Tissue ablation through water with erbium:YAG lasers.

We report the dynamics of vapor cavities generated by 200 microseconds long Er:YAG laser pulses under water and in gelatin. Acoustic transients were detected at the beginning of the laser pulse and when the cavity collapsed. Cavity expansion and collapse, and the associated acoustic transients are possible ablation mechanisms with the Er:YAG laser. Shortening of the pulse duration is suggested to minimize long range under water tissue damages.

Potential use of lasers for penetrating keratoplasty.

Experimental corneal trephination has been achieved with the 193 nm argon fluoride excimer and 2.9 microns hydrogen fluoride and Er:YAG laser systems. Compared with metal blades and other lasers, the 193 nm excimer laser creates the best quality corneal excision, but has a relatively slow etch rate through the stroma, and its use requires toxic gas. The mid-infrared laser systems trephine the cornea in less than 10 seconds, but cause a 10 microns to 15 microns zone of adjacent stromal damage and create wounds that are approximately 2.5 times larger than wounds made by metal scalpels. The wavelength and laser pulse duration influence the cutting characteristics of the laser. Optical delivery systems using an axicon lens, a rotating slit, and a computer controlled scanning optical system have been developed for penetrating keratoplasty. Selection of the optimal laser system for penetrating keratoplasty must await further experimental studies. Refinements of the laser cavity and delivery system are necessary before clinical studies can begin. A carefully controlled randomized clinical trial comparing laser trephination with conventional mechanical trephines will be necessary to determine the safety and efficacy of a laser trephination system.

Noncontact trephination of the cornea using a pulsed hydrogen fluoride laser.

We used a pulsed hydrogen fluoride infrared laser and a specially designed axicon lens to perform circular corneal trephinations in ten eye bank eyes. This noncontact system focused each laser pulse into an annulus on the cornea. Corneal perforation was achieved in seven to nine seconds at a repetition rate of 10 Hz, using a laser output energy of 100 mJ per pulse. A trephination, 90% of corneal thickness, 6.5 mm in diameter, was produced with 70 pulses.

Preliminary report on corneal incisions created by a hydrogen fluoride laser.

We created corneal incisions in eye bank eyes with a pulsed hydrogen fluoride infrared laser. This laser was selected because its emission spectrum (2.7 to 3.0 micron) closely corresponds to the absorption peak of water in the infrared region. Short pulses (200 nsec) of hydrogen fluoride laser light focused with a cylindrical lens resulting in radiant exposures of 1.3 J/cm2 at the corneal surface created linear cuts in the cornea with minimal thermal damage adjacent to the incision, suggesting that the pulsed hydrogen fluoride laser may be useful for corneal surgery.

The effect of thermal mode Nd:YAG laser radiation on vessels and ocular tissues. Experimental and clinical findings.

Ultrastructural examination of mesenteric vessels of pigmented rabbits after irradiation with the thermal mode of Nd:YAG laser showed an excellent hemostatic effect. Clinical experience parallels those findings.