Variable depth thermal lesions in rabbit corneas using a tunable thulium fiber laser

ABSTRACT Laser-induced thermal changes in the cornea have been used clinically for refractive surgery. This study describes the creation of variable depth thermal lesions in the cornea using a tunable Thulium fiber laser. Thermal lesions were created in fresh rabbit corneas, ex vivo, at three different wavelengths (1873 nm, 1890 nm, and 1904 nm) (n=6 corneas each). All other laser parameters were kept fixed with power of 5.5 W, 25-ms exposure time, and 650- P m-diameter spot, yielding a single pulse exposure of 138 mJ, and a fluence of 42 J/cm 2 . Optical coherence tomography (OCT) and histology were used to measure pre- and post-operative corneal thickness and lesion dimensions. OCT measurements of pre and post-operative corneal thickness and lesion depth (in microns) were: (1873 nm: 450+ 30, 801+ 95, 655+51), (1890 nm: 460+27, 618+70, 332+56), (1904 nm: 448+20, 550+42, 245+36), respectively. By comparison, histologic measurements were: (1873 nm: 470+25, 828+21, 540+31), (1890 nm: 457+13, 625+17, 350+ 43), (1904 nm: 465+ 40, 627+ 35, 239+ 23), respectively. OCT lesion depth measured 82%, 54%, and 45% of corneal thickness, compared to histologic analysis of 65%, 56%, and 38%. This is the first preliminary test of a compact and tunable Thulium fiber laser for creating variable depth thermal lesions in the cornea. The Thulium fiber laser may have potential use as a replacement for the Ho:YAG and diode lasers for thermal keratoplasty. Key Words: cornea, fiber, keratoplasty, laser, lesions, thermal, thulium, tunable