...continued from Which LASIK Laser Is Best?

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 now obsolete broad-beam lasers. The disadvantages include a slightly greater risk of decentration and overcorrection.

Spot scanning lasers — Spot scanning (or "flying-spot") lasers, which are the most common, utilize small-diameter laser beams (from 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.

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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 light waves travel through the eye. These wavefront devices individually guide the way the eye's cornea is reshaped to achieve a custom ablation. [See also: Wavefront or Custom LASIK]

Most modern excimer lasers now have automated eye tracking systems to keep the laser beam on target. Studies have demonstrated that eye trackers produce better outcomes, compared with lasers that in the past did not use eye tracking systems. [For more information, read about LASIK risks.]

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 effectively be targeted 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.

In recent years, increasing evidence has indicated that the zone where laser energy is applied to reshape the eye during LASIK may be too small to accommodate larger pupil sizes. If the pupil expands in low light beyond the zone where the eye was reshaped (ablated) for vision correction, then vision problems such as glare and haloes at night might occur.

Some surgeons believe that the diameter of the zone where laser energy is used (ablation zone) should be at least equal to the diameter of your pupil in dim light. If you have larger pupils, the type of excimer laser used may be important in relation to how large of an optical zone the machine is capable of creating. You should discuss this with your surgeon.

Ablation times also can differ among different lasers, ranging from 30 seconds to 60 seconds or longer. That may be important to you in terms of your comfort as you undergo a procedure. Even the sounds the lasers make can differ, and may be something about which you should ask your eye surgeon. You might also want to ask whether your surgeon uses a laser or a bladed instrument (microkeratome) to create the flap used in LASIK eye surgery, and how these two approaches might differ in terms of your comfort. [See also: Blade vs. Bladeless LASIK Debate]

Again, no matter which laser is used, remember that ultimately the skill and experience of your eye surgeon likely will be the most important factors affecting the outcome of your LASIK procedure.