Blood Flow In Iris Research Articles

Discrepancies in Vessel Density and Blood Flow Distribution in Different Areas of the Iris among Pediatric Type 1 Diabetes Mellitus and Adult Type 2 Diabetes Mellitus Patients

Introduction: Diabetes mellitus may compromise the vasculature of the iris, thereby leading to severe vision-threatening complications. This study aimed to investigate differences in iris blood flow indices between pediatric type 1 diabetes mellitus (T1DM) patients and adult type 2 diabetes mellitus (T2DM) patients. Methods: This was a cross-sectional study. Pediatric T1DM patients and healthy children were members of the Shanghai Children and Adolescent Diabetes Eye (SCADE) cohort who visited Shanghai Eye Hospital in February 2022. The adult T2DM patients and healthy adults were patients who visited Shanghai General Hospital from October 2021 to January 2022. Iris OCTA was acquired through a Cirrus HD-OCT 5000 angiography system (Carl Zeiss Meditec, Inc.). A unique iris OCTA quantification method was used, and the vessel area density (VAD) and vessel skeleton density (VSD) were obtained. The area from the pupillary margin to the corneoscleral limbus was taken as the whole iris blood flow index, and the inner third near the pupillary margin of the whole iris was taken as the pupillary margin blood flow index. Results: This study enrolled 34 pediatric T1DM patients, 34 age-matched healthy children, 34 adult T2DM patients, and 34 age-matched healthy adults. The whole iris and pupillary margin VAD and VSD of the pediatric T1DM patients were not different from those of healthy children. The whole iris VAD and VSD of the adult T2DM patients were lower than those of healthy adults, and the pupillary margin VAD and VSD were the same in these two groups. Compared with adult T2DM patients, pediatric T1DM patients had higher whole iris VAD and VSD and lower pupillary margin VAD and VSD values, all with statistical significance. Among diabetic patients, age, BMI, and glycated hemoglobin level were negative independent influencing factors for whole iris VAD and VSD, and age was a positive influencing factor for pupillary margin VAD and VSD. Conclusion: There are diverse alterations in iris vessel density and blood flow distribution between pediatric T1DM patients and adult T2DM patients.

Quantitative changes in iris and retinal blood flow after femtosecond laser-assisted in situ keratomileusis and small-incision lenticule extraction.

PurposeTo investigate the quantitative changes in iris and retinal blood flow indices after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small-incision lenticule extraction (SMILE).MethodsSeventy-nine patients who underwent FS-LASIK or SMILE were enrolled between July 2020 and September 2020. Participants were followed-up 1 day pre-operatively and 1 week, 1 month, 3 months post-operatively. Optical coherence tomography angiography (OCTA) was used to acquire and quantify the iris and retinal blood flow indices.ResultsThe iris vessel area density (VAD) and vessel skeleton density (VSD) decreased on post-operative day 1 but recovered on day 7. In both cases, the pupil diameter was positively associated with the post-operative iris blood flow indices (p = 0.0013, p = 0.0002). The retinal VAD and VSD in the superficial and deep capillary plexuses decreased after surgery and failed to recover after 90 days. The SMILE group showed significantly lower iris and retinal blood flow indices than the FS-LASIK group. For both procedures, axial length (p = 0.0345, p = 0.0499), spherical equivalence (p = 0.0063, p = 0.0070), and suction duration (p = 0.0025, p = 0.0130) were negatively correlated with the post-operative VAD and VSD.ConclusionsThe SMILE and FS-LASIK procedures induced a short-term decrease in the iris and retinal blood flow indices, although patients finally showed full visual recovery. This phenomenon should be carefully considered, especially in patients prone to anterior segment lesions.

The influence of new beta-adrenolytics nebivolol and carvedilol on intraocular pressure and iris blood flow in rabbits

BackgroundThe aim of this study was to assess the influence of propranolol, nebivolol, and carvedilol on intraocular pressure and blood flow in vessels of rabbit’s (New Zealand White) eyeball.MethodsThe study was carried out on New Zealand white rabbits. Intraocular pressure was measured with the applanation tonometer Möller–Wedel and Icare; blood flow was measured with Doppler Laser Blood Flow Monitor MBD3.ResultsFollowing a single administration into a conjunctival sac, all drugs decreased intraocular pressure. Iris blood flow was decreased following administration of propranol, but increased by nebivolol and carvedilol. After single and repeated oral administration of nebivolol and carvedilol an IOP decrease was demonstrated, but with no effect of all applied doses on iris or retina/choroid blood flow.ConclusionStudies performed on an animal model indicate that it is possible to reduce the intraocular pressure and increase ocular blood flow in humans, following topical administration of carvedilol and nebivolol. Confirmation of those results in clinical trials may lead to development of a new anti-glaucoma treatment. Further clinical studies of long-term nebivolol and carvedilol are recommended. They are necessary for evaluation of usefulness of those drugs for selected groups of patients, for example those with glaucoma and arterial hypertension.

Long-term effects of oral vitamin C supplementation on the endothelial dysfunction in the iris microvessels of diabetic rats

The current study was aimed to investigate effects of long-term supplementation of vitamin C on the iris microcirculation in streptozotocin (STZ)-induced diabetic rats. Diabetes was induced in male Wistar-Furth rats by intravenous injection of STZ (55 mg/kg b.w.). The rats were divided into three groups: control rats (CON), STZ-induced diabetic rats (STZ), and STZ rats supplemented with vitamin C (STZ-vitC). For supplementation of vitamin C, ascorbic acid (1 g/l) was added into the drinking water. The experiments were performed at different periods (8, 12, 24 and 36 weeks) after injection of STZ. Blood glucose, tissue lipid peroxidation and plasma vitamin C were measured. To examine the endothelial function, leukocyte adhesion to the venular endothelium was evaluated in the iris post-capillaries by means of counting the number of leukocytes labeled with rhodamine 6G. Blood flow perfusion in the iris was monitored using a laser Doppler flow meter. In the STZ rats, hyperglycemia was induced with an increase in HbA 1c and lipid peroxidation but with a decrease in the plasma vitamin C level which improved by vitamin C supplementation. The number of adherent leukocytes increased significantly, associated with reduction in the iris blood flow perfusion, at 8, 12, 24 and 36 weeks after injection of STZ. In the STZ-vitC rats, the iris blood flow perfusion was significantly increased in comparison with the STZ rats, while the leukocyte adhesion was decreased at 24 and 36 weeks. The statistical analysis shows that the leukocyte adhesion decreased with increase in the iris blood flow perfusion in STZ and STZ-vitC rats. In conclusion, vitamin supplementation suppressed leukocyte adhesion and thus endothelial dysfunction, associated with increase in iris blood flow perfusion in diabetes. The antioxidant vitamin C may be a therapeutic agent for preventing diabetic retinopathy.

Effects of N-nitropyrazoles on ocular blood flow of rabbits and retinal function recovery of rat eyes after ischemic insults.

Twelve compounds of N-nitropyrazoles were studied for their effects on ocular blood flow in rabbits and retinal function recovery in rat eyes after ischemic insults. Of the twelve N-nitropyrazoles examined, nine increased choroidal blood flow while five increased retinal blood flow significantly. On the other hand, all twelve compounds increased blood flow in iris and ciliary muscle without exception. As for retinal function recovery after ischemic insult in rat eyes, eight out of the twelve compounds showed more significant facilitation than the control. The structure activity relationship of the N-nitropyrazoles to increase ocular blood flow and to facilitate retinal function recovery after ischemic insults were discussed.

Iris Blood Flow Response to Acute Decreases in Ocular Perfusion Pressure: A Laser Doppler Flowmetry Study in Humans

The relationship between blood flow and ocular perfusion pressure in the iris vascular bed of the human eye has not been established yet. Consequently, it is not known whether the iris circulation has some autoregulatory capacity. The aim of the present study was to investigate this relationship in the particular case where the perfusion pressure was decreased by increasing the intraocular pressure.Using laser Doppler flowmetry, mean velocity, volume and flow of blood through the iris were measured in normal subjects during acute decreases of the mean ocular perfusion pressure induced by raising the intraocular pressure with a scleral suction cup. Two experimental paradigms were applied. In the first, the suction pressure was rapidly increased from baseline, in steps of 50–100 mmHg, to a level where the intraocular pressure was above the mean ophthalmic artery blood pressure. In the second, the suction pressure was increased from baseline in four successive steps of 50 mmHg each. The suction pressure was kept constant for 2 min at each step.With the first paradigm (nine eyes), a 72% decrease in perfusion pressure induced a 63% decrease of iris blood flow due mainly to a drop in blood velocity. Immediately after suction release, blood flow increased by 62% above baseline and then returned to its baseline value within 2 min. With the second paradigm (six eyes), a 28% decrease in perfusion pressure resulted in a 30% flow reduction, which was due to significant decreases (P<0.001) of both blood volume and velocity. Combining the results of both paradigms, we observed a significant linear correlation between iris blood flow and perfusion pressure (R =0.964, P<0.001). These results demonstrate that a decrease of the perfusion pressure due to an increase of the intraocular pressure induces a decrease of the iris blood flow. No evidence of an autoregulatory process in the iris vascular bed could be demonstrated. A reactive hyperemia was observed in response to a sudden increase in perfusion pressure occurring after a period of decreased blood flow.

Effect of decreased ocular perfusion pressure on iris blood flow measured by laser Doppler flowmetry

To determine whether iris blood flow (IBF) is regulated in response to an acute decrease in mean ocular perfusion pressure (PPm = MOAP-IOP, MOAP = mean ophthalmic arterial pressure) induced by increasing the intraocular pressure (IOP). Iris blood flow was measured using a slit lamp incorporating a laser Doppler flowmetry (LDF) module. The study was conducted on 12 normal volunteers (14 to 59 years old). IOP was raised using a scleral suction cup. In Exp. #1, the suction pressure was successively raised in steps of 50 to 100 mm Hg, each lasting about 10 sec, until IOP reached the MOAP level. In Exp. #2, the suction was raised to 200 mm Hg in 4 successive steps of 2 min duration. In Exp. #1, no significant change of IBF was observed for small decreases of PPm (< 23%); greater decreases of PPm resulted in a linear IBF decrease (p < 0.01). In Exp. #2, such a IBF versus PPm decrease was also observed (p < 0.001). Immediately after release of suction, a significant, transient IBF increase of 79% above baseline level was observed. These results suggest that some IBF regulation occurs for small PPm decreases (< 23%); no IBF compensatory mechanism appears to operate for further decreases of PPm (> 23%).

Ocular Blood Flow and Vascular Permeability in Endotoxin-Induced Inflammation

Blood flow was measured in several tissues of the rabbit eye following intravitreal injection of a dose of endotoxin that induces an inflammatory response. In separate experiments, the vascular permeability of the inflamed eye was estimated by iris fluorescein angiography and by measuring protein influx into the aqueous humor. The effect of topical corticosteroid treatment upon blood flow and vascular permeability was also measured. Following intravitreal endotoxin injection, minor changes in blood flow occurred in retina and optic nerve head. Marked changes were observed in blood flow in iris, ciliary processes, and choroid. Steroid treatment had no effect upon the increased blood flow 24 h after the endotoxin injection, although from a clinical standpoint the steroid-treated eyes appeared less inflamed. Fluorescein angiography demonstrated a massive increase in iris vessel permeability 6 and 24 h following endotoxin injection. Topical steroid treatment reduced fluorescein entry into the anterior chamber at both time periods. On the other hand, the increase in protein influx into the aqueous humor in the endotoxin-inflamed eye was not inhibited by steroid pretreatment. It is suggested that corticosteroids have a selective effect upon the permeability of different components of the blood-aqueous barrier, namely the ciliary processes and the iris vasculature.

Responses of intraocular pressure and iris blood flow to the administration of vasopressins

Responses of intraocular pressure and iris blood flow to the administration of vasopressins

Responses of iris blood flow to stimulation of the cervical sympathetic in the rabbit

o (1) The effects of α- and β-blocking agents (phentolamine and propranolol) on the responses of iris vessels to stimulation of the cervical sympathetic in albino rabbits were studied. Vascular responses were expressed in terms of percentage changes of vascular heat dissipation ( Cole and Rumble, 1970 ). (2) Using square wave stimulation at 21 Hz there was a linear relationship of vascular response to stimulus intensity and the action of the antagonists was shown by alterations in the slope of the stimulus/response line. (3) Phentolamine given by close arterial infusion, intravitreal injection or transcorneal iontophoresis markedly diminished the response to sympathetic stimulation but propranolol had little or no effect. In further experiments the log dose response curves to exogenous noradrenaline and isoprenaline showed the action of noradrenaline to be enhanced 24 hr after superior cervical ganglionectomy whilst the isoprenaline response was unchanged. (4) The experiments with blocking agents suggested the β-receptor sites subserved little or no part in the response to sympathetic stimulation. The ganglionectomy experiments indicate that sites in the iris responsible for isoprenaline uptake are either absent or extraneuronal.