Excimer laser system

The cool excimer laser, the most technologically advanced surgical tool to treat refractive errors, has revolutionized vision correction surgery. This remarkably precise ultraviolet laser creates invisible pulses of light that remove microscopic amounts of corneal tissue. Controlled by customized software, a computer calculates the number of laser shots required to achieve a patient's targeted refraction.

The excimer laser can be delivered in various ways. The older broad-beam lasers have about a 7-millimeter footprint that is partially masked by a diaphragm. As it opens, expanding outward from the center, the diameter of the beam that reaches the cornea increases. This means that the center of the nearsighted cornea receives the most treatment, leaving the edges tapered. The newer flying-spot, or scanning, lasers with small beam footprints emit less energy per pulse than the broad-beam machines. The computer programs tell the scanning mirrors within the laser exactly how to move to aim the beam and how many pulses to emit at a specific location. As the scanning beam moves back and forth across the cornea, the laser creates a smoother recontoured surface than the older lasers. These advanced machines also should improve refractive predictability.

In the 1970s, IBM scientists, experimenting with different gas mixtures to create new lasers, found that the 193-nanometer wavelength of laser energy can remove molecules of tissue with little damage to the surrounding area. Now known as the excimer laser, this wavelength is so exact that it can cut notches in a human hair and etch tiny microcircuits into computer chips. Used as a light scalpel, the excimer reacts with protein molecules, breaking molecular bonds. “Photoablating” – vaporizing corneal tissue at the submicron level – the excimer's short pulses penetrate to an exact and predictable depth. With unfathomable speed, each laser pulse can remove 39 millionths of an inch of tissue in 12 billionths of a second. Such extraordinary accuracy helps doctors achieve excellent control over the amount of tissue removed during the procedure.