Contact focusing multimodal probes for potential use in ophthalmic surgery with the Erbium:YAG laser

Vitreoretinal surgery is performed using mechanical dissection that sometimes results in iatrogenic complications, including vitreous hemorrhage, retinal breaks, incomplete membrane delamination, retinal distortion, microscopic damage, etc. The laser probe would be an ideal tool for cutting away pathologic membranes, however the depth of surgery should be precisely controlled to protect the retina. In this study, we optimized the design of such ultraprecise surgical microprobe formed by chains of dielectric spheres assembled directly inside the cores of the mid-infrared flexible delivery systems used in such surgeries. Specifically, our design is optimized for use of Erbium:YAG laser sources with extremely short optical penetration depth in tissue. By using numerical modeling, we demonstrate a potential advantage of five-sphere focusing chains of sapphire or ruby spheres with index n=1.71 for ablating the tissue with self-limited depth around 10-20 μm. We fabricated and tested such optimized structures formed by 300 μm ruby spheres with ophthalmic tissues, ex vivo. Single Er:YAG pulses of 0.2 mJ and 75 μs duration produced ablation craters in cornea epithelium for one, three, and five sphere structures with the latter generating the smallest crater depth (10 μm) with the least amount of thermal damage depth (30 μm). We show that integration of the ultraprecise laser ablation capability with illumination and suction tools would produce a single headpiece with versatile functionality in ultraprecise intraocular surgery.