Presbyopia affects everyone. Throughout our lives we gradually lose our ability to focus up close. Young children can focus on objects just a couple inches from their face. Teenagers can read something a few inches from their nose. College students see clearly at less than a foot away. By forty years of age, however, books must be held farther back to be read comfortably. The eyes didn’t suddenly go bad at forty. The eye had been gradually losing the ability to focus since birth due to growth of the lens inside the eye and a resulting loss in flexibility.
Since LASIK treats the cornea (on the outside), it has often been assumed that it does not affect the onset of presbyopia. Older LASIK patients have commonly been told that either they wear reading glasses like everyone else, or they correct one eye for near vision and the other eye for distance vision, a treatment known as monovision. While this is acceptable to some people, most people would prefer to avoid glasses entirely.
There exists an opportunity for LASIK (or some other refractive surgery) to correct vision for both near and far. Several companies have experimented with multifocal LASIK corrections but none have managed to show significantly satisfying results. Many of these LASIK treatments rely upon concentric rings of different prescriptions to provide a multifocal correction. Unfortunately, the cornea is human tissue and doesn’t react like plastic when treated with a laser. It can be sculpted but cannot adopt the same shapes and zonal profiles as a transparent plastic would.
Newer treatments are looking at using natural corneal shapes in order to provide a more subtle blend of near and far vision. Researchers have long realized that higher order aberrations can cause an increase in the depth of focus of optical systems. These aberrations can also lead to a degradation of image quality however. Many researchers believe that there exists a compromise between perfect vision and a good depth of focus. Such a compromise would result in good (but not perfect) vision at a wide range of distances. Currently several intraocular lenses (used in cataract surgery) provide such a solution. The question is whether LASIK could also provide for such a solution.
Wavefront LASIK has been used for nearly a decade now. Wavefront LASIK has been marketed as a method of providing better-than-normal-vision by treating more than glasses or contact lenses. In addition to treating near-sightedness, far-sightedness, and astigmatism, wavefront LASIK has sought to treat other optical aberrations (such as coma, spherical aberration, trefoil, and others). Wavefront LASIK has achieved a moderate amount of success. Studies have generally agreed that vision is better than conventional LASIK.
But what if correcting all aberrations is not optimal. Certainly an aberration free system would provide a perfect focus at one distance. But it would also provide a worse focus at every other distance. For young patients, this wouldn’t be a problem. Older patients, however, would find that a perfect focus at distance leads to worse vision at near. Perhaps in the future, wavefront LASIK will offer a new option for older patients. It could offer a vision profile of good vision at distance and near by simply correcting the wavefront to an ideal pattern that expanded the depth of field without degrading vision below 20/20. New evidence is showing that this future application might indeed by possible.