Because its causes are fundamentally different from those of myopia, hyperopia, and astigmatism, many ophthalmologists have concluded that there is no cure for presbyopia and that the only solution is for patients to wear reading glasses to compensate for their inability to focus at near. Toward the end of 1993, my associates and I began to develop a method for treating presbyopia that we believe will be the next frontier in refractive surgery. We have currently corrected approximately 1,500 eyes, and our results are continuing to improve. Our goal is to create satisfactory visual acuity for distance and near vision for both eyes simultaneously.
ADDRESSING PRESBYOPIA IN THE CORNEA
We call the developing technique presbyopic LASIK. It involves constructing a flap and precisely forming an annular ablation in a centralized region of the newly exposed corneal stroma. This technique produces an unablated central protrusion of the stroma and transforms the exterior surface of the preplaced flap into a multifocal surface that effectively provides good distance visual acuity of 20/25 or better and near vision of J2 or better.
In our evaluations, we observed that occluding the 3-mm central area of the cornea does not affect distance vision. Consequently, we realized that this area is an ideal site for near vision correction. The fact that the pupil naturally shrinks for near vision helps validate this assumption. We reshape the zone to be multifocal but leave the most peripheral area of the cornea for intermediate and distance vision. To create a circular ablation, we combine a PMNIA mask and our laser beam with a PTK program, providing a beam with a diameter larger than that of the mask, as well as a predetermined depth. Second-generation lasers allow us to create the annular ablation directly, and the profile displays a spherical pattern. In order to improve upon our results, decrease recovery time, and minimize the occurrence of symptoms such as glare, halos, and reduced contrast sensitivity, we make the pattern aspherical. The slope toward the unablated central zone is relatively steep, while the slope directed toward the periphery becomes flatter, giving the ablation its spherical shape.
This procedure corrects presbyopia by using a predetermined profile to help create an annular presbyopic correction zone in the corneal stroma. That profile is included in the form of programmed software and has different shapes that correspond with the concomitant preoperative defect. As a result, if the patient presents with only presbyopia, the module will be different than it would if he presented with myopia or hyperopia with or without astigmatism in addition to presbyopia. This means that the profile will not only correct the presbyopia, but also any other existing refractive defect, such as myopia, hyperopia, or astigmatism. Previously, surgeons have corrected each of these conditions separately, which requires more ablation time and is directly related to longer recovery time.
POSTOPERATIVE SATISFACTION
We have observed that patients treated with presbyopic LASIK recovered their near vision on the first postoperative day and have experienced no regression. Distance vision, however, required between 2 and 3 months on average to return to its maximum function. For this reason, it is advisable to correct one eye first, especially if the patient has very good UCVA, as I previously quantified as being at least 20/25. Once the treated eye achieves the maximum level of vision, the surgeon can treat the other eye. During the interim, the patient will have the advantages of monovision, but with better distance vision and fewer problems with stereopsis and aniseikonia. If the patient's eye requires cataract extraction after undergoing presbyopic LASIK, the reshaped cornea will provide good near vision following cataract removal.
CONCLUSION
In our experience, presbyopic LASIK has proven to be safe and effective for correcting presbyopia, and we hope that using the newest generation of lasers with advanced tracking systems and smoother ablation profiles will increase the efficacy of this procedure. Centration is critical for the success of the procedure; if it is not accurate, there is an increased risk of inducing astigmatism (possibly irregular), as well as the possibility of losing lines of BCVA. Using today's methods of customized ablation, the procedure is also reversible and can be enhanced.
