Non-contact, two-dimensional measurement of tissue circulation in choroid and optic nerve head using laser speckle phenomenon

Astaxanthin increases choroidal blood flow velocity

PURPOSE

Previous studies have reported that astaxanthin (AXT) has antioxidative and anti-inflammatory effects in addition to its ability to shorten blood transit times. As laser speckle flowgraphy (LSFG) can noninvasively visualize the hemodynamics of the choroidal circulation, we used the technique to evaluate whether continuous ingestion of 12 mg of AXT per day could increase quantitative blood flow velocity.

METHODS

In this randomized, double-blind, placebo-controlled study, we examined 20 healthy volunteers who ingested 12 mg AXT or placebo capsules over a 4-week period. LSFG was measured in the right eyes of all subjects at pre-ingestion, and at 2 and 4 weeks after the treatment of AXT. LSFG values were used to calculate the square blur rate (SBR), which is a quantitative index of relative blood flow velocity.

RESULTS

A significant increase of the macular SBR was seen 4 weeks after AXT ingestion when compared to the pre-ingestion values (Wilcoxon signed-rank test, P = 0.018). In contrast, no statistical difference in the macular SBR was detected in the placebo group (Friedman test, P = 0.598). No subjective or objective adverse events were found after the 12-mg AXT ingestion.

CONCLUSIONS

Results suggest that administration of AXT over a 4-week period can elevate the choroidal blood flow velocity without any adverse effects.

Association between optic nerve blood flow and objective examinations in glaucoma patients with generalized enlargement disc type

BACKGROUND

The purpose of this study was to investigate the correlations between microcirculation in the optic disc, average peripapillary retinal nerve fiber layer thickness cupping parameters, and visual field defects in glaucoma patients with the generalized enlargement disc type.

METHODS

A total of 38 eyes from 38 glaucoma patients with the generalized enlargement disc type were included. The microcirculation of the optic nerve head was examined with laser speckle flow graphy, and the mean blur rate in all areas, in vessel area, and in tissue area were calculated using the laser speckle flow graphy analyzer software. Average peripapillary retinal nerve fiber layer thickness was measured using Stratus optical coherence tomography, and cupping parameters were accessed using the Heidelberg retina tomograph. The mean deviation in the Humphrey field analyzer (30-2 SITA standard) was analyzed. The correlation between these parameters was evaluated using the Spearman rank correlation coefficient.

RESULTS

The correlation coefficient of mean blur rate in all optic disc area to the average peripapillary retinal nerve fiber layer thickness, vertical C/D, and mean deviation were r = 0.7546 (P < 0.0001), r = -0.6208 (P < 0.0001), and r = 0.6010 (P = 0.0001), respectively. The mean blur rate in tissue area of the optic disc showed r = 0.7305 (P < 0.0001), r = -0.6438 (P < 0.0001), and r = 0.6338 (P < 0.0001).

CONCLUSION

We found that the mean blur rate in the optic disc was significantly correlated with the average peripapillary retinal nerve fiber layer thickness, vertical C/D, and mean deviation in patients with the generalized enlargement disc type of glaucoma. In particular, the mean blur rate in tissue area was more highly correlated than the vessel area with other results of examination in glaucoma patients with the generalized enlargement disc type.

Reproducibility of retinal circulation measurements obtained using laser speckle flowgraphy-NAVI in patients with glaucoma

Background:

Laser speckle flowgraphy (LSFG) enables noninvasive quantification of the retinal circulation in glaucoma patients. In this study, we tested the intrasession reproducibility of LSFG-NAVI, a modified LSFG technique.

Methods:

Sixty-five eyes from 33 subjects (male (M):female (F) = 17:16) with a mean age of 49.4 ± 11.2 years were examined in this study. Two parameters indicating reproducibility – the coefficient of variation (COV) and the intraclass correlation coefficient (ICC) – were analyzed three times on the same day that mean blur rate (MBR) was measured using LSFG-NAVI. The sites analyzed were the retinal artery and vein, the optic disk, and the choroid. Following classification according to the Glaucoma Hemifield Test (GHT; SITA-Standard 30-2 program), the COV and ICC were examined in patients with (GHT+; 38 eyes, M:F = 20:18, average age 48.9 ± 12.8 years) and without (GHT−; 27 eyes, M:F = 13:14, average age 50.1 ± 8.7 years) abnormal glaucomatous visual fields.

Results:

For all subjects, the intrasession reproducibility of MBR in the optic disk (COV: 3.4 ± 2.0; ICC: 0.95) and choroid (COV: 4.7 ± 3.4; ICC: 0.98) was excellent. The reproducibility for the retinal vein (COV: 8.4 ± 5.6, ICC: 0.90) and retinal artery (COV: 10.9 ± 9.9, ICC: 0.9) was moderate. MBRs in the optic disk had good reproducibility in both the GHT+ group (COV: 3.8 ± 2.0; ICC: 0.97) and the GHT− group (COV: 2.9 ± 2.1; ICC: 0.95). Local assessment of the optic disk in normal or glaucoma patients showed that the COVs of the quadrant optic disk areas were best in the temporal area of MBR (3.4%, 4.2%, respectively).

Conclusion:

LSFG-NAVI showed favorable reproducibility in evaluation of retinal circulation of glaucoma patients, particularly in the optic disk and choroid.

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.

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.

The complex interaction between ocular perfusion pressure and ocular blood flow - relevance for glaucoma

Glaucoma is an optic neuropathy of unknown origin. The most important risk factor for the disease is an increased intraocular pressure (IOP). Reducing IOP is associated with reduced progression in glaucoma. Several recent large scale trials have indicated that low ocular perfusion pressure (OPP) is a risk factor for the incidence, prevalence and progression of the disease. This is a strong indicator that vascular factors are involved in the pathogenesis of the disease, a hypothesis that was formulated 150 years ago. The relation between OPP and blood flow to the posterior pole of the eye is, however, complex, because of a phenomenon called autoregulation. Autoregulatory processes attempt to keep blood flow constant despite changes in OPP. Although autoregulation has been observed in many experiments in the ocular vasculature the mechanisms underlying the vasodilator and vasoconstrictor responses in face of changes in OPP remain largely unknown. There is, however, recent evidence that the human choroid regulates its blood flow better during changes in blood pressure induced by isometric exercise than during changes in IOP induced by a suction cup. This may have consequences for our understanding of glaucoma, because it indicates that blood flow regulation is strongly dependent not only on OPP, but also on the level of IOP itself. Indeed there is data indicating that reduction of IOP by pharmacological intervention improves optic nerve head blood flow regulation independently of an ocular vasodilator effect.

Effects of prostaglandin F(2α) analogues on endothelin-1-induced impairment of rabbit ocular blood flow: comparison among tafluprost, travoprost, and latanoprost

We investigated the effects of prostaglandin F(2α) (PGF(2α)) analogues on the endothelin-1 (ET-1)-induced impairment of optic nerve head (ONH) blood flow and on ET-1-induced contraction in isolated ciliary artery segments. In male rabbits, one of four PGF(2α) analogues [0.0015% tafluprost, 0.0015% 15-hydroxyl tafluprost (15-OH tafluprost), 0.005% latanoprost, or 0.004% travoprost] was topically administered at various pretreatment times before intravitreal ET-1 injection. ONH blood flow was estimated by the laser speckle method, which expresses blood velocity as a quantitative index, the squared blur rate (SBR). SBR was measured just before (baseline value) and at 30, 60, and 120 min after ET-1 injection. SBR was significantly decreased from 4.47 ± 0.20 to 3.50 ± 0.10 (78.6 ± 2.4% of baseline) at 120 min after intravitreal ET-1 injection (5 pmol/eye). The ET-1-induced decrease was almost completely prevented by tafluprost and significantly inhibited by the other three analogues. The inhibitory effect lasted longest with tafluprost, as indicated by the effective pretreatment times (tafluprost: 90, 120, or 240 min; 15-OH tafluprost: 90, but not 120 or 240 min; latanoprost and travoprost: 120, but not 240 min). In vitro, the effects of PGF(2α) analogues on ET-1-induced contractions in male rabbit ciliary arteries were evaluated using an isometric tension recording system. Tafluprost, latanoprost, travoprost, and 15-OH tafluprost concentration-dependently relaxed the 10 nM ET-1-induced ciliary artery contraction. Improvement of the ocular circulation may be superior with tafluprost than with the other PGF(2α) analogues. The underlying mechanism may involve relaxation of ocular resistance vessels.

Laser speckle contrast imaging in biomedical optics

First introduced in the 1980s, laser speckle contrast imaging is a powerful tool for full-field imaging of blood flow. Recently laser speckle contrast imaging has gained increased attention, in part due to its rapid adoption for blood flow studies in the brain. We review the underlying physics of speckle contrast imaging and discuss recent developments to improve the quantitative accuracy of blood flow measures. We also review applications of laser speckle contrast imaging in neuroscience, dermatology and ophthalmology.

Changes in optic nerve head blood flow induced by the combined therapy of latanoprost and beta blockers

PURPOSE

To assess the effects of combined therapy with latanoprost and beta blockers on optic nerve head (ONH) blood flow in normal-tension glaucoma (NTG) patients.

METHODS

Intraocular pressure (IOP), ONH blood flow (laser speckle flowgraphy) and blood pressure were measured in 15 eyes of 15 NTG patients (41-76 years old) before treatment or after a 1-month washout period. Similar measurements were performed at 2 months after the commencement of treatment with latanoprost and at 3 months after the start of combined therapy of latanoprost with 0.5% timolol or 2% carteolol in a crossover study using the envelope method. Measurement was carried out 2-3 hr after the morning application of eyedrops.

RESULTS

Latanoprost decreased IOP with no significant change in ONH blood flow. Concomitant use of timolol or carteolol further decreased IOP with no significant difference between these two drugs. Only the combined therapy of latanoprost with carteolol significantly (p < 0.01) increased ONH blood flow by approximately 10%, compared to initial levels. There was no significant change in mean blood pressure, ocular perfusion pressure or pulse rate as a result of these therapies.

CONCLUSION

Topical latanoprost-carteolol combined therapy increased ONH blood flow in NTG patients, unlike latanoprost-timolol therapy. Because ocular perfusion pressure was unchanged, direct vasodilative effects were suspected as the mechanism.

Quantification of dynamic blood flow autoregulation in optic nerve head of rhesus monkeys

Autoregulation capacity has been classically assessed with a 'two-point' measurement or static autoregulation (sAR). In such an approach, stabilized hemodynamic parameters are determined before and after a perfusion pressure challenge. Analysis of dynamic autoregulation (dAR), an early phase of blood flow response to a sudden perfusion pressure change is emerging as a preferred approach to assess the capacity of autoregulation in many non-ocular tissues and has developed rapidly in the last decade. The purpose of this study was to develop a method to quantify dAR in the optic nerve head (ONH). In six pentobarbital (6-9 mg/kg/h, IV) anesthetized rhesus monkeys, dAR was elicited by increasing intraocular pressure (IOP) from 10 to 30 or 40 mmHg (IOP(10-30)/IOP(10-40)) manometrically via switch between reservoirs connected to the anterior chamber. Relative blood flow changes during dAR in the ONH, estimated with a laser speckle flowgraph (LSFG), were continuously measured for 1 min. Time-domain parameters of dAR response, including: BF(Deltamax) (maximal blood flow decrease, %), K(r) (descending slope of blood flow from baseline to BF(Deltamax)) and T(r) (descending time of blood flow from baseline to BF(Deltamax)) were extracted and analyzed offline. For each monkey, same procedure was repeated three times during three different visits. The test-retest repeatability and inter-ocular difference of the parameters was statistically evaluated. During IOP(10-30) and IOP(10-40), the mean arterial BP was 89 +/- 7 and 85 +/- 6 mmHg, respectively. Immediately after the reservoir was switched, the blood flow started to decline and reached maximal in approximately 4 s. The blood flow then returned back toward baseline despite continuous IOP increase, which took 8-11 s to reach the level of the raised reservoir. The general pattern of blood flow responses was similar between IOP(10-30) and IOP(10-40) and there was no statistically significant difference for T(r) (P > 0.05). However, IOP(10-40) caused greater BF(Deltamax) and deeper K(r) than IOP(10-30) (P < 0.0001 and P < 0.05, respectively). The blood flow during steady state, 5 min after IOP elevation, showed no statistically significant difference from baseline (P > 0.05). All dAR parameters (T(r), K(r) and BF(Deltamax)) showed no significant difference across the 3 visits (Repeat measures ANOVA, P = 0.7, 0.2 and 0.2, respectively); the corresponding coefficients of variance were 24%, 43% and 34% during IOP(10-30) and 11.8%, 30.3% and 19.0% during IOP(10-40). The mean dAR parameters between the eyes showed no statistically differences (P = 0.6) during both IOP(10-30) and IOP(10-40). The current study showed that a rapid ocular perfusion pressure decrease induced by a sudden IOP step increase evoked a transient and reproducible dAR response in the ONH of non-human primates measured with LSFG. Quantitative analysis of dAR may provide a direct view of vasomotorial activity in the resistant vessels and thus a new approach to assess the autoregulatory capacity in the ONH.

Estimation of blood microcirculation in integuments by non-invasive speckle-optical method under the photodynamic action

In studies on animals (rats, rabbits) an experimental technique for estimation of microhemocirculation parameters of tissue under treatment has been developed. This technique has been used to compare the changes of speckle-optical parameters of skin microhemodynamics in laser-irradiated and light-isolated areas in the course of photodynamic therapy. Strong correlation between efficiency of tissue response and injection-photoirradiation time interval has been established. The results obtained are confirmed by the data of microhemodynamics estimation in the course of photodynamic therapy by the method of intravital microscopy. The defined ways of modification of the speckle-optical module will make it possible to optimize the conditions of parameters registration taking into account the object features and to improve informativity and sensitivity of the method.

Effects of Topical Travoprost and Unoprostone on Optic Nerve Head Circulation in Normal Rabbits

PURPOSE

To evaluate the effect, and the duration of the effect, of topically administrated travoprost and unoprostone on optic nerve head (ONH) circulation in Dutch rabbits.

METHODS

First, travoprost (0.004% solution) or unoprostone (0.12% solution) was unilaterally instilled once, or once daily (travoprost) or twice daily (unoprostone) for 7 days in Dutch rabbits. The ONH tissue blood velocity (NB(ONH)) was measured using the laser speckle method at 30 and 60 min after a single instillation of travoprost or unoprostone, and before and at 1, 6, and 12 hr (travoprost or unoprostone) and 24 hr (travoprost only) after the last instillation of the aforementioned 7-day instillation regimen. Second, similar experiments were conducted with indomethacin (5 mg/kg) pretreatment.

RESULTS

Both travoprost and unoprostone significantly increased NB(ONH) only in the treated eyes after a single instillation (p = 0.011 to 0.038); this effect was abolished by indomethacin pretreatment. In the 7-day instillation regimen, NB(ONH) was increased by 11%, 40%, 17%, 16%, and 12% only in the treated eyes just before and at 1, 6, 12, and 24 hr after the final instillation of travoprost, respectively, and increased by 10%, 25%, 13%, and 14% only in the treated eyes just before and at 1, 6, 12 hr after the final instillation of the unoprostone, respectively.

CONCLUSIONS

Topical travoprost or unoprostone significantly increased the ONH blood velocity with a single instillation and the effect persisted for 24 hr after a 7-day instillation. The effects of these drugs against retinal and ONH circulation are probably associated with the production of endogenous prostaglandins.

Amelioration of Endothelin-1–Induced Optic Nerve Head Ischemia by Topical Bunazosin

PURPOSE

To investigate the effects of bunazosin hydrochloride, an alpha1-adrenergic blocker, on the impairment of optic nerve head (ONH) blood flow and depression of visual function induced by repeated intravitreal injections of endothelin-1 (ET-1) in rabbits.

METHOD

We injected ET-1 (20 pmol) into the right posterior vitreous of rabbits twice a week for 4 weeks, and the observation period was set at 8 weeks (starting the first injection). The animals that received ET01 were divided into two groups: twice a day for 8 weeks, o ne group received topical 0.01% bunazosin, while the second received the vehicle for bunazosin. The ONH blood flow was monitored using the laser speckle method, and visual function was assessed by examining visually evoked potentials (VEPs). Changes in the ONH cup/disk area and in the number of cells in the retinal ganglion cell layer (CCL) were also determined.

RESULTS

Repeated injections of ET-1 decreased the ONH blood flow, prolonged the VEP implicit time, enlarged the optic cup, and decreased the number of GCL cells. Topical bunazosin significantly decreased these impairments.

CONCLUSIONS

These results indicate that in rabbits, topical bunazosin suppresses the changes in ONH circulation and function induced by intravitreal ET-1.

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.

Imaging of choroidal hemodynamics in eyes with polypoidal choroidal vasculopathy using laser speckle phenomenon

PURPOSE

To compare the images of choroidal vasculature obtained by laser speckle flowgraphy (LSFG) and indocyanine green angiography (IA), and to evaluate the imaging of choroidal hemodynamics in eyes with polypoidal choroidal vasculopathy (PCV) using LSFG.

METHODS

We performed IA and wide-field LSFG, which measures the index of blood velocity (mean square blur rate; MBR) in 25 eyes with PCV. We constructed an MBR map of the sequential MBR images (600 x 280 pixels) from four or five pulsations during measurement (4.5 s). A grayscale composite map of a still image was obtained by averaging the cumulative sum of the MBR map. We compared the angiographic images of the grayscale composite map to IA results and evaluated the choroidal hemodynamics of 25 eyes with PCV in the MBR map.

RESULTS

The choroidal vasculature on the grayscale map had a resolution similar to the IA results. The grayscale map detected branching network vessels in 20 (80%) of the 25 eyes and polypoidal lesions in 11 (44%) eyes. The MBR map showed that the pulsations of the branching network vessels and polypoidal lesions were synchronized with the cardiac rhythm. The fluctuation rates of the PCV lesions during one pulsation ranged from 8.3% to 26.7% (mean, 13.6%) and from 7.3% to 24.6% (mean, 15.9%) for the intact choroid. The MBR map showed the watershed zone and highest signal intensity in the macula.

CONCLUSIONS

Using an MBR map, wide-field LSFG revealed the pulsating choroidal hemodynamics of the posterior fundus. A grayscale composite map showed the fine choroidal vasculature whose resolution was comparable to that of IA. The branching network vessels of PCV showed that pulsation was synchronized with the choroidal vessels. Wide-field LSFG showed the highest choroidal blood flow in the macular area and the presence of a watershed zone.

Filamentous middle cerebral artery occlusion causes ischemic damage to the retina in mice

BACKGROUND AND PURPOSE

Filamentous middle cerebral artery occlusion (fMCAO) is the most frequently used focal cerebral ischemia model in rodents. The proximity of the ophthalmic artery to the middle cerebral artery suggests that fMCAO induces retinal ischemia. We therefore tested whether fMCAO induces ischemia/reperfusion damage in retina in mice.

METHODS

SV129EV mice were subjected to transient (30 or 60 minutes) fMCAO followed by reperfusion under isoflurane anesthesia. Retinal perfusion was evaluated by intravenous injection of fluorescent microspheres combined with fluorescent microscopy using flat-mounted retinas. The fluorescent density of ipsilateral retina relative to contralateral retina was determined in each animal. Retinal injury was assessed by cresyl violet staining and in situ TUNEL.

RESULTS

Microsphere analysis demonstrated perfusion defect in the ipsilateral retina after 60 minutes fMCAO and effective restoration after reperfusion. Thirty minutes fMCAO did not produce evident histological changes, even after 2 days of reperfusion. Sixty minutes fMCAO followed by 2 hours reperfusion resulted in extensive cell damage in the inner nuclear (>30%) and ganglion cell (>50%) layers. TUNEL demonstrated very few positive cells, suggesting that damaged cells were mainly undergoing nonapoptotic cell death.

CONCLUSIONS

Sixty minutes fMCAO produces retinal injury in SV129EV mice. Potential visual dysfunction should be considered when a particular occlusion period is selected for studying neurological outcomes after fMCAO. Because visual disturbance is often associated with thrombotic/embolic stroke in humans, fMCAO represents an appropriate model for future studies aimed at understanding and ameliorating the changes that lead to retinal damage in these patients.

How can blood flow be measured?

Since vascular impairment has been hypothesized to play a role in several ocular diseases including glaucoma, diabetic retinopathy and age-related macular degeneration, the non-invasive assessment of ocular blood flow has received more and more attention. Despite the many advances that have been made in the last 30 years, there is still no gold standard for the evaluation of blood flow in humans available and sophisticated and expensive equipment is required. This article aims to review the different techniques available today for the assessment of ocular blood flow. Furthermore the advantages and the possible limitations of the techniques are discussed.

Plasma endothelin-1 levels depress optic nerve head circulation detected during the glucose tolerance test

PURPOSE

To determine the relationship between the changes in optic nerve head (ONH) circulation and the level of plasma endothelin-1 (ET-1) during the glucose tolerance test (GTT).

METHODS

Twenty-six healthy volunteers with normal GTT and 15 patients with mild hyperglycemia and abnormal GTT were studied. The ONH circulation [square blur rate (SBR) value], blood pressure, intraocular pressure (IOP), blood glucose, blood insulin and plasma ET-1 were determined before and every hour up to 3 h after an oral intake of 75 g of glucose.

RESULTS

The SBR increased in the normal glucose tolerance group at all times during the GTT, but it decreased significantly in the abnormal glucose tolerance group (P < 0.05). Before the GTT, the plasma ET-1 level was not significantly different in the two groups; however, the level increased 1 h after the oral GTT in the abnormal glucose tolerance group (P < 0.05). No significant changes were observed in mean blood pressure or IOP.

CONCLUSIONS

ONH circulation increased after glucose intake in the normal glucose tolerance group and remained high even after the blood glucose level had returned to its baseline. The decrease in ONH circulation in the abnormal glucose tolerance group was attributed partly to the increased ET-1.

Kinetics of blood flow during healing of excisional full-thickness skin wounds in pigs as monitored by laser speckle perfusion imaging

BACKGROUND/PURPOSE

The laser speckle perfusion imaging (LSPI) system is a new, non-invasive technique for rapidly and reproducibly measuring tissue perfusion. The high resolution and frame rate of the LSPI overcome many of the limitations of traditional laser Doppler imaging techniques. Therefore, LSPI is a useful means for evaluating blood flow in a variety of situations. The present study investigates the ability of the LSPI system to detect temporal changes in blood flow during the healing of cutaneous wounds in a well-characterized animal model.

METHODS

Full-thickness excisional skin wounds (2 x 2 cm) were created on the backs of juvenile female red Duroc pigs. Every week post-injury, the wounds were measured and photographed, and normalized blood flow values were determined using the LSPI system.

RESULTS

Tissue perfusion values were available after complete re-epithelialization and removal of the eschar, at day 21. At this point, wound blood flow was significantly elevated as compared with the surrounding, uninvolved skin. Wound blood flow declined steadily during healing, and approached normal values by day 35 post-injury.

CONCLUSION

The kinetics of blood flow during excisional wound healing in the red Duroc model are comparable with that previously observed in laser Doppler imaging of healing human skin wounds and hypertrophic scars. These results therefore confirm that the red Duroc is a good model of human wound healing, and further indicates that the LSPI is an excellent technique for evaluating angiogenesis and neovascularization during healing in this and other models.

Intravitreal injection of endothelin-1 caused optic nerve damage following to ocular hypoperfusion in rabbits

The purpose of this study was to investigate the time course of the ocular hypoperfusion, retinal damage, and optic nerve damage induced by intravitreal injection of endothelin-1 (ET-1) in rabbits. ET-1, at 5 pmol (20 microL, twice a week for 2 or 4 weeks), was injected from the pars plana into the posterior vitreous of the right eye. Optic nerve head (ONH) blood flow and retinal artery diameter, together with the neurofilament light chain (NF-L) content, retinal morphology, and axon density of the optic nerve, were evaluated at 2, 4, and 8 weeks after the first injection of ET-1 (n=7 or 8). Tissue blood velocity in ONH was measured using a laser speckle method, and the diameter of major retinal arteries on the rim of the ONH was calculated from fundus photographs by a masked observer. Histological analysis and immunoblot evaluation of NF-L in the optic nerve were performed to evaluate optic nerve damage. At 2 weeks after the first ET-1 injection, tissue blood velocity was decreased by approximately 20% (versus the contralateral eye), and the diameter of retinal arteries had decreased by approximately 40%. These changes were sustained at the same level until 8 weeks after the first ET-1 injection. At 4 and 8 weeks after the first ET-1 injection, the amount of NF-L in the optic nerve was significantly less in the ET-1 treated eyes than in the contralateral eyes. At 8 weeks after the first ET-1 injection, a loss of myelinated axons and increases in gliosis and connective tissue were noted in the optic nerve of the treated eye, and the optic nerve-axon number had decreased significantly (each, versus the untreated eye). Retinal ganglion cells in the retina were not observed any damage at 2, 4, and 8 weeks after ET-1 injection. In conclusion, intravitreal injection of ET-1 induced chronic hypoperfusion in the ONH and retina, which presumably caused decreases in NF-L content and axon number in the optic nerve noted in the later part of the observation period.

A comparison of two laser-based methods for determination of burn scar perfusion: laser Doppler versus laser speckle imaging

Laser Doppler perfusion imaging (LDI) is an established technique for early assessment of burn depth to help determine a course of treatment. Laser speckle perfusion imaging (LSPI) is an alternative laser based, non-invasive perfusion monitoring technique that offers rapid and high resolution images of tissue. We have evaluated the ability of the LSPI instrument in determining and monitoring burn scar perfusion over time and compared it with the LDI instrument as a standard.

METHODS

Ten patients with hypertrophic burn scars (time since injury: 1-8 months) were recruited. Burn scars were scanned with both instruments (LSPI and LDI) monthly over a period of 11 months. Clinical grading of the burn scars was assessed on every scan date using the Vancouver burn scar scale.

RESULTS

Comparison of the perfusion values determined by each instrument shows a strong positive correlation, r2=0.86 (n=63). Each instrument's output also correlated significantly with the clinical grading of the scar, indicating the expected decrease in perfusion as the clinical condition of the scars improved with time.

SIGNIFICANCE

The new LSPI instrument compared favorably with the established LDI instrument, yielding similar results. The considerably faster scan time and higher resolution of the LSPI method provides a distinct clinical advantage, both in terms of patient comfort and for reliably matching perfusion characteristics to their associated anatomical features. The fast temporal response of the LSPI instrument could be used to monitor near real-time responses to mechanical or pharmacological interventions to study dynamic vascular changes to burn damaged tissues.

Ocular blood flow changes after dynamic exercise in humans

PURPOSE

To investigate control mechanisms for ocular blood flow changes after dynamic exercise using two different methods.

METHODS

Changes over time in the tissue blood flow in the retina and choroid-retina of healthy volunteers were determined after dynamic exercise (Master's double two-step test), using scanning laser Doppler flowmetry (SLDF) and laser speckle flowgraphy (LSFG). Changes in intraocular pressure (IOP), blood pressure, plasma CO(2) gas concentration (pCO(2)), and levels of nitric oxide (NO) metabolites were examined.

RESULTS

Retinal blood flow measured by SLDF increased significantly only at 15 min after exercise. In contrast, normalized blur (NB) values in the choroid-retina, obtained by LSFG, increased significantly up to 60 min after exercise. Ocular perfusion pressure (OPP), calculated from IOP and blood pressure, increased significantly immediately and 15 min after exercise. The plasma NO metabolite levels increased significantly, although pCO(2) levels were unchanged.

CONCLUSIONS

Dynamic exercise changes OPP and produces increased tissue blood flow in the retina in the immediate postexercise period, while blood flow increases more persistently in the choroid-retina. Difference in control of blood flow in these two regions may be related to stronger autoregulatory mechanism of blood flow in the retina. Nitric oxide may play a role in the regulation of blood flow.

Effects of adenosine on optic nerve head circulation in rabbits

This study was performed to determine whether intravitreal or intravenous adenosine can alter the microcirculation in the optic nerve head (ONH) of rabbits. Capillary blood flow in the ONH was measured serially with a laser speckle tissue analyser for 2 hr after the intravitreal (0.1, 1.0 and 10 nmol) or intravenous (0.2 and 0.6 mg kg(-1)min) injections of adenosine. In addition, the effect of specific adenosine A(1) and A(2a) antagonists and an adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channel blockers on the adenosine-induced changes on the ONH blood flow was analysed. Intravitreal adenosine increased the capillary blood flow in the ONH in a dose-dependent manner, while intravenous adenosine had no effect. Co-administration of the specific adenosine A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 nmol) significantly suppressed (P=0.006, ANOVA) the increase in the ONH blood flow induced by adenosine (10 nmol). The specific A(2a) receptor antagonist, 8-(3-chlorostyryl) caffeine (CSC, 10 nmol), had a weak effect in inhibiting the increase but the change was not significant (P=0.08, ANOVA). Both specific A(1) and A(2a) receptor agonists, N(6)-cyclopentyladenosine (CPA, 10 nmol) and 2-p-(2-carboxyethyl) phenethyl-amino-5'-N-ethylcarboxamidoadenosine (CGS-21680, 10 nmol), increased the ONH tissue blood flow (P<0.01, ANOVA). Glibenclamide (10 nmol), a selective K(ATP) channels antagonist, suppressed the increase of ONH blood flow induced by 10 nmol adenosine significantly (P<0.001, ANOVA). On the other hand, 10 nmol of 8-Br-cAMP, a cAMP analog, failed to enhance the capillary blood flow in the ONH. These results indicate that adenosine increases the capillary blood flow in the ONH of rabbits, and it acts through A(1) and A(2a) receptors from the ablumenal side where pericytes are located. Activation of K(ATP) channels is strongly related to the mechanism of adenosine-induced increase in ONH blood flow, while the participation of adenylate cyclase is less likely.

Diurnal variation in microcirculation of ocular fundus and visual field change in normal-tension glaucoma

PURPOSE

Diurnal variations in microcirculation of the ocular fundus in normal-tension glaucoma (NTG) were examined to compare with the normal control eyes. The correlation between progression of visual field impairment and diurnal variations in ocular circulation was also studied.

METHODS

The subjects were 12 patients with NTG and 12 normal controls. Blood pressure (BP), intraocular pressure (IOP), ocular perfusion pressure (OPP), and square blur rate (SBR), an index of microcirculation acquired by the laser speckle method, were measured at 9 a.m. (morning), 3 p.m. (afternoon), and 9 p.m. (night). Diurnal variations in SBR were tested using the Friedman test and Wilcoxon signed ranks test. On the other hand, diurnal variations in BP, IOP, and OPP were tested by the analysis of variance. The visual field was evaluated at the same time as determining diurnal variation and again about 9 months later to calculate the change. The correlation between variation ratio in SBR and the change in visual field was examined by simple regression.

RESULTS

A significant decrease (P=0.04) was found in SBR at night, as compared with the morning value, in the optic nerve head (ONH) of NTG, although no significant diurnal variations were found in SBR either in the choroid-retina or in normal control eyes. Other parameters showed no significant diurnal variations. The larger diurnal variation was in SBR of the ONH, and the more exacerbated visual field impairment was (r=0.59, P=0.04).

CONCLUSION

These findings suggest that diurnal variations in the microcirculation of the ONH may play a role in the progression of NTG.

Relationship between optic nerve head microcirculation and visual field loss in glaucoma

PURPOSE

To study the relationship between optic nerve head blood flow velocity and visual field loss in patients with primary open-angle glaucoma (POAG) and normal tension glaucoma (NTG).

METHODS

This study included 44 eyes of 44 patients with POAG and 44 eyes of 44 patients with NTG. To evaluate optic nerve head blood flow velocity, the square blur rate (SBR) was measured by means of laser speckle flowgraphy. The correlation between SBR and Humphrey visual field indices was evaluated with linear regression analysis.

RESULTS

In the NTG group, the average SBR at the superior and inferior temporal neuroretinal rim was positively correlated with mean deviation (MD) (r = 0.349, p = 0.020). The SBR at the superior or inferior temporal neuroretinal rim was positively correlated with the sum of the total deviations in the corresponding hemifields (r = 0.299, p = 0.049; r = 0.354, p = 0.019, respectively). The correlations between SBR and MD did not differ statistically between the NTG and POAG groups; however, no significant correlation between SBR and visual field indices was observed in the POAG group.

CONCLUSION

These results suggested that the change in the circulation of the optic nerve head may be related to visual field damage in the NTG group but may be less involved in visual field damage in the POAG group.

Effects of kallidinogenase on ocular tissue circulation in rabbits

The purpose of this study is to evaluate the effects of kallidinogenase, a tissue kallikrein, on tissue circulation in the optic nerve head (ONH), choroid and retina. Kallidinogenase (1.0 IU/kg) or saline was injected intravenously into urethane-anesthetized rabbits, and the normalized blur value (NB), a quantitative index of in vivo tissue blood velocity, was measured in the ONH, choroid and retina before and for 90 minutes after injection, using the laser speckle method. The difference in NB values in the kallidinogenase group was significantly higher compared with that in the control group in the choroid (p < 0.05) and retina (p < 0.05, ANOVA of repeated measurements). In the ONH, however, there was no significant difference between the kallidinogenase group and the control group except transient increment 10 min after drug administration (p < 0.01, unpaired t-test). On the other hand, systemic condition parameters and intraocular pressure showed no intergroup difference significantly except for a transient decrease in blood pressure and increase in pulse rate in the kallidinogenase groups. Kallidinogenase increased blood velocity, and probably blood flow, in the choroid and retina of rabbits.

Drug delivery to the posterior segment from drops

The published evidence that instilled drugs can affect the blood supply to the retina and optic nerve head in humans is examined. As a background, seven techniques that have been used to measure flow are briefly described and criticized. For timolol, the corresponding measurements, obtained by a number of investigators are evaluated. The outcome is very erratic and does not allow any conclusion as to the effect of this drug on flow. Consideration is then given to the possible mechanism whereby a drug could affect blood flow; directly, by diffusion to receptors on the vessels, or indirectly, through more anterior receptors. The question is raised whether the small changes in circulation induced by drugs would not be swamped by those resulting from natural alterations in the ambient light level. The literature was analyzed in the hope of identifying discrete entry pathways, for example, through the lens or the suprachoroidal space, that are sufficiently permeable to allow a significant quantity of drug to pass. There was an indication that a drug might diffuse through the lens cortex in sufficient quantity to cause a measurable rise in its concentration in the vitreous. In general, however, there was insufficient quantitative data to allow any meaningful predictions to be made. Stimulated by recent evidence, it is suggested that drug penetration from the tear fluid takes place by direct diffusion across the conjunctiva into the sclera and orbit when the head is supine.

The impact of ocular blood flow in glaucoma

Two principal theories for the pathogenesis of glaucomatous optic neuropathy (GON) have been described--a mechanical and a vascular theory. Both have been defended by various research groups over the past 150 years. According to the mechanical theory, increased intraocular pressure (IOP) causes stretching of the laminar beams and damage to retinal ganglion cell axons. The vascular theory of glaucoma considers GON as a consequence of insufficient blood supply due to either increased IOP or other risk factors reducing ocular blood flow (OBF). A number of conditions such as congenital glaucoma, angle-closure glaucoma or secondary glaucomas clearly show that increased IOP is sufficient to lead to GON. However, a number of observations such as the existence of normal-tension glaucoma cannot be satisfactorily explained by a pressure theory alone. Indeed, the vast majority of published studies dealing with blood flow report a reduced ocular perfusion in glaucoma patients compared with normal subjects. The fact that the reduction of OBF often precedes the damage and blood flow can also be reduced in other parts of the body of glaucoma patients, indicate that the hemodynamic alterations may at least partially be primary. The major cause of this reduction is not atherosclerosis, but rather a vascular dysregulation, leading to both low perfusion pressure and insufficient autoregulation. This in turn may lead to unstable ocular perfusion and thereby to ischemia and reperfusion damage. This review discusses the potential role of OBF in glaucoma and how a disturbance of OBF could increase the optic nerve's sensitivity to IOP.

Effect of topical unoprostone on circulation of human optic nerve head and retina

The purpose of the present study was to study the effect of topical unoprostone on the circulation of human optic nerve head (ONH) and retina in normal subjects. Using laser-speckle tissue blood flow analysis, normalized blur (NB), a quantitative index of tissue blood velocity, was measured every 0.125 sec at a temporal ONH site, free of visible surface vessels. Measurements were averaged for 3 cardiac cycles (NB(ONH)). Color Doppler imaging (CDI) was also used to evaluate peak systolic blood velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI) in the central retinal artery (CRA) and mean blood velocity (MV) in the central retinal vein (CRV). For baseline comparison (Day 0), recordings of bilateral NB(ONH) and intraocular pressure (IOP), blood pressure (BP), and pulse rate (PR) were recorded in healthy volunteers before, and 45, 90, 180, and 270 min after instillation of one drop of unoprostone vehicle. On Day 1 (the day after baseline measurements), and twice daily for 7 days, one drop of 0.12% unoprostone was instilled into one eye and its vehicle into the other in a double-blinded manner. Measurements as on Day 0 were recorded on Days 1 and 7. CDI measurements were performed before and at 45 and 180 min after morning instillation on Days 1 and 7. During baseline recordings, there were no significant changes in any parameters. After administration of topical unoprostone, IOP was significantly lower bilaterally with more reduction in the unoprostone-treated eyes on Day 7. On Day 7, the NB(ONH) of the unoprostone-treated eyes was significantly higher 45 min after instillation than baseline (P = 0.035 with Bonferroni's correction). Analysis of variance for repeated measurements also revealed significant difference between Day 0 and Day 7 (P = 0.0017). BP, PR, NB(ONH) in the eye that received only the vehicle, PSV, EDV, and RI in the CRA in both eyes, and MV in the CRV in both eyes changed little. Tissue blood velocity in the ONH increased, at least temporarily, following instillation of unoprostone twice daily for 7 days. Although the clinical implication of the increase is unclear, the effects of topical unoprostone on human ONH circulation deserve further consideration.

Topical latanoprost and optic nerve head and retinal circulation in humans

The purpose of the present study was to study the effect of a single instillation of latanoprost on the human optic nerve head (ONH) and retinal circulation. Using laser-speckle tissue blood flow analysis, normalized blur (NB; a quantitative index of tissue blood velocity) was measured every 0.125 sec at a temporal ONH site free of visible surface vessels. Measurements were averaged for 3 cardiac cycles (NB(ONH)). Color Doppler Imaging (CDI) was also used to evaluate peak systolic blood velocity (PSV), endo-diastolic velocity (EDV), and resistive index (RI) in the central retinal artery (CRA) and mean blood velocity (MV) in the central retinal vein (CRV). One drop of 0.005% latanoprost was instilled into one eye and its vehicle into the other in eleven healthy volunteers in a double-blinded manner. Measurements of bilateral NB(ONH), CDI parameters, intraocular pressure (IOP), blood pressure (BP), and pulse rate (PR) were performed before, and 45, 90, 180, and 270 min after instillation. After a single instillation of latanoprost or the vehicle, there was no significant bilateral difference throughout the experimental period. The difference in NB(ONH) between that before and at each time point of measurement (delta NB(ONH)) in the latanoprost-treated eyes was significantly higher between 45 and 270 min after instillation than that in vehicle-treated eyes (P = 0.0003 to 0.0156); ANOVA for repeated measurements also revealed significant difference between both eyes (P < 0.00001). BP, PR, and NB(ONH) in the eye that received only the vehicle, PSV, EDV, and RI in the CRA in both eyes, and MV in the CRV in both eyes changed little. Tissue blood velocity in the ONH increased at least temporarily following a single instillation of topical latanoprost. Although the mechanism of the increase is unclear, the effects of latanoprost on ONH tissue circulation in humans may have clinical implications.

Optic nerve head circulation after intraocular pressure reduction achieved by trabeculectomy

OBJECTIVE

To study the effects of trabeculectomy and needling revision of poorly functioning blebs on the optic nerve head (ONH) circulation in patients with primary open-angle glaucoma (POAG).

DESIGN

Prospective, nonrandomized, self-controlled trial.

PARTICIPANTS

Nineteen POAG patients (age range, 52 +/- 12 years; mean +/- standard deviation) undergoing trabeculectomy and six POAG patients (age range, 62 +/- 14 years) undergoing needling revision of the bleb.

METHODS

Using the laser speckle method, the normalized blur (NB) value, a quantitative index of blood velocity, was determined every 0.125 seconds and averaged more than three cardiac pulses in the optic nerve head (NB(ONH)).

MAIN OUTCOME MEASURES

The NB(ONH) and intraocular pressure (IOP) in both eyes, and blood pressure (BP) and pulse rate (PR) were measured before and 2 days and 1, 4, and 8 weeks after trabeculectomy, and also before and 10 and 40 min after needling procedures.

RESULTS

Intraocular pressure in the operated eye was significantly decreased after trabeculectomy or needling procedures, and the ocular perfusion pressure was significantly increased by a maximum of 38%. The IOP in the unoperated eye, BP, and PR did not significantly change. The NB(ONH) did not significantly change in either the operated or unoperated eye.

CONCLUSIONS

Trabeculectomy and needling procedures induced little change in the ONH circulation.

The acute effects of stellate ganglion block on circulation in human ocular fundus

PURPOSE

To study the acute effects of local-anesthetic stellate ganglion block (SGB) on tissue circulation in the human fundus.

METHODS

Eleven patients with Bell's palsy (age 56+/-6 y, mean+/-SD) who underwent SGB for its treatment participated in the study. Using the laser speckle method, normalized blur (NB) value, a quantitative index of tissue blood velocity, was measured every 0.125 s over an area located halfway between the macula and the optic nerve head (ONH) with no discrete visible vessels and averaged over 3 pulses when fixation was satisfactory (NB(ch-ret)). NB(ch-ret) and intraocular pressure (IOP) in both eyes, blood pressure (BP), and pulse rate (PR) were measured before, and 10, 20, 30, and 60 min after SGB. SGB was induced by injecting 1% mepivacaine hydrochloride (5 ml) into the vicinity of the seventh cervical vertebra on the paralyzed side.

RESULTS

The IOP in the blocked side significantly decreased between 20 and 60 min following SGB, compared to the baseline, while IOP in the unblocked side remained unchanged. The NB(ch-ret) was significantly increased after 10 min by about 8% in the blocked side, but its effect almost disappeared at 60 min. There was no significant change in NB(ch-ret) in the unblocked side, BP or PR throughout the experimental period.

CONCLUSION

SGB increased tissue circulation in the fundus in the blocked side, but its effect was thought to be small and transient.

Effect of ifenprodil on ocular tissue circulation in rabbits

Ifenprodil tartrate has long been employed as a cerebral vasodilator with alpha and N-methyl-D-aspartate (NMDA) receptor antagonistic activities. The purpose of this study was to evaluate the effects of ifenprodil on ocular circulation in rabbits. Experiments were performed during the dark phase in Dutch rabbits conditioned to a schedule of alternating 12-hr periods of light and dark. Effects on ocular tissue blood velocity were estimated using the laser speckle method in the iris, posterior choroid, and optic nerve head (ONH). Measurements of tissue blood velocity were performed both after intravenous injection of ifenprodil at a dose of 0.2 mg/kg, 0.1 mg/kg, and the same volume of the vehicle, and after topical instillation of 0.5% ifenprodil (50 microl) twice daily for 1, 3 and 20 days unilaterally in a masked manner. Intraocular pressure (IOP) was also measured during the experimental period. Intravenous administration of ifenprodil caused a significant increase in blood velocity in the ONH, choroid, and iris, but ONH circulation was affected at a lower dose than uveal circulation. In the topical instillation experiment, IOP in the ifenprodil-treated eye was significantly lower, by approximately 2 mmHg, than that in the contralateral eye when the laser speckle measurement was performed. Twice-daily, unilateral 0.5% ifenprodil instillation significantly increased blood velocity in the iris after 3 days and that in the ONH and posterior choroid after 20 days in the treated eye. Topical 0.5% ifenprodil increased blood velocity in the iris, posterior choroid, and ONH after multiple dosings. After systemic administration, ONH circulation appeared to be influenced at a lower dose than was uveal circulation.

Measurement of microcirculation in optic nerve head by laser speckle flowgraphy in normal volunteers

PURPOSE

To report blood flow in the optic nerve head between the right and left eyes or the superior and inferior neuroretinal rims in normal volunteers using laser speckle flowgraphy.

METHODS

This prospective study included 120 eyes of 60 normal volunteers (mean age, 50.0 +/- 16.9 years; range, 21 to 77 years). The square blur rate was measured by laser speckle flowgraphy (Kyushu Institute of Technology, Iizuka, Japan). The sequence of eye measurements was randomized. In each eye, measurements were taken at the neuroretinal rim away from visible vessels. Linear regression analysis, paired two-tailed t test, and two-way analysis of variance were used for statistical analysis. P values less than.05 were accepted as statistically significant.

RESULTS

There was a significant correlation in square blur rate between the right and left eyes (r = 0.587, P <.001). Square blur rate in the superior temporal neuroretinal rim significantly correlated with that in the inferior temporal neuroretinal rim in each of the right (r = 0.546, P <.001) and left (r = 0.465, P <.001) eyes. Square blur rate in the right eye was higher than that in the left eye (P =.049). Square blur rate in the superior neuroretinal rim was higher than that in the inferior neuroretinal rim in both the right (P =.035) and left (P =. 005) eyes.

CONCLUSION

There were statistically significant differences of optic nerve head blood flow in normal volunteers using laser speckle flowgraphy between the right and left eyes and between the superior and inferior temporal neuroretinal rims. These normal data can be used for understanding physiological ocular hemodynamics.

Effects of semotiadil, a novel calcium antagonist, on the retina and optic nerve head circulation

The effects of semotiadil, a novel benzothiazine calcium antagonist, on the retinal and optic nerve head (ONH) tissue circulation were evaluated using the noninvasive laser speckle method. In urethane-anesthetized Dutch or albino rabbits, before and up to 90 min following intravenous injection of 400 microg/kg semotiadil fumarate (semotiadil group) or vehicle (control group), normalized blur value, a quantitative index of tissue blood velocity, in the retina (NB(retina)) or ONH (NB(onh)), was serially obtained with monitoring intraocular pressure (IOP) and systemic parameters: arterial pressure, pulse rate, arterial blood gas, and body temperature. There were no significant differences in IOP and the systemic parameters except arterial pressure between semotiadil and control groups during the experiments. Arterial pressure showed an acute and transient drop during the first 5 min after semotiadil administration. The time courses of the normalized blur value were significantly different between semotiadil and control groups in the retina (P = 0.0001, repeated measures two-way ANOVA), but not in the ONH (P = 0.6724). Changes in NB(retina) from the baseline in the semotiadil group was significantly greater than those in the control group 50 min or later after the administration (P < 0.0500, Mann-Whitney test). NB(onh) showed no significant differences between the two groups except during the first few min when arterial pressure acutely decreased in the semotiadil group. In conclusion, intravenously injected semotiadil increased the tissue blood velocity in the retina, but not in the ONH. This vascular selectivity in the ocular neural tissues differs from those of other calcium antagonists, such as nicardipine.

Effect of ifenprodil on aqueous humor dynamics and optic nerve head circulation in rabbits

The purpose of this study was to study the effects of ifenprodil, a cerebral vasodilator with alpha and N-methyl-D-aspartate (NMDA) receptor antagonistic activities, on aqueous humor dynamics and optic nerve head (ONH) circulation in rabbits. Experiments were performed during the dark phase in rabbits conditioned to a schedule of alternating 12-hr periods of light and dark. Effects on blood-aqueous barrier permeability (K(d)), aqueous flow rate (F), outflow facility to general blood circulation (C(gen)), and uveoscleral outflow (F(u) were determined fluorophotometrically. Effects on ONH tissue circulation were estimated using the laser speckle method. Unilateral topical administration of 0.5% ifenprodil solution decreased intraocular pressure (IOP) with a maximum reduction of 3.4 mmHg and an effect duration of 3 hr without effects on the contralateral eye. A single instillation of 0.5% ifenprodil had no significant effect on K(d), F, or C(gen), whereas it substantially increased F(u). Twenty-day, twice-daily unilateral 0.5% ifenprodil instillation significantly increased tissue blood velocity in the ONH only in the treated eye.

Measurement of microcirculation in the optic nerve head by laser speckle flowgraphy and scanning laser Doppler flowmetry

PURPOSE

To evaluate and compare blood flow measurements by laser speckle flowgraphy and scanning laser Doppler flowmetry in the optic nerve head of normal volunteers.

METHODS

This prospective study included 60 eyes of 60 normal volunteers (50.0 years; range, 21 to 77 years). Measurements were taken at the temporal neuroretinal rim away from visible vessels. The square blur rate, a quantitative index of relative blood velocity, was measured by laser speckle flowgraphy. Using scanning laser Doppler flowmetry, volume, flow, and velocity were measured at the same neuroretinal rim locations.

RESULTS

The average square blur rate, volume, flow, and velocity were 7.11 +/- 1.65, 7.74 +/- 3.19, 151.85 +/- 70.63, and 0.53 +/- 0. 23 arbitrary units, respectively (n = 60). Square blur rate correlated significantly with flow and velocity (r =.361, P =.005; r =.359, P =.005, respectively). However, there was no significant correlation between square blur rate and volume (r =.101, P =.441). Although square blur rate decreased significantly with increasing age (r = -.375, P =.003), volume, flow, or velocity showed no significant correlation with age (r = -.249, P =.054; r = -.166, P =. 205; r = -.143, P =.275, respectively). Square blur rate also decreased significantly with mean blood pressure (r = -.315, P =. 014), but volume, flow, or velocity showed no significant correlation with mean blood pressure (r = -.159, P =.225; r = -.059, P =.654; r = -.043, P =.742, respectively).

CONCLUSION

We found only a weak correlation between the blood flow indexes, as measured by laser speckle flowgraphy and scanning laser Doppler flowmetry because of basic differences in the principles of measurement.

The acute effects of cigarette smoking on human optic nerve head and posterior fundus circulation in light smokers

PURPOSE

To study the acute effects of cigarette smoking on tissue circulation in the optic nerve head (ONH) and posterior fundus in smokers with a short smoking history.

METHODS

Ten healthy smokers whose length of smoking history was within 2 years (age 25 +/- 1 years; smoking index (number of cigarettes smoked per day x length of smoking history in years) 16 +/- 4, mean +/- SE) were included in the study. Using the laser speckle method, normalised blur (NB) value, a quantitative index of tissue blood velocity, was measured every 0.125 s and averaged over three pulses across an area located in the temporal site of the ONH free of visible surface vessels (NBONH) and across an area located halfway between the macula and the ONH with no discrete vessels visible (NBch-ret). NBONH, NBch-ret and intraocular pressure (IOP) in one randomly chosen eye, and blood pressure (BP) and pulse rate (PR) were measured before, and 1, 5, 10, 15, 20, 25, 30, 45, 60 and 90 min after sham smoking. One week later, NBONH, NBch-ret and IOP in the same eye, and BP and PR were measured after cigarette smoking according to the same time schedule as in the control experiment.

RESULTS

After sham smoking, no parameter showed a significant change during the experiment. Differences in NBONH from the baseline were not significant between the smoking experiment and sham smoking experiment, while NBch-ret showed a significant difference at 30 min. Inter-group difference in the time course of the difference from baseline was significant (ANOVA, p = 0.0246, 0.0021). BP and PR were significantly increased between 1 and 20 min after smoking while IOP showed no significant change at any time of measurement.

CONCLUSIONS

In light smokers, cigarette smoking showed little effect on tissue blood velocity in the ONH and slightly decreased that in the posterior fundus, suggesting a significant increase in vascular resistance in these tissues.

Effects of scleral buckling and encircling procedures on human optic nerve head and retinochoroidal circulation

AIMS

To study the effects of segmental scleral buckling and encircling procedures on tissue circulation in the human optic nerve head (ONH) and choroid and retina.

METHODS

Using the laser speckle method, the normalised blur (NB) value, a quantitative index of tissue blood velocity, was measured every 0.125 seconds and averaged over three pulses in the optic nerve head (NB(ONH)) and choroid and retina (NB(ch-ret)) in 10 patients with unilateral rhegmatogenous retinal detachment (mean age 52 (SD 17)). NB(ONH), NB(ch-ret), and intraocular pressure (IOP) in both eyes, and blood pressure (BP) were measured before, and 1, 4, and 12 weeks after the scleral buckling and encircling procedure.

RESULTS

NB(ch-ret) on the buckled side was significantly reduced after surgery and smaller than that in the unoperated contralateral eye throughout the study period (ANOVA, p<0.0001). NB(ch-ret) on the unbuckled side, in the foveal area, NB(ONH), IOP, and BP showed no significant change.

CONCLUSIONS

It was indicated that the segmental scleral buckling procedure with encircling elements decreased tissue blood velocity in the choroid and retina on the buckled side but caused no significant change on tissue circulation in other areas of the fundus or ONH.

Experimental optic cup enlargement caused by endothelin-1-induced chronic optic nerve head ischemia

PURPOSE

Vascular insufficiency of the optic nerve head may contribute to glaucomatous optic neuropathy, especially in normal-tension glaucoma. We investigated the effect of chronic optic nerve head ischemia, created by repeated intravitreal injection of endothelin-1 (ET-1), on the morphology and function of the optic nerve.

METHODS

In pigmented rabbits, we injected ET-1 (10(-6) M, 10 microL) into the posterior vitreous of one eye twice a week for 4 weeks (N = 7). The vehicle for ET-1 was injected into the contralateral eye as a control (N = 7). The subsequent observation period was set at 8 weeks. The microcirculation of the optic nerve head was noninvasively monitored with a laser speckle circulation analyzer. To evaluate the changes of visual function, visual-evoked potentials were recorded. Morphologic changes of the optic nerve head were analyzed with stereography, and the ratio of cup area (CA) to disk area (DA) was measured by calculating the number of pixels in each area with a microcomputer.

RESULTS

Capillary blood flow in the optic nerve head was continuously below 80% of the baseline throughout the study. The visual-evoked potential latency was significantly delayed in ET-1-treated eyes. The CA/DA ratio was significantly increased relative to baseline in the ET-1 treated eyes. Histologic examination showed axonal loss and demyelination affecting the prelaminar portion of the optic nerve. The intraocular pressure was not significantly different from the control value.

CONCLUSION

Optic nerve head ischemia could contribute to the enlargement and excavation of the disk cup independent of the intraocular pressure level.

Effect of topical betaxolol on tissue circulation in the human optic nerve head

There have been no reports to date on long-term betaxolol instillation effects on the human optic nerve head (ONH) tissue circulation. The purpose of this study was to study the effect of topical 0.5% betaxolol on tissue blood velocity in the human ONH. Using a laser-speckle tissue blood flow analyzer, normalized blur (NB; a quantitative index of tissue blood velocity) was measured every 0.125 seconds at a temporal ONH site free of visible surface vessels. Measurements were averaged for 3 cardiac cycles (NB(ONH)). For baseline comparison (day 0), recordings of bilateral NB(ONH) and intraocular pressure (IOP), blood pressure (BP) and pulse rate (PR) were recorded in healthy volunteers before, and 2, 4.5, and 7 hr after, instillation of 30 microL of betaxolol vehicle, and again on day 21; IOP was also recorded on days 7 and 14. On day 1 (the day after baseline measurements), and twice daily for 3 weeks, 30 microL of 0.5% betaxolol into one eye and 30 microL vehicle was instilled into the other in a double-blind study. Measurements as on day 0 were again recorded on day 21; IOP was also recorded on days 7 and 14. During baseline recordings, no significant changes were noted in any parameters. After administration of topical betaxolol, IOP was significantly reduced, bilaterally, with greater reduction in the betaxolol-treated eyes on day 21. Also on day 21, the NB(ONH) of the betaxolol-treated eyes was significantly higher 4.5 hr after instillation than that of the comparable baseline recording (p = 0.035 with Bonferroni's correction); BP, PR, and NB(ONH) in the eye which received only the vehicle showed little change. Tissue blood velocity in the human ONH was increased at least temporarily by instillation of topical betaxolol twice daily for 3 weeks. Although the obtained increase is small and may be clinically insignificant, the potential of betaxolol that can affect the ONH tissue circulation in humans after 21 days of instillation is thought to deserve further investigation.

Effect of lomerizine, a new Ca(2+)channel blocker, on the microcirculation in the optic nerve head in conscious rabbits: a study using a laser speckle technique

We examined the effect of a new Ca(2+)channel blocker, lomerizine (KB-2796), and compared it with that of nilvadipine, on the optic nerve head circulation in conscious rabbits using a laser speckle method. Lomerizine (0.03, 0.1 and 0.3 mg kg(-1), i.v.) and nilvadipine (0.003, 0.01 and 0.03 mg kg(-1), i.v.) each significantly increased the normalized blur values (an index of tissue blood velocity) in the optic nerve head in a dose-dependent manner. Neither lomerizine nor nilvadipine caused a significant change in intraocular pressure. Lomerizine produced no significant change in mean arterial blood pressure, although at 0.3 mg kg(-1), i. v. heart rate was significantly increased 5 min after its administration. In contrast, nilvadipine significantly decreased mean arterial blood pressure at 5 to 15 min after its administration and increased heart rate at 5-30 min after its administration (both effects being dose-dependent). Our results indicate that while lomerizine, like nilvadipine, increased tissue blood velocity in the optic nerve head, it did not affect mean arterial blood pressure at the doses that affected optic nerve head circulation, unlike nilvadipine. The plasma concentration of lomerizine (free base) obtained from rabbits at 15 min after administration at a dose of 0. 03 mg kg(-1)i.v., when time there was a significant increase in tissue blood velocity in the optic nerve head, was very similar to plasma concentration with healthy subjects receiving lomerizine at 10 mg (5 mgx2) day(-1), p.o., a dose that achieved a significant reduction in the frequency and mean duration of headache attacks but did not affect the blood pressure or heart rate. These results suggest that lomerizine may be clinically effective in favorably affecting the optic nerve circulation without producing systemic effects such as the hypotension seen during treatment with other Ca(2+)channel blockers.

Effect of topical amosulalol on tissue circulation in the optic nerve head

The effect of topical 0.1% amosulalol on tissue circulation in the albino rabbit optic nerve head (ONH) was investigated using a laser speckle tissue circulation analyzer. Amosulalol was administered into one eye twice daily for 20 days, and vehicle was administered into the other eye in a masked, randomized manner. Intraocular pressure (IOP) was measured every 5 days. The normalized blur value (NB), a quantitative index of tissue blood flow velocity in the ONH, was measured before treatment and 2 hours after the last instillation on day 20. The IOP was also measured at 5-day intervals. Amosulalol decreased IOP by approximately 2 mmHg in the treated eyes (P < 0.01). There was no significant difference in NB between eyes before the first instillation, whereas NB was significantly greater (by approximately 16%) in the amosulalol-treated eye than in the control eye after completion of instillations (P < 0.01). The difference between NB after completion of instillations and that before the first instillation was significantly greater in the ONH of the amosulalol-treated eye than in the contralateral control eye (P < 0.01). Twice-daily instillation of 0.1% amosulalol for 20 days induced a significant increase in tissue blood velocity in the ipsilateral ONH in albino rabbits.