Types of Modern Excimer Lasers Used for LASIK

Slit scanning lasers — Slit scanning lasers use relatively small beams linked to a rotational device with slit holes that enlarge. The laser beams scan across these holes during surgery, producing a gradually enlarging ablation zone. The approach provides a uniform beam and — potentially — smoother ablations than obsolete broad-beam lasers. The disadvantages include a slightly greater risk of decentration and overcorrection unless an eye-tracker is being used with the laser.

Spot scanning lasers — Spot scanning (or "flying-spot") lasers, which are the most common, use small-diameter laser beams (0.8 to 2 mm) scanned across the cornea to produce the ablation zone. This approach has the potential to produce the smoothest ablations, to more readily allow customized ablations and to better treat irregular astigmatism.

Wavefront-guided lasers — Many excimer lasers are connected to a device that detects and "maps" defects in the eye's optical system, based on how lightwaves travel through the eye. These wavefront devices individually guide the way the eye's cornea is reshaped to achieve a custom LASIK ablation. Both slit scanning and spot scanning lasers have the ability to be used for wavefront-guided treatments.

Excimer Lasers and Eye Tracking

Most modern excimer lasers have automated eye tracking systems to keep the laser beam on target. Studies have shown that eye trackers produce better outcomes and decrease LASIK complications compared with past lasers that did not use eye tracking systems.

Indications and Features of Excimer Lasers

In the following chart, OZ stands for optical zone, meaning the maximum size of the pupil allowing light to pass through the eye that can be targeted effectively for correction with a specific laser. TZ stands for the maximum treatment area, including a transition zone that can be used in an ablation to achieve vision correction in the targeted area.