Subfoveal Choroidal Blood Flow Research Articles

Change in three-dimensional choroidal vessel network after AR device assisted 1-hour visual task in 2D/3D mode in young healthy subjects.

The purpose of the study was to investigate the changes of choroidal blood perfusion in different layers and quadrants and its possible related factors after 1 h visual task by augmented reality (AR) device in two-dimensional (2D) and three-dimensional (3D) mode, respectively. Thirty healthy subjects aged 22-37 years watched the same video source in 2D and 3D mode separately using AR glasses for 1 h with a one-week interval. Swept-source optical coherence tomography angiography (SS-OCTA) was performed before and immediately after watching to acquire choroidal thickness (ChT), three-dimensional choroidal vascularity index (CVI) of large- and middle-sized choroidal vessels and choriocapillaris flow voids (FV%) at macular and peripapillary area. Near point of accommodation (NPA) and accommodative facility (AF) were examined to evaluate the accommodative ability. Pupil diameters by infrared-automated pupillometer under scotopic, mesopic and photopic condition were also obtained. Compared with pre-visual task, the subfoveal CVI decreased from 0.406 ± 0.097 to 0.360 ± 0.102 after 2D watching (p < 0.001) and to 0.368 ± 0.102 after 3D watching (p = 0.002). Pupil sizes under different illuminance conditions became smaller after both 2D and 3D watching (all p < 0.001). AF increased after both 2D and 3D watching (both p < 0.05). NPA receded in post-3D watching (p = 0.017) while a not significant tendency was observed in post-2D. A reduction in subfoveal choroidal blood flow accompanied with pupil constriction was observed immediately after 1 h visual task using AR glasses in 2D and 3D mode. Accommodative facility improved after 2D and 3D watching with AR glasses, whereas decrease in the maximum accommodation power was only found in 3D mode.

Evaluation of choroidal thickness and choroidal vascular blood flow in patients with thyroid-associated orbitopathy (TAO) using SD-OCT and Angio-OCT.

The aim of this study was to evaluate changes in choroidal thickness and in choroidal vascular blood flow in patients with thyroid-associated orbitopathy (TAO) and their relationship with clinical features and disease activity using spectral domain optical coherence tomography (SD-OCT) and Angio-OCT technology. Eighteen patients and control subjects underwent a complete eye examination, OCT, and Angio-OCT. We also obtained angiographic scans at 3 different consecutive levels (L1, L2, and L3) below the choriocapillary. The subfoveal choroid was significantly thicker in TAO patients than the control eyes (285.6275 ± 32.5μm compared with 135.89 ± 19.8μm, respectively, p= 0.0089). The correlation analysis in the TAO group showed a significant correlation between the choroidal thickness and EUGOGO clinical score (r= 0.84, p= 8.44032E-07). Vascular flow of choriocapillary was markedly reduced in subjects with TAO compared with healthy subjects (49.78 ± 4.5 vs. 53.36 ± 1.07; p= 2.5105E-07) and vascular flow of the deeper layer L3 resulted higher in subjects with TAO than in healthy subjects (46.9 ± 20.23 and 41.475 ± 3.06; p= 0.01168). Subfoveal choroidal thickness and choroidal blood flow were significantly different in patients with TAO compared with healthy subjects.

Regulation of Choroidal Blood Flow During Isometric Exercise at Different Levels of Intraocular Pressure.

There is evidence that choroidal blood flow (ChBF) is regulated in a complex way during changes in ocular perfusion pressure (OPP). We hypothesized that ChBF regulates better in response to changes in mean arterial pressure (MAP) than in intraocular pressure (IOP). Eighteen volunteers (mean age, 26 years) were recruited for a randomized, three-way crossover design. MAP was varied via isometric exercise. IOP was either kept normal or elevated by 10 or 20 mm Hg by using a suction cup. Subfoveal ChBF was measured continuously for 8 minutes with laser Doppler flowmetry and OPP was calculated as 2/3*MAP-IOP. For data analysis, values from all subjects were pooled according to either IOP or MAP values, and correlation analyses were done. When data were grouped according to IOP, no correlation was observed between ChBF and MAP, but ChBF was lower the higher the IOP (P < 0.001). When data were grouped according to MAP, a significant correlation was found between ChBF and IOP (P < 0.001). When data were pooled according to IOP, the correlation between ChBF and OPP was weaker (P < 0.05). The OPP at which ChBF significantly increased from baseline was 61.3% ± 4.9% without suction cup, 65.2% ± 3.5% when IOP was increased by 10 mm Hg, and slightly lower when IOP was increased by 20 mm Hg (56.3% ± 4.8%, P = 0.07), but this effect did not reach the level of significance. The present study provides further evidence that the regulation of ChBF during changes in OPP is controlled by complex mechanisms in humans and has less capacity to adapt to IOP elevation than to MAP increase.

Choroidal blood flow after the first intravitreal ranibizumab injection in neovascular age-related macular degeneration patients.

To analyse choroidal blood flow (ChBF) changes after the first intravitreal ranibizumab injection in naïve, age-related macular degeneration (ARMD) patients. Subfoveal ChBF was assessed by laser Doppler flowmetry (LDF) in newly diagnosed ARMD patients. Both treated and untreated eyes were assessed in each subject at each visit before the first intravitreal ranibizumab injection as well as 24hr (day 1) and 7days after (day 7). Central macular thickness (CMT), best-corrected visual acuity (BVCA), systemic haemodynamic parameters and LDF parameters were evaluated at each visit. Nonparametric tests were used to compare data between visits and between treated and untreated eyes. Seventeen ARMD patients were included (12 women and five men, 78±8years old). At day 7 postintravitreal ranibizumab injection, the normalized choroidal blood velocity (ChBVel) change in the treated eye group was significant (-10.2%; p=0.006). The choroidal blood volume (ChBVol) did not change significantly after intravitreal injection of ranibizumab. There was a trend for a reduction in ChBF at day 7 (-9.1%, p=0.08). The sensitivity of the experiment was 12% for ChBVel, 16% for ChBVol and 9% for ChBF. In conclusion, the laser Doppler technique provides feasible and noninvasive measurements of blood flow parameters before and after intravitreal injection of antivascular endothelial growth factor (anti-VEGF) in patients with exudative ARMD. Choroidal blood velocity decreased as early as 7days after intravitreal ranibizumab injection, suggesting a vasoconstriction effect of anti-VEGF in large choroidal vessels in front of choriocapillaris (the site of LDF measurement).

Factors Associated With Choroidal Blood Flow Regulation in Healthy Young Subjects.

To analyze regulation of subfoveal choroidal blood flow (FLOW) during isometric exercise in healthy subjects in dependence of intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP), age, sex, fasting glucose, cholesterol, triglycerides, creatinine, and C-reactive protein levels and hematocrit. We retrospectively analyzed results obtained in 261 healthy subjects who underwent a period of 6 minutes of isometric exercise during which FLOW was measured continuously and MAP was measured every minute. From these data, OPP and choroidal pressure/flow curves were calculated. Subjects were grouped into tertiles with regard to the dependent variables, and pressure/flow relationships were compared. Choroidal blood flow started to increase at OPP values of approximately 65% dependent on the MAP/IOP tertile. A significant increase of FLOW from baseline was noted at 67.7 ± 2.1% in the lowest MAP tertile, at 67.7 ± 2.0% in the second MAP tertile, and at 61.8 ± 2.0% in the highest MAP tertile (P = 0.01). At the three IOP levels, FLOW started to increase at an OPP increase of 69.8 ± 2.1%, 70.1 ± 2.2%, and 65.4 ± 1.9% above baseline, respectively (P = 0.03). Choroidal pressure/flow curves were independent of the other variables. The present analysis indicates that FLOW regulation during isometric exercise is dependent on absolute MAP as well as IOP levels. This indicates that regulation depends on pressure levels at both the arterial and the venous side of the choroidal circulation and highlights the complexity of FLOW regulation during changes in OPP that cannot be simply characterized by classical autoregulation models.

LDF and assessment of autoregulation

AbstractThe main advantage of laser Doppler flowmetry is its excellent time resolution. This allows for continuous measurement of tissue blood flow during changes in perfusion pressure. As such the technique is optimally suitable to assess autoregulation, referring to the ability of a vascular bed to maintain its blood flow in response to changes in perfusion pressure. In the eye the technique has been applied for both measuring optic nerve head blood flow and subfoveal choroidal blood flow. For both vascular beds data have been obtained using either an experimental increase or decrease in ocular perfusion pressure. In addition, data are available showing the complex regulation of ocular blood flow when both mean arterial pressure and intraocular pressure are modified.

Choroidal blood flow and choroidal thickness

AbstractA progressive decrease of the choroidal blood flow related to macular degeneration was observed with glaucoma and aging. Abnormal regulation of the choroidal blood flow in patients suffering from neovascular AMD or Diabétic microangiopathy was also reported. Recent clinical studies have shown a decrease of the choroidal thicknessof in high myopia, AMD or in retinal dystrophies and increased choroidal thickness in central serous chorioretinopathy. Continuous real time Laser Doppler Flowmetry (LDF) has been used in humans for the evaluation of the subfoveal choroidal circulation and the investigation of the regulatory processes of the choroidal blood flow in response to various physiological stimuli, such as increase and decrease of the ocular perfusion pressure. The correlation of the subfoveal choroidal blood flow with the anatomical changes of the choroidal circulation, as observed by enhanced depth imaging optical coherence tomography(EDI‐OCT), was investigated in healthy volonteeres. No significant correlation was found between the subfoveal choroidal thickness and the choroidal blood flow. However, decreased subfoveal choroidal thickness was associated with decreased refractive error and axial length.

Pulsatile versus non‐pulsatile choroidal blood flow in Primary Open‐Angle Glaucoma (POAG)

AbstractPurpose After demonstrating altered subfoveal choroidal blood flow(F)in POAG (AbouSamra et al,Acta Ophthal 2012,we now studied the waveform of the pulsatile component of F(FP) in normal subjects and POAG patients. Methods Using laser Doppler Flowmetry (LDF,F and FP were measured in 17 healthy controls and 19 age‐ and sex‐matched POAG patients. We determined the waveform amplitude A(=1‐FPdiast/FPsyst) during the heart beat and the times T(d‐s) and T(s‐d) to increase from the diastolic to the systolic and to decrease from the systolic to the diastolic values of FP, respectively. Results Both mean F and mean FP were significantly (p &lt; 0.001 and p = 0.02, respectively) reduced in the POAG compared to the control group. However mean FP/mean F was not significantly different between groups. Relative to the brachial artery value, the A‐value at the subfovea was significantly increased in POAG compared to controls. The mean vascular resistance (R = mean perfusion pressure /mean F) was markedly increased(p &lt; 0.0001 in the POAG group. There was no significant differences in T(d‐s) and T(s‐d) between the groups. Conclusion These LDF‐based findings further support the presence of hemodynamic alterations in the subfoveal choroid in POAG.

Choroidal circulation measurements by laser Doppler flux metry

AbstractContinuous real time Laser Doppler Flowmetry (LDF), has been used in humans, for the evaluation of the subfoveal choroidal circulation and the investigation of the regulatory processes of the choroidal blood flow in response to various physiological stimuli, as increases and decreases of the ocular perfusion pressure. A progressive decrease of the choroidal blood flow was observed with the aging and the progession of the age related macular degeneration. Abnormal regulation of the choroidal blood flow in patients suffering with neovascular AMD or Diabétic microangiopathy were also reported. The correlation of the subfoveal choroidal blood flow with the anatomical changes of the choroidal circulation as observed by OCT are under investigation.

This issue of Acta, printed and electronic

This issue of Acta, printed and electronic

Choroidal hemodynamic in myopic patients with and without primary open‐angle glaucoma

To investigate the change in subfoveal choroidal blood flow in patients with glaucoma and to assess the effect of myopia, as one of the vascular risk factors for glaucoma on this flow. Subfoveal choroidal blood flow in groups of 12 myopic and glaucomatous eyes has been investigated by means of the laser Doppler flowmetry (LDF), comparing the results with those of 17 myopic eyes without glaucoma, 34 non-myopic glaucomatous eyes and of 50 control eyes. The subfoveal choroidal LDF parameters, that is, blood velocity (ChBVel), volume (ChBVol), and flow (ChBF), as well as the vascular resistance were studied in each group. Statistical analysis was performed by means of anova and t-test according to the Bonferroni procedure for multiple comparisons. Pearson correlation was used to establish the correlations between the hemodynamic parameters and the degree of myopia in dioptres. All LDF parameters (ChBVel, ChBVol and ChBF) were significantly reduced in glaucomatous patients (1.3 ± 0.4, 0.14 ± 0.06 and 4 ± 2 respectively) and myopic patients with primary open-angle glaucoma (POAG) (1.3 ± 0.4, 0.08 ± 0.04 and 2 ± 0.7 respectively) and without POAG (1.2 ± 0.3, 0.11 ± 0.08 and 2 ± 1 respectively) in comparison with age-matched controls (1.5 ± 0.4, 0.27 ± 0.1 and 8 ± 2 respectively). On the other hand, the choroidal vascular resistance (Rm) was increased in the previously described studied patients groups (16 ± 7, 26 ± 9 and 24 ± 9 respectively) compared with controls (7 ± 2). The LDF parameters did not differ significantly between myopic subjects without and with POAG (p = 0.09, p = 0.09, p = 0.2, p = 0.08 and p = 0.9 respectively). Compared to patients with emmetropic glaucomatous, significant reduction in the ChBVol and ChBF and increased Rm were recorded in patients with glaucomatous myopia (p = 0.05, p = 0.04 and p = 0.04 respectively). Pearson correlation demonstrated a significant correlation between the degree of myopia in dioptres and the ChBF (p = 0.012). The subfoveal choroidal LDF parameters were reduced in patients with POAG and myopia. Theses alterations are more in glaucomatous patients with myopia in comparison with age-matched glaucomatous patients without myopia. These data suggest that the impaired choroidal circulation caused by myopia might be an important additional risk factor involved in the glaucomatous damaging process.

Relationship Between Choroidal Thickness and Choroidal Circulation in Healthy Young Subjects

To investigate the relationship between the choroidal thickness and choroidal blood flow in healthy young subjects. Retrospective, cross-sectional study. We examined 25 eyes of 25 healthy young Japanese subjects. The subfoveal choroidal thickness was measured by enhanced depth imaging optical coherence tomography (EDI-OCT). The total choroidal blood flow and subfoveal choroidal blood flow were evaluated by pulsatile ocular blood flow using Langham OBF computerized tonometry and the choroidal blood flow using laser Doppler flowmetry. The refractive error, intraocular pressure, and axial length were also measured. The mean refractive error was -3.4 ± 3.1 diopters, mean intraocular pressure 15.3 ± 1.7 mm Hg, and axial length 25.4 ± 2.0 mm. The subfoveal choroidal thickness was correlated positively (r = 0.785, P < .01) with the refractive error and negatively (r = -0.735, P < .001) with the axial length. No significant correlation was found between the subfoveal choroidal thickness and the pulsatile ocular blood flow or choroidal blood flow. Our results suggested that there were no significant correlations between the subfoveal choroidal thickness and the total choroidal blood flow and the subfoveal choroidal blood flow in healthy young subjects; however, decreased subfoveal choroidal thickness was associated with decreased refractive error and axial length.

Effect of Nifedipine on Choroidal Blood Flow Regulation during Isometric Exercise

To determine whether nifedipine, an L-type calcium channel blocker, alters choroidal blood flow (ChBF) regulation during isometric exercise in healthy subjects. The study was carried out in a randomized, placebo-controlled, double-masked, two-way crossover design. Fifteen healthy male subjects were randomly assigned to receive either placebo or nifedipine on two different study days. Subfoveal ChBF was measured with laser Doppler flowmetry while the study participants performed isometric exercise (squatting). This was performed before drug administration and during infusion of nifedipine and placebo, respectively. Mean arterial pressure (MAP) and intraocular pressure (IOP) were measured noninvasively, and ocular perfusion pressure (OPP) was calculated as &frac23; MAP-IOP. MAP and OPP increased significantly during all squatting periods (P < 0.01). The increase in ChBF was less pronounced than the increase in OPP during isometric exercise. Nifedipine did not alter the OPP increase in response to isometric exercise, but it significantly augmented the exercise-induced increase in ChBF (P < 0.001 vs. placebo). Although ChBF increased by a maximum of 14.2% ± 9.2% during the squatting period when placebo was administered, the maximum increase during administration of nifedipine was 23.2% ± 7.2%. In conclusion, the data of the present study suggest that nifedipine augments the ChBF response to an experimental increase in OPP. In addition, it confirms that the choroidal vasculature has a significant regulatory capacity over wide ranges of OPPs during isometric exercise. (ClinicalTrials.gov number, NCT00280462.).

Subfoveal choroidal blood flow and central retinal function in early glaucoma

To assess subfoveal choroidal blood flow (ChBF) in patients with early manifest glaucoma (EMG) and to compare blood flow with functional measures of central retinal integrity, standard automated perimetry (SAP) and pattern electroretinogram (PERG). Subfoveal ChBF was determined by confocal, real-time laser Doppler flowmetry in 24 patients with EMG [>-6 dB mean deviation (MD), age range: 29-77 years, visual acuity: 20/25-20/20] and 23 age-matched control subjects. All patients had a therapeutically (topical beta-blockers with or without prostaglandin analogues) controlled intraocular pressure (IOP < 20 mmHg). Subfoveal choroidal blood volume (ChBVol), velocity (ChBVel) and ChBF were determined as the average of three 60 second recordings. In all patients and controls, the PERG and SAP (Humphrey 30-2), following standardized protocols, were also recorded. In patients with EMG, reductions in average ChBVel and ChBF were roughly equal, respectively, by 30% and 33.4% (p < 0.01), when compared to control subjects, so that there was no significant difference in ChBVol between the two groups. Pattern electroretinogram amplitudes were reduced by 46% (p < 0.01) in patients compared to controls. No correlation was found between any of the ChBF parameters and PERG amplitude, or Humphrey 30-2 MD and pattern standard deviation. The results suggest a significant alteration of both ChBVel and ChBF in EMG, which does not appear to be associated with the severity of central retinal dysfunction. These findings may contribute to a better understanding of the pathophysiology of early glaucomatous damage in EMG and have implications for the treatment of this pathologic condition.

Choroidal Blood Flow Regulation after Posture Change or Isometric Exercise in Men with Obstructive Sleep Apnea Syndrome

Obstructive sleep apnea (OSA) syndrome generates hypertension, atherosclerosis, and endothelial and autonomic dysfunction, which may mutually interact with ocular vascular regulation. Exercise and posture changes can be used to manipulate blood pressure, ocular perfusion pressure (OPP), or both. It was hypothesized that choroidal vascular reactivity in response to isometric exercise and posture changes could be altered in OSA patients. Healthy men were matched 1:1 for body mass index, sex, and age with patients with newly diagnosed OSA without cardiovascular comorbidities. All subjects underwent sleep studies and cardiovascular phenotyping (24-hour blood pressure monitoring, arterial stiffness measurements, and cardiac and carotid echography). Choroidal reactivity was assessed by laser Doppler flowmetry, which measured subfoveal choroidal blood flow. During exercise, blood pressure parameters increased significantly within the same range, with a similar profile over time in OSA patients and control subjects. A significant linear relationship (P = 0.0003) was noted between choroidal vascular resistance and the OPP changes during exercise in OSA patients and control subjects. From the sitting to the supine position, a significant decrease in mean arterial pressure occurred in both groups (10.9%-13.4%; P < 0.001). In both populations, no significant change in choroidal blood flow or vascular resistance was found during the posture change. Choroidal blood flow responses to exercise and posture changes were unchanged after 6 to 9 months of continuous positive airway pressure treatment. This study strongly suggests that the regulation of choroidal blood flow, which depends on the orthosympathetic and parasympathetic systems, is unaltered in men with OSA who have no comorbidities.

Role of Adenosine in the Control of Choroidal Blood Flow during Changes in Ocular Perfusion Pressure

The purpose of the present study was to investigate whether the nucleoside adenosine is involved in the regulatory processes of choroidal blood flow (ChBF) during an experimental decrease in ocular perfusion pressure (OPP). In this randomized, double-masked, placebo-controlled, two-way crossover study, 14 subjects received either intravenous adenosine or placebo on two different study days. The suction cup method was used for a stepwise increase in intraocular pressure (IOP). Subfoveal ChBF was measured by laser Doppler flowmetry. Mean arterial pressure (MAP) and IOP were measured noninvasively. Ocular perfusion pressure was calculated as OPP = 2/3MAP - IOP. Adenosine increased ChBF significantly versus placebo before application of the suction cup (P < 0.05). When the suction cup was applied, a significant decrease in OPP was observed. This effect was comparable on all study days. The decrease in OPP was paralleled by a significant decrease in ChBF (maximum between -43% and -52%) which was less pronounced than the decrease in OPP (maximum between -62% and -64%). Neither placebo nor adenosine influenced the ChBF increase during suction cup-induced changes in OPP. The data of the present study confirm that the human choroid shows some regulatory capacity during a decrease in OPP. Adenosine influences basal vascular tone in the choroid but is not involved in the regulatory mechanisms during an increase in IOP. (ClinicalTrials.gov number, NCT00712764.).

Choroidal blood flow response to isometric exercise in patients with obstructive sleep apnea syndrome.

Abstract Purpose Obstructive sleep apnea syndrome (OSA) has been recently reported to be associated with ischemic and glaucomatous optic neuropathy. The physiopathology of these diseases includes an abnormal regulation in the optic nerve head vasculature. The aim of our study was to characterize the choroidal vascular reactivity to acute increase in ocular perfusion pressure due to exercise in OSA patients. Methods Fourteen newly diagnosed OSA patients were included in this prospective study. Control subjects were matched with OSA patients for body mass index (BMI), gender and age. At the screening visit, each subject underwent a general exam, cardiovascular, neurologic and ophthalmological examinations, and underwent complete overnight polysomnography. The LDF instrument used in this study to measure subfoveal choroidal blood flow (ChBF) measured the following parameters: ChBVel (kHz); volume, ChBVol (in arbitrary units, AU) and the relative flow, ChBF = ChBVel  ChBVol (in AU). Vascular choroidal reactivity was tested during squatting. Results OSA patients exhibited a similar choroidal reactivity during increase in OPP (i.e. stability of choroidal blood flow) than controls until an increase of OPP about 145%. We found a similar vascular resistance increase in both groups during increase of OPP. Conclusion This prospective comparative study explored for the first time the choroidal blood flow of OSA patients and showed that subfoveal ChBF reactivity to gas in OSA patients differed from that of healthy control subjects. These preliminary results suggest that choroidal vasculature of OSA patients remained vasoconstricted when OPP increased, due to a chronic sympathetic activation.

Influence of change in body position on choroidal blood flow in patients with obstructive sleep apnea syndrome

Abstract Purpose Obstructive sleep apnea syndrome (OSA) has been reported to be associated with ischemic and glaucomatous optic neuropathy (especially normal tension glaucoma). OSA per se is able to generate hypertension, atherosclerosis and autonomic dysfunction, all conditions possibly interacting with ocular vascular regulation. The aim of our study was to characterize the choroidal vascular reactivity to change in body position in OSA patients, as compared with matched healthy control subjects. Methods Eighteen newly diagnosed OSA patients were included in this prospective study. Control subjects were matched with OSA patients for body mass index (BMI), gender and age. At the screening visit, each subject underwent a general exam, cardiovascular, neurologic and ophthalmological examinations, and overnight polysomnography. The LDF instrument used in this study to measure subfoveal choroidal blood flow (ChBF), ChBVel , velocity (kHz); and volume, ChBVol (in arbitrary units, AU) Vascular choroidal reactivity was tested during the change in body position from the sitting to the supine position (10 min). Results OSA patients exhibited a similar choroidal reactivity during change in body position than controls with increased ChBVel (+15%), decreased ChBVol (‐11.6%), and unchanged ChBF. IOP increased by 14.2% in the supine position whereas ocular perfusion pressure remained stable. Conclusion This prospective comparative study showed for the first time unimpaired choroidal vascular reactivity in otherwise healthy OSA patients. This suggests OSA patients, without comorbidities, has long‐term adaptive mechanisms active in ocular microcirculation.

Choroidal Blood Flow and Progression of Age-Related Macular Degeneration in the Fellow Eye in Patients with Unilateral Choroidal Neovascularization

Cardiovascular risk factors such as smoking, hypertension, and atherosclerosis seem to play an important role in the development of choroidal neovascularization (CNV). Recent studies have also provided evidence suggesting that choroidal and retinal blood flow is decreased in patients with AMD. On the basis of these results, the hypothesis for this study was that lower choroidal blood flow is associated with an increased risk of CNV in patients with AMD. Forty-one patients with unilateral choroidal neovascular AMD were included in this observational longitudinal study. The fellow eyes of the patients served as study eyes. Subfoveal choroidal blood flow (FLOW) and fundus pulsation amplitude (FPA) were assessed with laser Doppler flowmetry and laser interferometry, respectively. A multivariate COX-regression model was used to test the hypothesis that low choroidal perfusion parameters are associated with the development of CNV. Of the 37 patients that were followed up until the end of the study, 17 developed CNV and 20 did not. The univariate COX-regression analysis shows that lower FLOW, systolic blood pressure, intraocular pressure, and FPA are risk factors for development of CNV. Moreover, the more advanced the AMD in the study eye, the higher the risk for CNV to develop in the fellow eye. Multivariate COX regression analysis indicated that only FLOW (P = 0.0071), FPA (P = 0.0068), and staging (P = 0.031) had statistically significant influences on the progression to CNV. The present study indicates that lower choroidal perfusion is a risk factor for the development of CNV in the fellow eye of patients with unilateral CNV.

CHOROIDAL BLOOD FLOW AFTER ISOVOLEMIC HEMODILUTION IN AN EYE WITH RETINAL VEIN OCCLUSION AND THE CONTRALATERAL HEALTHY EYE

To evaluate the effect of hemodilution on subfoveal choroidal blood flow in the human eye with or without retinal vein occlusion. Choroidal blood flow was measured using laser Doppler flowmetry in 28 patients with retinal vein occlusion in 1 eye. Isovolemic hemodilution was performed when hematocrit was >35%. Laser Doppler flowmetry parameters, velocity, volume, and flow were measured in both eyes in 4 sessions: 1 hour before and 1 hour after the first hemodilution on Day 1 and Day 7. Hematocrit decreased significantly by 23.7%, 19.8%, and 16.1% in the first hour, on the first day, and the seventh day after hemodilution, respectively (P < 0.001). The ocular perfusion pressure of the healthy eye and the eye with retinal vein occlusion decreased by 7.7% and 7.2% after 1 hour and by 5.3% and 4.7% 1 day after hemodilution, respectively (P < 0.01). After hemodilution, subfoveal choroidal blood velocity, volume, flow, and vascular resistance did not significantly change in either eye. Laser Doppler flowmetry measurement in the subfoveal choroid is a feasible technique for blood flow assessment in patients with retinal vein occlusion. A substantial change of hematocrit after isovolemic hemodilution does not lead to a significant change in choroidal blood flow. Vascular regulation is expected to keep blood flow constant and needs to be further explored.