Retinal Vessel Diameter Changes Research Articles

Dynamic Changes in Retinal Vessel Diameters and Arteriovenous Ratio within 10 Days of Birth

Purpose This study monitored the dynamic changes in retinal vascular width and the AVR in full-term neonates within 1–10 days of birth. Methods It was conducted at hospitals in the Anhui province from October 2020 to March 2022. A total of 700 full-term, healthy infants were chosen randomly within 10 days of birth, and the Star Pupil Medical Cloud Data System (XBDS) was used to collect fundus images. Infants within 6 days of birth were grouped into groups one to six, while those within the 7th to 10th days were grouped into group seven. The fundus photographs were imported into Image-Pro-Plus (IPP) software. The optic disc diameter was measured. The retinal artery and vein’s diameter was measured at a distance between 0.5- and 1.0-disc diameter from the optic disc’s margin. The AVR was also calculated. Finally, each group’s retinal vessel diameters and AVR were compared separately to show their dynamic changes. Results There were differences in the retinal artery diameter between groups one and two, three and four, four and five, and five and six. For retinal vein diameter, there were differences between groups one and two and groups six and seven. There were also differences in the AVR between all groups. In addition, there was a significant positive correlation between the small retinal artery and vein diameters. Conclusion The retinal artery and vein diameters and AVR in neonates change dynamically during the first 10 days of life. The AVR undergoes the most dramatic change daily and is considerably smaller than the AVR in adults. Hence, this study found that the external environment undergoes significant changes following birth that affect the microcirculation. Then, the retinal central vascular system undergoes similar emergency and adaptive alterations.

Short-term effect of angiotensin-converting enzyme inhibitor on retinal vessel diameter in patients with systemic hypertension

Purpose To determine the retinal vessel diameter changes after angiotensin-converting enzyme (ACE) inhibitor treatment in a group of hypertensive patients. Methods This study included 60 treatment-naive hypertensive patients who were treated with ACE inhibitor. Sixty healthy volunteers served as control group. An optical coherence tomography scan protocol including the measurement of peripapillary retinal vessel diameters was performed at baseline and at 1st month. The diameters of superior temporal artery (STA), inferior temporal artery (ITA), superior temporal vein (STV), inferior temporal vein (ITV), superior nasal artery (SNA), inferior nasal artery (INA), superior nasal vein (SNV) and inferior nasal vein (INV) were statistically compared. Results The baseline diameters of the STA, ITA, SNA, and INA were significantly decreased in the patient group compared with the control group (all p < 0.05). There was a significant increase at 1st month after the treatment in comparison to baseline measurements (all p < 0.05). When compared with the controls, only the diameter of SNV showed a significant decrease at baseline (p = 0.031). After the treatment, the diameters of SNV and INV were significantly increased compared with baseline measurements (p = 0.049 and p = 0.035, respectively). There were no significant differences between the control group and the patient group at 1st month (all p > 0.05). Conclusion Short-term treatment with ACE inhibitor led to a significant improvement in the retinal vessel diameters of patients with hypertension.

Retinal Vessel Diameter Changes in COVID-19 Infected Patients

ABSTRACT Purpose: To evaluate the longitudinal changes in retinal vessel diameters in patients with coronavirus disease 2019 (COVID-19). Methods: This study included 25 patients with COVID-19 (Group 1) and 25 healthy subjects (Group 2). The diameters of peripapillary temporal and nasal retinal arteries and veins were measured at baseline and at 4 months after remission. Results: The baseline diameters of the inferior temporal vein and the artery were increased in group 1 compared to controls (p = .007 and p = .041, respectively). There was also an increase in the diameters of the inferior and superior nasal veins and arteries in group 1 at baseline (p = .001, p = .019, p = .037, and p = .008, respectively). Retinal vessel diameters decreased after remission in all quadrants in comparison to baseline measurements (all p < .05). Conclusion: Increased retinal vessel diameters were measured in COVID-19 patients during the disease. Measurement of retinal vessel diameters may be a noninvasive method of estimating the vascular risk.

Changes in oxygen saturation and the retinal nerve fibre layer in patients with optic neuritis associated with multiple sclerosis in a 6-month follow-up.

PurposeOptic neuritis (ON) is an inflammatory demyelinating disorder of the optic nerve, which can be the first manifestation of multiple sclerosis (MS). The main goal was to assess changes in the retinal nerve fibre layer (RNFL) and in retinal oxygen saturation [arterial (AS), venous (VS) and arterio‐venous (A‐V) difference] in the affected and unaffected eye.MethodsFifty patients with ON due to MS within 3 months of onset of symptoms were enrolled (17 males, mean age 35.3). All patients were examined at baseline (V1) and after 6 months (V2) using optical coherence tomography (OCT) to get RNFL values; automatic retinal oximetry to obtain saturation values; and ultrasound to exclude arterial stenosis, and orbital colour Doppler imaging was performed in the ophthalmic artery.ResultsAt V1, AS was significantly increased in affected eye compared to unaffected eye (99.5% versus 98.0%, p = 0.03). Significant decrease in A‐V difference from baseline was detected in both eyes for ON eye: 32.0% versus 29.0%, p = 0.004; for fellow eye: 31.4% versus 30.0%, p = 0.04. We did not observe any changes in retinal vessel diameter. There were no changes observed in blood flow in ophthalmic artery. At V1, there were no significant differences in RNFL, and significant loss of RNFL was confirmed in the affected eye at V2 (95 μm versus 86 μm, p = 0.0002) and in comparison with the fellow eye (86 μm versus 94 μm, p = 0.0002). There were no correlations between RNFL and saturation values at V1, although at V2, there was a negative correlation between the RNFL and AS (Spearman's rho = −0.480, p = 0.003) and between the RNFL and VS (rho = −0.620, p = 0.00007).ConclusionRetinal oximetry is altered in both eyes in MS patients with unilateral ON. During the course of the disease, the retinal oxygen consumption decreases to a different degree in each eye and this change is not completely followed by changes in the RNFL thickness, suggesting either sub‐clinical ON or systemic effects in the clinically unaffected eye. Since this is the first and initial longitudinal evaluation of the saturation changes in MS patients, the clinical value of these findings needs to be deeper evaluated in the future studies.

Retinal vessel diameter changes after 6 months of treatment in the Idiopathic Intracranial Hypertension Treatment Trial

Background/AimsPrior studies support an association between increased retinal venule diameter and elevated intracranial pressure (ICP). The purpose of this study was to test the hypothesis that retinal venule diameters decrease...

Ramazan Orucunun Vasküler Retina ve Ön Kamara Parametrelerine Etkisi

Aim: In this study, we aimed to evaluate the effects of Ramadan fasting on retinal vascular and anterior chamber parameters. Materials and Methods: The study included 60 healthy eyes of 30 volunteers (15 males, 15 females) who visited our clinic between May and July 2017. We performed measurements of intraocular pressure (IOP), anterior chamber volume (ACV), central corneal thickness (CCT), central macular thickness (CMT), optic disc retinal nerve fiber layer (OD-RNFL) and subfoveal choroidal thickness (SFCT) and retinal vascular analysis (the central retinal artery equivalent [CRAE], central retinal vein equivalent [CRVE], and artery-to-vein ratio [AVR]). The measurements were repeated in the 4th and 12th hours of the daily fasting period and 1st postprandial hour on the last 5 days of the Ramadan month, and one month after the Ramadan month. Results: The mean participant age was 29.30±8.12 years. The twelfth-hour SFCT, CRAE, and CRVE measurements were statistically significantly lower than the values measured one month after Ramadan (p=0.033, p=0.020, p=0.025, respectively). However, no statistically significant difference was observed in the IOP, ACV, CCT, CMT, OD-RNFL, and AVR measurements. Discussion and Conclusion: We found that fasting for 12 hours or longer caused changes in retinal vessel diameter and choroidal thickness.

Acute and chronic effects of soccer game on the retinal vessel diameters in middle-aged adults.

Although changes in retinal vessel diameter is a new biomarker for the evaluation of cardiovascular risk factors, limited information is available regarding the effects of endurance exercises on retinal microcirculation. Thus, we aimed to evaluate both chronic and acute effects of soccer game on the diameters of retinal vessels in middle-aged players. Retinal vessel diameters were measured in 12 middle-aged amateur players (44.4±7.0 years of age) with more than four years of soccer playing experience and 12 age-matched sedentary adults (49.7±7.1 years of age). In soccer players, diameters were also measured immediately after the soccer game. Cardiovascular risk profiles (anthropometry and body composition and blood pressure [BP]) and physical activity levels were also measured. Soccer players had wider retinal vessels than controls (P<0.05), resulting in greater arteriolar-to-venular diameter ratio (AVR) (P<0.05). Greater sports-related physical activity, lower body mass index (BMI) and fat mass were observed for soccer players compared to the controls (P<0.05), whereas BP did not differ. Physical activity level correlated positively with temporal retinal arteriolar (TRA) diameter and with AVR (P<0.05), whereas TRA diameter correlated negatively with BMI and fat mass (P<0.05). A significant correlation between temporal retinal venule (TRV) diameter and TRA diameter (P<0.05) was observed. The acute soccer game increased BP (P<0.05) and induced TRV dilatation (P<0.05). In middle-aged amateur soccer players, improvement of the retinal microcirculation was observed. Cardiovascular risk factors and physical inactivity were associated with adverse retinal microvascular alterations. In terms of acute effects, soccer play causes venular, but not arteriolar dilatation for middle-aged adults.

Retinal Vessel Diameter Changes in Relation to Dark Adaptation and Acute Hyperglycemia.

The purpose of this experimental clinical study was to assess the effects of dark adaptation and acute changes in glycemia on retinal vessel diameters in men. The study included 14 patients (mean age 63 years, range 48–74 years) with type 2 diabetes mellitus and minimal or no diabetic retinopathy. Retinal vessel diameters were assessed using infrared photography before and after dark adaptation, first while fasting and then at peak hyperglycemia during an oral glucose tolerance test (OGTT). Dark adaptation was accompanied by retinal vasodilatation, both during fasting (mean glycemia 7.6 ± 1.7 mM) and postprandial hyperglycemia (15.7 ± 4.2 mM). When fasting, the increase in vein diameter during dark adaptation was 2.0% after 20 min (P=0.018) and 2.9% after 40 min (P=0.010). When subjects were hyperglycemic, the increase during dark adaptation was 2.8% for retinal vein diameters (P=0.027) and 2.0% for retinal artery diameters after 20 min (P=0.002) and 1.7% for retinal artery diameters after 40 min (P=0.022). For identical conditions of light/dark adaptation, retinal vessels were dilated when subjects were fasting compared to postprandial hyperglycemia. Thus, darkness and fasting were both associated with retinal vasodilation in this short-term experiment in patients with type 2 diabetes. Future studies should determine whether both the stimuli of vasodilation lead to retinal hyperperfusion, which would support that they may be involved in the aggravation of diabetic retinopathy.

Effects of different endurance exercise modalities on retinal vessel diameters in unipolar depression

BackgroundPsychiatric disorders are associated with a high prevalence of cardiovascular disease. Regular exercise is known to reduce depressive symptoms and improve vascular function, in turn lowering cardiovascular risk. We aimed to investigate the effects of different exercise modalities on retinal vessel diameters as a microvascular biomarker and depression severity index in patients suffering from unipolar depression. Methods23 patients (female: 19, male: 4, age: 36.7, Beck-Depression-Inventory-II (BDI-II) score: 30.7) were enrolled in this two-armed randomized controlled trial. Static vessel analysis was performed to obtain central retinal arteriolar (CRAE) and venular (CRVE) diameter equivalents and the arterio-venous diameter ratio (AVR). Maximal bicycle ergometer exercise testing yielded maximal fitness parameters. Patients were assigned to either high intensity low volume (HILV) or moderate continuous aerobic training (MCT). Both intervention groups trained three times a week during a 4-week intervention period. ResultsModerate interaction effects were found for AVR (ɳp2 = 0.12) whereby HILV showed a larger increase in AVR (HILV: pre: 0.89 (0.04), post: 0.91 (0.04), SMD = −0.50) compared to MCT (MCT: pre: 0.85 (0.06), post: 0.86 (0.05), SMD = −0.18). Parallel group trials revealed a 67% possibly beneficial effect of HILV over MCT. Moderate interaction effects on depression severity reduction (ɳp2 = 0.06) were found, whereby the effect size was slightly larger in MCT. ConclusionBoth exercise interventions improved AVR as well as BDI-II. HILV may be more effective in improving cerebrovascular health. The exercise-induced effects on retinal vessel diameter changes were relatively small and the clinical relevance remains to be investigated in larger and longer-term exercise trials.

Dynamic changes in retinal vessel diameter during acute hyperglycemia in type 1 diabetes

AimsTo investigate changes in retinal vessel diameter during acute hyperglycemia in patients with type 1 diabetes. MethodsWe conducted a study on 11 subjects with type 1 diabetes. Euglycemia was maintained for 3h followed by induction of hyperglycemia and simultaneous bolus of rapid acting insulin. Two fundus photos were captured during euglycemia and five fundus photos, blood glucose and blood pressure were taken every 30min for 2.5h post-prandial. Central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE) were measured over the study visit and examined using generalized linear mixed models. ResultsIn a multivariate mixed model, mean CRAE and CRVE were reduced at 90min post-prandial in both zones B and C. In repeated measures analysis, arterioles exhibited a significant association with change in vessel caliber per change in blood glucose. Inconsistent effects of blood pressure on vessel diameter were also measured. ConclusionsWe document a change in retinal vessel diameter during acute hyperglycemia in persons with type 1 diabetes. Larger controlled studies are required to further investigate this phenomenon and to more accurately assess if hyperglycemia has direct effects on retinal vessel diameter.

Changes in retinal vessel diameters after intravitreal aflibercept in patients with diabetic macular edema

PurposeTo evaluate changes in retinal vessel diameters after loading doses with intravitreal aflibercept in patients with diabetic macular edema (DME).MethodsThis was a three months prospective, interventional study. We included 17 patients with DME, central retinal thickness &gt;300 μm and no active proliferative diabetic retinopathy. Previous treatment with any intravitreal vascular endothelial growth factor inhibitor was not allowed within 4 months prior to inclusion. All patients received 3 monthly intravitreal injections of aflibercept, and vessel diameters were evaluated at baseline and four weeks after the last injection. Retinal arterial and venous diameters were measured in 50‐degree disc‐centered images using the Oxymap model T1 (Oxymap, Reykjavik, Iceland) as the average diameter of the four major arterioles and venules from the four quadrants. Paired t‐test was used to test for differences in mean oxygen saturations from baseline to follow‐up.ResultsMedian age and duration of diabetes were 59.5 and 2.6 years at baseline. Median HbA1c and CRT were 65 mmol/mol and 336 μm, respectively, and 23.5% were women. Venous diameter decreased from baseline to follow‐up (157.9 μm vs. 153.2 μm, p = 0.03), whereas arterial diameter was unchanged (115.4 μm vs. 116.1, p = 0.70).ConclusionsRetinal venous diameter decreased after treatment with 3 monthly intravitreal injections of aflibercept in patients with DME, whereas no difference was found in the retinal arterial diameter. As previous studies have demonstrated that retinal venules dilate with increasing severity of diabetic retinopathy, our results suggest that treatment with intravitreal aflibercept causes positive changes to retinal vessel geometry.

Recent versus chronic fine particulate air pollution exposure as determinant of the retinal microvasculature in school children

BackgroundMicrovascular changes may represent an underlying mechanism through which exposure to fine particulate matter with a diameter ≤ 2.5µm (PM2.5) contributes to age-related disease development. We investigated the effect of recent and chronic exposure to PM2.5 on the microcirculation, exemplified by retinal vessel diameters, using repeated measurements in 8- to 12-year-old children. Methods221 children (49.1% girls; mean age 9.9 years) were examined repeatedly (25 one, 124 two, and 72 three times) adding up to 489 retinal vessel examinations. Same-day exposure to PM2.5 was measured at school. In addition, recent (same and previous day) and chronic (yearly mean) exposure was modelled at the child's residence using a high-resolution interpolation model. Residential proximity to major roads was also assessed. Changes in retinal vessel diameters associated with recent and chronic exposures were estimated using mixed models, while adjusting for other known covariates such as sex, age, BMI, blood pressure and birth weight. ResultsEach 10µg/m³ increment in same-day exposure to PM2.5 measured at school was associated with 0.35µm (95% CI: 0.09–0.61µm) narrower retinal arterioles and 0.35µm (−0.03 to 0.73µm) wider venules. Children living 100m closer to a major road had 0.30µm (0.05–0.54µm) narrower arterioles. ConclusionsBlood vessel diameters of the retinal microcirculation of healthy school-aged children respond to same-day PM2.5 exposure. Furthermore, children living closer to major roads had smaller arteriolar diameters. Our results suggest that the microcirculation, with retinal microvasculature as a proxy in this study, is a pathophysiological target for air pollution in children.

Changes in retinal vessel diameters in migraine patients during attack-free period.

To evaluate the retinal vessel diameters in patients with migraine by optical coherence tomography (OCT). In this cross-sectional study, 124 eyes of 62 patients with a diagnosis of unilateral migraine during attack-free period and 42 age- and sex-matched control subjects were included. Migraine patients were divided into the ≤2 migraine attacks per month group and the ≥5 migraine attacks per month group. All subjects underwent complete ophthalmological and neurological examinations before measurements. Retinal vessel diameters and choroidal thickness were examined with the Spectralis OCT. The mean diameters of the arteries in the eyes on the headache side of control group, ≥5 migraine attacks per month and ≤2 migraine attacks per month group at 480 µm from the optic disk (Raster 3) were 119.54±46.69, 136.68±25.93 and 119.34±31.75 µm respectively with a steady decline to 105.57±32.15, 118.18±31.87 and 108.05±38.77 µm at 1440 µm (Raster 7), the last measurement point, respectively. The retinal artery diameter measurements were significantly increased in ≥5 migraine attacks per month patients at four out of five measured points compared to control group (P<0.05). There were no statistical differences at any of the points of vein measurements. The choroidal thickness measurements were significantly decreased in ≥5 migraine attacks per month patients at all measured points compared to control group (P<0.05). The retinal artery diameter is found to increase significantly and the choroidal thickness is found to decrease in the eyes on the headache side in ≥5 migraine attacks per month patients compared to control group.

Surgically induced changes in retinal vessel diameter, retinal nerve fibre layer thickness, and the optic disc after 23-gauge pars plana vitrectomy.

The aim of the study is to investigate the retinal vascular calibre, retinal nerve fibre layer's thickness, and optic disc changes in patients after pars plana vitrectomy. We examined 40 eyes in 40 patients who had undergone unilateral pars plana vitrectomy at three time points: prior to surgery, and at 3 and 6months after the operation. The diameters of central retinal arteries and veins were measured using retinal photographs. The central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE) were calculated using the revised Parr-Hubbard formula. Retinal nerve fibre layer thickness was obtained using Stratus optical coherence tomography. The cup-to-disc vertical ratio of the optic disc was evaluated using stereo optic disc photography. There were no significant differences between the eyes of individual patients before the operation. Cup-to-disc vertical ratios of the optic disc were significantly increased 3 and 6months postoperatively (p<0.01, p<0.01), and there was a significant difference between the operative eye and fellow eye at the same time points (p<0.01, p<0.01). Changes in CRAE and CRVE in the operative eyes were significantly larger than the fellow eyes 6months postoperatively (p<0.01, p<0.01). The retinal nerve fibre layer thickness showed no significant changes. While there were no changes in retinal nerve fibre layer thickness, vitrectomy induced changes in the cup-to-disc vertical ratio of the optic disc and retinal vessel diameter for at least 6months after surgery.

The Time Course of Changes in Retinal Vessel Diameter in Response to Differing Durations of Flicker Light Provocation.

To determine the response of retinal vessels to differing durations of flicker light (FL) stimulation. We recorded retinal arterial and venous vessel dilation to 12.5 Hz FL provocation of varying duration (5, 7, 10, and 20 seconds) in 12 healthy young individuals (age range, 26-45 years). All participants underwent a full ocular examination including IOP and blood pressure measurements. Maximum dilation (MD) did not show a significant dependence on flicker duration in arteries, whereas maximum constriction (MC) did. In veins, however, MD significantly increased with flicker duration. Approximately 80% to 90% of MD in arteries is reached within 10 seconds of FL stimulation. The vast majority of arterial dilatory capacity is reached within 10 seconds of FL stimulation even though venous dilation continues strongly. Since MC of arteries shows a significant dependence on flicker duration, measurements at two different durations can provide more information about the retinal vascular system than at a single flicker duration alone.

Retinal vessel diameter changes in different severities of diabetic retinopathy by SD-OCT.

To evaluate retinal vessel diameters in relation to different severity grades of diabetic retinopathy (DR) using spectral-domain optical coherence tomography (SD-OCT). Patients with varying degrees of nonproliferative DR (NPDR) underwent circular OCT scans centered on the optic nerve head using a SD-OCT. These cases were retrospectively reviewed. The presence and severity of DR was assessed using Early Treatment Diabetic Retinopathy Study protocols. The 5 largest retinal arterioles and venules were labeled and measured on OCT scans for each patient according to previously published methods. Vertical vessel inner contour diameter, vertical vessel outer contour diameter, and reflectance shadowing width were among the documented parameters. Of 59 eyes from 45 patients examined, 30 (50.2%) and 29 (49.8%) had mild and severe NPDR, respectively. Eyes with severe NPDR had narrower mean arteriolar vertical vessel inner diameter (87.9 ± 10.8 μm), vertical vessel outer diameter (119.1 ± 9.7 μm), and vessel shadow width (78.8 ± 10.9 μm) than eyes with mild NPDR (89.8 ± 12.1 μm, 120.9 ± 12.9 μm, 81.3 ± 15.3 μm). However, the differences were not statistically significant (p = 0.53, 0.55, 0.47). No correlation was shown between the severity of NPDR and arteriolar parameters (p = 0.31, 0.59, 0.75). Wider venular diameters were associated with increasing severity of NPDR (p&lt;0.001, &lt;0.001, 0.007, respectively). The association remained after multivariate adjustment for age, sex, eye, and cataract surgery (p = 0.04, 0.01, 0.007, respectively). Wider retinal venule diameter was significantly associated with the severity of NPDR by SD-OCT-assisted measurement. Prospective studies would be needed to evaluate whether change in retinal venule could be used as a clinical indicator of DR progression.

Ageing effect on flicker-induced diameter changes in retinal microvessels of healthy individuals.

PurposeTo compare flicker‐induced retinal vessel diameter changes in varying age groups with low cardiovascular risk.MethodsRetinal vascular reactivity to flicker light was assessed by means of dynamic retinal vessel analysis in 57 participants aged 19–30 years, 75 participants aged 31–50 years and 62 participants aged 51–70 years participants. Other assessments included carotid intima–media thickness (c‐IMT), augmentation index (AIx), blood pressure profiles, blood lipid metabolism markers and Framingham risk scores (FRS).ResultsRetinal arterial dilation amplitude (DA) and postflicker percentage constriction (MC%) were significantly decreased in the oldest group compared to the middle‐aged (p = 0.028; p = 0.021) and youngest group (p = 0.003; p = 0.026). The arterial constriction slope (SlopeAC) was also decreased in the oldest group compared to the youngest group (p = 0.027). On the venous side, MC% was decreased in the middle‐aged and oldest groups in comparison with the youngest group (p = 0.015; p = 0.010, respectively). Additionally, men exhibited increased arterial DA (p = 0.007), and percentage dilation (MD%, p < 0.001) in comparison with women, but only in the youngest age group. Both AIx and c‐IMT scores increased with age (both p < 0.001); however, no correlations were found between the observed differences in the measured retinal vascular function and systemic parameters.ConclusionIn individuals with low cardiovascular risk, there are age‐related differences in flicker‐induced retinal vessel diameter changes throughout the entire functional response curve for arteries and veins. Gender differences mainly affect the arterial dilatory phase and are only present in young individuals.

Regulation of blood flow in the retinal trilaminar vascular network.

Light stimulation evokes neuronal activity in the retina, resulting in the dilation of retinal blood vessels and increased blood flow. This response, named functional hyperemia, brings oxygen and nutrients to active neurons. However, it remains unclear which vessels mediate functional hyperemia. We have characterized blood flow regulation in the rat retina in vivo by measuring changes in retinal vessel diameter and red blood cell (RBC) flux evoked by a flickering light stimulus. We found that, in first- and second-order arterioles, flicker evoked large (7.5 and 5.0%), rapid (0.73 and 0.70 s), and consistent dilations. Flicker-evoked dilations in capillaries were smaller (2.0%) and tended to have a slower onset (0.97 s), whereas dilations in venules were smaller (1.0%) and slower (1.06 s) still. The proximity of pericyte somata did not predict capillary dilation amplitude. Expression of the contractile protein α-smooth muscle actin was high in arterioles and low in capillaries. Unexpectedly, we found that blood flow in the three vascular layers was differentially regulated. Flicker stimulation evoked far larger dilations and RBC flux increases in the intermediate layer capillaries than in the superficial and deep layer capillaries (2.6 vs 0.9 and 0.7% dilation; 25.7 vs 0.8 and 11.3% RBC flux increase). These results indicate that functional hyperemia in the retina is driven primarily by active dilation of arterioles. The dilation of intermediate layer capillaries is likely mediated by active mechanisms as well. The physiological consequences of differential regulation in the three vascular layers are discussed.

Retinal vessel diameter changes induced by transient high perfusion pressure.

To investigate the effects of transient high perfusion pressure on the retinal vessel diameter and retinal ganglion cells. The animals were divided into four groups according to different infusion pressure and infusion time (60 mm Hg-3min, 60 mm Hg-5min, 100 mm Hg-3min, 100 mm Hg-5min). Each group consisted of six rabbits. The left eye was used as the experimental eye and the right as a control. Retinal vascular diameters were evaluated before, during infusion, immediately after infusion, 5min, 10min and 30min after infusion based on the fundus photographs. Blood pressure was monitored during infusion. The eyes were removed after 24h. Damage to retinal ganglion cell (RGC) was analyzed by histology. Retina became whiten and papilla optic was pale during perfusion. Measurements showed significant decrease in retinal artery and vein diameter during perfusion in all of the four groups at the proximal of the edge of the optic disc. The changes were significant in the 100 mm Hg-3min group and 100 mm Hg-5min group compared with 60 mm Hg-3min group (P1=0.025, P2=0.000). The diameters in all the groups recovered completely after 30min of reperfusion. The number of RGC showed no significant changes at the IOP in 100 mm Hg with 5min compared with contralateral untreated eye (P>0.05). Transient fluctuations during infusion lead to temporal changes of retinal vessels, which could affect the retinal blood circulation. The RGCs were not affected by this transient fluctuation. Further studies are necessary to evaluate the effect of pressure during real-time phacoemusification on retinal blood circulation.

Effects of acute bouts of endurance exercise on retinal vessel diameters are age and intensity dependent

Alterations of retinal vessel diameters are associated with increased cardiovascular risk. We aimed to investigate changes in retinal vessel diameters in response to acute dynamic exercise of different intensities and whether these changes are age dependent. Seventeen healthy seniors (median (IQR) age 68 (65, 69) years) and 15 healthy young adults (median (IQR) age 26 (25, 28) years) first performed a maximal treadmill test (MTT) followed by a submaximal treadmill test (SMTT) and a resting control condition in randomised order. Central retinal arteriolar (CRAE) and central retinal venular (CRVE) diameter equivalents were measured before as well as 5 (t5) and 40 (t40) minutes after exercise cessation using a static retinal vessel analyser. Both exercise intensities induced a significant dilatation in CRAE and CRVE at t5 compared to the control condition (P < 0.001). At t40, the mean increase in CRAE and CRVE was greater for MTT compared to that for SMTT (CRAE 1.7 μm (95 % confidence interval (CI) −0.1, 3.6; P = 0.061); CRVE 2.2 μm (95 % CI 0.4, 4.1; P = 0.019)). However, the estimated difference at t5 between seniors and young adults in their response to MTT compared to SMTT was 5.3 μm (95 % CI 2.0, 8.5; P = 0.002) for CRAE and 4.1 μm (95 % CI −0.4, 8.6; P = 0.076) for CRVE. Wider arteries and veins after maximal versus submaximal exercise for seniors compared to young adults suggest that myogenic vasoconstriction in response to exhaustive exercise may be reduced in seniors. Age-related loss of vascular reactivity has clinical implications since the arteriolar vasoconstriction protects the retinal capillary bed from intraluminal pressure peaks.Electronic supplementary materialThe online version of this article (doi:10.1007/s11357-014-9650-3) contains supplementary material, which is available to authorized users.