Wetzel W, Brinkmann R, Koop N, Schröer F, Birngruber R
Eye Surgery Center Weinheim, Germany.
Ger J Ophthalmol. 1996 Sep;5(5):281-4.
The energy of the erbium: YAG laser (2.940-nm wave-length) can be used for minimally traumatic photoablation due to its high absorption at the tissue water and its consequently low penetration depth. Laser sclerostomy ab externo, an application of this principle, has undergone advanced clinical investigation. Another potential application is photofragmentation of the lens for cataract extraction. A laboratory model Er: YAG laser (flashlamp-pumped. 200-microseconds pulse length, 5-Hz repetition frequency) was coupled to a short low-OH quartz fiber (400 microns in diameter). The laser energy was applied by direct contact of the fiber tip to human lenses with very dense cataract. The lenses rested in a small cuvette filled with an aqueous-humor-analogous fluid. The fragmentablation rate was evaluated in relation to the number of pulses and the pulse energy. A laser-triggered flash-photography unit was engaged to visualize the ablation dynamics. We found tissue-ablation rates to range from 4 to 19 micrograms/pulse, depending on the nucleus density and ulse energy. The maximal size of the removed fragments was always below 500 microns. During ablation, rapidly increasing and collapsing cavitation bubbles were photographed at the distal tip of the application fiber. The impact radius of these cavitation effects markedly exceeded the pure penetration depth of laser radiation at a 2.9-microns wavelength. A clinical application of the method should be possible as judged by the results obtained for tissue-ablation rate and fragment size. Cavitation-bubble dynamics seems to be responsible for the high fragmentation efficiency. Special application probes have to be developed to optimize ablation and to prevent inadvertent destruction of the posterior lens capsule by cavitation effects.
钇铝石榴石激光（波长2.940纳米）的能量因其在组织水分中的高吸收性以及由此导致的低穿透深度，可用于微创光蚀。基于此原理的激光外路巩膜造口术已进行了深入的临床研究。另一个潜在应用是用于白内障摘除的晶状体光破碎。一台实验室型铒：钇铝石榴石激光（闪光灯泵浦，脉冲长度200微秒，重复频率5赫兹）与一根短的低羟基石英光纤（直径400微米）相连。通过将光纤尖端直接接触患有极致密白内障的人晶状体来施加激光能量。晶状体放置在一个装有类似房水的液体的小比色皿中。根据脉冲数和脉冲能量评估碎片消融率。使用激光触发的闪光摄影装置来观察消融动态。我们发现组织消融率在4至19微克/脉冲之间，具体取决于核密度和脉冲能量。去除碎片的最大尺寸始终低于500微米。在消融过程中，在应用光纤的远端尖端拍摄到快速增大和塌陷的空化气泡。这些空化效应的影响半径明显超过了波长为2.9微米的激光辐射的纯穿透深度。根据组织消融率和碎片大小所获得的结果判断，该方法有可能应用于临床。空化气泡动态似乎是高破碎效率的原因。必须开发特殊的应用探头以优化消融并防止空化效应意外破坏晶状体后囊膜。
