Evaluation of ultrasound-assisted thrombolysis using custom liposomes in a model of retinal vein occlusion.

PURPOSE: To study the potential efficacy of ultrasound (US) assisted by custom liposome (CLP) destruction as an innovative thrombolytic tool for the treatment of retinal vein occlusion (RVO). METHODS: Experimental RVO was induced in the right eyes of 40 rabbits using laser photothrombosis; the US experiment took place 48 hours later. Rabbits were randomly divided into four equal groups: US+CLP group, US+saline group, CLP+sham US group, and no treatment group. The latter three groups acted as controls. Fundus fluorescein angiography and Doppler US were used to evaluate retinal blood flow. RESULTS: CLP-assisted US thrombolysis resulted in restoration of flow in seven rabbits (70%). None of the control groups showed significant restoration of retinal venous blood flow. CONCLUSIONS: US-assisted thrombolysis using liposomes resulted in a statistically significant reperfusion of retinal vessels in the rabbit experimental model of RVO. This approach might be promising in the treatment of RVO in humans. Further studies are needed to evaluate this approach in patients with RVO. Ultrasound assisted thrombolysis can be an innovative tool in management of retinal vein occlusion.

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.