Joanna Harazny

Principle, validity, and reliability of scanning laser Doppler flowmetry.

PurposeThe objective of this study is to present the reliability and validity of scanning laser Doppler flowmetry (SLDF) performing a high-definition topography of perfused vessels of the retina and the optic nerve head with simultaneous evaluation of blood flow. MethodsThe examination of blood flow by SLDF is based on the optical Doppler effect. The data aquisition and evaluation system is a modified laser scanning device; the wavelength of the laser source is 670 nm, with a power of 100 μW (Heidelberg Engineering, HRF). The reliability of SLDF was estimated by performing five seperate measurements in 10 eyes on 5 days. The validity of the method was tested by two experiments. First, in an experimental set-up, the capability of SLDF to measure the velocity of a moving plane in absolute units was estimated. Second, comparative measurements were performed of retinal blood flow in 16 normal eyes and in 33 glaucomatous eyes with SLDF and a commercially available single-point laser Doppler flowmeter (Oculix). ResultsWe found SLDF to produce a high reliability. The reliability coefficients rx of flow, volume, and velocity were 0.82, 0.81, and 0.83, respectively. Comparative measurements of the retinal blood flow by SLDF and a single-point laser Doppler flowmeter of corresponding retinal points showed a linear and significant relationship between flow (r = 0.83, p < 0.0001), volume (r = 0.51, p < 0.0001), and velocity (r = 0.59, p < 0.0001). In the experimental set-up, SLDF was able to quantitatively measure velocity in absolute units. ConclusionsSLDF enables the visualization of perfused vessels of the jux-tapapillary retina and the optic nerve head in high resolution by two-dimensional mapping of the optical Doppler shift and a reproducible evaluation of capillary blood flow.

Automatic full field analysis of perfusion images gained by scanning laser Doppler flowmetry

BACKGROUND Scanning laser Doppler flowmetry (SLDF) enables the measurement of the laser Doppler frequency shift in retinal tissue. This process allows the quantification of retinal and optic nerve head perfusion in an area of 2.7 mm × 0.7 mm within 2 seconds and with a spatial resolution of 10 μm × 10 μm. Owing to the local heterogeneity of the retinal microcirculation itself and to heart associated pulsation the capillary retinal blood flow depends on location and time. Because of technical limitations measurements of flow are only valid in retinal points with adequate brightness and focus, and away from big vessels. To include the heart beat associated pulsation and the spatial heterogeneity of retinal blood flow into the evaluation of blood flow an algorithm was developed examining automatically the whole SLDF perfusion image. AIM To report intraobserver reliability and interobserver reliability of a new method for analysing automatically full field perfusion images. METHOD The base of blood flow calculation by the automatic full field perfusion image analyser (AFFPIA) was 16 384 intensity time curves of all pixels of the whole perfusion image gained by the SLDF. AFFPIA calculates the Doppler frequency shift and the haemodynamic variables flow, volume, and velocity of each pixel. The resulting perfusion image was processed with respect to (1) underexposed and overexposed pixels, (2) saccades, and (3) the retinal vessel tree. The rim area and the saccades were marked interactively by the operator. The capillaries and vessels of the retinal vessel tree were identified automatically by pattern analysis. Retinal vessels with a diameter greater than 30 μm, underexposed or overexposed areas, and saccades were excluded automatically. Based on the whole perfusion image total mean flow, total mean volume, total mean velocity, standard deviation, cumulative distribution curve of flow, and the capillary pulsation index were calculated automatically. Heart beat associated pulsation of capillary blood flow was estimated by plotting the mean capillary flow of each horizontal line against time. Intraobserver reliability was estimated by measuring 10 eyes of 10 subjects on five different days by one observer. Interobserver reliability of AFFPIA was evaluated by analysing 10 perfusion maps by five different operators. To find a baseline of retinal blood flow, perfusion maps of 67 eyes of normal subjects with a mean age of 40.4 (SD 15) years were evaluated by AFFPIA. RESULTS The coefficient of reliability of the intraobserver reproducibility of flow was 0.74. The coefficient of reliability of the interobserver reproducibility was 0.95. The juxtapapillary retinal capillary flow was temporally 484 (SD 125), nasally 450 (117); the rim area capillary flow was 443 (110). The mean capillary pulsation index of retinal flow was 0.56 (0.14). CONCLUSION Retinal blood flow evaluation by the AFFPIA increases significantly the interobserver reliability compared with conventional evaluation of 100 μm × 100 μm areas in SLDF images with the original Heidelberg retina flowmeter software. The intraobserver reliability of AFFPIA was in the same range as conventional evaluation.

Increased Wall:Lumen Ratio of Retinal Arterioles in Male Patients With a History of a Cerebrovascular Event

Arterial hypertension is a major risk factor for stroke, and retinal vessels can be regarded as a mirror of the cerebral vasculature. Whether vascular remodeling of retinal arterioles with ageing and hypertension plays a role in cerebrovascular risk stratification has not yet been adequately addressed. In study 1, retinal arteriolar structure was assessed in 182 normotensive volunteers and 117 patients with essential hypertension. In study 2, we compared retinal arteriolar structure among 74 normotensive volunteers, 47 patients with treated essential hypertension, and 18 subjects with a history of a cerebrovascular event. Retinal arteriolar structure was assessed using scanning laser Doppler flowmetry and automatic full-field perfusion imaging analysis. In study 1, wall:lumen ratio of retinal arterioles revealed a significant correlation with age (r=0.198; P=0.001). In study 2, wall:lumen ratio was highest in patients with a history of a cerebrovascular event compared with treated hypertensive and normotensive subjects (0.46±0.08, 0.36±0.14, and 0.35±0.12; P=0.007). When the treated group with hypertension was divided into 2 subgroups according to the quality of blood pressure control, patients with poor blood pressure control showed higher wall:lumen ratio than subjects with good blood pressure control (0.40±0.13 versus 0.31±0.13; P=0.025). Thus, assessment of wall:lumen ratio of retinal arterioles emerged as an attractive tool to identify treated patients with hypertension with increased cerebrovascular risk.

Impaired Endothelial Function of the Retinal Vasculature in Hypertensive Patients

Background and Purpose— Arterial hypertension constitutes a central factor in the pathogenesis of stroke. We examined endothelial function of the retinal vasculature as a model of the cerebral circulation. Methods— Thirty-eight young subjects (19 hypertensive and 19 normotensive) were treated with the AT1-receptor blocker candesartan cilexetil and placebo, each over 7 days. Retinal capillary flow and blood flow velocity in the central retinal artery were assessed with scanning laser Doppler flowmetry and pulsed Doppler ultrasound, respectively. NG-mono-methyl-L-arginine (L-NMMA) was infused to inhibit nitric oxide (NO) synthesis. Diffuse luminance flicker was applied to stimulate NO release. Results— In normotensive subjects, L-NMMA decreased retinal capillary flow by 8.2%±13% (P < 0.05) and flickering light increased mean blood flow velocity in the central retinal artery by 19%±29% (P < 0.01). In contrast, no significant change to these provocative tests was seen in hypertensive subjects. Treatment with candesartan cilexetil restored a normal pattern of reactivity in retinal capillaries (L-NMMA: decrease in perfusion by 10%±17%, P < 0.05) and the central retinal artery (flicker: increase in mean blood flow velocity by 42%±31%, P < 0.001) in hypertensive patients. Conclusions— Endothelial function of the retinal vasculature is impaired in early essential hypertension but can be improved by AT1-receptor blockade.

Visual field defect and perfusion of the juxtapapillary retina and the neuroretinal rim area in primary open-angle glaucoma

Abstract • Background: At this time little information is available about the relationship between glaucomatous visual field defects and impaired blood flow in the optic nerve head. The purpose of this study was to examine blood flow of the juxtapapillary retina and the rim area of the optic nerve head in primary open-angle glaucoma with a borderline visual defect. • Methods: Juxtapapillary retinal and neuroretinal rim area blood flow was measured by scanning laser Doppler flowmetry (SLDF). The visual field was evaluated by static perimetry (Octopus-G1). The optic nerve head was assessed on 15° color stereo photographs. We examined 116 eyes of 91 patients with POAG with controlled IOP and 66 eyes of 44 healthy individuals. The POAG group was divided into eyes with a mean defect lower than 2 dB (POAG group I) and in eyes with a mean defect equal to or greater than 2 dB (POAG group II). The mean age of POAG group I and POAG group II was 55±11 years and 57±10 years, respectively. The mean age of the control group was 45±15 years. The eyes of POAG group I had an average C/D ratio of 0.71±0.18 with an average mean defect of the visual field of 0.97±0.68 dB; the eyes of POAG group II had an average C/D ratio of 0.80±0.17 with an average mean defect of the visual field of 8.2±6.0 dB. The intraocular pressure on the day of measurement in POAG group I was 18.2±3.7 mmHg, in POAG group II 17.6±4.0 mmHg, and in the control group 15.1±2.5 mmHg. For statistical analysis, age-matched groups of 32 normal eyes of 32 subjects (mean age 52±10 years) were compared to 18 glaucomatous eyes of 18 patients (POAG group I, mean age 55±11 years) and 59 glaucomatous eyes of 59 patients (POAG group II, mean age 55±10 years). • Results: In the eyes of POAG group I and POAG group II, both juxtapapillary retinal blood flow and neuroretinal rim area blood flow were significantly decreased compared to an age-matched control group: neuroretinal rim area “flow” POAG group I −65%, POAG group II −66%; juxtapapillary retina “flow” POAG group I −52%, POAG group II −44%. All eyes of the POAG group I (MD<2 dB) and 56 of 61 eyes of the POAG group II (MD>=2 dB) showed a retinal perfusion lower than the 90% percentile of normal blood flow. We found no correlation between reduction of juxtapapillary or papillary blood flow and mean defect in POAG eyes. • Conclusion: Glaucomatous eyes with no defects or borderline visual field defects as well as glaucomatous eyes in an advanced disease stage show significantly decreased optic nerve head and juxtapapillary retinal capillary blood flow.

Analysis of retinal arteriolar structure in never-treated patients with essential hypertension.

Objective Increased wall-to-lumen ratio of small arteries is a predictor of adverse cardiovascular prognosis. We aimed to analyze retinal arteriolar structure in never-treated patients with essential hypertension and to test whether elevated blood pressure is associated with an increased wall-to-lumen ratio of retinal arterioles. Methods The study cohort comprised 21 untreated male patients with essential hypertension (mean age 39.1 ± 5.4 years) and 29 untreated normotensive men (mean age 36.7 ± 5.9 years). Wall-to-lumen ratio of retinal arterioles was assessed in vivo using scanning laser Doppler flowmetry. Results Patients with essential hypertension had a higher wall-to-lumen ratio of retinal arterioles than normotensive individuals (0.36 ± 0.1 vs. 0.28 ± 0.1, P = 0.028). Wall cross-sectional area of retinal arterioles did not differ between the study groups. The growth index, indicating the percentage of difference in average wall cross-sectional area of retinal arterioles between both groups, was 18%. Both systolic (r = 0.360, P = 0.010) and diastolic (r = 0.536, P < 0.001) blood pressures were related to wall-to-lumen ratio of retinal arterioles. Multiple regression analysis including a variety of known cardiovascular risk factors revealed that blood pressure is independently associated with an increased wall-to-lumen ratio of retinal arterioles (systolic blood pressure: β = 0.417, P = 0.012; diastolic blood pressure: β = 0.548, P = 0.001). Conclusion The changes in arteriolar structure of retinal vessels in our study cohort revealed a similar pattern to that observed previously by other investigators in subcutaneous small arteries in essential hypertension. Blood pressure emerged as an important and independent determinant of wall-to-lumen ratio of retinal arterioles.

Wall-to-lumen ratio of retinal arterioles and arteriole-to-venule ratio of retinal vessels in patients with cerebrovascular damage.

PURPOSE There is evidence that generalized retinal arteriolar narrowing, which can be measured by the arteriole-to-venule ratio (AVR) of retinal vessels, predicts cerebrovascular events. The wall-to-lumen ratio (WLR) and wall cross-sectional area (WCSA) of retinal arterioles reflect structural arteriolar parameters. The primary objective was to test the association between WLR and AVR in a distinct cohort of patients with cerebrovascular damage. METHODS In this cross-sectional study, 23 patients (57.5 +/- 9.4 years) with acute transitory ischemic attack or lacunar cerebral infarct were compared with two age-matched control groups: 83 subjects with essential hypertension (53.7 +/- 5.5 years) and 16 normotensive subjects (52.2 +/- 8.3 years). Retinal arteriolar parameters (WLR, WTH, and WCSA) were assessed in vivo with scanning laser Doppler flowmetry (SLDF). AVR and a qualitative evaluation of retinal vessels were obtained from digital retinal color photographs. The intima-media thickness (IMT) of the carotid artery was measured. RESULTS WLR (0.44 +/- 0.1 vs. 0.34 +/- 0.1 vs. 0.30 +/- 0.1, P < 0.001) and carotid IMT (P < 0.05) were significantly greater in the cerebrovascular event group compared with normotensive subjects. WLR and WCSA were significantly higher in the cerebrovascular event group compared with subjects with mild arterial hypertension. AVR was similar in all three study groups (0.75 +/- 0.07 vs. 0.74 +/- 0.07 vs. 0.78 +/- 0.1, P = 0.18). CONCLUSIONS The increase in WLR and WCSA of retinal arterioles, as well as in IMT in patients with cerebrovascular damage suggests vascular hypertrophy in the microvascular and macrovascular bed. The lack of association between AVR of retinal vessels and WLR of retinal arterioles may point to different stages of cerebrovascular disease and/or different pathophysiological changes in the arteriolar wall.

New software analyses increase the reliability of measurements of retinal arterioles morphology by scanning laser Doppler flowmetry in humans.

Objective The investigation of the retinal arterioles offers the unique opportunity to analyze in vivo arteriolar remodeling in arterial hypertension in humans. We analyzed the reliability of assessing retinal arteriolar morphology with our new version of the software analyses for scanning laser Doppler flowmetry. Method In the test–retest reliability study, 10 eyes of 10 healthy persons were measured during 5 days under routine laboratory conditions with the Heidelberg Retinal Flowmetry. In a second study, interobserver and intraobserver reliability was analyzed from retinal images of 18 patients with three types of arterial hypertension by three readers and the most experienced reader analyzed all images twice on two different days. Images were analyzed by the old and the newly developed software versions. To characterize the reliability, the coefficients of variation were calculated. Results The test–retest study analyzed with the new program showed that the variation coefficients of vessel and lumen diameter, wall thickness, wall/lumen ratio and new calculated parameter: lumen/vessel diameter ratio of retinal arterioles were significantly less than 10%, with the exception of the wall cross-sectional area (12.5%). The interobserver and intraobserver reliability showed in nearly all circumstances coefficients of variations of less than 10% and did not differ across various readers and patient groups. Conclusion The new software ‘SLDF version 4.0’ clearly improved the reliability of assessing the structural parameters of the retinal arterioles. The application delivers reliable measurements of the retinal arteriolar structure in vivo in humans.

Central Pulse Pressure Is an Independent Determinant of Vascular Remodeling in the Retinal Circulation

Pulse pressure has been recognized as a risk factor for stroke. Moreover, it was shown that central pulse pressure relates more strongly to vascular disease and outcome than (peripheral) brachial pulse pressure. Because vascular remodeling in the retinal circulation mirrors the 1 in the cerebral circulation and represents an easy, noninvasive possibility to assess microvascular changes in humans, we analyzed the impact of central pulse pressure on retinal vascular structure in humans. The study cohort comprised 135 nondiabetic patients across a wide range of blood pressure values. Parameter of retinal arteriolar remodeling (wall-to-lumen ratio) was assessed noninvasively and in vivo by scanning laser Doppler flowmetry. Central pulse pressure and augmentation index normalized to a heart rate of 75 beats per minute were assessed by pulse wave analysis. Central pulse pressure correlated with wall-to-lumen ratio (r=0.302; P<0.001), central augmentation index normalized to a heart rate of 75 beats per minute correlated with wall-to-lumen ratio (r=0.190; P=0.028), and in accordance pulse pressure amplification (peripheral pulse pressure/central pulse pressure) was negatively correlated with wall-to-lumen ratio (r=−0.223; P=0.009). In contrast, central mean arterial pressure was not correlated with wall-to-lumen ratio (r=0.110; P=0.203). Multiple regression analysis revealed an independent relationship between wall-to-lumen ratio and central pulse pressure (&bgr;=0.277; P=0.009), but not with other classical cardiovascular risk factors. Thus, central pulse pressure, indicative of changes in large conduit arteries is an independent determinant of vascular remodeling in small retinal arterioles. Such a relationship indicates a coupling and crosstalk between the microvascular and macrovascular changes attributable to hypertension.

Wall-to-lumen ratio of retinal arterioles is related with urinary albumin excretion and altered vascular reactivity to infusion of the nitric oxide synthase inhibitor N-monomethyl-L-arginine.

Objective We hypothesized that wall-to-lumen ratio (WLR) of retinal arterioles might serve as an in-vivo parameter of vascular damage. To test this hypothesis we examined whether WLR of retinal arterioles is related with increased urinary albumin excretion and altered vascular reactivity to infusion of the nitric oxide synthase inhibitor N-monomethyl-L-arginine (L-NMMA). Methods Thirty-nine never-treated male patients aged 18–65 years with a body mass index at least 25 kg/m2 and without diabetes mellitus or secondary or stage 3 arterial hypertension were examined. WLR of retinal arterioles was assessed using scanning laser Doppler flowmetry. Urinary albumin-to-creatinine ratio (UACR) was measured from first morning spot urine. Vascular reactivity was measured by the change of aortic augmentation index (aAIx) to infusion of L-NMMA. Results UACR was related with WLR of retinal arterioles (r = 0.352, P = 0.032). In response to L-NMMA infusion aAIx increased (from 10.7 ± 11 to 19.7 ± 11%, P < 0.001). The change of aAIx to L-NMMA infusion was inversely related with WLR of retinal arterioles (r = −0.462, P = 0.003) even after adjustment for changes of hemodynamic parameters to L-NMMA infusion (partial r = −0.475, P = 0.005). The relationships of UACR and the change of aAIx to L-NMMA infusion with WLR of retinal arterioles were found to be independently of other cardiovascular risk factors (ß = 0.386, P = 0.006; ß = −0.369, P = 0.004, respectively) in multiple regression analyses with separate models for both parameters. Conclusion Increased WLR of retinal arterioles may thus serve as an in-vivo marker of vascular damage.