hemoglobin oxygenation in retinal vessels and to evaluate the sensitivity and reproducibility of the measurement. Using a fundus camera equipped with a special dual wavelength transmission filter and a color charge-coupled device camera, two monochromatic fundus images at 548 and 610 nm were recorded simultaneously. The optical densities of retinal vessels for both wavelengths and their ratio, which is known to be proportional to the oxygen saturation, were calculated. From 50-deg images, the used semiautomatic vessel recognition and tracking algorithm recognized and measured vessels of 100 microm or more in diameter. On average, arterial and venous oxygen saturations were measured at 98+/-10.1% and 65+/-11.7%, respectively. For measurements in the same vessel segments from the five images per subject, standard deviations of 2.52% and 3.25% oxygen saturation were found in arteries and veins, respectively. Respiration of 100% oxygen increased the mean arterial and venous oxygen saturation by 2% and 7% respectively. A simple system for noninvasive optical oximetry, consisting of a special filter in a fundus camera and software, was introduced. It is able to measure the oxygen saturation in retinal branch vessels with reproducibility and sensitivity suitable for clinical investigations.

Effect of aging on retinal artery blood column diameter measured along the vessel axis

PURPOSE

To determine whether retinal branch arteries of healthy persons in different age groups show different longitudinal vessel profiles at baseline and during dynamic reaction to flicker stimulation.

METHODS

Thirty-three healthy subjects (age groups: 21-27 years, 40-59 years, and 60-85 years) were examined with the use of a retinal vessel analyzer. A monochromatic flicker of 12.5 Hz was applied for 60 seconds. Arterial diameters were measured in vessel segments of 1 mm in length to obtain the longitudinal vessel profile. Differences in amplitude and frequency of arterial width changes were characterized by the parameter spectral edge frequency (SEF).

RESULTS

SEF was significantly different between the young group and the senior group in each phase of the arterial reaction to flicker (baseline, dilation, constriction, relaxation; P < 0.05; Mann-Whitney U test). No significant difference within any age group was found in any phase of the arterial reaction. No significant difference between the middle-aged and either young or elderly subjects was found at baseline. However, after stimulation, the middle-aged group displayed a significant difference compared with the young group, with values resembling those of the elderly group.

CONCLUSIONS

In healthy elderly subjects, retinal arteries assumed a significantly less regular longitudinal vessel profile than those of young subjects. Middle-aged subjects assumed a more irregular profile only in the stimulated states of dilation, constriction, and relaxation. Early age-related changes in vessel profile are noted only after metabolic demand. These changes might be a cause for impaired blood flow and blood-vessel wall interaction.

Functional in vivo assessment of retinal artery microirregularities in glaucoma

PURPOSE

We investigated whether retinal branch arteries in healthy subjects, and non-treated and treated primary open-angle glaucoma (POAG) patients show irregular local patterns during dynamic reaction to acute increases of different magnitudes in intraocular pressure (IOP).

METHODS

Nine POAG patients and nine age-matched normal volunteers were examined with the retinal vessel analyser (RVA) using a suprasystolic IOP increase (Study 1). Fourteen POAG patients and 13 age-matched controls were examined using a moderate IOP increase for 100 seconds (Study 2). Longitudinal arterial profiles were obtained for the chosen time intervals. The high-frequency waviness (HFW) of these profiles was analysed quantitatively.

RESULTS

No significant changes in HFW were found in controls in different phases of the arterial reaction. Significant increases in HFW from baseline to dilation (Study 1, P < 0.03) and from dilation to constriction (Study 2, P < 0.05) were found in POAG patients. High-frequency waviness was higher in POAG patients than in controls during dilation (P < 0.05) in both studies.

CONCLUSIONS

Our results indicate a local vessel wall difference in glaucoma patients compared with age-matched controls. Increasing HFW might worsen hydraulic resistance of the vessel segment to blood flow. Significant increase of arterial microirregularities in the POAG retina during vascular dilation might be an indication for vascular endothelial alterations in glaucoma, leading to impaired perfusion in response to IOP increase.

Quantitative assessment of optic nerve head pallor

Ischaemia, loss of neural tissue, glial cell activation and tissue remodelling are symptoms of anterior ischaemic as well as glaucomatous optic neuropathy leading to pallor of the optic nerve head. Here, we describe a simple method for the pallor measurement using a fundus camera equipped with a colour CCD camera and a special dual bandpass filter. The reproducibility of the determined mean pallor value was 11.7% (coefficient of variation for repeated measurements in the same subject); the variation over six healthy subjects was 14.8%. A significant difference between the mean pallor of an atrophic disc and that of the contralateral eye of the same individual was found. However, even the clinically unaffected eye showed a significantly increased pallor compared to the mean of the healthy control group. Thus, optic disc pallor measurement, as described here, may be helpful in the early detection and follow-up of optic neuropathy.

Influence of flickering light on the retinal vessels in diabetic patients

OBJECTIVE

Stimulation of the retina with flickering light increases retinal vessel diameters in humans. Nitric oxide is a mediator of the retinal vasodilation to flicker. The reduction of vasodilation is considered an endothelial dysfunction. We investigated the response of retinal vessels to flickering light in diabetic patients in different stages of diabetic retinopathy.

RESEARCH DESIGN AND METHODS

We studied 53 healthy volunteers, 68 type 1 diabetic patients, and 172 type 2 diabetic patients. The diameter of retinal vessels was measured continuously online with the Dynamic Vessel Analyzer (DVA). Diabetic retinopathy was classified using Early Treatment Diabetic Retinopathy Study criteria. Changes in vasodilation are expressed as percent change over baseline values.

RESULTS

After adjustments for age, sex, and antihypertensive treatment, the response of retinal arterioles to diffuse luminance flicker was significantly diminished in patients with type 1 diabetes compared with healthy volunteers. The vasodilation of retinal arterioles and venules decreased continuously with increasing stages of diabetic retinopathy. The retinal arterial diameter change was 3.6 +/- 2.1% in the control group, 2.6 +/- 2.5% in the no diabetic retinopathy group, 2.0 +/- 2.7% in the mild nonproliferative diabetic retinopathy (NPDR) group, 1.6 +/- 2.2% in the moderate NPDR group, 1.8 +/- 1.9% in severe NPDR group, and 0.8 +/- 1.6% in proliferative diabetic retinopathy group.

CONCLUSIONS

Flicker responses of retinal vessels are abnormally reduced in diabetic patients. This decreased response deteriorated with increasing stages of retinopathy. The response was already reduced before clinical appearance of retinopathy. The noninvasive testing of retinal autoregulation with DVA might prove to be of value in early detection of diabetic vessel pathological changes.