Parasympathetic Dominance Decreases the Choroidal Blood Flow Velocity Measured Using Laser Speckle Flowgraphy

BACKGROUND

This study aimed to examine the changes to choroidal blood flow velocity using laser speckle flowgraphy (LSFG) in healthy eyes after warm water immersion at 40°C.

METHODS

Data regarding the right eyes of 23 healthy volunteers were included. The mean blur rate (MBR) of the macula, which represents the choroidal blood flow velocity, was evaluated using LSFG. Intraocular pressure (IOP), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean blood pressure (MBP), ocular perfusion pressure (OPP), and MBR were assessed at baseline, immediately after immersion (0 minutes), and 10, 20, and 30 minutes later.

RESULTS

At 0 minutes, SBP, DBP, MBP, and OPP values were lower than those at baseline. The MBR significantly declined immediately after immersion to -6.0 ± 5.2%. However, there were no changes in these parameters after 10, 20, or 30 minutes. A significant positive correlation was observed between the MBR, SBP, DBP, MBP, and OPP values. In healthy individuals, the dominant parasympathetic activity induced by warm stimulation reduced the choroidal hemodynamic rate in the macula and decreased systemic circulatory dynamics, which normalized after 10 minutes.

CONCLUSIONS

These findings suggest that the dominant parasympathetic activity induced by warm water immersion at 40°C may lead to a reduction in the systemic circulation rate and choroidal blood flow rate in the macula. These findings may help prevent and treat various retinal choroidal diseases, in which sympathetic hyperactivity is involved in the pathogenesis of the disease.

Changes in Choroidal Circulation Hemodynamics Measured Using Laser Speckle Flowgraphy after a Cold Pressor Test in Young Healthy Participants

Using laser speckle flowgraphy (LSFG), we investigated the time course of changes in choroidal circulation hemodynamics after a cold pressor test in healthy eyes. This prospective study included the right eye of 19 young healthy participants. The macular mean blur rate (MBR) was measured with LSFG. The MBR, intraocular pressure (IOP), systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), mean blood pressure (MBP), and ocular perfusion pressure (OPP) were evaluated at baseline; immediately after the test and 10, 20, and 30 min later. Immediately after the test (0 min), SBP, DBP, MBP, and OPP were significantly elevated compared with those at baseline. The macular MBR significantly increased by +10.3 ± 7.1% immediately after the test. However, there was no change after 10, 20, and 30 min in the above parameter. A significant positive correlation of the macular MBR with the SBP, MBP, and OPP was observed. In young healthy individuals, increased sympathetic activity induced by a cold pressor test increases choroidal hemodynamics in the macula along with an increase in systemic circulatory dynamics, which normalizes after 10 min. Therefore, LSFG may provide a novel approach for assessing sympathetic activity and intrinsic vascular responsiveness in the eye.

Decrease in Ocular Blood Flow Thirty Minutes After Intravitreal Injections of Brolucizumab and Aflibercept for Neovascular Age-Related Macular Degeneration

Purpose

Intravitreal injections of anti-vascular endothelial growth factor (VEGF) agents such as brolucizumab and aflibercept are used widely to treat neovascular age-related macular degeneration (nAMD); however; they may theoretically affect the ocular blood flow. We investigated the short-term changes in the ocular blood flow between eyes with nAMD treated with intravitreal brolucizumab injections (IVBr) and intravitreal aflibercept injections (IVA).

Methods

This study included 21 eyes of 21 Japanese patients with nAMD treated with either IVBr or IVA at Kurume University Hospital from April 2021 through June 2022. The rates of ocular blood flow at the optic nerve head (ONH mean blur rate [MBR]-vessel) and at the choroid (CHOR MBR) were analyzed before and 30 minutes after injections using laser speckle flowgraphy.

Results

In the IVBr-treated group, the ONH MBR-vessel and CHOR MBR rates decreased significantly by 10.6% and 16.9% from baseline to 30 minutes after IVBr, respectively. In the IVA-treated group, ONH MBR-vessel and CHOR MBR rates decreased significantly by 9.4% and 6.1% from baseline to 30 minutes after IVA, respectively. There was no significant difference in the rates of decrease in the ONH MBR-vessel or CHOR MBR between the IVBr-treated and IVA-treated groups.

Conclusion

Intravitreal injections of brolucizumab and aflibercept in eyes with nAMD cause significant decreases in ocular blood flow at the ONH and the choroid 30 minutes after injection. The rate of decrease in ocular blood flow was not significant between the eyes treated with brolucizumab and aflibercept. However, 3 of 10 eyes treated with brolucizumab but none of 11 eyes treated with aflibercept had more than a 30% decrease in the ocular blood flow at the choroid 30 minutes after injection.

Retinal Microvascular Resistance Estimated from Waveform Analysis Is Significantly Higher With a Threshold Value in Central Retinal Vein Occlusion

Purpose

Evaluation of blood flow is useful for understanding the severity of central retinal vein occlusion (CRVO). Actual blood flow may be determined by the resistivity of the retinal vein in CRVO. We have previously evaluated mean blur rate (MBR) to reflect total retinal blood flow velocity in CRVO cases using laser speckle flowgraphy (LSFG). This study evaluated retinal total vascular resistance in CRVO cases using the new index of total capillary resistance (TCR) from LSFG.

Methods

We measured the TCR of 68 CRVO patients who visited Nagasaki University Hospital between 2009 and 2016 and 42 age-matched controls without systemic disease. We compared TCRs among control eyes, CRVO fellow eyes, and CRVO affected eyes. A CRVO threshold value was then obtained from the receiver operating characteristic curve.

Results

MBR was significantly lower for CRVO affected eyes (20.3 ± 8.2) than for control eyes (37.5 ± 8.4; P < 0.01) and CRVO fellow eyes (36.4 ± 10.0; P < 0.01, Dunn's test). TCR was significantly higher for CRVO affected eyes (1.20 ± 0.55) than for control eyes (0.68 ± 0.2; P < 0.01) and CRVO fellow eyes (0.81 ± 0.28; P < 0.01, Dunn's test). The threshold for the presence of CRVO was 0.93 and area under the curve was 0.84.

Conclusions

By measuring TCR in addition to MBR, more detailed information regarding CRVO pathology can be obtained.

Translational Relevance

Comparison of values before and after treatment may be useful for evaluating the effects of treatment.

Evaluation of blood flow on optic nerve head after pattern scan and conventional laser panretinal photocoagulation

To evaluate the changes in the blood flow on retina and the optic nerve head (ONH) after conventional laser treatment and to compare it to that after patterned scanning laser (PASCAL) treatment in patients with severe nonproliferative diabetic retinopathy (S-NPDR).In this prospective, cross-sectional study, the blood flow on retina and the ONH was assessed by laser speckle flowgraphy using the mean blur rate (MBR) in 39 eyes with S-NPDR before, 1, 4, 8, 12 weeks after panretinal photocoagulation (PRP). Of 39 eyes, 17eyes with 17 patients treated by conventional laser and 22 eyes with 22 patients treated by PASCAL.The mean age was 55.5 ± 11.5 years in the conventional laser group, 55.6 ± 11.8 years in the PASCAL group. The MBR-vessel, which can be dominantly expressed as retinal blood flow, was significantly reduced after PRP treated by conventional laser (P < .001), but did not change after PRP treated by PASCAL. The ratio of MBR-vessel to the baseline was significantly lower in the conventional laser group only at Week 1 (P = .045). The MBR-tissue, which can be dominantly expressed as the ONH blood flow, did not significantly change after PRP in the both group. The multiple stepwise regression analysis revealed that the laser burns was an independent factor significantly correlated with the ratio of MBR-vessel at Week 1 to the baseline (β = -0.550, P = .012).The retinal blood flow was significantly reduced during the 12 weeks only after completion of PRP by conventional laser treatment. Our results indicate that short pulse on PRP treatment performed by the PASCAL would not significantly reduce the retinal blood flow.

Choroidal circulation impairment during the anterior recurrence of Vogt-Koyanagi-Harada disease confirmed with indocyanine green angiography and laser speckle flowgraphy

PURPOSE

To assess choroidal inflammation-related circulatory changes associated with the anterior recurrence of Vogt-Koyanagi-Harada (VKH) disease, using indocyanine green angiography (ICGA) and laser speckle flowgraphy (LSFG).

METHODS

This retrospective case series included 17 eyes of 11 patients with VKH disease showing recurrent inflammatory findings in the anterior, but not posterior, segment (i.e. anterior recurrence). Indocyanine green angiography (ICGA) and LSFG were performed at the time of recurrence and one month after the initiation of corticosteroid therapy. The number and total area of hypofluorescent dark dots (HDDs) on ICGA were independently counted by three physicians and measured with ImageJ, respectively. Mean blur rate (MBR), a quantitative index of relative blood flow velocity, was calculated via the LSFG Analyzer software.

RESULTS

Hypofluorescent dark dots (HDDs) were identified on ICGA in 13 of 17 eyes (76%) with the anterior recurrence of VKH disease. The number and total area of HDDs significantly decreased from 203 ± 101 dots to 59 ± 51 dots and from 48 789 ± 24 251 pixels to 15 664 ± 13 254 pixels, respectively. The change ratio of MBR significantly increased by 17.9 ± 16.3% after the treatment. Importantly, there was no significant association between the change ratios of HDDs and MBR.

CONCLUSIONS

These findings on LSFG and ICGA clearly demonstrated subclinical involvement as well as post-treatment improvement of choroidal circulation impairment due to granulomatous inflammation in eyes with the anterior recurrence of VKH disease. The present data suggest the validity of using these two examinations, capable of detecting different circulatory changes, in the management of recurrent VKH disease.

What ocular and systemic variables affect choroidal circulation in healthy eyes

The aim of the study was to investigate the relationship between choroidal blood flow and systemic and ocular variables in patients with healthy eyes.In this prospective cross-sectional study, we examined 241 eyes of 241 healthy Japanese subjects (92 males and 149 females; mean age, 37.8 ± 17.0 years). The mean blur rate, a measure of the relative blood flow of the choroid, was determined using laser speckle flowgraphy. The total cross-sectional choroidal, luminal, and stromal areas of the choroid were determined by the binarization method. We investigated the correlation between choroidal MBR and systemic and ocular variables.Choroidal mean blur rate correlated with age (r = -0.385, P < 0.001) and choroidal thickness (r = 0.264, P < 0.001). The choroidal area correlated with choroidal mean blur rate (r = 0.374, P < 0.001), age (r = -0.184, P = 0.004), axial length (r = -0.251, P < 0.001), and choroidal thickness (r = 0.468, P < 0.001). The luminal area correlated with choroidal mean blur rate (r = 0.403, P < 0.001), age (r = -0.244, P < 0.001), axial length (r = -0.218, P = 0.001), and choroidal thickness (r = 0.435, P < 0.001). On multiple stepwise regression analyses, age (β = -0.321, P < 0.001) and luminal area (β = 0.320, P < 0.001), heart rate (β = 0.136, P = 0.018), and mean ocular perfusion pressure (β = 0.126, P = 0.045) were independent factors indicating the choroidal mean blur rate. Furthermore, axial length (β = -0.352, P < 0.001), choroidal mean blur rate (β = 0.273, P < 0.001), age (β = -0.247, P < 0.001), gender (β = -0.226, P < 0.001), and mean ocular perfusion pressure (β = 0.193, P = 0.002) were independent factors indicating the luminal area.The choroidal blood flow positively correlated with the luminal area and negatively correlating with age. In addition, the luminal area was negative correlated with age. It is suggested that aging causes a reduction in choroidal blood flow and luminal area, and as a result of aging effect, decreased choroidal blood flow would correlate with decreased luminal area.

Laser speckle and hydrogen gas clearance measurements of optic nerve circulation in albino and pigmented rabbits with or without optic disc atrophy

PURPOSE

The purpose of this study was to evaluate the correlation between laser speckle flowgraphy measurements of mean blur rate (MBR) and hydrogen gas clearance measurements of capillary blood flow (CBF) in the optic nerve head (ONH) of albino and pigmented rabbits, with or without chronic ischemia-induced ONH atrophy.

METHODS

The ONH MBR and ONH CBF were measured at baseline, 30 and 60 minutes after the intravenous administration of endothelin-1 (ET-1) (10(-10) mol/kg) in six albino and six pigmented rabbit eyes. The ONH MBR and ONH CBF were also measured in nine pigmented rabbit eyes that underwent the intravitreal administration of ET-1 (20 pmol) twice per week for 4 weeks to provoke chronic ischemia-induced ONH atrophy.

RESULTS

In the group that received intravenous ET-1, average measurements of ONH MBR and ONH CBF at all time points were correlated in both the albino (r = 0.88, P < 0.001, n = 18) and pigmented rabbits (r = 0.85, P < 0.001, n = 18), with no intrarabbit correlations (P = 0.524). The ONH MBR and ONH CBF were also correlated in the model of chronic ischemia-induced ONH atrophy (r = 0.78, P = 0.013, n = 9). Pooled ONH MBR and ONH CBF measurements in both the intravenous and intravitreal groups were also highly correlated (r = 0.87, P < 0.001, n = 45), with no significant intergroup differences in the relationship between ONH MBR and ONH CBF (P = 0.138).

CONCLUSIONS

Regardless of the presence of fundus pigmentation or ONH atrophy, ONH MBR and ONH CBF were highly correlated, suggesting that MBR in the ONH tissue is usable for interindividual and intergroup comparisons.

The effect of intravitreal bevacizumab on ocular blood flow in diabetic retinopathy and branch retinal vein occlusion as measured by laser speckle flowgraphy

Background

This study evaluated the effect of intravitreal injection of bevacizumab (IVB) on macular edema associated with diabetic retinopathy (DME) or branch retinal vein occlusion (BRVOME) using laser speckle flowgraphy.

Methods

A comparative interventional study of 25 eyes from 22 patients with macular edema (DME group: 12 eyes; BRVOME group: 13 eyes) who underwent IVB. Mean blur rate (MBR) was measured in the retinal artery, retinal vein, optic nerve head (ONH), and choroid before and after IVB.

Results

In the BRVOME group, there was no significant change in MBR in the retinal artery, retinal vein or ONH, but choroidal MBR decreased significantly (P=0.04). In the DME group, the MBR in the retinal artery, retinal vein, ONH, and choroid decreased significantly (P=0.02, P=0.04, P<0.001, and P=0.04, respectively). In the DME group, pre-IVB MBR in the ONH was significantly correlated with post-IVB foveal thickness (R= −0.71, P=0.002). There was no such correlation in the BRVOME group in the ONH.

Conclusion

IVB had a suppressive effect on circulation in eyes with DME but not in those with BRVOME. This suggests that this noninvasive and objective biomarker may be a useful part of pre-IVB evaluations and decision-making in DME.

Pulse-waveform analysis of normal population using laser speckle flowgraphy

PURPOSE

Laser speckle flowgraphy (LSFG), a new, non-invasive method of measuring the mean blur rate (MBR) of ocular blood flow, allows for the analysis of the pulse waveform of a heartbeat as it changes dynamically. Here, we investigated the relationship between the pulse waveform and clinical parameters, particularly age.

MATERIALS AND METHODS

Sixty eyes of 60 healthy subjects without diabetes were enrolled from among patients undergoing annual health examinations. LSFG, and its analysis software, were used to determine pulse waveform parameters including MBR, skew, blowout score (BOS), blowout time (BOT), rising rate and falling rate in the optic nerve head (ONH), both specifically in the tissue area and in the ONH overall. Fifteen clinical parameters were also recorded, including age and blood pressure, as well as triglyceride and creatinine levels.

RESULTS

Skew, BOT and falling rate had a strong correlation (|r| > 0.60) with age, but not with the other clinical parameters. This correlation with age was stronger in the tissue area (BOT: p < 0.0001, r = - 0.68; skew: p < 0.0001, r = 0.65; falling rate: p < 0.0001, r = 0.61) than in the ONH overall (BOT: p < 0.0001, r = -0.67; skew: p < 0.0001, r = 0.60; falling rate: p < 0.0001, r = 0.59). Stepwise multiple regression analysis revealed that tissue area falling rate was an independent factor indicating age, and conversely that age was an independent factor indicating tissue area falling rate.

CONCLUSIONS

The significant correlation of LSFG-measured tissue area falling rate with age suggests that it may be a new candidate biomarker for age-dependent microcirculation.