Stanford University, Hansen Experimental Physics Laboratory, 452 Lomita Mall, Stanford, California 94305, USA.
J Biomed Opt. 2011 Feb;16(2):028004. doi: 10.1117/1.3542045.
Decreasing the pulse duration helps confine damage, shorten treatment time, and minimize pain during retinal photocoagulation. However, the safe therapeutic window (TW), the ratio of threshold powers for thermomechanical rupture of Bruch's membrane and mild coagulation, also decreases with shorter exposures. Two potential approaches toward increasing TW are investigated: (a) decreasing the central irradiance of the laser beam and (b) temporally modulating the pulse. An annular beam with adjustable central irradiance was created by coupling a 532-nm laser into a 200-μm core multimode optical fiber at a 4-7 deg angle to normal incidence. Pulse shapes were optimized using a computational model, and a waveform generator was used to drive a PASCAL photocoagulator (532 nm), producing modulated laser pulses. Acute thresholds for mild coagulation and rupture were measured in Dutch-Belted rabbit in vivo with an annular beam (154-163 μm retinal diameter) and modulated pulse (132 μm, uniform irradiance "flat-top" beam) with 2-50 ms pulse durations. Thresholds with conventional constant-power pulse and a flat-top beam were also determined. Both annular beam and modulated pulse provided a 28% increase in TW at 10-ms duration, affording the same TW as 20-ms pulses with conventional parameters.
降低脉宽有助于限制损伤、缩短治疗时间并减轻视网膜光凝时的疼痛。然而，安全治疗窗口（TW）——即 Bruch 膜热机械破裂和轻度凝固的阈值功率比也随曝光时间缩短而减小。研究了两种增加 TW 的潜在方法：（a）降低激光束的中心辐照度；（b）对脉冲进行时间调制。通过以 4-7 度的角度将 532nm 激光耦合到 200μm 芯多模光纤中，创建了具有可调中心辐照度的环形光束。使用计算模型优化了脉冲形状，并使用波形发生器驱动 PASCAL 光凝器（532nm）产生调制激光脉冲。使用环形光束（154-163μm 视网膜直径）和调制脉冲（132μm，均匀辐照度“平顶”光束）在体内对荷兰兔进行了急性轻度凝固和破裂阈值测量，脉冲持续时间为 2-50ms。还确定了具有传统恒功率脉冲和平顶光束的阈值。环形光束和调制脉冲在 10ms 脉宽下均可将 TW 提高 28%，从而与具有传统参数的 20ms 脉冲具有相同的 TW。
