Use of bursts of 1.54-μm microsecond laser pulses for cataract destruction

Abstract The possibility of using bursts of microsecond pulses of an Yb,Er : glass laser (λ = 1.54 μm) for cataract destruction was investigated experimentally in vitro for the first time. The energy in a laser pulse was limited from below by the eye lens destruction threshold and from above by the radiation resistance of the input end face of the radiation-supplying fibre. The energy of a burst consisting of three microsecond laser pulses, separated by time intervals of 850 μs, was 255 ± 15 mJ, and the burst repetition rate was 15 Hz. The hydroacoustic signal, generated after each burst pulse in the water around the lens, contained two components. The first occurred immediately after the laser pulse transmission, and the second was delayed by 250 to 350 μs. The amplitude of the second component of the hydroacoustic signal exceeded the amplitude of the first component and was maximum (50.0 ± 8.0 MPa) for the signal induced by the second pulse in the burst. The efficiency of cataract destruction by microsecond-pulse bursts generated by an Yb,Er : glass laser was found to depend on the lens nucleus density, to exceed significantly the efficiency of cataract destruction by single microsecond pulses of this laser, and to be comparable with the efficiency of eye lens destruction by a 1.44-μm Nd : YAG laser.</jats:p

In vitro study of cataract extraction by bursts of microsecond 1.54-μm laser pulses

Abstract Laser extraction of a model porcine eye cataract has been performed for the first time in an in vitro experiment using a 1.54-μm Yb, Er : glass laser generating bursts of microsecond pulses. We used effective pulse repetition rates from 36 to 75 Hz and average laser output powers from 3.9 to 5.25 W. The results demonstrate for the first time that, at an effective pulse repetition rate of 45 Hz, burst repetition rate of 15 Hz, three microsecond pulses per burst, and a burst energy from 260 to 265 mJ, the laser step duration in cataract extraction is 130 ± 10 s, which is comparable to the ultrasonic phacoemulsification and laser extraction time in the case of a Nd : YAG laser emitting at 1.44 μm. Acoustometry and high speed video recording of hydroacoustic processes accompanying interaction of water with 1.54-μm radiation from the Yb, Er : glass laser generating bursts of microsecond pulses have made it possible for the first time to detect overlap of hydroacoustic processes at the pulse spacing in bursts reduced to under 700 μs. In the case of overlap of hydroacoustic processes, despite the increase in average power and effective pulse repetition rate, acoustic wave generation is ineffective because pulses propagate through bubbles formed in the water. Laser cataract extraction is shown to be most effective at a lower average power, lower effective pulse repetition rate, and burst pulse spacing of 850 ± 10 μs.</jats:p