Laser trephination of the cornea.

A high degree of astigmatism is a frequency complication limiting visual acuity after cornea transplantations. The major surgical factor appears to be the difficulty in creating a truly round recipient opening due to distortion of the globe and the cornea resulting from the forces applied during manual trephination. A laboratory laser system has been developed that cuts circular buttons without deforming the cornea. It includes a pulsed hydrogen fluoride laser (wavelength, 2.7-3 μm), modified to produce a homogeneous beam and 50-ns pulses of 130 mJ at 10 Hz. With this laser it is possible to produce sharp corneal cuts with an approx. 50-μm wide zone of stormal tissue alteration adjacent to the excision. An optical system is mounted to focus each laser pulse into an annulus of approx. 100-μm width, the diameter of which can be varied from 5 to 8 nm. Using this system, laser trephinations could be produced in <10 s on human donor cornea.