Atomic force microscopy and scanning electron microscopy for characterization of interface surface roughness after ELITA femtosecond laser treatments

Abstract

Purpose To characterize and compare the corneal interface surface roughness of the ELITA femtosecond laser flap and smooth incision lenticular keratomileusis (SILK) to iFS femtosecond laser flap with atomic force microscopy (AFM) and scanning electron microscopy (SEM). Methods The iFS flap with 700 nJ pulse energy, ELITA flap with 50 nJ, and ELITA SILK with 50 nJ were performed on ex-vivo porcine eyes. After the femtosecond laser treatment and mechanical separation, the posterior surface of the laser treated interface was trephined, fixated, and dehydrated. The corneal interface surface roughness was assessed with AFM in contact mode in air. With AFM, 3 eyes were treated for each treatment method and 5 locations near the corneal center on each eye were evaluated with 20 µm x 20 µm scanning area per location and 512 x 512-pixel resolution. The root-mean-square (RMS) roughness for each treatment method were measured. With SEM, 1 eye was treated for each treatment method and representative images were taken with x100 and x250 magnification. Results The RMS roughness of iFS flap, ELITA flap, and ELITA SILK were 236 (mean) ± 64 nm (standard deviation), 114 ± 33 nm, and 203 ± 84 nm, respectively. ELITA flap interface surface roughness was significantly less than that of iFS flap (p < 0.000001) and ELITA SILK (p < 0.001). Conclusions ELITA flap produced a smoother corneal interface surface compared to the iFS flap and ELITA SILK, while the iFS flap and ELITA SILK produced similar corneal interface surface roughness.