| Objective：High Intensity Focused Ultrasound (HIFU) uses Ultrasoundto transfer energy to the target tissue to achieve the goal of treatment. Themain treatment mechanism of HIFU includes thermal effect and cavitationeffect. The thermal effect of HIFU refers to, when ultrasound is absorbedby the organization, the sound energy is converted to heat energy,whichmakes the temperature of the target group within the instantaneous risen tomore than60℃and has no effect on target area organization. HIFUtechnique is widely used in medical fields such asgynecology,oncology,urology surgery.The application in ophthalmology ismainly concentrated on treatment of refractory glaucoma. HIFU has highaccuracy and focal region in biology has amounted to micron level, whichprovide the theory basis for us to apply to cornea. There are a lot ofliteratures about corneal refractive state changes caused by thermal effectof electromagnetic waves such as laser, radio frequency andmicrowave.Our early experiment has proved HIFU thermal effect canchange corneal refractive state in vitro rabbit eye. To further understand the biological effects of HIFU on living rabbits cornea, we established animalmodels of rabbits cornea irradiated by HIFU and observed for a period of3months in this experiment.In the first part, we established living animalmodels of rabbits cornea of HIFU irradiation with different power of HIFUto study the morphology changes of rabbits corneal tissue, so as topreliminarily determine the feasible range of HIFU irradiation power onliving rabbit corneas. In the second part, we irradiated living rabbit corneawith different HIFU power and corneal diameter to study the biologicaleffects of HIFU on the rabbits cornea and to observe the changes of rabbitcorneas refractive status after HIFU irradiation.Methods: In the first part,we selected CZF ultrasonic therapeuticapparatus in the experiment. The treatment parameter was set to: pulse1000, focal length5mm, the frequency of10.20MHz, irradiation time6s(the time for a constant speed motor rotate a circle). Irradiation pattern wasdesigned for circular ring and irradiation area was9mm area surroundingthe corneal stroma. On the basis of early experiment in vitro rabbitscornea,we selected irradiation power of0.5W,1W,1.5W,2W to theanimal models. We choosed3healthy New Zealand white rabbits (6eyes)and randomly divided rabbits into the experimental group and the blankcontrol group. The experimental group included4groups depending on thepower of HIFU irradiation, and each group had1eye. The remaining1rabbit (2eyes) was the blank control group. We observed the cornea, anterior chamber, lens of the experimental group under slit lampmicroscope and observed the fundus under indirect ophthalmoscope inpreoperation and1day postoperation. We also put to death all animals toobserve the focal region by different irradiation power after corneal tissueHE staining in1day postoperation.In the second part, we choosed13healthy New Zealand white rabbits and randomly divided rabbits intogroup A、B and C (group A1W/9mm, group B1.5W/9mm, group C1W/7mm),according to difference of HIFU irradiation power andirradiation corneal diameter.Group A included10eyes and group Bincluded8eyes and group C included8eyes. The rabbits were examinedwith slit-lamp microscope, auto refractometer, corneal topography,specular microscopy and non-contact tonometer preoperation and in3days,10days,1months,2months,3months postoperation respectively.Results:In the first part1.Slit lamp microscope: Rabbits cornea weretransparent, and crystal was transparent in preoperation. Irradiation rings oncornea were pale after HIFU irradiation.With the increase of the irradiationpower, irradiation gray ring were cloudy.2.Fundus examination: Therewasn’t obviously abnormal in preoperation and postoperation.3.Pathological section: Focal regions in the corneal stroma were oval, deepblue dye and boundaries clear in postoperation. With the increase of theHIFU irradiation power, focal regions showed a trend of larger gradually.And corneal tissue outside irradiation area hadn’t any obvious change. In the Second part1.Slit lamp microscope: Part of the cornealepithelium defected in irradiated area of24eyes (92.3%) after operationimmediately,with sodium fluorescein staining dyeing in the correspondingparts;while26eyes (100%) corneal epithelium completed3days later, withno sodium fluorescein staining dyeing.HIFU irradiation rings were opacityat first, and gradually became weak with the extension of observation timeafter postoperative.Irradiation rings couldn’t be identified in3monthspostoperation by naked eye,but only knowed under slit lamp microscope.2.Corneal topographic: Compared with preoperation, corneal curvature ofcentral3mm in1,2,3months postoperation were lower statisticallysignificant (P <0.05). Central corneal curvature in1month postoperationwas reduced.With the extension of postoperative observation time,therewas a trend of reduce gradually.3. Automatic refractometer: Diopter waspositively to increase trend, developing to the direction of hyperopia, whichwas consistent with the central corneal curvature.4. Non-contactintraocular pressure: Compared with preoperation, IOP was reduced in3,10days postoperation,and the difference was statistically significant (P <0.05).5. Corneal endothelial cell counts: No density decrease of cornealendothelial cells were found after operation compared with preoperation.(P＞0.05).Conclusions:1. Through the corneal tissue morphologicalobservision by different power of HIFU irradiation in living rabbit eyes, when HIFU treatment parameters as follows: pulse1000, focal length5mm, the frequency10.20MHz, irradiation time6s and irradiation diameter9mm, it is relatively safe to choose irradiation power1.5W or less onrabbit cornea.2. This study found that HIFU irradiated peripheral cornea ofrabbits can flat corneal and reduce the central curvature,which shows thatHIFU irradiated rabbit cornea may change refractive status.3. According toobservations of IOP and corneal endothelial cell after HIFU irradiation,HIFU is safe applied in rabbits cornea. |
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