Determining Femtosecond Laser Parameters for Clear Corneal Incisions

Abstract

Purpose: : To determine appropriate settings for femtosecond laser clear corneal incisions (CCI).

Methods: : We performed 150 kHz femtosecond laser (FS) incisions using a mask in 16 human corneal-scleral rims mounted in an artificial anterior chamber. Free hand diamond blade incisons performed in one side of each cornea were compared to FS laser incisions created in the opposite side. Factors studied were laser raster energy (1.6 or 2.1 uJ), laser spot and line (S/L) separation (3 x 2 um to 4 x 3 um), one, two, or three plane incisons, incision angulation, incision depth, and angulation for each plane. The target incision dimensions were an internal corneal entry width of 2.4 mm and a length maximum of 4 mm. Spectral domain OCT was performed immediately after the procedures. The corneas were then fixed in glutaraldehyde and prepared for LM, SEM, and TEM.

Results: : The diamond blade incisions (1 or 2 plane; 4 and 8 eyes) created minimal surface damage, but had irregular wound edges on both surfaces. A planned single plane diamond created a curved incision and a small posterior wound gape whereas the single plane FS incision was straight with minimal internal wound gape. In two plane incisions, the initial 300 microns were similar between instruments, but the 2nd part with the diamond blade was curved, with similar internal wound gape as the single plane. The 3 plane FS laser (4 corneas) had some pockets of intrastromal gas bubbles, mostly in the 3rd posterior part of the overlapping incisions which varied with S/L separation and raster energy.

Conclusions: : The FS laser-created 1, 2, and 3 plane incisions were more regular in shape and were associated with less internal wound gape compared to mechanical diamond blade incisions. Wound parameters were predictable and repeatable. Laser created incisions have the potential to allow predictable incisions and therefore potentially better wound integrity and more predictable surgically induced astigmatism.

Keywords: cataract • laser • cornea: clinical science