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In our experience so far, PML is a very successful procedure that has been well-accepted by patients and is in high demand at our centre. Currently, about 50% of our patients are PML candidates
We have been performing a technique know as PML (Presbyopic Multifocal LASIK) for almost six years now with excellent results; patients have been very satisfied with both their near and far vision. The procedure was studied, developed and patented at the Istituto Laser Microchirurgia Oculare in Brescia, Italy, and is designed to be customized to suit different presbyopic patients' needs.
The purpose of this article is to describe the PML technique and to demonstrate the benefits of treatment customization by presenting several case studies (one myopic-presbyope, one hyperopic-presbyope, one emmetropic-presbyope and one mixed astigmatic-presbyope).
It is important to emphasize the fact that presbyopia should be treated slightly differently to other "classical" visual defects with regards to patient care and management of expectations. Specifically, I use the patient satisfaction questionnaire, which has been prepared and validated by SICR (the Italian Refractive Surgery Society), in order to monitor the rate of satisfaction of patients treated with PML.1
The presbyopic challenge
In every aspect of refractive surgery, our goal has always been to surgically correct visual defects, i.e. myopia, hyperopia, astigmatism, and presbyopia. Correction of these defects is possible through corneal surgical procedures or lenticular surgery.
Of all the visual defects, presbyopia has been the most challenging to correct, partly because the mechanisms of accommodation and the causes of presbyopia are complex and not fully understood. Thus far, it has largely been managed through the use of progressively stronger spectacles, which gradually take over the near focus work of the crystalline lens.
Presbyopia is also unique in that it is the only refractive error that is considered to be progressive in nature. Although our management and most of our experience seems to point to the progressive nature of presbyopia, in truth, we do not know for sure that it truly progresses. It may be that in our "prosthetic culture" we have merely become unnecessarily dependent on our glasses and contacts.
In any case, a surgical alternative to the correction of presbyopia is appealing because of the enormous pool of presbyopic patients with a desire for good uncorrected vision. Mild hyperopes and emmetropes who have never worn glasses are particularly uncomfortable with presbyopia and its associated inconveniences.
Why is LASIK best?
The mission of presbyopic surgery, as with all other refractive surgeries, should be to eliminate the symptoms of the refractive error, rather than to correct the anatomical defect itself. For this reason, I think an approach that provides pseudoaccommodation is natural and appropriate. If we can provide patients with good functional vision at multiple distances, it is not necessary to restore true accommodative function by dynamically adjusting optical power of the eye.
There are several potential sites for correction of presbyopia. The cornea is probably the most common target, as it is the area that refractive surgeons are most comfortable with operating on. Theoretically, the anterior chamber provides another site for the correction of presbyopia, but this is as yet theoretical and is likely to prove extremely difficult in reality. The human crystalline lens can be replaced with a multifocal or accommodative intraocular lens, of which many different styles are now under development and coming to market. Finally, a number of scleral implant or ciliary muscle surgical procedures have been developed. This approach, however, is complicated, largely untested, and seems "more surgical" than is necessary.
As a familiar corneal procedure, LASIK appears to be the most popular and easiest surgical approach to presbyopic correction. In addition to surgeon familiarity with LASIK, patients in the presbyopic baby boomer generation are also familiar with and accepting of the procedure. In addition, LASIK can be performed bilaterally on the same day, is relatively quick and painless, and has proven to be quite safe. In my opinion, LASIK is ideal for presbyopia because of the absence of haze and its associated refractive complications, the absence of regression, and the presence of a regular and, hopefully, thin flap that can protect the multifocality created in the stroma.
Even with LASIK, we have several options available to us for addressing presbyopia. In most circumstances, we take a monofocal approach and have surgically induced monovision, but bifocal and multifocal approaches are increasing in popularity.