Excimer Laser
The Excimer laser is the industry standard for refractive surgery. It has been used in both LASIK and PRK procedures since 1987 (FDA approved in 1995). Known for their low heat emittance (relatively heatless) and high degree of precision, Excimer lasers modify corneal tissue as a means of improving (or eliminating) refractive error.
How to Compare Laser Systems
See the LASIK Equipment page for a comparative matrix of the different FDA Approved excimer laser systems. This page includes a red star rating based on the following criteria:
1) Speed
Faster treatment speeds increase predictability and reduce the incidence of complications.¹
2) Type/Size of Beam
Smaller beams tend to be more precise, but can also increase treatment time if the laser speed is not enhanced.
a) Type¹
- Slit Scanning: Small laser beams rotate and are regulated by slits of varying size. Ablation zone enlarges over the course of surgery.
- Pros: Uniform beam, smoother ablations than original Broad Beam lasers (now obsolete)
- Cons: Greater risk of decentration, overcorrection
- Spot Scanning ('flying spot'): Small beams (0.8-2.0mm) scan the cornea.
- Pros: Smoother ablation than Slit Scanning, more customizable, more adept at treating astigmatism
- Cons: Slower procedure (unless laser speed is increased relatively); more expensive than slit scanning
- WaveFront ('Custom LASIK'):
- Pros: Most individualized treatment; smoothest ablation; best vision results
- Cons: More expensive
b) Size
While a larger laser beam will be able to operate more quickly on a larger area, they are less accurate than small laser beams. Depending upon the speed of the laser, a small beam can effectively cover the same area as a large beam and in the same amount of time. General wisdom dictates that smaller beams are preferable to a point (but extremely small beam sizes will increase treatment length). The ideal laser system uses multiple laser beams in tandem at a high frequency.
3) Treatment Range
The OZ and TZ of a particular laser are restrictive on the type of eye the laser can effectively treat. This is not an indication of laser quality, but rather of range.
a) Optical Zone (OZ)
- Maximum pupil size that can be effectively corrected by a specific laser.
b) Treatment Zone (TZ)
- Maximum treatment area for a specific laser.
c) Treatment Range Lasers with larger treatment ranges are able to treat a wider range of refractive errors. Select a LASIK center that uses a laser within your treatment range so you avoid wasting time (and money in some cases) on your pre-LASIK consultation.
4) Tracking/Guidance System
The tracking and guidance systems import data from initial eye examinations to individualize the LASIK procedure to the unique characteristics of your eye. The key factor to consider here is speed. Faster tracking/guidance systems are able identify eye movement and respond more quickly thereby decreasing the risk of errors during surgery. There are two kinds of tracking system: video and laser guided. The latter is preferred for its quicker response time and greater visual accuracy.
5) Shaping Effects
Does the laser enable smooth ablation? How does it change the correction of your natural lens? Does the mode of incision lead to higher risk of adverse side effects?
a) Flat or Curved
Traditional excimer lasers severely alter the curvature of the eye when removing tissue from the cornea. More specifically, they create a flattened area with an edge in the middle of the eye leading to problems such as night vision, glare, and the halo effect. More modern lasers attempt to preserve the curvature of the eye and maintain its biomechanical idiosyncracies.
b) Smoothness
Smaller laser beams operating at faster speeds are able to produce smoother surface results on your cornea. Smoother tissue results in faster healing and fewer negative side effects.
External Links
Sources
- 1) All About Vision
- 2) EyeMD
