Reshaping Treatment Technology

History

Laser Vision Correction has always been performed with an excimer laser, a device that uses ultraviolet light to reshape the cornea by disintegration of designated cells. As you can imagine, laser technology has evolved remarkably.

Early lasers were known as broad beam or slit beam lasers and were able to treat only defocus errors. The treatment beam passed through an aperture which gradually expanded, creating a microscopic divot deepest in the center because it was exposed the longest to the beam. Later, a slit type of aperture was added to treat astigmatism. It enabled the surgeon to create a narrow steepened area along a prescribed axis, defined by the location of astigmatism in your eyes. Later still, other forms of masks were developed to enable the surgeon to treat imbalanced, irregular astigmatism.

The single greatest technological advancement since the introduction of the first excimer laser to North America in the late 1980's is Wavefront technology. In addition to removing defocus errors, it can treat higher order aberrations. Dr Demong uses Wavefront treatment in all approved ranges of correction because of its precision.

Wavefront Technology

Even when you can read the letters on an eye chart, some may not appear as crisply as they should as a result of fine irregularities in your vision, called higher order aberrations. They affect quality of vision and can produce problems such as glare, haloes and other troublesome distortions, especially under dim lighting situations. Using Wavefront treatment, many of these problems can now be reduced or eliminated.

While conventional lasers are still in use at most Centres, a few, including Demong Associate Eyecentre, offer Wavefront treatment lasers. Wavefront treatment lasers can be operated in either Wavefront mode or Conventional, non-Wavefront mode, depending upon the treatment limitations of the laser. The basic difference between the two modes is that a Wavefront scan produces a template that guides the treatment in Wavefront mode whereas the surgeon sets the parameters manually in Conventional mode. It is important to understand which treatment you will undergo.

Wavefront treatment involves three vital steps. If any one of these steps is missed or compromised, the treatment is Conventional, not Wavefront.

Step 1: Capture

• you need to see where higher order irregularities are and the degree of involvement
• using a Wavefront scanner at the time of the assessment, a detailed image of the visual system is created, showing defocus error and higher order aberrations
• the scan will form the template for treatment of your vision error, if Wavefront treatment is performed
• many Centres perform Wavefront scanning but few are able to proceed to Wavefront treatment

Step 2: Match

• the landmarks in your eyes as the scanner "saw" them have to be aligned with the landmarks the treatment laser "sees" 
• the structures within your eyes tend to shift when you move from the upright position for scanning to the reclining position for treatment. The laser needs to be able to find and compensate for any twisting of those structures, known as cyclotorsion.
• finally, the template must be superimposed over the landmarks so that reshaping will occur in precisely the correct areas defined by it.

Step 3: Treat

• the treatment laser has to be able to deliver the refined treatment prescribed by the Wavefront template. It requires:
  • an advanced eye tracking system. Since your eyes move slightly with each beat of your pulse and each breath, the system must be able to follow those slight movements while the laser is reshaping the eye. The eye tracker must be locked into position before starting treatment and it must remain on until treatment is completed.
  • the treatment beam must be integrated with the tracking system so it can respond immediately to each subtle movement. This ensures that the treatment is actually being delivered as prescribed.
  • the treatment beam must be very narrow, able to deliver just the right depth of treatment in one area while backing off in another area, even if they are less than a millimeter apart. A movable treatment beam less than 1mm in width is required. Without that, the treatment is classified as a broad beam treatment which does not recognize or treat the distinctions between depths of various aberrations.

Not every laser has the technology to facilitate either the transfer of the template from the scanner to the treatment laser, nor to track eye movement accurately at the time of treatment to ensure the level of refinement Wavefront treatment can offer. As a result, visual outcomes vary with the type of laser used and the type of treatment mode used.

LADAR4000

Dr. Demong uses the LADAR4000, the first and only laser of its type in Canada. It was developed on the first fully integrated platform that proved better results than Conventional Laser Vision Correction. 

The system analyzes the template provided from the LADARWave at the time of your assessment and has a patented process to identify landmarks, compensating for cyclotorsion. The most exciting part of this technology, however, lies in the treatment phase of the Wavefront process. The LADAR4000 features:

• the most robust eye tracking system in the industry. At 4000 times each second, the tracker scans your eye for movement and within 1 millisecond, the treatment beam simultaneously adjusts to ensure your treatment is directed to exactly the prescribed areas. The nearest competitor's technology tracks only 200 times each second and reacts in just under 8 milliseconds.
• a 0.8mm treatment beam with a rounded Gaussian profile that produces a smooth finish from contact point to contact point as the beam pulses repeatedly, reshaping your eyes in the desired fashion

The result? Optimal vision with the most precise technology available, particularly when it's combined with the IntraLase Femtosecond laser.

No two manufacturers offer identical ranges of treatment, making it essential to understand the differences when making comparisons. A search of individual manufacturers' websites, including www.ladarvision.com will help you compare the differences. As well, when making comparisons, you need to determine whether the advanced Wavefront treatment modes are actually used by the surgeon and how often. Dr. Demong uses IntraLASE for all LASIK treatments and Custom Cornea Wavefront treatment for all treatments within the approved ranges of correction.