图形视觉诱发电位在豚鼠眩光致盲激光能量密度阈值检测中的作用

目的 利用图形视觉诱发电位(PVEP)测定导致豚鼠眩光致盲的激光能量密度阈值.方法 健康成年雄性豚鼠27只,均在颅骨前囟前6mm、后10mm分别钻孔,植入长5mm、直径1.2mm的不锈钢螺钉,分别作为测量PVEP的参考电极和记录电极.根据实验选择的激光器波长不同(分别为635、660、690nm)将豚鼠随机分为3个组,每组9只(18眼),分别在照射前、照射后即刻记录PVEP,如激光照射引发眩光致盲,则在照射后2d和4d继续记录PVEP.将照射前测量PVEP的P波潜伏期和振幅作为正常对照值.激光照射后立即记录PVEP,记录不到PVEP波形时则将此时对应的电流作为该波长激光引起眩光致盲的阈值电流,计算对应功率(P)值,绘制电流-能量(p-I)曲线,计算各波长激光引起眩光致盲所需的能量密度阈值.将照射后2d和4d记录的PVEP的P波潜伏期和振幅与正常对照值比较,检验豚鼠视觉功能恢复的情况.结果 波长为635、660、690nm的激光器眩光致盲能量密度阈值分别为356.36×10-9、349.58×10-9、343.93×10-9J/cm2.三组中发生眩光致盲的豚鼠在2d后PVEP中P波潜伏期与其正常对照值比较差异均无统计学意义(t=- 0.356,P=0.729; t=0.492,P=0.633; t=- 0.445,P=0.666),振幅与正常对照值比较差异有统计学意义(t=1 1.01,P=0.000;t=5.223,P=0.000; t=5.702,P=0.000),4d后再次测量PVEP,三组P波潜伏期和振幅与其正常对照值比较差异均无统计学意义(潜伏期:t=1.329,P=0.213; t=2.040,P=0.069; t=-0.894,P=0.392;振幅:t=-3.030,P=0.768; t=0.194,P=0.850; t=-0.948,P=0.365).结论 635、660、690nm波长激光的眩光致盲能量密度阈值约350×10-9J/cm2.在测定激光造成眩光致盲的能量密度阈值时,PVEP可作为较好的检测指标且不会造成眼底器质性损伤.

Determination of laser energy density threshold leading to glare-induced blindness by pattern visual evoked potential in guinea pigs

Objective To explore the application of pattern visual evoked potential(PVEP) in examination of energy density threshold of laser beam that may lead to glare-induced blindness in guinea pigs.Methods Stainless steel bolts(5mm in length,1.2mm in diameter),as reference electrode and recording electrode for the PVEP measurement,were implanted into skulls of 27 guinea pigs,located in 6mm proximal to bregma and 10mm distal to bregma.These guinea pigs were randomly divided into three groups with 9(18 eyes) for each group,and they were exposed to laser beam at wave length of 635nm,660nm and 690nm,respectively.The PVEP was recorded in each group before and immediately after laser irradiation,and also on day 2 and day 4 after laser irradiation in guinea pigs blinded immediately after laser exposure.The latency and amplitude of P wave in PVEP before irradiation was considered as control value for each group.When PVEP could not be recorded instantly after laser irradiation,the intensity of electric current applied at that time was considered as threshold value of each laser beam.The power of electricity(P) values was then calculated,and energy density threshold that led to glare-induced blindness was figured out according to current-power curve(P-I curve).On day 2 and day 4 after irradiation,PVEP was additionally recorded,and latency and amplitude of P wave were compared with that of control values to examine the recovery of visual function of the blind guinea pigs.Results The energy density thresholds of the three laser beams at wave length of 635nm,660nm,690nm respectively were 356.36×10-9J/cm2,349.58×10-9J/cm2 and 343.93×10-9J/cm2.In guinea pigs became blind after exposure to laser beams at wave length of 635nm,660nm,690nm,the latencies of P wave recorded 2 days after blindness were not significantly different with control value of each group(t=-0.356,P=0.729;t=0.492,P=0.633;t=-0.445,P=0.666),while the difference in amplitudes was statistically significant(t=11.01,P=0.000;t=5.223,P=0.000;t=5.702,P=0.000).Four days after blindness,the latencies and amplitudes of P wave recorded on the guinea pigs were also compared with the control values,but no statistically significant difference was found(latency: t=1.329,P=0.213;t=2.040,P=0.069;t=-0.894,P=0.392;amplitude: t=-3.030,P=0.768;t=0.194,P=0.850;t=-0.948,P=0.365).Conclusions The energy density threshold of laser beams,at length wave of 635nm,660nm,690nm,may lead to glare-induced blindness in guinea pigs is around 350×10-9J/cm2.PVEP examination is a useful and harmless way to determine the energy density threshold of laser beam which will cause blindness.