Femtosecond Lasers in Ophthalmology: Surgery and Imaging

Ophthalmology has traditionally been the field with prevalent laser applications in medicine. The human eye is one of the most accessible human organs and its transparency for visible and near-infrared light allows optical techniques for diagnosis and treatment of almost any ocular structure. Laser vision correction (LVC) was introduced in the late 1980s. Today, the procedural ease, success rate, and lack of disturbing side-effects in laser assisted in-situ keratomileusis (LASIK) have made it the most frequently performed refractive surgical procedure (keratomileusis(greek): cornea-flap-cutting). Recently, it has been demonstrated that specific aspects of LVC can take advantage of unique light-matter interaction processes that occur with femtosecond laser pulses.

In this chapter, we will first (Part 2) outline important laser–tissue interaction mechanisms; within the femtosecond time regime, laser–tissue interaction is characterized by a cut with superior precision and minimal collateral damage. This will motivate the use of amplified femtosecond pulse lasers as a versatile, precise and minimally invasive scalpel. In addition, various aspects of solid-state laser technology and the underlying physics in the creation and amplification of femtosecond laser pulses are presented. A real-world surgical laser system, designed for reliable and safe clinical use, is described and compared with the LVC industry standard ArF excimer laser. Optimized scanning strategies for surgical procedures are described, e.g., customized flap cutting. Second (Part 3), we will summarize diagnostic applications of femtosecond lasers in ophthalmology. Recently, we applied two-photon laser scanning microscopic imaging techniques to investigate the ultrastructures of human cornea and retina with submicron resolution. Namely, second harmonic generation (SHG) imaging was employed to characterize the ultrastructures of collagen fibrils in cornea, sclera, and lamina cribrosa. Two-photon excited autofluorescence (TPEF) imaging was utilized to resolve the morphology and spectrum of individual lipofuscin granules in retinal pigment epithelial (RPE) cells.