Retrobulbar circulation in patients with age-related maculopathy

Correlation between retinal oxygen saturation and the haemodynamic parameters of the ophthalmic artery in healthy subjects

PURPOSE

The aim of the study was to obtain the values of oxygen saturation in retinal vessels and ophthalmic blood flow parameters in a healthy Caucasian population and assess whether the oximetry parameters are affected by the flow rate or the vascular resistance.

METHODS

The spectrophotometric retinal oximetry and colour Doppler imaging (CDI) of retinal vessels were successfully performed with 52 healthy subjects (average age 29.7 ± 5.6 years). The retinal oximeter simultaneously measures the wavelength difference of haemoglobin oxygen saturation in retinal arterioles and venules. The arteriolar and venular saturation in both eyes was measured. The peak systolic (PSV) end diastolic (EDV) velocities, resistive (RI) and pulsatility (PI) indices were obtained for both eyes using CDI in the ophthalmic artery. A paired t-test and two sample t-tests were used for statistical analyses. The correlation was assessed using the Pearson coefficient correlation.

RESULTS

The mean oxygen saturation level was 96.9 ± 3.0% for the retinal arterioles and 65.0 ± 5.1% for the retinal venules. The A-V difference was 31.8 ± 4.6%. The mean of the measured haemodynamic parameters was PSV 46.6 ± 9.4 cm/s, EDV 12.0 ± 3.5 cm/s, PI 1.68 ± 0.38 and RI 0.74 ± 0.05. No significant difference in oxygen saturation and haemodynamic parameters was found between the left and the right eyes or the dominant and non-dominant eye. The oximetry and ultrasound values were sex independent. The Pearson correlation coefficient demonstrated a significant yet weak negative correlation between A-V difference and RI (r = -0.321, p = 0.020).

CONCLUSIONS

A negative correlation between A-V difference and resistance index was observed, suggesting that reduced oxygen consumption may reflect the increased vascular tone of the ophthalmic vessels, which is likely determined by autoregulatory mechanisms.

Radial Peripapillary Capillary Plexus Sparing and Underlying Retinal Vascular Impairment in Intermediate Age-Related Macular Degeneration

Purpose

To examine location-specific retinal vascular changes in intermediate age-related macular degeneration (iAMD) using age-matched, high-density en face optical coherence tomography angiography (OCTA) cluster analysis.

Methods

En face OCTA images of the 6 × 6 mm macular area were retrospectively acquired from 60 iAMD eyes and 60 age-matched normal eyes and then subdivided into 126 × 126 (47.62 × 47.62 µm) grids within the superficial and deep vascular complex. Grid-wise vessel perfusion (VP) were compared between iAMD and normal eyes from the corresponding 10-yearly age cohort, forming difference plots. Difference plots were further separated by normative topographical map spatial clusters (C_1-6), derived from normal_database eyes (n = 236, 20–81 years old).

Results

Overall difference plots showed decreased VP in the superficial (−12.19%) and deep vascular complex (−6.44%) of iAMD compared to normal eyes (P < 0.0001 both comparisons). Cluster-based difference plots highlighted nonuniform changes in the superficial vascular complex, with sparing of VP at the nasal macula (corresponding to the radial peripapillary capillary plexus) versus decreased VP toward the temporal macula and foveal avascular zone (FAZ) (C_1–6 all comparisons P < 0.0001, except C₁ vs. C₂P > 0.99 and C₄ vs. C₅P = 0.11). The deep vascular complex displayed diffusely decreased VP, greater at the FAZ (P < 0.0001).

Conclusions

High-density en face OCTA cluster analysis suggests relative sparing of the radial peripapillary capillary plexus and impairment of underlying retinal vasculature, supporting potential anterograde transsynaptic degeneration in iAMD. These location-specific data may better guide future diagnostic and management protocol of iAMD.

Laser Acupuncture in Open-Angle Glaucoma Treatment: A Retrospective Study of Eye Blood Flow

Patients with glaucoma can show blood flow anomalies at the eye vessel level. A causal relationship is reasonably expected, but so far, it has not been demonstrated. Traditional Chinese medicine indicates that acupuncture can promote specific blood perfusion in specific body districts. Ninety-eight patients with open-angle glaucoma were treated with an ultralow light-level laser, according to a specific acupuncture protocol, and their blood flow was measured before and after a six-week treatment cycle. Doppler measurements showed significant modifications in both pulsatility and resistivity indexes. The most relevant outcome of this study is that the applied treatment demonstrated its effectiveness not only in vasodilation but also in perfusion control that seems to restore appropriate functionality. The protocol therefore should be investigated in future controlled studies and perhaps in other blood perfusion-related pathologies.

Different effect of serotonin on intracellular calcium ion dynamics in the smooth muscle cells between rat posterior ciliary artery and vorticose vein

5-hydroxytriptamine (5-HT: serotonin) is an important transmitter that causes vessel constriction, although few studies have examined the effect of 5-HT on venous smooth muscles. The intracellular Ca(2+) concentration ([Ca(2+)]i) plays an essential role in stimulus-response coupling in numerous tissue/cells including vascular smooth muscle cells. The present study was performed to examine whether differences between arteries and veins in the response to 5-HT can be detected under confocal microscope with respect to [Ca(2+)]i dynamics. In posterior ciliary arteries of rats, 5-HT induced a [Ca(2+)]i increase. The 5-HT-induced responses were caused by both Ca(2+) influx and mobilization. Agonist and antagonist experiments revealed that arterial smooth muscles possess 5-HT1a, 1b, 2 (Gprotein-coupled type) and 5-HT3 (ion channel type) receptors, and that 5-HT2 in particular plays a major role in these responses. For vorticose veins, the 5-HT-induced responses were also caused by both Ca(2+) influx and mobilization. However, the cAMP dependent pathway (5-HT4-7) was found to be significant in vasocontraction with respect to 5-HT in these vessels. Thus, Ca(2+) mobilization was induced by 5-HT2 and 5-HT4-7 in a vessel-dependent manner, whereas Ca(2+) influx universally was induced by 5-HT3. These results indicate that the posterior ciliary arteries and vorticose veins in the same tissue might differ greatly in their responses to stimulus.

Colour Doppler analysis of ophthalmic vessels in the diagnosis of carotic artery and retinal vein occlusion, diabetic retinopathy and glaucoma: systematic review of test accuracy studies

Background

Colour Doppler analysis of ophthalmic vessels has been proposed as a promising tool in the diagnosis of various eye diseases, but the available diagnostic evidence has not yet been assessed systematically. We performed a comprehensive systematic review of the literature on the diagnostic properties of Colour Doppler imaging (CDI) assessing ophthalmic vessels and provide an inventory of the available evidence.

Methods

Eligible papers were searched electronically in (Pre) Medline, Embase and Scopus, and via cross-checking of reference lists. The minimum requirement to be included was the availability of original data and the possibility to construct a two-by-two table. Study selection, critical appraisal using the QUADAS II instrument and extraction of salient study characteristics was made in duplicate. Sensitivity and specificity was computed for each study.

Results

We included 11 studies (15 two-by-two tables) of moderate methodological quality enrolling 820 participants (range 30 to 118). In 44.4% participants were female (range 37–59% in specific subgroups). CDI was assessed for internal carotid stenosis, diabetic retinopathy, glaucoma, and branch or central retinal vein occlusion diagnosis. There was insufficient data to pool the results for specific illnesses. For the assessments of ophthalmic arteries, mean sensitivity was 0.69 (range 0.27–0.96) with a corresponding mean specificity of 0.83 (range 0.70–0.96). Mean sensitivity of the central retinal artery assessments was 0.58 (range 0.31–0.84) and the corresponding mean specificity was 0.82 (range 0.63–0.94).

Conclusions

Robust assessments of the diagnostic value of colour Doppler analysis remain uncommon, limiting the possibilities to extrapolate its true potential for clinical practice.

PROSPERO 2014:CRD42014014027.

Evaluation of retrobulbar blood flow by color doppler ultrasonography after intravitreal ranibizumab injection in patients with neovascular age-related macular degeneration

PURPOSE

This study aimed to evaluate the changes in retrobulbar blood flow by using color Doppler sonography in patients who had undergone intravitreal ranibizumab injection for neovascular age-related macular degeneration (AMD).

METHODS

The study comprised 37 AMD patients who had undergone intravitreal 0.5 mg ranibizumab injection. The ophthalmic artery, central retinal artery, and short lateral posterior ciliary artery of both eyes of patients were evaluated by color Doppler sonography. Peak systolic velocity, end-diastolic velocity, and resistance index were calculated before injection, and after injection on day 7 and day 30. The pre- and postinjection values were compared using Wilcoxon signed rank test.

RESULTS

In a comparison with the preinjection values of peak systolic velocity, end-diastolic velocity, and resistance index, the postinjection values at both day 7 and day 30 showed no statistically significant difference in ophthalmic artery, lateral posterior ciliary artery, and central retinal artery (p > 0.05). Similarly, for the same parameters, pre- and postinjection values in the uninjected fellow eye showed no statistically significant difference (P > 0.05).

CONCLUSIONS

Intravitreal ranibizumab injection for neovascular AMD does not cause a significant change in the retrobulbar blood flow in either the injected eye or the fellow eye.

Short-term effects of intravitreal bevacizumab (Avastin(®)) on retrobulbar hemodynamics in patients with neovascular age-related macular degeneration

PURPOSE

To evaluate the short-term effects of intravitreal bevacizumab on retrobulbar hemodynamics in patients with neovascular age-related macular degeneration (AMD).

METHODS

This study was carried out at Ataturk Training and Research Hospital 1st Ophthalmology Clinic, Ankara. Fourteen patients with neovascular AMD, who were treated with intravitreal injection of bevacizumab, were included in this study. Peak systolic velocity (PSV), end-diastolic velocity (EDV) and resistivity index (RI) were measured with colour Doppler imaging (CDI) in the ophthalmic artery, central retinal artery (CRA) and posterior ciliary artery.

RESULTS

The mean age of the 14 patients was 78 ± 9 (64-87). Of the 14 patients, eight were men and six were women. Colour Doppler imaging measurements of EDV (p = 0.015) and RI (p = 0.009) parameters of CRA revealed statistically significant difference among all three periods. End-diastolic velocity values decreased at the end of the 1st week and returned close to preoperative values at the end of the 1st month after the procedure. Also, EDV of posterior ciliary artery (PCA) decreased at the end of the 1st week and returned close to preoperative values at the end of the 1st month after the procedure. Resistivity index of PCA showed a temporary increase at the end of the 1st week and returned close to preoperative values at the end of the 1st month after the procedure.

CONCLUSION

Injection of bevacizumab decreased blood velocities of CRA and PCA and increased RI of CRA and PCA in the early postoperative period and returned to preoperative values at the end of the first month.

In vitro simulation of the first technique for non-invasive measurement of volumetric ophthalmic artery blood flow in humans

BACKGROUND AND OBJECTIVE

To evaluate the accuracy, reproducibility, and variability of volumetric flow measurements taken by color Doppler imaging ultrasound, using an in vitro "phantom" model to simulate the ophthalmic artery.

MATERIALS AND METHODS

An agar flow phantom with two wall-less lumens was constructed to simulate the ophthalmic artery. Velocity and volumetric flow measurements were taken for various flow rates and ultrasound probe positions. The measurements were analyzed for accuracy, reproducibility, and variability.

RESULTS

Velocity measurements were more accurate than flow measurements (8 of 24 vs 3 of 24 accurate trials). The average coefficient of variation for volumetric blood flow was 11.4% (n = 120). Volumetric flow significantly correlated with velocity (R(2) = 0.408, n = 600, P < .001). The highest correlation was achieved using the large lumen with the probe held at 75 degrees , offset to the flow (R(2) = 0.862, n = 75).

CONCLUSION

Based on an in vitro model, non-invasive color Doppler imaging recordings of volumetric flow measurements in the ophthalmic artery significantly correlated with velocity and higher correlations were found using the larger lumens, although the data showed a lack of high accuracy in measurements of flow and velocity.

Blood velocity measurement in the posterior segment of the rabbit eye using combined spectral Doppler and power Doppler ultrasound

BACKGROUND

It is challenging for the current Doppler imaging to detect blood flow in small retinal vessels. Power Doppler, with its high sensitivity to detect minimal blood flow, can be used with spectral Doppler to measure blood velocity in small vessels of the eye and orbit.

METHODS

Sixteen eyes of twelve normal pigmented rabbits were studied, using a dedicated small animal, high-resolution imaging unit (Vevo 770) and 17.6 MHz ultrasound probe. Spectral Doppler (ISPPA = 67.1 W/cm(2), ISPTA = 483.7 mW/cm(2), MI = 0.5) was combined with power Doppler (ISPPA = 137.7 W/cm(2), ISPTA = 83.1 mW/cm(2), MI = 0.77) to measure the blood velocity over each identified vessel, including the central retinal artery and vein, branch retinal artery and vein, choroidal vein, and the long and short posterior ciliary artery. Three readings from each vessel were averaged to reduce measurement error. Three indices were calculated from the arterial blood velocity readings: the resistive index, the pulsatility index and the A/B ratio.

RESULTS

The highest arterial blood velocity was measured over the long posterior ciliary artery; peak systolic velocity was 18.29 cm/s and end diastolic velocity was 16.63 cm/s, while the lowest arterial blood velocity was measured over the branch retinal artery; peak systolic velocity was 5.08 cm/s and end diastolic velocity was 3.25 cm/s. On the other hand, the highest venous blood velocity was measured over the choroidal veins (7.0 cm/s), and the lowest venous blood velocity was measured over the branch retinal vein (2.88 cm/s). No statistically significant difference was observed between the nasal and temporal retinal arterial blood velocity. Combining power Doppler with spectral Doppler imaging caused no damage and is a safe technique to measure blood velocity.

CONCLUSION

A combination of spectral Doppler and power Doppler ultrasound can be used as a noninvasive and efficient tool for reproducible measurement of the blood velocity in the posterior segment.

Topographic variation of the choroidal watershed zone and its relationship to neovascularization in patients with age-related macular degeneration

PURPOSE

To evaluate the patterns of choroidal watershed zones (WZs) in exudative age-related macular degeneration (AMD) and to describe their relationship with choroidal neovascularization (CNV).

METHODS

We retrospectively evaluated 50 digital indocyanine green video-angiograms of 50 patients with exudative AMD demonstrating one or more WZs. In addition, the relationship between the site of CNV and the WZ was analysed.

RESULTS

A stellate WZ was observed in 30 of 50 (60%) patients. Choroidal neovascularization occurred within the centre of the WZ in all cases. The WZ was vertically oriented in 18 of 50 (36%) patients. When the WZ coursed through or extended into the fovea, CNV occurred within the WZ, but it occurred at its margin when the WZ did not involve the fovea. An angled WZ coursing through the fovea with CNV occurring within it was observed in two of 50 (4%) patients.

CONCLUSIONS

In exudative AMD, the WZ most commonly conformed to the stellate pattern, followed by the vertical and angled patterns. Choroidal neovascularization occurred within the WZ in 44 of 50 (88%) patients. When the WZ did not involve the fovea (12%), CNV occurred at its margin. The relationship between the site of CNV and macular WZs suggests that macular WZs may be areas which are vulnerable to AMD and which are predisposed to CNV by the resulting hypoxia-ischaemia.

Age-related macular degeneration and the aging eye

Age-related macular degeneration (AMD) is an ocular disease that causes damage to the retinal macula, mostly in the elderly. Normal aging processes can lead to structural and blood flow changes that can predispose patients to AMD, although advanced age does not inevitably cause AMD. In this review, we describe changes that occur in the macular structure, such as the retinal pigment epithelium and Bruch's membrane, with advancing age and in AMD. The role of genetics in AMD and age-related changes in ocular blood flow that may play a role in the pathogenesis of AMD are also discussed. Understanding the pathophysiology of AMD development can help guide future research to further comprehend this disease and to develop better treatments to prevent its irreversible central vision loss in the elderly.

Ocular blood flow in diabetes and age-related macular degeneration

The 2 leading causes of blindness in adults in the industrialized nations, diabetic retinopathy and age-related macular degeneration, have been investigated thoroughly with respect to their pathogenesis. In recent years, it has been discovered that dysfunctional ocular microcirculation appears to play a part in the development of both diseases. In diabetic retinopathy, it has been shown that the disease is associated with early retinal vascular dysregulation. In the later states of the disease, retinal tissue hypoxia is a major trigger of sight-threatening neovascularization. In age-related macular degeneration, there is increasing evidence that reduced blood flow in the choroid is associated with the development and progression of the disease. Knowledge of the pathophysiological vascular states underlying these diseases is essential for the assessment and development of future therapies.

The Relationship Between Retrobulbar and Choroidal Hemodynamics in Non-Neovascular Age-Related Macular Degeneration

BACKGROUND AND OBJECTIVE

To evaluate the relationship between retrobulbar and choroidal hemodynamics in non-neovascular age-related macular degeneration.

PATIENTS AND METHODS

Thirteen patients with age-related macular degeneration were assessed by both color Doppler imaging and scanning laser ophthalmoscope indocyanine green (ICG) angiography. Color Doppler imaging was used to measure peak systolic and end diastolic velocity (from which the resistance index, a measure of the resistance to flow downstream, was calculated) in the retrobulbar vessels. Scanning laser ophthalmoscope ICG angiograms were analyzed by area dilution analysis for quantitative choroidal fluorescence intensity assessment. Color Doppler imaging parameters were correlated with scanning laser ophthalmoscope ICG area dilution analysis parameters.

RESULTS

A good correlation was found between the posterior ciliary arteries resistance index and scanning laser ophthalmoscope ICG area dilution analysis fluorescence duration.

CONCLUSIONS

Scanning laser ophthalmoscope ICG area dilution analysis "duration" may serve as an alternative to color Doppler imaging in assessing the resistance to blood flow in the posterior ciliary arteries.

Topography of the posterior arteries supplying the eye and relations to the optic nerve

PURPOSE

The aim of the study was to investigate the arterial blood supply of the intraorbital part of the optic nerve.

METHODS

The location, course, length and diameter of the central retinal artery (CRA) and posterior ciliary arteries were studied in 19 adult white male preserved cadavers of between 35 and 75 years of age.

RESULTS

In right eyes, the first branch of the intraorbital part of the ophthalmic artery was the CRA in 26.3% (5/19) and the CRA and medial posterior ciliary artery in 21% (4/19) of eyes. In left eyes, the first branch of the intraorbital part of the ophthalmic artery was the CRA in 47.4% (9/19) and the CRA and medial posterior ciliary artery in 26.3% (5/19) of eyes. The CRA was observed as a single branch in 57.9% and a trunk in 42.1% of right eyes, and as a single branch in 52.6% and a trunk in 47.3% of left eyes. The outer diameter of the CRA measured 0.6 +/- 0.1 mm (min-max 0.5-0.9 mm) in right eyes and 0.6 +/- 0.2 mm (min-max 0.4-0.9 mm) in left eyes. The CRA entered the optic nerve 7.5 +/- 2.2 mm (min-max 5.3-12.5 mm) behind the ocular bulb in right eyes and 7.4 +/- 2.3 mm (min-max 5.3-14.1 mm) behind it in left eyes, at its lower and medial side. The posterior ciliary arteries ran forward, divided into multiple branches and pierced the sclera close to the optic nerve medially, laterally or superiorly. The longitudinal capillaries ran between the optic nerve and the CRA antero-posteriorly, while the transverse capillaries surrounded the optic nerve. Collaterals from both the longitudinal and transverse capillaries joined to form a complicated capillary plexus.

CONCLUSION

This article confirms the well known variability of the arterial circulation of the intraorbital part of the optic nerve. Better understanding of the arterial anatomy of the intraorbital part of the optic nerve should enable appropriate modification of surgical techniques.

Chlamydia pneumoniae is not detectable in subretinal neovascular membranes in the exudative stage of age-related macular degeneration

PURPOSE

Age-related macular degeneration (AMD) is the most frequent cause of severe visual impairment in western countries, but its aetiology remains unclear. A growing body of evidence suggests that inflammation contributes to the pathogenesis of AMD, similarly to that shown for atherosclerosis. In view of a number of shared risk factors between the two entities and the hypothesized link between Chlamydia pneumoniae infection and atherosclerosis, we investigated whether C. pneumoniae might be involved in exudative AMD.

METHODS

To examine whether C. pneumoniae contributes to the development of subretinal neovascular (SRNV) membranes in AMD, 13 consecutive SRNV membranes surgically excised from patients with exudative AMD were collected and assayed for the presence of C. pneumoniae or other bacterial pathogens by means of polymerase chain reaction (PCR).

RESULTS

The age of patients ranged from 68 to 85 years (median 73.5 years). In all 13 SRNV membranes, no DNA of either C. pneumoniae or other pathogens was found by PCR.

CONCLUSIONS

These findings indicate that C. pneumoniae is not associated with the development of SRNV membranes in exudative AMD.

Retinal haemodynamics in patients with age-related macular degeneration

OBJECTIVE

To investigate whether there is an association between the magnitude of retinal haemodynamic abnormalities in patients with age-related macular degeneration (AMD) and the degree of severity of the AMD.

METHODS

A retinal laser Doppler system (Canon CLBF 100) was used to measure retinal arterial haemodynamic parameters in 25 eyes of 25 patients with AMD and nine eyes of nine age-matched control subjects. Severity of AMD was classified into Mild (n=11), Moderate (n=7), or Severe (n=7). The pulsatility ratio (PR), the pulsatility index (PI), and the resistivity index (RI) were determined.

RESULTS

PR, PI, and RI in the patients with AMD were each significantly higher than in the control group, and increased monotonically with increasing severity of AMD. However, there were no differences in mean blood velocity, arterial diameter, or blood flow rate among the groups. This suggests that the increased blood flow pulsatility in the retinal arteries of the eyes with AMD is not due to increased distal vascular resistance, but instead is likely due to a loss of compliance in the arterial vasculature leading to the eye.

CONCLUSION

Our results suggest that an increasing vascular rigidity in the systemic arterial circulation is directly associated with an increasing severity of AMD.

Correlation between capillary blood flow of retina estimated by SLDF and circulatory parameters of retrobulbar blood vessels estimated by CDI in diabetic patients

BACKGROUND

The aim of this study was to investigate the correlation between the recordings of scanning laser Doppler flowmetry (SLDF) of the retina and the recordings of color Doppler imaging (CDI) of the retrobulbar circulatory parameters in diabetic patients without diabetic retinopathy.

METHODS

Twenty-three diabetic patients without diabetic retinopathy were evaluated using SLDF for the apparent retinal circulation and using CDI for the apparent retrobulbar circulation in the central retinal artery, the central retinal vein and the short posterior ciliary artery. The circulatory parameters estimated in the retinal tissue using SLDF were velocity, volume and flow. The Circulatory parameters that were recorded using the CDI method were peak systolic velocity (PSV), end-diastolic velocity (EDV), mean velocity (MV), pulsatility (PI) and resistivity index (RI). We obtained the correlation coefficients between parameters of SLDF and CDI. Multiple regression analysis was performed with "flow" parameter of SLDF recordings as a dependent variable and all estimated CDI parameters as independent variables. Multiple linear regression was also performed, including the "flow" parameter of SLDF recordings as a dependent variable and PI of the CDI parameters of all the measured blood vessels as independent variables.

RESULTS

The "velocity" parameter of SLDF was significantly correlated with the PI in the central retinal artery (P=0.02), PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery, as recorded by CDI (P=0.003; P=0.02; P=0.002; P=0.01). The "volume" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.03; P=0.03) and the PSV in the short posterior ciliary artery (P=0.03), as recorded by CDI. The "flow" parameter of SLDF was significantly correlated with the PI and RI in the central retinal vein (P=0.01; P=0.01) and the PSV, MV, PI and RI in the short posterior ciliary artery (P=0.003; P=0.03; P=0.002; P=0.01) as measured by CDI. The multiple regression analysis was statistically non-significant (P=0.86). The multiple linear regression analysis indicated that from among the PI of the evaluated blood vessels, the PI of the short posterior ciliary artery was the most significant predictor of the "flow" parameter of SLDF (P=0.01).

CONCLUSION

This study suggests a positive correlation between the recordings of SLDF of the retinal tissue and the retrobulbar circulatory parameters of the CDI in diabetic patients without diabetic retinopathy.

Reproducibility and clinical application of a newly developed stabilized retinal laser Doppler instrument

PURPOSE

To describe a newly developed stabilized retinal laser Doppler instrument, to report the reproducibility of retinal blood flow measurements, and to present examples of its clinical application.

DESIGN

Experimental study.

METHODS

The intrasession, intersession, and interobserver reproducibility of retinal blood flow measurements obtained using the Canon Laser Blood Flowmeter model CLBF 100 was assessed. Intrasession: the coefficients of variation (CV) for repeated measurements (5X) of retinal vessel diameter (D), time-average centerline blood velocity (V(av)), and blood flow (F) were calculated at 18 sites along temporal retinal arteries and 18 sites along temporal retinal veins using both eyes in six healthy volunteers. Intersession: the correlation coefficients and average differences between two sets of measurements at the same 36 retinal sites made by one examiner on two different days were calculated. Interobserver: the correlation coefficients and average differences between two sets of measurements at nine sites (five arterial and four venous) in five eyes of five of the volunteers made by two examiners on the same day were calculated. Results from two patients, one with branch retinal vein occlusion (BRVO), and one with central retinal vein occlusion (CRVO), are used to illustrate abnormal retinal circulatory characteristics.

RESULTS

intrasession: CV (mean +/- SD) for D, V(av), and F were 5.5% +/- 2.2%, 13.1% +/- 6.3%, and 13.8% +/- 4.7% in arteries and 3.5% +/- 2.1%, 11.9% +/- 5.9%, and 12.7% +/- 5.5% in veins. Intersession/interobserver: strong correlations between measurements made by one examiner on two different days and by two examiners on the same day were found in D, V(av), and F. Average differences in F were 16.4% +/- 12.8% for intersession and 12.6% +/- 7.0% for interobserver comparisons. Results from the patient with BRVO show marked differences in flow characteristics in the affected quadrant compared with an unaffected quadrant in the same eye, and to the fellow eye. Results from the patient with CRVO show a dramatic improvement in flow characteristics after clearing of the occlusion.

CONCLUSIONS

The reproducibility results and the fact that blood flow is measured in actual units of microl/min indicate that the instrument can be used for reliable comparison of blood flow characteristics at different retinal vascular sites in the same eye, at comparable sites in both eyes, and for comparison between patients and healthy control subjects.