Retinal Arteriolar Blood Flow Research Articles

Inverse correlation between coronary and retinal blood flows in patients with normal coronary arteries and slow coronary blood flow

BackgroundThe “Slow Coronary Flow” (SCF) phenomenon in the presence of angiographically normal coronaries is attributed to microvascular and endothelial dysfunction. The microcirculation can be non-invasively assessed by measuring retinal blood flow velocity.The aim of the present study was to evaluate the efficacy of the “Retinal Functional Imager” (RFI) device as a noninvasive method of diagnosing patients with slow coronary flow. MethodsCoronary blood flow velocity assessed by corrected TIMI Frame Count and retinal arterioles blood flow assessed by RFI were measured in 28 consecutive patients with normal coronary arteries. The patients were divided into 2 groups: a slow coronary flow (SCF) and a normal coronary flow (NCF) groups. ResultsInverse correlation was found between retinal and coronary blood flows so that higher retinal arterial flow velocity was observed in the SCF group (3.8 ± 1.1 mm/s vs. 2.9 ± 0.61 mm/s, respectively, p = 0.022). RFI provided 73% sensitivity and 77% specificity for diagnosing SCF using ROC analysis. Additionally, patients with SCF had higher values of serum LDL cholesterol (104.7 ± 18.93 mg/dl vs. 81.55 ± 14.62 mg/dl in NCF, p = 0.005), Glucose (96.9 ± 23.0 mg/dl vs. 83.55 ± 9.7 mg/dl in NCF, p = 0.024), and lower percentage of statin consumption (40.0% vs. 76.9% in NCF, p = 0.049). ConclusionsSlow coronary blood flow can be non-invasively diagnosed with Retinal Functional Imager. Patients with normal coronary arteries and slow coronary blood flow have high retinal arteriolar blood flow. Early non-invasive diagnosis of SCF might help detect individuals who are at higher risk to develop coronary atherosclerosis, and to provide them with early preventive measures.

Vasomotor effect of intravitreal juxta‐arteriolar injection of L‐lactate on the retinal arterioles following acute branch retinal vein occlusion in minipigs

Abstract Purpose After branch retinal vein occlusion (BRVO), the retinal territory affected by the occlusion becomes hypoxic and the arterioles crossing this territory are often constricted. The purpose of the current experimental animal study is to investigate the effect of intravitreal juxta‐arteriolar microinjection of L‐lactate on the retinal arteriolar diameter following acute BRVO in minipigs. Methods Under general anesthesia, 9 eyes of 9 minipigs were evaluated. Argon laser endo‐photocoagulation was used to create BRVO. Two hours after BRVO, an intravitreal juxta‐arteriolar microinjection of 50 µl L‐lacate 1 mM (pH=7.4) was performed. The procedure was recorded in real time and retinal arteriolar diameter changes were measured in vivo using a Retinal Vessel Analyzer. Results Two hours after BRVO, the retinal arteriolar diameter decreased from 210 ± 16 AU to 183 ± 14 AU in the affected territories (p=0.04). Five minutes following L‐lactate juxta‐arteriolar microinjection, the retinal arteriolar diameter increased to 241 ± 16 AU (p< 0.01). The vasodilatory effect of L‐lactate persisted and remained significant till the end of the study period (243 ± 15 AU at 30 min, p<0.01). Conclusion We measured a significant vasodilation after intravitreal juxta‐arteriolar L‐lactate microinjection in eyes with experimental BRVO. L‐lactate microinjection can be of potential interest in acute BRVO, reversing the arteriolar vasoconstriction, thus leading to increase of the retinal arteriolar blood flow and possibly to improvement of the retinal cellular function in the occluded territory.

Assessment of retinal arteriolar hemodynamics in patients pre‐ and post‐cataract extraction

Abstract Purpose We have previously demonstrated that artificial light scatter results in the erroneous elevation of retinal vessel diameter and blood flow using densitometry based techniques. The aim of this study was to determine the impact of cataract on the quantitative, non‐invasive assessment of retinal arteriolar blood flow. Methods Of the original 30 recruited patients who were scheduled for extra‐capsular cataract extraction using phacoemulsification and intraocular lens implantation, ten patients between the ages of 61 and 84 (mean 73 ± 8) successfully completed the study protocol. Two visits were required to complete the study, one prior to the surgery and one at least six weeks after the surgery. Cataract status was documented using the Lens Opacity Classification System (LOCS, III) on the first visit. Retinal arteriolar hemodynamics were measured using the high intensity laser setting of the Canon Laser Blood Flowmeter (CLBF) on each visit. Results Group mean retinal arteriolar diameter and blood flow were significantly lower following extracapsular cataract extraction (Wilcoxon signed‐rank test, p=0.022 and p=0.028 respectively); however, centreline blood velocity was unchanged (Wilcoxon signed‐rank test, p=0.074). The primary reason for failure to complete the study protocol was due to poor retinal image quality impairing CLBF measurement. Conclusion Densitometry assessment of vessel diameter is extraneously impacted by the presence of cataract. Care needs to be exercised in the interpretation of studies of retinal vessel diameter and blood flow that utilize densitometry techniques.

Retinal arteriolar hemodynamic response to an acute hyperglycemic provocation in early and sight-threatening diabetic retinopathy

The aim was to quantify the magnitude of retinal arteriolar vascular reactivity to a hyperglycemic provocation in diabetic patients stratified by severity of retinopathy and in age-matched controls. The sample comprised 20 non-diabetic controls (Group 1), 19 patients with no clinically visible DR (Group 2), 18 patients with mild-to-moderate non-proliferative DR (Group 3) and 18 patients with diabetic macular edema (Group 4). Retinal hemodynamic measurements using the Canon Laser Blood Flowmeter (CLBF-100) were acquired before and 1 h after drinking a standardized oral glucose load drink. The magnitude of the retinal vascular response, as well as max:min velocity ratio and wall shear rate (WSR), was calculated and compared across groups. A significant change in blood glucose level was observed for all groups ( p < 0.05). The change in blood glucose elevation was significantly less in Group 1 compared to the other groups. No significant change in arteriolar diameter, blood velocity, blood flow, max:min velocity ratio and WSR was found in patients with diabetes and in age-matched subjects without diabetes. The results of this study indicate that retinal arteriolar blood flow is unaffected by acute elevation of blood glucose using an oral glucose load drink in patients with diabetes and in age-matched controls. This lack of a blood flow response to acute hyperglycemia in patients with early sight-threatening DR may be explained by a loss of retinal vascular reactivity.

Impact of simulated light scatter on the quantitative, noninvasive assessment of retinal arteriolar hemodynamics

We determine the impact of artificial light scatter on quantitative, noninvasive assessment of retinal arteriolar hemodynamics. One eye from each of 10 healthy young subjects between the ages of 18 and 30 (23.6+/-3.4) is randomly selected. To simulate light scatter, cells comprising a plastic collar and two plano lenses are filled with solutions of differing concentration of polystyrene microspheres (Polysciences Inc., USA). We prepare 0.002, 0.004, 0.006, and 0.008% microsphere concentrations as well as distilled water only. The Canon laser blood flowmeter (CLBF) is used to noninvasively assess retinal arteriolar blood flow. After a preliminary screening to confirm subject eligibility, seven arteriolar blood flow measurements are taken by randomly placing the cells between the instrument objective lens and the subjects' cornea. To achieve a baseline, subjects are first imaged with no cell in place. Both low- and high-intensity CLBF laser settings are assessed. Our light scatter model results in an artifactual increase of retinal arteriolar diameter (p<0.0001) and thereby increased retinal blood flow (p<0.0001). The 0.006 and 0.008% microsphere concentrations produce significantly higher diameter and flow values than baseline. Centerline blood velocity, however, is not affected by light scatter. Retinal arteriolar diameter values are significantly less with the high-intensity laser than with the low-intensity laser (p=0.0007). Densitometry assessment of vessel diameter is increasingly impacted as the magnitude of artificial light scatter increases; this effect can be partially negated by increasing laser intensity. A cataract is an inevitable consequence of aging and, therefore, care must be exercised in the interpretation of studies of retinal vessel diameter that use similar densitometry techniques.

Effect of Caffeine on Retinal Arteriolar Vascular Reactivity in Young, Normal Subjects

The purpose was to compare the effect of various caffeine dosages on retinal arteriolar blood flow. Measurements were collected using laser Doppler flowmetry and densitometry, permitting the noninvasive simultaneous measurement of blood velocity and vessel diameter to derive blood flow. A double blind, triple crossover design was used. Measurements were collected from 12 healthy subjects (21-30yr) before and for 2hr after the ingestion of 200 or 400mg of caffeine, or placebo (each in tablet form). Subjects did not ingest caffeine for 24hr prior to data collection. All subjects were tested for all dosages with a period of 1 week between visits. Data analyses were performed using repeated measures ANOVA, with statistical significance set at p<0.05. Caffeine did not significantly affect retinal arteriolar diameter, blood velocity, blood flow or the ratio of maximum to minimum blood velocity. However, over the 2-hour study period, vessel diameter (p<0.0001), flow (p=0.03) and max:min ratio (p=0.00001) decreased significantly for all dosages, including placebo. Baseline blood pressure and pulse rate did not differ across dosages or across test days. Both systolic (p=0.01) and diastolic (p=0.0001) BP increased significantly for all dosages following drug administration, while PR decreased significantly (p<0.0001). Subjects in all treatment conditions experienced decreased arteriolar diameter, blood flow, max:min ratio and PR over the 2-hour study period whereas BP increased in all groups. These effects were independent of caffeine / placebo dosage. This suggests that the common precaution of banning caffeine ingestion for 24 hours prior to study data collection may be unnecessary.

Endothelin-1-mediated retinal artery vasospasm and the rabbit electroretinogram.

Electroretinogram (ERG) changes invariably accompany the selective interruption of the retinal circulation that occurs in human central retinal artery occlusion. Since arteriolar ligation or ocular hypertension in the rabbit eye is occasionally used to model human central retinal artery occlusion, we conducted the present study to determine whether selective interruption of the retinal circulation of the rabbit eye alters retinal function as measured by the ERG. The vasoconstrictor, endothelin-1, was injected into the vitreous of rabbits' eyes to induce complete vasospasm and selective interruption of the retinal circulation. This procedure was compared to vascular ligation of the ophthalmic and ciliary arteries in which both the retinal and choroidal circulations were interrupted. A total of 8 rabbits was studied. Circulation was monitored angiographically in half of the eyes, and retinal function was monitored by the ERG in the remaining eyes. Endothelin-1 obliterated retinal arteriolar blood flow without affecting choroidal blood flow for at least 1 hr. Although ERG a-wave amplitude showed a small decline over 2 hr, b-wave and oscillatory potential amplitudes (measures of inner retinal function) showed no loss over this period. In contrast, ligation of the ophthalmic and ciliary arteries produced complete obliteration of both retinal arteriolar and choroidal blood flow and complete loss of the ERG after 2 min. Endothelin-1 induces acute, selective interruption of retinal arteriolar blood flow which has no significant physiologic effect on inner retinal function of the rabbit as monitored by the ERG. The avascular rabbit retina appears to be a poor choice for modeling human retinal artery occlusion.