Laser Eye Surgery - Technology

Over the past few years there has been a concerted effort on the part of Refractive Surgeons and researchers to increase the number of people achieving 20/20 vision, attempt to get a significant number of these people to get 20/15 (significantly better than 20/20) vision, to decrease or eliminate night glare and halos, and to decrease or eliminate contrast sensitivity loss. This branch of work has been called Custom Ablation, or having a different ablation patterns dependant on the patient's prescription and eyes. There have been several directions of research in the custom ablation area. Most laser companies have pursued the idea of wavefront modeling.

This posits that there are microscopic flaws that exist in a human cornea that prevent an eye from seeing better than 20/20, and if removed, would allow an eye to theoretically see 20/10 which is close to the theoretical limit of the resolution of the eye. To this end, several different wavefront modeling systems that detect these small abnormalities were employed, and many companies have now received FDA approval for their safety. These systems take a map generated of a patients cornea, and segmentally laser small abnormalities by transferring that map to the laser. It is important to remember that the FDA has not said that these systems actually improve the quality of vision, or give better visual results, just that they are safe to use and no worse than a normal non-wavefront system.

Unfortunately, although there has been a significant amount of hoopla surrounding the introduction and usage of these systems, there are serious problems and limitations to his technology.

First of all, there is no way to line up the wavefront map from the machine that makes it to how the eye is lined up underneath the laser. Although tracking systems on lasers can help line up an eye, they cannot compensate for tilt or of torsion (turning of the eye), which can completely throw off how the ablation lines up on the cornea. In fact, there is the theoretical possibility of actually creating abnormalities if he cornea is not lined up right. The answer thus far has been to use a magic marker line to help line up the cornea. This is probably less than ideal as a 1-2 mm wide marker is being used to lineup abnormalities that are on the order of thousandths of mm (microns).

Second, only about 10% of the population has significant abnormalities in their cornea, or what are called higher order aberrations. That would indicate that wavefront ablation is not useful for the other 90%.

Third, the ablation profile does not change, this extra smoothing step is only in the center part of the cornea. That means that the steep sides of some ablation profiles that can cause night glare and halos as the pupil opens upon them at night are not the target goal of this ablation. Fortunately, because the laser follows a wavefront map, one of the unintended effects is that it is more effective on the outer curvature of the cornea than in a normal ablation, therefore helping make a smoother profile and decreasing the steep sides of the ablation.

Fourth, the wavefront maps created were many times not reproducible, and were very dependant on the operator/technician. This introduced a level of inaccuracy to the results that may not be acceptable for measuring such small aberrations.

Visit Our Media Room.

---