We have investigated the nonlinear refractive index of ex-vivo pig cornea by a combined approach using the standard z-scan technique on extracted corneas or corneal slices, as well as studying the deviations caused by self-focusing during femtosecond laser processing of the pig eyes. The experiments yield consistently an upper limit of 1.2 MW for the critical power of self-focusing in porcine cornea, and a value of 2 x 10(-19) m(2)/W for its nonlinear refractive index. We also demonstrate that due to this nonlinear refraction the cutting depth of typical fs-laser surgery processing in cornea may depend considerably, albeit in a well controllable way, on the laser parameters.

Strands and vitreous adhesion bands can either be dissected noninvasively, transpupillarily by photodisruptive pulses of a Nd:YAG laser, operated in the photodisruptive mode, or invasively using an Er:YAG laser and specialized fibers. The previously used CO₂, Ho:YAG, and ultraviolet lasers have become less popular in the recent past. When using the transpupillary method, specialized contact lenses are required. Noninvasive methods avoid the risks incurred with invasive methods, but they require specialized knowledge, which is not available usually in vitreoretinal services. The invasive laser method provides a number of advantages typical of laser-tissue interaction. Advances in electrosurgical methods have opened the door to a new class of miniaturized electrosurgical equipment with which tissue dissection is made possible by plasma due to dielectrical breakdown which allows the pulse energy to be reduced to a very low level, resulting in a highly localized tissue effect. None of these methods has yet been considered for clinical use, mainly because the presently used mechanical methods are thought to be optimal by the majority of vitreoretinal surgeons.

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Retinopexy may be produced by either of two mechanisms following transpupillary irradiation of the retina with the Nd:YAG laser. Which of these mechanisms is operative will depend on the degree of disruption produced within the elastic component of Bruch's membrane. Small defects in the elastic component of Bruch's membrane are soon completely bridged by regenerated retinal pigment epithelium (RPE) cells. However, there is a risk of subretinal neovascularization in such defects. Large defects in the elastic component of Bruch's membrane are not completely bridged by regenerating RPE cells before proliferating Müller cells invade this region and spread from it, mushroom-like, within the choroid. In this case subretinal neovascularization does not occur. In the former instance (small defects) retinopexy is achieved by a process of interdigitation between the microvilli of Müller and RPE cells; and in the latter (large defects) via a press-stud-like anchorage of Müller cells within the choroid. It has not yet been established whether these two retinopexy phenomena, observed after irradiation of rabbit retinas, occur in the same way in man.