Lesion Of Retinal Arteries Induced By Q-switched Nd: YAG Laser With Different Intensity In Pigmented Rabbits

Objective:To observe the histological changes of branch retinal arteries by directly radiation of Q-switched Nd:YAG laser with different intensity,and search the connection between the power of laser and lesion of retinal arteries in order to testify the safty of the therapy by Q-switched Nd:YAG laser.Methords:There is eighteen pigmented rabbits with thirty-six eyes.Two rabbits with four eyes were choosed at random to control.Other sixteen rabbits with thirty-two eyes were divided into four groups by average.The groups were A,B,C,D. Every four rabbits of each group was radiated by Nd:YAG laser with corneal contact lens.The Q-switched Nd:YAG laser was focused on the retinal arteries which distance from optic papilla about 1PD.One rabbits in each group was sacrified at two hours,there days,one week and one month after Q-switched Nd:YAG laser.Light microscopy and scan electron microscopy examination were performed for the histological changes of retina and retinal arteries.Result:(1)Slit-lamp biomicroscopy revealed the change of retinal:At the moment Nd:YAG laser was giving, the branch retinal arteries were not obviously changed ,we only saw some dove-colour retinal burn speekles on the retinal in A group, the boundary of these retinal burn speekles was obsure and the diameters were about 0.3mm; In B group ,C group and D group, the contraction of the branch retinal arteries was gradually obviouse with the increasing of power,the blood stream became thin,the dilating time of branch retinal arteries was prolong.The colour of retinal burn speekles changed from white to super white with the diameter enlarged gradually. The hemorrhage became more seriouse.Three days and one week after Q-switched Nd:YAG laser, the colour of retinal burn speekles was thin and the diameters were decurtate.The hemorrhages were obviously absorbed in the first three groups and vitreous hemorrhages in D group was observed.Those hemorrhages were gradually absorbed in the next one month. (2)Light microscopy examination: compared with control group,in the four groups, the retinal arteries broadened and presenced an increased amount of blood cells. Endothelial cell had no changed.The edema of nerve fiber layer and ganglion cell layer was observed in A group.With the increasing of energy power,injury occured from the inner layer to outer layer . Pyknosis and subretinal hemorrhage was found. In D group, we noted that out of the artries there were a lot of blood cells.After three days, neutrophils were observed in the nerve fiber layer and disapeared in the next week.One month later, the retinal was regeneration in A group and B group and was repaired by fibrous connective tissue in the C group and D group.(3)Electron microscopy examination: compared with control group,the retinal arteries were not obviously changed in A group,B group and C group.But in D group,the cytoplasm of endothelial cell was irregularity.A lot of pseudopodia and the edema of mitochondria were observed obviously. After one month, the endothelial cells recovery.Conclusion:1.The retinal arteries were irradiated by 1064nm Q-switched Nd:YAG laser, 1.4mJ laser energy could damage the retinal arteries but 0.8mJ ~1.2mJ couldn't.The threshold of power that cause damage of retinal arteries was 1.4 mJ possibly.2. The threshold of power that cause damage of retinal was lower than the retinal arteries.The damages of retinal arteries and retinal caused by laser under 1.2mJ were recoverability,however, the damages of retinal caused by 1.4mJ of laser was not .So, Q-switched Nd:YAG laser can induce the injury of retina and retinal arteries,but the damage can be recovered when the power was under the threshold.