In the early days of laser refractive surgery, the laser systems were relatively simple. Laser energy was produced in a relatively circular simple pattern which expanded outward. The surgeon maintained control of the treatment alignment manually while using an aiming reticle viewed through the surgical microscope.
In those days, if a patient had excessive movement or oscillation of their eye, it could be quite challenging to maintain proper centration of the laser treatment. It is always best to maintain perfect centration of treatment in order to obtain the best optical results.
Any significant deviation from center can lead to suboptimal results and even induced astigmatism or other optical aberrations. Decentration and related optical aberrations were actually a rare but important complication after LASIK or PRK in its early days. Innovations in technology have reduced their incidence considerably, however.
The system I use, the Visx Star S4 IR™ excimer laser (AMO), uses a proprietary eye tracking system called ActiveTrak™ 3-D Active Eye Tracking which uses automated pupil centering and is the first FDA approved system to track eye movements in 3 dimensions.
I have been very impressed with the ability for this system to remain focused and centered on the intended treatment zone of the cornea during LASIK.
Patients are given valium prior to the refractive surgery which actually helps to suppress involuntary eye movement during the procedure. In addition, the patient is instructed to remain focused on a fixation light and the surgeon has an aiming reticule for aiming purposes.
Nonetheless, a small number of patients do have trouble keeping their eye perfectly still during LASIK. Despite these movements, I have found that the ActiveTrak™ system is able to deliver outstanding results.
Under correction due to movement or significant decentration of the treatment zone is no longer a major concern as it was with the older systems. I’ve experienced patients who had what I thought was significant oscillating movements during surgery. At the end of those cases, I felt sure that there would be under correction requiring touch up retreatment.
Yet surprisingly, I found in those particular cases, that there was little or no under correction which demonstrates to me just how well the tracking system on this laser is able to function.
Another feature of the Visx Star S4 IR™ system is the IR or Iris Registration function.
While performing the preoperative scanning, a photographic image of the patient’s iris is taken. Several spots on the iris are identified and these are then used during surgery to adjust for any rotational misalignment.
This feature helps to further align the eye and make sure that the treatment delivers the maximum amount of appropriate treatment, particularly with regard to astigmatism and other higher order aberrations.
Since Visx has a very advanced Wavefront analysis system, accurate placement of treatment to allow for fingerprint accurate customization of the LASIK treatment is required.
The combined technological features of tracking and iris registration in conjunction with the customized wavefront treatments of the Visx Star S4 IR™ system is what gives me the confidence that my patients are obtaining the best optical treatments available during their refractive surgery.