All-Laser LASIK, and What Each Laser Does

The femtosecond laser: the flap

The femtosecond laser emits pulses of infrared light lasting a few quadrillionths of a second. Because each pulse is so brief, it delivers its energy without heating the surrounding tissue, and because the beam can be focused at a precise depth inside a transparent cornea, it can separate tissue along a plane without touching the surface. In LASIK it creates the hinged flap in about 15 to 20 seconds, at a thickness and diameter the surgeon programs for each eye. This is the stage that used to be done with a blade.

The excimer laser: the correction

The excimer laser works on exposed tissue rather than inside the cornea. It emits ultraviolet light at 193 nanometers, a wavelength that breaks the molecular bonds in corneal tissue and removes it a fraction of a micron at a time, with almost no heat. Under the lifted flap, it removes tissue in the pattern derived from your measurements: flattening the center for nearsightedness, steepening it for farsightedness, and reshaping it asymmetrically for astigmatism. The active treatment takes between 10 and 60 seconds per eye. An eye tracker registers the position of the eye hundreds of times a second and steers every pulse to the right spot.

Why using two lasers changed LASIK

Moving both stages to lasers improved the procedure in three ways:

• Predictability: a laser flap is the thickness it was programmed to be, so the surgeon knows exactly how much tissue remains for the correction and for the future
• Safety: the flap complications associated with a mechanical blade became rare
• Reach: thinner, uniform flaps let patients with moderately thin corneas or higher prescriptions have LASIK safely

What all-laser LASIK does not change

It does not change who is a candidate in the fundamental sense. A cornea with keratoconus, a prescription beyond the safe treatment range, or an eye with active disease is not made suitable by better lasers. The consultation measurements decide candidacy, and if LASIK is not right for your eyes you will be offered PRK, SMILE or the EVO ICL instead. It also does not change recovery: expect a gritty, watery first evening, clear vision by the next morning for most patients, and a few weeks of dryness and fluctuation.