Mechanisms of intraocular photodisruption with picosecond and nanosecond laser pulses

Abstract

NdYAG laser photodisruption with nanosecond (ns) pulses is an established method for intraocular surgery. In order to assess whether an increased precision can be achieved by the use of picosecond (ps) pulses, the plasma size, the shock wave characteristics, and the cavitation bubble expansion after optical breakdown with ps-and ns-laser pulses were investigated by time-resolved photography and acoustic measurements. NdYAG laser pulses with a duration of 30 ps and 6 ns, respectively, were focused into a water-filled glass cuvette. Frequency doubled light from the same laser pulses was optically delayed between 2 ns and 136 ns and used as illumination light source for photography. Since the individual events were well reproducible, the shock wave and bubble wall position could be determined as a function of time. From the slope of these r(t) curves, the shock wave and bubble wall velocities were determined, and the shock wave pressure was calculated from the shock velocity. The plasma size at various laser pulse energies was measured from photographs of the plasma radiation. The breakdown thresholds at 30 ps and 6 ns pulse duration were found to be 15 p J and 200 pJ, respectively. At threshold, ps-plasmas are shorter than ns-plasmas, but at the same pulse energy they are always -2.5 times longer. The initial shock pressures were 17 kbar after ps-pulses with an energy of 50 pJ, and 21 kbar after 1 m J ns-pulses. The pressure amplitude decayed much faster after the ps-pulses. The maximum expansion velocity of the cavitation bubble was 350 m/s after a 50 pJ ps-pulse, but 1,600 m/s after a 1 m J ns-pulse. The side effects of intraocular microsurgery associated with shock wave emission and cavitation bubble expansion can be considerably reduced by the use of ps-pulses, and new applications of photodisruption may become possible. o 1994 WiIey-~iss, Inc.

Retinal light toxicity

“…The amount of damage is related to the rate of delivery and amount of energy absorbed. 32,33,[68][69][70][71][72][73][74] The most common clinical application of photomechanical damage in ophthalmology is the use of radiation from the Nd:Yag laser, which is typically used to create an iridotomy in patients with closed-angle glaucoma or cause retraction of an opacified posterior lens capsule in patients after cataract surgery. Pulsed lasers are rarely used in vitreoretinal surgery because of the potential for collateral retinal damage, particularly full thickness retinal defects and haemorrhage.…”

“…Pulsed lasers are rarely used in vitreoretinal surgery because of the potential for collateral retinal damage, particularly full thickness retinal defects and haemorrhage. 68,[72][73][74] …”

Laser−Micropipet Combination for Single-Cell Analysis

“…This laser-micropipet combination takes advantage of a shock wave produced by a highly focused, pulsed laser microbeam. [36][37][38] The laser pulse is focused at the glass/buffer interface of a cell chamber in which the cell to be lysed is cultured. The 5-ns light pulse is believed to cause localized plasma formation at its focal point producing a cavitation bubble.…”

Photoablation of inner limiting membrane and inner retinal layers using the Erbium:YAG‐laser: An in vitro study

“…Picosecond or femtosecond optical breakdown enables very precise and tractionless microsurgical dissections [42][43][44]. However, it is not well-suited for the selective ablation of the ILM because the achievement of this goal would require precise focusing of the laser beam with micrometer accuracy over the whole target area.…”