In vitro study of laser optic nerve sheath decompression with a Tm:YAG and Er:YAG laser

Purpose. To evaluate the potential of mid-infrared laser photoablation as a technique for Optic nerve sheath decompression, a highly controversial procedure with a high failure rate which might be due the current invasive surgical techniques. Methods. A Tm(Thulium):YAG laser (prototype New Star Lasers, CA, 2.01 μm,250μS, 5Hz) and an Er:YAG laser(294 Quantronix, NY, 2.94μm ,250μs, 2Hz) were used to ablate the optic nerve sheath of fresh eye-bank eyes. The energy per pulse was varied from 90 to 200 mJ for the Tm YAG laser and from 0.5 to 8 mJ for the Er:YAG laser. The ablated specimens were prepared for histology and scanning electron microscopy, to quantify the tissue removal and thermal damage. Results. Full-thickness perforation of the dura mater could be achieved with minimal (about 10 μm) thermal damage with the Er:YAG laser with 20 pulses at 4 mJ per pulse. With the Tm:YAG laser perforation was more difficult to achieve, and much more thermal damage (about 150 μm) was observed. Conclusions. Our study shows the potential of laser photoablation as a minimally invasive tool for Optic nerve sheath decompression.