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Determination of Ablation Pattern and Laser Parameter for a Non-mechanical Trephination with a new Fiber Optic Device for the 308nm Excimer Laser
Specht H., Völcker H. E., Kruse F. E.,
Ruprecht-Karls-Universität Heidelberg, Universitäts-Augenklinik (Heidelberg)
Purpose: Compared to conventional methods a newly developed non-mechanical Excimer laser trephine with a new fiber optic unit offers distinct advantages for penetrating keratoplasty. Here we describe the optimized parameters of application for this simple trephine which can be used in conjunction with small, mobile, laser units.
Method: A motor driven trephine was developed which can be centered by use of s suction ring. It is used in conjunction with a fiber that is connected to a small, mobile, commercially available 308nm Excimer laser. In a pre clinical study freshly enucleated pig an human eyes were used. The following parameters were examined: Power density (5mJ/mm² 20mJ/mm²), repetition rate (10 Hz 100 Hz), fiber diameter (100µm, 200µm, 300µm), overlap (0%, 25%, 50%, 75%). Conventional histology of cuts with the laser trephine was performed.
Results: The laser trephine is easy to use and allows to precisely cut both porcine and human corneas. Histology showed smooth cutting edges and thermal damage of less than 10µm. The minimum necessary time up to the complete perforation was with approximately 1.5 min at 300µm diameter of the ablation pattern without overlap and a repetition rate of 100 Hz. The power density was about 20mJ/mm².
Conclusions: Dependent on the so-called overlap of the laser area and power densities the cut accuracy and the time necessary to complete perforation ca be modified. Our new laser trephine system offers advantages over the current method of Excimer laser trephination and its practicability should allow widespread clinical use.