Screening of optimal ultrasound parameters after intravitreal injection of microbubble in normal rabbit eyes

Background

Ultrasound microbubbles play important effects on delivery of drug or gene, which can significantly improve the transfection efficiency of drug or gene after ultrasonic irradiation.However, different ultrasonic irradiation parameters have different biological effects on different cells.

Objectives

This study was to investigate the effects of ultrasound microbubble on normal rabbit retina in different ultrasound intensities and irradiation time and provide the experimental basis for the treating study of fundus diseases with ultrasound microbubble.

Methods

Eighteen clean New Zealand albino rabbits were randomized into blank control group, simple ultrasound radiation group, simple intraocular injection group and intraocular injection+ low, moderate and high intensity ultrasound groups.No intervention was performed in the blank control group.Only 2.0 W/cm² ultrasound radiated for 60 seconds or 0.1 ml microbubbles were injected in vitreous cavity respectively in the simple ultrasound radiation group or simple intraocular injection group.The ultrasound with the intensity of 0.5, 1.0 and 2.0 W/cm² radiated the eyes with intraocular injection of microbubbles for 60 seconds in the intraocular injection+ low, moderate and high intensity ultrasound groups, respectively.The photography of ocular anterior segment, direct ophthalmoscopy and color fundus photography were performed before operation, immediately after operation and 1 day, 7 days after operation.The retinas were isolated in the seventh day and hematoxylin & eosin staining was carried out for the evaluation of retinal morphology.The ultrastructure of the retinas was examined by transmission electron microscope.This study protocol was approved by Ethic Committee of Experimental Animals Use and Care in Shenzhen Eye Hospital.

Results

There were not abnomal findings by slit lamp microscope and ophthalmoscope in the eyes of various groups at different time points.In the intraocular injection+ moderate and high intensity ultrasound groups, the loosening of retinal layers, disorder of photoreceptors, thinning of inner and outer nuclear layers as well as the decrease of retinal ganglion cells (RGCs) were exhibited under the optical microscope, and mitochondrial swelling of photoreceptors, noneven of chromatin in nucleus and losing of RGCs were found under the transmission electron microscope.However, the retinal morphology and ultrastructure were normal in the blank control group, simple ultrasound radiation group, simple intraocular injection group and intraocular injection+ low intensity ultrasound group.

Conclusions

Ultrasound irradiation in the intensity 0.5 W/cm² for 60 seconds is safe and suitable for retina in the eyes with intraocular injection of microbubble.This result provides an experimental basis for the management of fundus diseases by ultrasound microbubble.