Biomedical subjects

G Michelson

Publications and source records attributed to G Michelson.

At least 37 records · Page 2Linked to original sources

PubMed1997

Increased vascular resistance for venous outflow in central retinal vein occlusion.

PURPOSE: The authors quantified the vascular resistance for venous outflow in central retinal vein occlusion (CRVO). METHODS: The blood velocity in the central retinal vein (CRV) and central retinal artery (CRA) was measured by pulsed Doppler sonography (4-Mhz probe), and the pulse curve of the intraocular pressure (IOP) was evaluated by pneumotonometry. With multichannel data acquisition and storage software, the velocity-pulse curve of the CRV and CRA, the IOP-pulse curve, the arterial blood pressure, and the electrocardiogram were measured simultaneously in real-time mode. The relationships between the pulse curves of the blood velocity in the CRV and CRA and the IOP were calculated off-line. The onset time, the time of half maximum, and the time to the maximum of the pulse curves were evaluated. A relative index R' for the retinal outflow resistance was calculated by R' = deltaIOP/deltaVcrv. The authors examined 23 eyes of 23 patients with CRVO not older than 2 weeks and 23 eyes of 23 age-matched controls. There was no significant difference between the mean age of the control group (46 +/- 16 years) and that of the CRVO group (54 +/- 20 years). RESULTS: In eyes with CRVO, the authors found significantly lower systolic, diastolic, and mean outflow velocity. The amplitude of the CRV velocity pulse was significantly decreased compared with control eyes. In CRVO, the mean CRV velocity pulse amplitude (deltaVvein) was 1.77 +/- 1.0 cm/second, and in controls, it was 2.08 +/- 0.61 cm/second (P < 0.005). There was no significant difference in the mean IOP, but the IOP pulse amplitude (deltaIOP) was significantly higher in CRVO compared with controls (deltaIOP: CRVO 2.82 +/- 1.45 mmHg, control 1.96 +/- 0.56 mmHg, P < 0.005). The relative resistance index R' for venous outflow was significantly increased in eyes with CRVO (2.0 +/- 1.1 mmHg/cm/sec) compared with controls (1.1 +/- 0.44 mmHg/cm/s, P < 0.001). CONCLUSION: In eyes with CRVO, the systolic, diastolic, and mean velocity and the amplitude of the CRV velocity-pulse curve were significantly decreased and the resistance for retinal venous outflow was significantly increased compared with controls.

Adult↗

PubMed1997

[Correlation of ultrasound biomicroscopy with histological findings in diagnosis of giant cell arteritis].

BACKGROUND: A biopsy of the temporal arteries is still the appropriate method to prove the diagnosis of giant cell arteritis. We evaluated the potential use of high-resolution ultrasound-biomicroscopy in the diagnosis of giant cell arteritis. PATIENTS AND METHODS: In a prospective study we examined 16 patients (8 women and 8 men) with a mean age of 71 years with the clinical suspicion of a giant cell arteritis. Additionally to the clinical examination the temporal arteries were imaged in all patients using the ultrasound-biomicroscopy (Zeiss-Humphrey Instruments). The results were correlated to the histopathologic changes of the temporal arteries excised bilaterally at the same location. RESULTS: Histopathological evaluation revealed a granulomatous arteritis in 4 out of 16 examined patients. The temporal arteries of these patients also showed characteristic changes using ultrasound biomicroscopy like middle-reflective shadowing of the arterial lumen and a condensation and enlargement of the muscularis media. Ultrasound-biomicroscopy allowed a precise evaluation of the temporal arteries due to a high-resolution sonographic image. The morphological differentiation between a normal and an affected artery was possible. A positive correlation between histopathological and clinical findings was seen in all patients. CONCLUSION: In this preliminary study the ultrasound-biomicroscopy seemed to be an appropriate non-invasive tool for the morphological imaging and evaluation of temporal arteries.

Aged↗

PubMed1997

[Are there genuine and pseudo-normal pressure glaucomas? Body position-dependent intraocular pressure values in normal pressure glaucoma].

BACKGROUND: Elevation of intraocular pressure in the supine position has been previously described in literature. Aim of this study is to investigate the elevation of intraocular pressure in normal tension glaucoma and its effect on the morphology of the optic disc, visual field function and capillary blood flow of the retina and optic disc. PATIENTS AND METHODS: 56 eyes of 28 preperimetric and advanced normal tension glaucoma patients were prospectively evaluated. Ten eyes of ten normal patients served as a control group for the measurements of the intraocular pressure. In the course of a 24-h pressure profile applanation tonometry was performed in the morning in a supine and three and ten minutes later in a sitting position with Draeger's and Goldmann's tonometers. Arterial blood pressure was measured at the same time. The optic disc's morphology was evaluated by stereo photographs and Laser Scanning Tomography. As a sensory test computer perimetry was used. Capillary blood flow was measured at defined areas of the retina and optic disc. An intraocular pressure above 21 mm Hg in the supine position was used as a criterium to define two groups of normal tension glaucoma patients. RESULTS: In the supine position a statistically significant elevation of intraocular pressure was observed in 24 normal tension glaucoma patients by 6.2 +/- 2.8 mm Hg up to 21.8 +/- 3 mm Hg. Diastolic blood pressure in the supine position (80 +/- 10.5 mm Hg) was significantly lower than in the sitting position (94 +/- 11 mm Hg, p = 0.021). 12 of 28 normal tension glaucoma patients showed an intraocular pressure lower than 22 mm Hg in the supine position. In these patients a tendency towards a higher incidence for the occurrence of optic disc haemorrhages and significantly higher values for blood flow (p < 0.0005) and volume (p < 0.005) in the retina and optic nerve head could be shown. In this group of normal pressure glaucoma patients a higher incidence of migraine and vasospastic complaints was reported in the patients' history. CONCLUSION: In this study some normal tension glaucoma patients showed intraocular pressures in the supine position higher than 21 mm Hg and a lower diastolic arterial pressure. The higher incidence of haemorrhages and higher values for flow and volume parameters of the optic disc in normal tension glaucoma patients with an intraocular pressure lower than 22 mm Hg implicate the existence of two entities: real and pseudo normal tension glaucomas.

Adult↗

PubMed1997

Effect of breathing 100% oxygen on retinal and optic nerve head capillary blood flow in smokers and non-smokers.

AIM: The effect of breathing 100% oxygen on retinal and optic nerve head capillary blood flow in smokers and non-smokers was investigated using scanning laser Doppler flowmetry (SLDF) as a new non-invasive method to visualise and quantify ocular blood flow. METHOD: 10 eyes of 10 young healthy non-smoking volunteers (mean age 26 (SD 3) years) and nine eyes of nine young healthy smoking volunteers (mean age 26 (4) years) were investigated. All participants were asked not to smoke or consume caffeine containing drinks for at least 4 hours before the measurements. Blood flow measurements were performed before and after 100% oxygen was applied to the subjects through a mask over a period of 5 minutes (6 litres per minute). Juxtapapillary retinal and optic nerve head blood flow were determined in arbitrary units using SLDF representing a combination of laser Doppler flowmetry and a scanning laser system allowing visualisation and quantification of the retinal and optic nerve head blood flow. Blood flow was determined in an area of 100 microns x 100 microns. The level of carboxyhaemoglobin was determined in all subjects. A Wilcoxon matched pairs signed ranks test (non-parametric) was used for statistical evaluation. RESULTS: In the non-smoking group, retinal 'flow' was reduced by 33% (p = 0.005), optic nerve head 'flow' by 37% (p = 0.005). In the smoking group retinal flow was reduced by 10% (p = 0.01), optic nerve head flow by 13% (p < 0.008). The difference in reactivity to oxygen breathing between smokers and non-smokers was highly significant (p < 0.00001). Increased carboxyhaemoglobin levels were not found in either of the groups. A significant reduction of the mean arterial blood pressure of 6% (5%) (p < 0.02) was observed in the non-smoking group after administration of oxygen. CONCLUSION: These results indicate that hyperoxia leads to a decrease in capillary blood flow of the retina and optic nerve head secondary to vasoconstriction, and that smokers do not respond to oxygen breathing as non-smokers do. The findings might be based on factors such as long term effects of nicotine on the sympathetic and parasympathetic nervous system.

Adult↗

PubMed1996

Influence of age on retinal and optic nerve head blood circulation.

PURPOSE: To quantify the influence of age on the retinal perfusion, the authors investigated the microcirculation of the retina and optic nerve head (ONH) and the blood flow velocity in the central retinal artery (CRA). METHOD: The authors examined two groups of healthy volunteers. In group 1 (n=36 eyes of 36 subjects; mean age, 41.5 +/- 14.9 years), retinal and ONH microcirculation was analyzed by scanning laser Doppler flowmetry. In group 2 (n=49 eyes from 49 subjects; mean age, 44.4 +/- 15.4 years), CRA blood flow velocity was examined using pulsed Doppler sonography. RESULTS: Blood flow velocity of the CRA showed a negative correlation to age (systolic velocity, r= -0.47, P=0.001; diastolic velocity r= -0.49, P=0.001). The slope of the linear regression was -0.62 cm/second per 10 years for systolic blood velocity and -0.51 cm/second for diastolic blood velocity. Resistivity index (RI) (RI=[systolic velocity--diastolic velocity]/systolic velocity) as a marker of the rigidity of the vessel increased significantly with age (r=0.40, P=0.004). The slope was 0.03 per 10 years. Retinal microcirculation (flow omega-ret) decreased significantly with age (r= -0.63, P=0.00001). The slope was -34.9[AU] per 10 years. Optic nerve head blood flow showed no significant correlation to age (r= -0.30, P=0.071). CONCLUSION: The authors' data indicate that there is a significant decrease of retinal and CRA blood flow of approximately 6% to 11% per decade. Optic nerve head blood flow seems not to be influenced by age.

Adult↗

PubMed1996

Perfusion of the juxtapapillary retina and the neuroretinal rim area in primary open angle glaucoma.

PURPOSE: The objective of this study is to evaluate capillary blood flow of the juxtapapillary retina and neuroretinal rim area in primary open angle glaucoma (POAG) by a new noninvasive method performing a high-definition topography of perfused vessels of the retina and the optic nerve head with simultaneous evaluation of blood flow. METHODS: Juxtapapillary retinal and neuroretinal rim area blood flow were measured by scanning laser Doppler flowmetry (SLDF). This new technique is a combination of a laser Doppler flowmeter with a scanning laser system by which the retinal perfusion is simultaneously quantified in 16,000 sites of a retinal area of 2.7 x 0.7 mm. In study I, retinal and optic nerve head blood flow were evaluated by SLDF in 43 patients with POAG and 43 healthy individuals. The mean age of the POAG group was 56 +/- 12 years and of the control group 42 +/- 15 years. In study II, age-matched normals (n = 21) were compared with glaucoma eyes with topical therapy (n = 30) and with glaucoma eyes without topical therapy (n = 16). RESULTS: In study I, the eyes with POAG had an average cup/disc ratio (C/D) of 0.75 +/- 0.20, with an average mean defect of the visual field of 5.3 +/- 5.4 dB. The actual intraocular pressure was 17.8 +/- 4.18 mm Hg in the POAG group and 15.45 +/- 1.82 mm Hg in the control group. For statistical analysis, two age-matched groups of 28 normal eyes of 28 persons with 27 glaucomatous eyes of 27 patients were compared. In normals the blood flow of the neuroretinal rim area was significantly higher than that of the juxtapapillary retinal area (+7.73%, p < 0.01). In POAG 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 -71% and juxtapapillary retina flow -49%. The decrease of neuroretinal rim area blood flow did significantly correlate with C/D. We found no correlation between reduction of juxtapapillary retinal blood flow and C/D or mean defect. Both glaucoma eyes with and glaucoma eyes without topical therapy showed significant decreased juxtapapillary blood flow compared to normals. We found no significant difference in the juxtapapillary blood flow between glaucoma eyes with and without topical therapy. CONCLUSIONS: In POAG, optic nerve head blood flow and juxtapapillary blood flow were significantly decreased.

Adult↗

PubMed1996

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

PURPOSE: The 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. METHODS: The examination of blood flow by SLDF is based on the optical Doppler effect. The data acquisition and evaluation system is a modified laser scanning device; the wavelength of the laser source is 670 mm, with a power of 100 microW (Heidelberg Engineering, HRF). The reliability of SLDF was estimated by performing five separate 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 normal eyes and in 33 glaucomatous eyes with SLDF and a commercially available single-point laser Doppler flowmeter (Oculix). RESULTS: We found SLDF to produce a high reliability. The reliability coefficients r1 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. CONCLUSIONS: SLDF enables the visualization of perfused vessels of the juxtapapillary 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.

Evaluation Studies as Topic↗

PubMed1996

Perfusion of the juxtapapillary retina and optic nerve head in acute ocular hypertension.

Chronically elevated intraocular pressure (IOP) is often associated with glaucomatous optic nerve atrophy. Impaired blood flow may play a role in the pathogenesis of this disease. We present data concerning juxtapapillary retinal and optic nerve-head blood flow during acute increases in IOP. With the combination of a laser Doppler flowmeter and a scanning-laser system (Scanning Laser Doppler Flowmeter, SLDF; Heidelberg Engineering) the perfusion of the retina and the optic nerve head was quantified and visualized. Juxtapapillary retinal and optic nerve-head blood flow was measured simultaneously by SLDF during variations in IOP induced by a suction cup in nine healthy volunteers. The ocular pressure was increased for 2 min to IOP +15 mmHg, then to IOP +30 mmHg, and finally, to IOP +45 mmHg. Ocular perfusion pressure (PP) was calculated as the mean arterial blood pressure minus the IOP. The declines in juxtapapillary retinal flow as expressed in present per 10-mmHg IOP elevation ranged from 3.6% to 14.1% (median 7.4%). Over all measurements we found a significant linear relationship between juxtapapillary retinal blood flow and PP (r = 0.55, P < 0.0001). The observed decrease in optic nerve-head blood flow with increasing IOP was significantly greater as compared with the retinal blood flow decrease (8.4%/10 mmHg versus 7.4%/10 mmHg, P < 0.05). SLDF enables the quantification and visualization of perfused capillaries of the retina and the optic nerve head in high resolution. Acute elevations of IOP led to a decreases in juxtapapillary retinal and optic nerve-head blood flow of 7.4% and 8.4%/ 10-mmHg IOP increase, respectively.

Acute Disease↗

PubMed1995

[2-dimensional mapping and retinal and papillary microcirculation using scanning laser Doppler flowmetry].

PURPOSE: To present clinical applications of a new non-invasive method imaging in a high-definition the topography of perfused retinal vessels. METHOD: By a combination of a laser Doppler flowmeter with a scanning laser system the perfusion of the retina and the optic nerve head is visualized and quantified. The principles of measuring blood flow by Laser Doppler Flowmetry are based on the optical Doppler effect: laser light scattered by a moving particle is shifted in frequency by an amount delta f. Our data acquisition and evaluation system is a modified laser scanning tomograph. The technical data are: retinal area of measurement 2.7 mm x 0.7 mm, 10 degree-field with 256 points x 64 lines, measurement accuracy 10 microns, wavelength 670 nm and 790 nm, light power 100 microW, data acquisition time 2,048 s. Every line is scanned 128 times by a line-sampling rate of 4,000 Hz. By performing a discrete Fast Fourier Transformation over 128 intensities of each retinal point the laser Doppler-shift is calculated for each retinal point. With these data a 2-D map with 256 x 64 points of the retinal perfusion is created. The brightness of the picture-point is coded by the value of the Doppler shift. We estimated the reliability and the validity of the method. Perfusion-pictures of the superficial retinal layer and in the optic nerve head were presented. RESULTS: The reliability-coefficients r1 of "Flow", "Volume" and "Velocity" were 0.85, 0.83, and 0.85 respectively. The blood flow measurements by the presented method ("Scanning Laser Doppler Flowmetry") in an artificial capillary gave a linear relationship (r-value 0.973, p < 0.00001) between defined blood velocities and the measured blood flow. By the confocal technique, dependent on the focus, capillaries of the retinal superficial vasculature of the optic nerve head became visible with a high resolution. Off line the blood flow of areas of 110 microns x 110 microns were calculated in terms of laser Doppler flowmetry. CONCLUSION: "Scanning Laser Doppler Flowmetry" facilitates the visualisation of perfused retinal capillaries and vessels in high resolution. The representation of the function of the retinal circulation by SLDF leads to an image similar to the anatomical situation. The 2-dimensional mapping of local blood flow leads to a physiological picture of the retinal perfusion with visible vessels and capillaries.

Adult↗

PubMed1995

[Intraocular pressure after filtering operation or combined filter-cataract operation].

BACKGROUND: The prevalence of glaucoma is 2% and of cataract 25% in patients at the age of 65 to 75 years. To this moment the discussion is open about the optimal therapy when there is simultaneous cataract and glaucoma. We evaluated and compared the intraocular pressure and the visual acuity in patients with filtering-surgery and combined surgery (= filtering surgery plus simultaneous cataract surgery). METHOD: In a retrospective study 56 eyes of 45 patients operated by filtering surgery and 46 eyes of 40 patients operated by combined surgery were examined. RESULTS: Patients with combined surgery showed significant higher frequency of fibrin in the anterior chamber compared to patients with filtering-surgery. After 12 months there was no significant difference in intraocular pressure between both groups. The IOP of the last examination was 16 +/- 4 mm Hg in eyes with combined surgery and 14 +/- 4 mm Hg in eyes with filtering surgery. Eyes with combined surgery showed an increase of visual acuity from 0.2 +/- 0.2 to 0.4 +/- 0.3, eyes with filtering surgery a decrease of visual acuity from 0.7 +/- 0.3 to 0.6 +/- 0.3. CONCLUSION: Combined surgery is perioperatively associated with a higher frequency of complications, but showed 12 months postoperatively equal values of regulated intraocular pressure.

Aged↗

PubMed1995

Two dimensional mapping of the perfusion of the retina and optic nerve head.

AIM: To present a new non-invasive method of performing a high definition topography of perfused vessels of the retina and the optic nerve head with simultaneous evaluation of blood flow. METHOD: By a combination of a laser Doppler flowmeter with a scanning laser system the perfusion of the retina and the optic nerve head is visualised. The principles of measuring blood flow by laser Doppler flowmetry are based on the optical Doppler effect: laser light scattered by a moving particle is shifted in frequency by an amount delta f. Our data acquisition and evaluation system is a modified laser scanning tomograph. The technical data are retinal area of measurement 2.7 mm x 0.7 mm, 10 degrees field with 256 points x 64 lines, measurement accuracy 10 microns, wavelength 670 nm and 790 nm, light power 100 microW and 200 microW, data acquisition time 2.048 s. Every line is scanned 128 times by a line sampling rate of 4000 Hz. By performing a discrete fast Fourier transformation over 128 intensities of each retinal point the laser Doppler shift is calculated for each retinal point. With these data a two dimensional map with 256 x 64 points of the retinal perfusion is created. The brightness of the pixel is coded by the value of the Doppler shift. Offline capillary blood flow is estimated in arbitrary units according to the theory of laser Doppler flowmetry in every region of interest of the perfusion picture. We estimated the reliability and the validity of the method. Retinal blood flow was measured by scanning laser Doppler flowmetry (SLDF) while varying intraocular pressure by a suction cup of three healthy volunteers. Measurements of retinal blood flow performed in 47 eyes by the presented method (SLDF) were correlated with data gained by a commercially available laser Doppler flowmeter. Perfusion pictures of the superficial retinal layer and of deep prelaminar layers in the optic nerve head are presented. RESULTS: The reliability coefficients r1 of 'flow', 'volume', and 'velocity' were 0.84, 0.85, and 0.84 respectively. We found a significant linear relation between SLDF flow and the ocular perfusion pressure (r = 0.84, p < 0.001). Comparative measurements of the retinal blood flow by SLDF and a commercially available laser Doppler flowmeter showed a linear and significant relation (flow r = 0.6, p < 0.0001, volume r = 0.4, p < 0.01). Capillaries of the retinal superficial vasculature or deep ciliary sourced capillaries of the optic nerve head became visible with a high resolution by the confocal technique dependent on the focus. Offline, the blood flow variables of areas of 100 microns x 100 microns were calculated. CONCLUSION: SLDF enables the visualisation of perfused capillaries and vessels of the retina and the optic nerve head in high resolution by two dimensional mapping of perfusion variables which are encoded by the Doppler signal. This method achieves simultaneously qualitative and quantitative evaluation of capillary blood flow of distinct areas of the capillary meshwork.

Humans↗

PubMed1995

Advanced primary open-angle glaucoma is associated with decreased ophthalmic artery blood-flow velocity.

Recent findings indicate that low-tension glaucoma is associated with impaired ocular blood flow. In the present study we evaluated the blood-flow in the ophthalmic artery in regulated open-angle glaucoma. Using pulsed Doppler sonography (4 MHz), the blood-flow velocity in the ophthalmic artery of 183 eyes of 95 persons with open-angle glaucoma was examined (mean age, 66.6 +/- 14.5 years). The patients showed advanced glaucomatous optic-nerve atrophy (cup-to-disk ratio, 0.74 +/- 0.27) and regulated intraocular pressure (IOP: range, 8-25 mm Hg; mean, 16.4 +/- 3.9 mm Hg). The blood pressure (BP) was 140 +/- 22 (systolic) and 79 +/- 14 mm Hg (diastolic). The control group (84 eyes of 44 persons: mean age, 69.7 +/- 7.7 years; IOP range, 10-22 mm Hg; mean IOP, 15.2-2.6 mm Hg; BP, 143 +/- 20/81 +/- 9 mmHg was matched for age and circulatory risk factors. The vascular resistance index (RIO) was calculated by the equation RIO = (systolic blood velocity-diastolic blood velocity)/systolic blood velocity. We found that the blood velocity in the ophthalmic artery was significantly decreased in glaucomatous eyes in contrast to normal eyes: systolic peak velocity, 36.9 +/- 16.2 cm/s (normal, 40.2 +/- 10.9 cm/s; P < 0.001); diastolic peak velocity 9.9 +/- 4.4 cm/s (normal, 11.7 +/- 4.0 cm/s, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1995

Clinical investigation of the combination of a scanning laser ophthalmoscope and laser Doppler flowmeter.

In this report we present the clinical applications of a new noninvasive method of imaging in high definition the topography of perfused retinal vessels. By the combination of a laser Doppler Flowmeter with a scanning laser system the retinal circulation can be visualized and quantified. The principles of measuring blood flow by laser Doppler flowmetry are based on the laser Doppler effect: laser light scattered by a moving particle is shifted in frequency. The scanning laser system is a modified laser scanning tomograph (technical data: retinal area of measurement, 2.7 x 0.7 mm; 10 degrees field with 256 points x 64 lines; horizontal digital resolution, 10 microns; wave-length, 670 nm; light power, 100 micro W; data acquisition time, 2.048 s). Every line is scanned 128-times at a line-sampling rate of 4000 Hz. By the performance of discrete fast fourier transformation over 128 intensities of each retinal point the laser Doppler shift is calculated for each retinal point. With these data a 2-dimensional map of the retinal perfusion with 256 x 64-points is created. The brightness of the picture point is coded by the value of the Doppler shift. By this method we examined health eyes with normal intraocular pressure (IOP) and artificially increased IOP and eyes with glaucomatous optic nerve atrophy, proliferative diabetic retinopathy with areas of capillary occlusion, arterial hypertension with microinfarction of the retina, and central retinal artery occlusion. The application of "scanning laser Doppler flowmetry" (SLDF) leads to the visualization of perfused vessels and capillaries of the retina in high resolution. The examination of perfused retinal arterioles, veins, and capillaries by this method represents the anatomical situation. In SLDF the area of normal or impaired retinal circulation becomes visible (capillary nonperfusion, proliferative vascular structures), whereby the extent of the perfusion is proportional to the brightness of the imaged vessel; the brighter the vessels or capillaries, the higher the blood flow inside the vessels. Retinal areas with low capillary flow are "dark" and show no visible vessel. In imaging of an eye with central retinal artery occlusion, retinal arterioles, veins, or capillaries were invisible due to the lack of retinal perfusion. Only ciliary-source vessels of the optic nerve head were bright and visible, indicating normal ciliary circulation. SLDF facilitates the visualization of perfused retinal capillaries and vessels in high resolution. The representation of the function of the retinal circulation by SLDF leads to an image similar to the anatomical situation. The two-dimensional mapping of local blood flow leads to a physiological picture of the retinal perfusion with visible vessels and capillaries.

Adult↗

PubMed1994

Dipivefrin reduces blood flow in the ciliary body in humans.

PURPOSE: Adrenergic substances are used widely for lowering intraocular pressure in the treatment of glaucoma. The hypothetic mechanisms for lowering the intraocular pressure by adrenergic drugs are decreased blood flow in the ciliary body and direct receptor-related reduction of aqueous humor production. The aim of this study is to measure noninvasively the blood flow in the anterior uvea in humans after topically administered dipivefrin. METHOD: The blood flow of iris and ciliary body was measured by laser Doppler flowmetry. Laser Doppler flowmetry blood flow and results of the electrocardiogram were simultaneously measured and stored over a period of 3 minutes. In the authors' setup, laser light was projected by a fiber optic transcorneally onto the iris or 2 mm transscerally from the limbus into the ciliary body. For improvement of the signal-to-noise ratio, a statistical averaging procedure was performed by averaging 100 sweeps of 2 seconds of the digitalized laser Doppler flowmetry signals triggered by the R-onset of the electrocardiogram (averaging laser Doppler flowmetry). Using this method, reproducible pulse curves of blood flow of iris and ciliary body were established with systolic maxima and diastolic minima. In a double-blind study design involving 33 young, healthy persons (mean age, 25 +/- 7 years), the effect of topically administered dipivefrin, naphazoline, and NaCl solution (0.9%) on the blood flow of iris and ciliary body was examined. RESULTS: Dipivefrin reduces significantly (average, 49%) the mean blood flow in the ciliary body. Naphazoline and NaCl solution do not change the blood flow in the ciliary body. Dipivefrin, naphazoline, and 0.9% NaCl show no significant effect on the iridal blood flow. CONCLUSION: The observed data suggest that dipivefrin decreases ciliary body blood flow.

Administration, Topical↗

PubMed1994

Regulation of ocular blood flow during increases of arterial blood pressure.

The blood flow in the uvea in cats and monkeys during acute increases of arterial blood pressure is well controlled by a sympathetic mechanism protecting the eye from overperfusion. Ocular macrocirculation (ophthalmic artery) and ocular microcirculation (iris) were examined in 22 healthy subjects during acute increases of arterial blood pressure induced by physical exercise (125 W). With a data acquisition and storage software in real time mode several parameters of ocular perfusion and systemic functions were measured simultaneously. Blood flow parameters were measured in the ophthalmic artery by pulsed Doppler sonography and in the iris by laser Doppler flowmetry. Systolic, diastolic, and mean velocities of the ophthalmic artery peak velocity pulse curve, the ophthalmic artery mean velocity pulse curve, and the iris velocity pulse curve were estimated off line. The ophthalmic artery mean velocity pulse curve resembles the integrated velocity of all erythrocytes in the vessel including the slowly running cells near the vessel wall. The iris velocity pulse curve was calculated by a special statistic procedure (ALDF). After exercise there was a significant increase in systolic and diastolic blood pressure and heart rate. The pulse curve of the ophthalmic artery showed significantly increased systolic and decreased diastolic velocities. The vascular resistance of the branches of the ophthalmic artery increased significantly. The iridal vasculature showed no significant change in blood cell velocity but an increased vascular resistance. It was observed that the elevated perfusion pressure was associated with an increased vascular resistance and a constant mean blood velocity in the ophthalmic artery and iridal vessels. The parallel elevation of vascular resistance and blood pressure during exercise may be the reason for a constant blood flow in the ophthalmic artery and the iris. This may be accounted for by a sympathetic mechanism for protecting the eye from overperfusion.

Adult↗

PubMed1994

Ocular macro- and microcirculation after topical application of clonidine and metipranolol.

We investigated the effect of clonidine (Isoglaucon, an alpha-agonist) and metipranolol (Betamann, a beta-antagonist) on the blood flow in the ophthalmic artery and the anterior uvea of 40 young, healthy volunteers (mean age, 23.5 +/- 2 years) in a prospective, randomized simple blind study. The blood flow in the iris and ciliary body was detected by laser-Doppler flowmetry (bpm, 403a; TSI; wavelength, 780 nm; power, < 1.6 mW). The blood flow in the ophthalmic artery was measured by pulsed Doppler sonography (4 MHz, EME). The blood pressure, pulse respiration, and intraocular pressure (IOP) were recorded. Vascular resistance (RF) was calculated by the equation RF = (RRmean--IOP)/blood flow. Group 1 was treated with a single drop of Betamann (3 mg/ml) applied topically, and group 2 was treated with Isoglaucon (2.5 mg/ml). Measurements were made before and 30 min after application. Both drugs significantly lowered the IOP by about 7% (P = 0.01). Clonidine did not affect the blood velocity in the ophthalmic artery. In group 2 (metipranolol) we found a significant increase in the blood velocity in the ophthalmic artery during the diastolic period (from 11.0 +/- 3.7 to 11.9 +/- 2.2 cm/s, P = 0.05). Both clonidine and metipranolol decreased the iridal blood flow [clonidine, from 9.3 +/- 3.9 to 7.6 +/- 3.1 (flux), P = 0.05; metipranolol, from 7.5 +/- 2.9 to 6.5 +/- 2.6 (flux), P = 0.05]. Vascular resistance in the iris increased under the effect of clonidine (P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Topical↗

PubMed1994

Simultaneous measurement of ocular micro- and macrocirculation, intraocular pressure, and systemic functions.

SIMOMIMA (simultaneous measurement of ocular micro- and macrocirculation) is a 32-channel system for display and analysis of biophysical data on ocular perfusion. Using SIMOMIMA in the real-time mode, several parameters of ocular perfusion and systemic functions were simultaneously measured noninvasively and stored during varying periods of measurement; including ocular macroperfusion (pulsed Doppler sonography: ophthalmic artery), ocular microperfusion (laser Doppler flowmetry; iris, ciliary body, choroid), intraocular pressure, cardiac pulse, respiration, and arterial blood pressure. All data were digitalized and stored by a microcomputer for further data processing. With SIMOMIMA in the off-line mode, several parameters of the ocular and systemic circulation may be examined and correlations between them may be calculated, including absolute values for the ophthalmic-artery blood velocity expressed in centimeters per second; the pulse-wave velocity expressed in centimeters per second; relative values for the microcirculatory blood flow of the iris, ciliary body, or choroid; and absolute values for and the time course of the intraocular pressure, heart rate, and respiration rate. In contrast to the ophthalmic-artery pulse curve, the microcirculatory blood flow in the iris showed no obvious synchronization with the ECG or the respiration rate. The blood-cell velocity and the blood content in the iridal meshwork fluctuated with frequencies ranging between 0.5 and 4 Hz. By a special statistical procedure called averaging laser Doppler flowmetry (ALDF), the influence of the pulsations of the arterial blood pressure (diastolic systolic blood pressure) on the iridial blood flow becomes visible.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗

PubMed1991

[Absolute blood flow in the ophthalmic artery].

Knowledge about the total blood flow in the ophthalmic artery (OA) is very important in some ocular disorders. We estimated the total blood flow (BF) in the OA by measuring simultaneously the inner diameter of the OA (Doph) and the mean blood velocity (VMmean) of the same OA. Doph in [mm] was estimated with digitalized subtraction angiography (DSA) of the OA. The blood velocity was measured by pulsed Doppler sonography (4 MHz, 39 +/- 4 mm orbital depth, sample volume 4 mm, EME, Uberlingen). In addition to the pulse curve outline formed by the peak velocities, a pulse curve mean line was established as formed by mathematical integration of the relative strengths of all velocities at given time point. This pulse curve mean line resembles the mean velocity of all red blood cells in the OA at any time during the heart cycle with a systolic maximum (VMsys), a diastolic minimum (VMdia) and a mean blood velocity (VMmean). The pulse curve mean line always shows lower velocities than the pulse curve outline. The total blood flow (BF) in ml/min in the OA was calculated by: BF = (Doph/2)2 x 3.14 x VMmean. The pulsatile fraction (BFP) of the BF was calculated by: BFP = BF-[(Doph/2)2 x 3.14 x VMdia]. Twenty eyes of 13 neurological patients were examined (mean age 58.6 +/- 15.3 years). The inner diameter of the OA was on average 1.14 +/- 0.26 mm (min. 0.52, max. 1.88). The mean blood velocity VMmean was on average 10.38 +/- 4.16 cm/s (min. 6.35, max. 21.8).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiography, Digital Subtraction↗