Retrobulbar haemodynamics in non-arteritic anterior ischaemic optic neuropathy.
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Ciliary Arteries↗
Biomedical subjects
G T Feke
Publications and source records attributed to G T Feke.
Retinal haemodynamics in patients with age-related macular degeneration.
OBJECTIVE: To investigate whether there is an association between the magnitude of retinal haemodynamic abnormalities in patients with age-related macular degeneration (AMD) and the degree of severity of the AMD. METHODS: A retinal laser Doppler system (Canon CLBF 100) was used to measure retinal arterial haemodynamic parameters in 25 eyes of 25 patients with AMD and nine eyes of nine age-matched control subjects. Severity of AMD was classified into Mild (n=11), Moderate (n=7), or Severe (n=7). The pulsatility ratio (PR), the pulsatility index (PI), and the resistivity index (RI) were determined. RESULTS: PR, PI, and RI in the patients with AMD were each significantly higher than in the control group, and increased monotonically with increasing severity of AMD. However, there were no differences in mean blood velocity, arterial diameter, or blood flow rate among the groups. This suggests that the increased blood flow pulsatility in the retinal arteries of the eyes with AMD is not due to increased distal vascular resistance, but instead is likely due to a loss of compliance in the arterial vasculature leading to the eye. CONCLUSION: Our results suggest that an increasing vascular rigidity in the systemic arterial circulation is directly associated with an increasing severity of AMD.
Aged↗
Retinal blood flow in nonischemic central retinal vein occlusion.
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Blood Flow Velocity↗
Diversity of response of optic nerve head circulation to timolol maleate in gel-forming solution.
PURPOSE: This randomized, double-masked, placebo-controlled, two-period crossover study was conducted to investigate the effects of 0.5% timolol maleate in gel-forming solution on intraocular pressure (IOP) and blood circulation in the optic nerve head in patients with untreated ocular hypertension. METHODS: The effects of 0.5% timolol in gel-forming solution on IOP and optic nerve head capillary blood speed were studied in 12 patients with untreated ocular hypertension. Optic nerve capillary blood speed was measured using the laser Doppler technique before and at the end of each treatment period. RESULTS: In each patient, IOP decreased after treatment with timolol (mean decrease 16.8% versus placebo). Systemic blood pressure and pulse rate did not differ significantly after treatment with topical timolol from values after placebo. The mean change from baseline in Doppler broadening was 10.6% greater after treatment with timolol than after placebo. There was no significant change in mean Doppler broadening from baseline after treatment with either timolol or placebo. However, optic nerve head capillary blood speed increased in six patients, and was within the range of placebo response in six patients after treatment with timolol. Spearman correlation analysis of the baseline with Doppler broadening measurements after treatment showed a correlation for placebo but not for timolol. The percent change in Doppler broadening after timolol treatment was correlated with iris color. CONCLUSION: These results indicate that administration of timolol for 4 weeks reduces IOP in patients with ocular hypertension and generally does not change the blood circulation in the optic nerve head. Individual patients, however, showed variable changes in optic nerve head circulation after topical administration of timolol. Although the sample size was small, these changes in optic nerve head circulation were correlated with iris color.
Adrenergic beta-Antagonists↗
Regulation of retinal and optic nerve blood flow.
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Adult↗
Retinal blood flow increases following short-term aspirin usage in type I diabetics with no or minimal retinopathy.
In a double-masked, randomized, placebo-controlled, two-period crossover study, we measured the effect of aspirin on retinal blood flow in 8 type I diabetic patients, 5 with no observable retinopathy, and 3 with 1-10 observable microaneurysms and no other signs of retinopathy. Each patient ingested 1 capsule/day of either aspirin (650 mg) or placebo for 14 days. Following a 1-month washout period, the treatment was reversed. The bidirectional laser Doppler technique and monochromatic photography were used to measure the blood flow rate in a major temporal retinal artery in 1 eye of each patient at baseline and on the 14th day of each treatment period. Retinal blood flow increased following aspirin in 7 of the 8 patients. Using a standard crossover analysis we found a mean aspirin-placebo treatment difference of 21 +/- 17% (mean +/- 95% CI), which was statistically significant (p = 0.03). Retinal blood flow increased following aspirin by 44 +/- 10% (mean +/- SEM) in the 5 patients with no retinopathy (p = 0.04), but only by 8 +/- 10% (n.s.) in the 3 patients with minimal retinopathy.
Adult↗
Retinal hemodynamics in middle-aged normal subjects.
The laser Doppler technique and monochromatic photography were used to measure the total retinal blood flow, temporal/nasal differences in blood flow and the relationship between blood flow and vessel diameter in 5 healthy subjects, aged 54-58 years. Systemic blood pressure (BP) and intraocular pressure were also measured, and the retinal perfusion pressure was calculated. The measurements were compared to those previously obtained from a younger group of 7 healthy subjects, aged 25-38 years. Total retinal blood flow was 73 +/- 13 microliters/min in the middle-aged subjects and was not significantly different from the value measured in young subjects (80 +/- 12 microliters/min). Retinal perfusion pressure was significantly higher in the older subjects, primarily due to elevated systemic BP. The similarity in total flow between the two groups, even though the retinal perfusion pressures were higher in the older group, is an indication of an increased vascular resistance to flow. The increase may be an aging phenomenon or an indication of a well-functioning autoregulatory capacity in the retinal vasculature of the older subjects.
Adult↗
Retinal blood flow changes in type I diabetes. A long-term follow-up study.
PURPOSE: The authors previously reported that blood speeds in the retinal arteries were significantly lower in patients with type I diabetes than in controls without diabetes. The purpose of this long-term, follow-up study was to characterize the natural course of changes in blood speed and blood flow in these patients. METHODS: Twenty-four patients were followed up with serial annual measurements of the blood flow in a temporal retinal artery using the bidirectional laser Doppler technique and monochromatic photography. The follow-up period ranged from 2 to 6 years (mean, 3.8 years). Using standardized color fundus photography and fluorescein angiography, a retinopathy score was generated for each eye studied. Linear regression analysis was used to compute the slope of the change in retinal blood flow for each patient during the follow-up period. RESULTS: Retinal blood flow slopes were negative in 15 patients and positive in 9 patients. Multiple linear regression analysis showed that the retinal blood flow slopes were significantly related to the retinal blood flow measured at entry to the study and to the median duration of diabetes during the follow-up period (R2 = 0.56; P = 0.0002). There was a positive correlation between the retinal blood flow slopes and the median retinopathy score during the follow-up period (P = 0.47; P = 0.02). CONCLUSIONS: As duration of diabetes becomes longer and retinopathy becomes more severe, there is a transition from negative to positive retinal blood flow slopes. This bimodal relationship between the change in retinal blood flow and the duration of diabetes reflects the complex pathologic alterations that occur in the diabetic retina.
Adult↗
Optic nerve head circulation after topical calcium channel blocker.
PURPOSE: Our purpose was to investigate the effects of the calcium channel blocker verapamil on intraocular pressure and blood circulation in the human optic nerve head. METHODS: The effects of three different concentrations of topical verapamil (0.063%, 0.125%, and 0.25%) on intraocular pressure and optic nerve head capillary blood speed were measured in 12 healthy normal subjects. In a randomized, double-masked design, each subject received one drop of either verapamil or placebo in one eye and the opposite treatment in the fellow eye. Anterior optic nerve circulation was assessed at baseline and 90 min after instillation of the drops using the laser Doppler technique. RESULTS: The intraocular pressure was significantly reduced compared with baseline in both verapamil- and placebo-treated eyes at each concentration. The reductions of intraocular pressure were greater in verapamil-treated eyes (12-17%) than in placebo-treated eyes (9-12%). No systemic effect on heart rate or blood pressure was detected after administration of topical verapamil. The capillary blood speed in the optic nerve head was increased in both verapamil- and placebo-treated eyes at each concentration, although the only statistically significant increases were with the 0.25% concentration. The mean +/- SEM increase compared with baseline at the 0.25% concentration was 10.4 +/- 3.6% in verapamil-treated eyes (p = 0.017), and 11.6 +/- 4.4% in placebo-treated eyes (p = 0.026). CONCLUSIONS: These results indicate that topical administration of verapamil lowers the intraocular pressure and increases the capillary blood speed in the optic nerve head in normal subjects. Changes measured in verapamil-treated eyes were also observed in placebo-treated eyes, indicating a crossover effect.
Administration, Topical↗
[The new laser Doppler velocimetry for the measurement of retinal circulation and its clinical application].
We developed a new laser Doppler instrument to measure retinal blood flow. This instrument is equipped with an eye tracking system, which maintains the laser beam on the retinal vessel, thus enabling the measurement of patients with poor visual acuity and poor fixation. In diabetic patients even those without retinopathy, the retinal blood flow decreased compared to the control subjects. This was mainly the result of decreased retinal blood speed and no significant change in the arterial diameter. In diabetic patients requiring panretinal photocoagulation, we studied the regional changes in retinal blood flow following superior or inferior half fundus argon laser treatment, which produced a significant retinal blood flow decrease only in the treated area. We also studied the retinal circulatory changes in retinal branch vessel occlusion. In retinal branch view occlusion, the blood flow in arteries supplying the affected lesion showed 80-90% decrease compared to the arteries supplying the unaffected region. In retinal branch artery occlusion, the retinal blood flow in occluded arteries showed 40-50% decrease compared to the non-occluded arteries. In one patient with retinal branch vein occlusion in whom we measured the retinal blood flow over 18 months, the blood flow increased with the development of collateral vessels. The results showed that retinal circulatory abnormalities can be also evaluated quantitatively during the course of retinal vascular occlusive disease by our newly developed laser Doppler instrument, which proved that this instrument is a clinically very useful tool.
Adult↗
Color Doppler ultrasound analysis of ocular circulation after topical calcium channel blocker.
PURPOSE: To investigate the effect of topical administration of the calcium channel blocker verapamil on intraocular pressure and retrobulbar hemodynamics. METHODS: In this randomized, prospective, double-masked study, we examined the effects of single-dose topical administration of verapamil in ten normal human volunteers by using color Doppler ultrasound imaging to measure hemodynamic parameters. Limitations of this study include single-dose application of verapamil and relatively small sample size. RESULTS: No systemic effect on heart rate or blood pressure was detected after administration of topical verapamil. The intraocular pressure significantly decreased compared with baseline two hours after topical 0.125% and 0.25% verapamil (P = .015 and .040, respectively). Pourcelot's ratio, an index of vascular resistance, measured in the central retinal artery was significantly reduced after topical application of 0.125% verapamil (P = .008). The change in Pourcelot's ratio primarily resulted from an increased end diastolic velocity in the central retinal artery. No significant differences compared with baseline values were detected in the color Doppler ultrasound measurements of the posterior ciliary arteries and the central retinal vein two hours after topically administered verapamil. CONCLUSIONS: Topical administration of verapamil decreases intraocular pressure and alters ocular hemodynamics, reducing the vascular resistance index in the central retinal artery.
Administration, Topical↗
Optic nerve head circulation in untreated ocular hypertension.
AIMS: The laser Doppler technique was used to compare the capillary blood speed measured at localised sites of the optic nerve head in stable, untreated ocular hypertensive patients with that measured in healthy normal subjects. The stereophotogrammetric technique was also used to measure the retinal nerve fibre layer thickness at the disc margin in the eyes of the patients. METHODS: Doppler broadening measurements were made at superior and inferior temporal disc sites in 18 eyes of 10 ocular hypertensive patients and in 12 eyes of seven age and sex-matched normal subjects. RESULTS: On average, Doppler broadening and, hence, capillary blood speed were significantly higher (p = 0.018) in the patients than in the normal subjects. The largest values of Doppler broadening in the patients were measured at sites adjacent to the thinnest retinal nerve fibre layer. Linear regression analysis showed a significant inverse relation (p = 0.0004) between Doppler broadening and nerve fibre layer thickness in left eyes, and a nearly significant relation (p = 0.06) in right eyes. At temporal sites of the optic nerve head there is a compensatory relation between a thinning nerve fibre layer and a locally increasing blood supply to the optic nerve head. CONCLUSION: Together with previous observations of fluorescein filling defects in similar patients, these results indicate that there is spatial heterogeneity of blood flow in the optic nerve head in stable, untreated ocular hypertensive patients.
Adult↗
Quantitative circulatory measurements in branch retinal vessel occlusion.
We used the laser Doppler technique to quantify retinal circulatory abnormalities in three patients with branch retinal artery occlusion and in two patients with branch retinal vein occlusion, each of whom had shown delayed filling on fluorescein angiography. Blood flow in occluded arteries was 40-50% lower than in non-occluded arteries of the same branching order. In the patients with branch retinal vein occlusion blood flow in arteries supplying the affected regions was 80-90% lower than in arteries supplying the unaffected regions. One vein occlusion patient was measured serially over 18 months. Blood flow increased from 4 to 12 microliters/min in the artery supplying the affected region in this patient. The results demonstrate that retinal circulatory abnormalities can be evaluated quantitatively during the course of retinal vascular occlusive disease, and suggest that the efficacy of therapy can be monitored using our techniques.
Aged↗
Regional retinal blood flow reduction following half fundus photocoagulation treatment.
Regional changes in retinal blood flow following inferior and subsequent superior argon laser half fundus photocoagulation treatment were measured in six diabetic patients with advanced retinopathy. Centreline blood velocity, vessel diameter, and blood flow in major inferior and superior temporal retinal arteries were measured at baseline and following each treatment using the bidirectional laser Doppler technique and monochromatic fundus photography. Inferior fundus laser treatment produced a significant blood flow decrease in inferior temporal arteries ranging from 60% to 78%. Blood flow changes in superior temporal arteries were not significant, ranging from -7% to +14%. Subsequent superior fundus laser treatment produced a significant blood flow decrease in superior temporal arteries ranging from 50% to 66%. Subsequent blood flow changes in inferior temporal arteries were not significant, ranging from -19% to +21%. The results indicate that regional laser treatment produces a regional reduction in retinal blood flow, consistent with measurements of preretinal and intraretinal oxygen tension which have indicated increases in oxygen over photocoagulated regions.
Adult↗
Retinal circulatory abnormalities in type 1 diabetes.
PURPOSE: To quantify retinal circulatory abnormalities in patients with type 1 diabetes; to 1 diabetes; to compare blood speed and blood flow in major temporal retinal arteries as well as total retinal arterial cross-section measured in patients to that measured in controls without diabetes; to determine which factors are related to the measured abnormalities within the patient group. METHODS: The laser Doppler technique and monochromatic fundus photography were used to measure retinal circulatory parameters in 39 patients with type 1 diabetes with duration of diabetes between 7 and 20 years and 13 age-matched controls without diabetes. Blood pressure, intraocular pressure, and heart rate were measured in all subjects. Glycosylated hemoglobin was measured in the patients. Retinopathy was assessed using standardized color fundus photography and fluorescein angiography. RESULTS: Total retinal arterial cross-section was, on average, 17% higher (P = 0.007) in the patients than in the controls, and it increased with increasing duration of diabetes (P = 0.006). Arterial blood speed was, on average, 33% lower (P = 0.0001) in the patients than in the controls, and it decreased with increasing duration of diabetes (P = 0.03). CONCLUSIONS: The retinal circulation of patients with type 1 diabetes with no retinopathy or background retinopathy is characterized by dilated major arteries with reduced blood speeds. Dilation of the larger retinal arteries, with the accompanying decrease in vascular resistance to flow in those vessels, appears to counteract an increase in resistance to flow at the level of the smaller retinal vessels.
Adult↗
Retinal blood flow alterations associated with scleral buckling and encircling procedures.
The bidirectional laser Doppler technique and monochromatic photography were used to measure the absolute blood flow rate in the major temporal retinal arteries in seven patients following unilateral scleral buckling and encircling procedures, and in two patients before and after removal of scleral buckling elements. In the seven patients who had undergone uncomplicated scleral buckling procedures the arterial flow rates were on average 50% lower (p = 0.01) in the surgically treated eyes than in the contralateral eyes. Removal of scleral buckling elements in two patients produced increases of 73% and 44% in arterial blood flow rates.
Adult↗
[Analysis of optic nerve head circulation in diabetics using a laser Doppler technique].
The authors measured the red blood cell speed distributions in the capillaries of the optic nerve head using a laser Doppler technique. We calculated the widths of Doppler-broadened frequency spectra of laser light scattered from temporal sites on the optic nerve head in 34 Type I diabetic patients (mean age, 29.5 years; 12 patients having no retinopathy; 22 having background retinopathy) and in 29 age- and sex-matched normal controls. Doppler broadening proportional to the red blood speed was 763 +/- 113 Hz (mean +/- SD) in the diabetics and 912 +/- 167 Hz in the controls. The difference was statistically significant. Mean blood pressure and intraocular pressure in the diabetics were not significantly different compared to controls. Our finding of abnormally low capillary blood speeds suggests that pathologic alterations occur in the microvasculature of the optic nerve head in the early stages of diabetic retinopathy.
Adult↗
[Retinal blood flow changes in eyes with rhegmatogenous retinal detachment and scleral buckling procedures].
Bidirectional laser Doppler technique and monochromatic photography was used to measure the absolute blood flow rate (F) in the major superior or inferior temporal retinal arteries in 3 patients with rhegmatogenous retinal detachment, in 4 patients following unilateral scleral buckling procedures, and in one patient before and after removal of scleral buckling elements. In 2 of the eyes with retinal detachment, F in arteries supplying the detached portion of the retina was approximately 30% lower than in arteries supplying the attached portion. On average, F measured in the arteries supplying the detached portion of the retina in 2 patients was 8.9 +/- 1.3 microliters/min, 67% lower than normal controls. F measured in the arteries supplying the attached portion of the retina in 3 patients was 15.2 +/- 3.9 microliters/min, on average, 43% lower than in normal controls. In 4 patients who had undergone uncomplicated, unilateral scleral buckling procedures, F in an artery of the affected eye was compared with F in the corresponding artery of the fellow eye. F in the artery of the affected eyes was 8.7 +/- 3.2 microliters/min, on average, 59% lower than that of the fellow eyes (p less than 0.05), and 68% lower than in normal controls (p less than 0.0001). Removal of scleral buckling elements in one patient produced a 79% increase in F in the measured artery. Then, F returned to normal levels after removal of scleral buckling elements.
Adult↗