Ocular Integrity After Anterior Ciliary Sclerotomy and Scleral Ablation by the Er:YAG Laser

PURPOSE

To establish the risk of ocular rupture after proposed surgical reversal of presbyopia by anterior ciliary sclerotomy (ACS) or by the Er:YAG laser (HOYA Continuum, Tokyo, Japan).

METHODS

A total of 45 pig eyes (15 control eyes) were examined. Fifteen eyes were placed into one of two study groups and another 15 eyes were used as controls. One group underwent scleral incisions with the use of a diamond knife, and the other group underwent Er:YAG laser scleral incisions. In both study groups, 8 radial incisions, 2 parallel cuts each at 4 quadrants, 2 mm apart, 4 mm long, and starting 2 mm away from the limbus, were made. A 3-kg steel weight was released from a measured height to the pig's eye, and ocular rupture energy (joules) was measured.

RESULTS

The mean rupture energy was 26.0 J for control eyes, 15.7 J for the ACS eyes, and 12.2 J for the Er:YAG laser eyes. The ACS and the Er:YAG laser eyes ruptured at significantly lower energies (ACS, P < .001; Er:YAG, P < .001) than the control eyes. Comparison of the ACS group and the Er:YAG laser group showed no statistically significant difference (P = .052) in rupture energy.

CONCLUSIONS

Scleral incisions by ACS and the Er:YAG laser significantly weakened ocular integrity compared with control eyes. Any patients undergoing ACS or Er:YAG laser scleral incision should be informed of the attendant potential risk after ocular trauma.

Delivery of midinfrared (6 to 7-microm) laser radiation in a liquid environment using infrared-transmitting optical fibers

Ablation at wavelengths near lambda = 6.45 microm results in tissue ablation with minimal collateral damage (< 40 microm) yet yields a high ablation rate that is useful for human surgery. However, delivery of this wavelength has been limited to that in air and thus to applications in which the target tissue can be readily exposed. The goal of this study is to investigate the potential of a pulsed infrared laser at lambda = 6.45 microm for noncontact ablation in a liquid environment. To this end we investigated fiber delivery in combination with the use of infrared transparent liquids. Transmission characteristics and damage thresholds for two types of fiber materials (silver halide and arsenic sulfide), for high-power pulsed laser radiation were determined using the Mark III free electron laser. Both fibers had comparable bulk losses (0.54 dB/m and 0.62 dB/m, respectively) while the arsenic sulfide fibers showed more coupling losses (37 versus 27%). Damage thresholds were higher in arsenic sulfide fibers than in silver halide fibers (1.12 GW/cm2 versus 0.54 GW/cm2), but both fibers were sufficient to deliver radiant exposures well above the ablation threshold in tissue. Seven different perfluorocarbon liquids (PFCLs), known for their transparency at lambda = 2.94 microm, were investigated and their optical transmission was determined using Fourier transform infrared and direct Beer's law measurements. All of the PFCLs tested had similar values for an absorption coefficient mu(a) at a given wavelength (mu(a) = 0.05 mm(-1) at lambda = 2.94 microm and mu(a) is approximately 3 mm(-1) at lambda = 6.45 microm). Pump-probe imaging showed the ablation sequence (lambda = 6.45 microm) at the fiber tip in a water environment, which revealed a fast expanding and collapsing bubble. In contrast, the volatile PF-5060 showed no fast bubble expansion and collapse, but rather formation of nontransient gas bubbles. Perfluorodecalin did not show any bubble formation at the radiant exposures used. It was shown that using the lambda = 6.45 microm wavelength delivered via fiber optics in combination with perfluorodecalin allows a noncontact laser surgical procedure. Deeper structures, however, are effectively shielded because the radiant exposure of the beam will fall below the ablation threshold owing to the absorption by perfluorodecalin. This may optimize the efficacy and safety of laser-based vitreoretinal surgery.