Determination of laser energy density threshold leading to glare-induced blindness by pattern visual evoked potential in guinea pigs / 解放军医学杂志

ABSTRACT

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 currentpower 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.