Study On Corneal Injury Induced By 3.74μm Infrared Laser And 1～2μm Supercontinuum Light Source In Rabbits

[Background and objective]In recent years,the 3～5μm infrared laser and supercontinuum sources are getting wide range of applications.With the continuous progress of fiber optic technology and the increasing output power,the risk of human damage is gradually increasing,but there are few researches about its damage effect in domestic and foreign studies.In this study,the typical band of the two types of lasers（3.74μm infrared laser and 1～2μm supercontinuum）were selected to measure the threshold of rabbit corneal injury,observe the repair characteristics of the ultra-threshold dose damage by various technical means,and summarize the histopathological changes and repair rules of the two types of lasers.This work provides a solid experimental basis for the formulation of the laser safety standards,the determination of damage degree,and the repair process.[Methods]1.Experiment of corneal injury threshold caused by 3.74μm infrared laser and 1～2μm SC light source in rabbits:group of 3.74μm at the light spot area was 1.89 mm²,the irradiation time of 0.1s,1.0s and 10.0s,The spot area of rabbit cornea irradiated by 1～2μm SC light source was 3.14mm²,the irradiation time was 0.13～0.27 s.The corneal injury of New Zealand white rabbits was observed 1h after irradiation with different doses of laser.The damage threshold ED₅₀ was calculated,which was the corresponding laser dose when the damage incidence is 50%.2.Experiment of corneal injury effect and repair process caused by 3.74μm infrared laser and 1～2μm SC light source in rabbits:The corneal injury was observed by gross,slit lamp,and OCT at immediately,6 h,1d,3d,7d,14d,28d,90d,and 180d after irradiation with several times of threshold dose.In addition,the repair process after injury was studied by HE and immunohistochemical staining.[result]1.The corneal injury thresholds of New Zealand white rabbits were 3.73 J/cm²,7.91 J/cm² and 31.1 J/cm² under the irradiation time of 0.1s,1.0s and 10.0s,the threshold damage observed under the slit lamp was manifested as a"white band"of shallow corneal scattering,and the injury was repaired 24 h after irradiation.2.The irradiation time of 1～2μm SC light source was 0.15 s,the damage threshold was 16.7 J/cm²,and the observation threshold damage under the slit lamp was slightly enhanced by slight full layer reflection,and the injury was repaired 24 h after irradiation.3.The corneal injury induced by 3.74μm laser in rabbits deepened with the increase of irradiation dose.At a dose of 16 J/cm²,the lesion was slightly superficial under the slit lamp,and it could be repaired to transparency at 28 days,and the OCT and pathological manifestations of injury affected the injury was affected by the epithelial layer and the superficial layer of the corneal stroma,and it returned to normal at 28 days;under the slit lamp at the 32 and 64 J/cm² doses,the full layer of the cornea was scattered"white band",reflective enhancement was still visible after 180 days,the OCT and pathological manifestations of injury affected the entire cornea layer,and the corneal stroma thinned after 180 days;Under the slit lamp at 128 J/cm² dose,the central depression is presented,the surrounding bulging"crater",the reflection enhancement is still visible after 180 days,the injury of OCT and pathology shows that the corneal stroma disintegrates and disappears or even carbonizes,and the corneal stroma thinned after 180 days.4.During the repair of 3.74μm laser corneal damage,the inflammatory reaction was obvious at 6h to 3d,the corneal edema of the injured area,accompanied by different degrees of redness and swelling of the conjunctiva of the eye,the increase of ocular endocrine,and the infiltration of neutrophils;The neonatal corneal epithelium can be seen 1 d after the injury of the corneal epithelium to cover the injured area;Stromal cell-free regions are produced 3d after matrix damage,and peripheral stromal cells are filled into cell-free regions at 7d-28d;retrocorneal fibrous membrane is produced at 3d-28d after endothelial damage.5.Immunohistochemical staining showed no positive cell production at any time point in the 16 J/cm² dose group,and immunohistochemistry at 32 J/cm²,64 J/cm²,and128 J/cm²showed the presence ofα-SMA positive cells in the stromal layer 3 days after injury,Collagen III positive cells 7 days after injury,and both stained positive cells disappeared at 90 days.6.The energy density reaching 33 J/cm² could destroy the corneal endothelium and cause full-thickness corneal injury in group of 1～2μm SC light.The energy density reaching 66 J/cm² under the slit lamp is manifested as a"white band"of full-layer scattering of the cornea,and reflective enhancement is still visible at 180 days.Pathology shows that the lesion involves the entire corneal layer,and the corneal stroma thins after 180 days.[Conclusion]1.The corneal injury thresholds of New Zealand white rabbits were 3.73 J/cm²,7.91 J/cm² and 31.1 J/cm² under the irradiation time of 0.1s,1.0s and 10.0s,the corneal injury threshold with irradiation time by 3.74μm laser obeys H_th=9.72t^0.46.and compared with the MPE value corresponding to the current safety standard IEC-60825,the safety factors are more than 10,indicating that there is sufficient safety space for the irradiation regulations in this band.2.The damage threshold 16.7 J/cm² at the irradiation time in 0.15s by 1～2μm SC light source is nearly 4 times of that 3.73 J/cm² at the irradiation time by 3.74μm infrared laser.3.3.74μm laser damage is dose-dependent,threshold dose damage mainly involves the epithelial layer,deepening with the increase of irradiation dose,2 times threshold dose damage involves the shallow matrix layer,4 times,8 times,16 times the threshold dose damage involves the entire corneal layer,and 16 times the threshold dose even causes the cornea to approach penetrating injury.1 to 2μm SC light source 2x and4x threshold dose injury directly penetrate the entire cornea layer,resulting in endothelial damage.4.The 3.74μm laser and 1-2μm SC light source administered to the 2 times threshold dose group returned to normal 28 d after injury,while the corneal transparency and pathological structure of the 3.74μm laser and 1-2μm SC light source4-16 times and above after the injury until 180 d could not return to normal.5.3.74μm positive cells expressingα-SMA appeared 3 d-28d after injury in the 4-16 times threshold dose groups of the laser,indicating the appearance of fibroblasts;Positive cells expressing Collagen III appeared in 7d-28d,indicating the production of nascent collagen fibers,staged scarring;No positively expressed cells were seen in the 2times threshold dose group,indicating that this dose did not cause corneal scarring.