Ocular blood flow changes after dynamic exercise in humans

Macular choroidal blood flow velocity decreases with regression of acute central serous chorioretinopathy

AIM

To quantitatively evaluate the time course of macular choroidal blood flow velocity in acute central serous chorioretinopathy (CSC).

METHODS

This retrospective observational case series included 21 eyes of 20 patients (17 men, 3 women; mean age, 53.0 years) with treatment-naïve acute CSC. Laser speckle flowgraphy was performed to calculate macular mean blur rate (MBR), an indicator of relative blood flow velocity at the first visit, 3 and 6 months thereafter. Changes in average MBR values were compared with visual improvement at 6 months.

RESULTS

Subretinal fluid completely resolved in all eyes within 6 months, while best-corrected visual acuity (BCVA) significantly improved at 6 months compared to the initial BCVA. During the follow-up period, the average MBR significantly decreased to 92.8% and 82.3% at 3 and 6 months, respectively, against baseline (100%). Importantly, there was a negative correlation between the BCVA recovery and the MBR decrease, showing the possible association of MBR increase with poor visual prognosis. Multiple regression analysis demonstrated no significant correlation between MBR and ocular perfusion pressure.

CONCLUSIONS

These results indicate that macular choroidal blood flow velocity decreases concurrently with regression of CSC, suggesting a validity of choroidal blood flow elevation in the pathogenesis of acute CSC.

Increased macular choroidal blood flow velocity during systemic corticosteroid therapy in a patient with acute macular neuroretinopathy

Purpose

The precise mechanism causing outer retinal damage in acute macular neuroretinopathy (AMN) remains unclear. In this study, choroidal blood flow velocity was quantitatively evaluated using laser speckle flowgraphy (LSFG) in a patient with AMN who received systemic corticosteroid therapy.

Methods

Corticosteroids were systemically administrated across 4 months for an AMN patient. LSFG measurements were taken ten consecutive times before treatment and at 1 week and 1, 3, and 10 months after the onset of therapy. The square blur rate, a quantitative index of relative blood flow velocity, was calculated using LSFG in three regions: Square 1, the macular lesion with findings of severe multifocal electroretinography amplitude reduction, and Squares 2 and 3, funduscopically normal-appearing retinal areas with findings of moderate and mild multifocal electroretinography amplitude reduction, respectively.

Results

The AMN lesion gradually decreased after treatment and improved results were detected on the Amsler chart, as well as on optical coherence tomography and scanning laser ophthalmoscopy. When the changing rates of the macular flow were compared with the mean square blur rate level before treatment (100%), 14.6%, 24.5%, 12.9%, and 16.3% increases were detected in Square 1 (macular lesion) at 1 week and 1, 3, and 10 months after treatment, respectively. Similarly, in Square 2 (normal-appearing area next to the lesion), 12.6%, 18.6%, 6.7%, and 8.3% increases were also noted at 1 week and 1, 3, and 10 months after treatment, respectively. In Square 3 (normal-appearing area apart from the lesion), 16.0%, 15.1%, 19.1%, and 3.8% increases were measured at 1 week and 1, 3, and 10 months after treatment, respectively.

Conclusion

In a patient with AMN, choroidal blood flow velocity at the lesion site, which was examined with LSFG, sequentially increased during systemic corticosteroid therapy, together with improvement of visual function. The present findings suggest that choroidal circulation impairment relates to the pathogenesis of AMN, extending over a wider area in the posterior pole than the site of an AMN lesion per se.

Autoregulation in the ocular and cerebral arteries during the cold pressor test and handgrip exercise

The aim of this study was to determine whether autoregulation exerts similar effects in the ocular and cerebral vessels, which are both branches of the internal carotid artery. Ocular blood flow velocities, cerebral blood flow velocity and blood pressure were measured in 11 subjects during a 2-min resting period, static handgrip exercise (HG) and a cold pressor test (CPT). Blood velocity data for the superior and inferior temporal retinal arterioles (STRA and ITRA, respectively) and the retinal and choroidal vasculature (RCV) were obtained for 4 s during the measurement using laser speckle flowmetry. Mean blood flow velocity in the middle cerebral artery (MCAVmean) was measured by transcranial Doppler ultrasound. The conductance index (CI) of each vessel was calculated by dividing blood flow by mean arterial pressure. Blood flow velocity in the RCV increased by 19 ± 9% from resting baseline level during the CPT (P < 0.05), while blood flow in the STRA, ITRA and MCAVmean did not. The CI of the MCA decreased. The RCV blood flow velocity, ITRA blood flow and MCAVmean increased by 8 ± 1, 9 ± 3 and 11 ± 4%, respectively, during the HG (P < 0.05). Conversely, STRA blood flow remained unchanged. The HG did not significantly change the CI in any of the vessels measured. These findings suggest that cerebral blood flow velocity was maintained during the CPT, but autoregulation does not work well in the RCV during the CPT and HG.

The short-term influence of exercise on axial length and intraocular pressure

PURPOSE

The aim of this study is to investigate the short-term influence of a period of dynamic exercise on axial length (AXL) and intraocular pressure (IOP) in young adult subjects.

PATIENTS AND METHODS

In all, 20 young adult subjects (10 myopes and 10 emmetropes) participated. Baseline measures of ocular biometrics, IOP and ocular pulse amplitude (OPA) were taken following a 20-min rest period. Subjects then performed 10 min of moderate intensity, low impact dynamic exercise (bicycle ergometry). Measures of ocular biometrics, IOP and OPA were repeated immediately after, and then 5 and 10 min after this exercise task. Systemic blood pressure and pulse rate were also monitored. A repeated measures analysis of variance was used to investigate the changes in the measured parameters.

RESULTS

Exercise resulted in significant changes in a range of ocular parameters. A small but significant decrease in AXL was observed following exercise (P<0.0001). The largest change in AXL was noted immediately following exercise (mean decrease -17±10 μm). IOP and OPA also decreased significantly following exercise (P<0.0001). A moderate but significant positive association was found between the changes in AXL and the changes in IOP (r(2)=0.36, P<0.0001). There were no significant differences found between the myopic and emmetropic subjects in the magnitude of changes observed in ocular parameters following exercise.

CONCLUSION

The physiological effects of dynamic exercise lead to changes in a range of ocular parameters, including significant reductions in IOP, OPA and decreases in AXL.

Use of laser speckle flowgraphy in ocular blood flow research

Laser speckle flowgraphy (LSFG) allows for the quantitative estimation of blood flow in the optic nerve head, choroid, retina and iris in vivo. It was developed to facilitate the non-contact analysis of ocular blood flow in living eyes, utilizing the laser speckle phenomenon. The technique uses a fundus camera, a diode laser, an image sensor, an infrared charge-coupled device (CCD) camera and a high-resolution digital CCD camera. Normalized blur (NB), an approximate reciprocal of speckle contrast, represents an index of blood velocity, and shows a good correlation with tissue blood flow rates determined with the microsphere method in the retina, choroid or iris, as well as blood flow rates determined with the hydrogen gas clearance method in the optic nerve head. The square blur ratio (SBR), another index for quantitative estimation of blood velocity, is proportional to the square of the NB. The SBR is theoretically a more exact measurement which is proportional to velocity, whereas the NB is an approximation. Normalized blur was calculated in earlier versions of LSFG because of technical limitations; the SBR is used in current versions of the LSFG instrument. As these values are in arbitrary units, they should not be used to make comparisons between different eyes or different sites in an eye. Clinical protocols, calibration, evaluation procedures and possible limitations of the LSFG technique are described and the results of ocular blood flow studies using LSFG are briefly summarized. The LSFG method is suitable for monitoring the time-course of change in the tissue circulation at the same site in the same eye at various intervals, ranging from seconds to months. Unresolved issues concern the effect of pupil size on measurement results, the effects of various stimulations, and how to measure choroidal and retinal blood flow velocity separately without using the blue-component of argon laser.

MRI reveals differential regulation of retinal and choroidal blood volumes in rat retina

The retina is nourished by two unique (retinal and choroidal) circulations. The lack of depth-resolved blood volume (BV) imaging techniques hampers investigation of vascular-specific regulation of the retina in vivo. This study presents a high-resolution, laminar-specific magnetic resonance imaging (MRI) study to image retinal and choroidal BVs, their responses to physiologic challenges in normal and Royal-College-of-Surgeons (RCS) rats (a model of retinal degeneration). Retinal and choroidal BVs were imaged by MRI (30×30×800 μm) with intravascular administration of monocrystalline iron oxide nanocolloid (MION) contrast agent. Relative baseline BV and BV changes due to physiologic challenges were calculated in normal and RCS rat retinas. BV-MRI revealed two well-resolved retinal and choroidal vascular layers located on either side of the retina and an intervening avascular layer. The ratio of choroidal:retinal BV in normal rats at baseline was 9.8±3.2 in control rat retinas (N=7). Hyperoxia decreased retinal BV (-51±17%, p<0.05) more than choroidal BV (-28±14%), and hypercapnia increased retinal BV (52±11%, p<0.01) more than choroidal BV (12±11%). BV-MRI in degenerated retinas of RCS rats (N=7) revealed thinning of the avascular layer and an increase in relative baseline retinal and choroidal BVs. Only hypercapnia-induced BV changes in the retinal vasculature of RCS rats were significantly different (smaller) from controls (p<0.05). These findings suggest that BV in both retinal vasculatures is regulated. The relative baseline BV in both vasculatures increased in retinal degeneration. BV-MRI provides clinically relevant data that may prove useful for early detection and longitudinal probing of retinal diseases, and could complement optical imaging techniques.

Elevated choroidal blood flow velocity during systemic corticosteroid therapy in Vogt-Koyanagi-Harada disease

PURPOSE

Laser speckle flowgraphy (LSFG) can be used to non-invasively visualize the haemodynamics of choroidal circulation and the vascular pattern. The purpose of this study was to examine the ability of LSFG to quantitatively evaluate blood flow velocity at the macula in patients with Vogt-Koyanagi-Harada (VKH) disease before and after systemic corticosteroid therapy.

METHODS

Prednisolone (200 mg/day) was systemically administered in 10 VKH disease patients with serous retinal detachment at the macular area. The drug was gradually tapered to zero over a 6-month period. Laser speckle flowgraphy measurements were taken in the 20 eyes of these patients at their initial visit and at 1, 4 and 12 weeks after the onset of therapy. Square blur rate (SBR), a quantitative index of relative blood flow velocity, was calculated using LSFG.

RESULTS

Serous retinal detachment resolved within 4 weeks after treatment and visual acuities improved to > 1.0 in almost all cases. There were significant increases in average SBR at the macula at 4 weeks after treatment compared with at 1 week after treatment, and also at 12 weeks after treatment compared with at 4 weeks after treatment.

CONCLUSIONS

These results suggest that systemic corticosteroid therapy improves inflammation-related impairment in choroidal blood flow velocity at the macula. Laser speckle flowgraphy can evaluate the effect of systemic corticosteroid therapy by enabling comparisons between measurements of blood flow velocity, which is considered to reflect inflammation activity in the choroid.