Neural Adaptation and Multifocal Visual Outcomes
Results from a recent mix-and-match multifocal IOL study, which will be presented at the American Academy of Ophthalmology (AAO) meeting in November, have demonstrated excellent functional vision at all three distances and maximized spectacle independence with neural adaptation. The time for neural adaptation varies between patients, ranging from shortly after surgery to several months postoperative.
DEFINING NEURAL ADAPTATION
Neural adaptation is the capacity of the human brain to adapt to new stimuli, situations, and experiences. Understanding the process of neural adaptation is
essential for ophthalmologists to better anticipate its impact on presbyopic patients who request multifocal IOLs.
Neural adaptation allows patients to perceive higher quality images than one might otherwise expect from a multifocal IOL. To transition between three visual depths, the brain must learn how to suppress near vision when gazing at distant objects and restrict distance vision when focusing at near—a task that is made possible by neural adaptation. As people age, neural adaptation becomes more difficult. Pepin et al1 showed that neural adaptation is not a fixed phenomenon but rather it continues to improve distance, intermediate, and near vision for at least 6 months after lens implantation. Thus, patients who expect spectacle independence and visual success overnight are over-optimistic.
DETERMINING NEURAL ADAPTATION
In the past, there was no scientific means to measure neural adaptation or predict which patients would adapt faster, slower, or not at all. We are currently studying this phenomenon in a group of 100 patients between the ages of 40 and 75 years.
In 80% of my patients, neural adaptation occurs within the first 6 weeks after surgery; however, some may require more than 3 months before neural adaptation occurs. A minority of patients (less than 5%) never adapt.
Discussing neural adaptation with patients is essential to the success of the outcome—and more specifically essential to patient satisfaction. The surgeon should be honest about neural adaptation, informing patients that it may take several months to occur. If the patient is well informed and truly understands the process, he is less likely to blame the surgeon for faulty results. In many instances, neural adaptation occurs before the expected time frame, and in these cases the patient is even more satisfied with the outcome. Patients should also understand that adaptation issues are not always negative; rather, it is probably a sign that the IOLs are working properly.
MIX AND MATCH STUDY
I currently use a staged approach for multifocal IOL implantation, heavily favoring the mix-and-match method; however, I customize IOL selection according to the patient (eg, hobbies, job, gender). Because each lens has its particular advantages and disadvantages, the use of two IOL designs allows the surgeon to compensate for some of the weaknesses of each IOL. In my practice, the combination of the ReZoom and Tecnis Multifocal (both manufactured by Advanced Medical Optics, Inc., Santa Ana, California) has been effective. I opt for these two lenses because the Tecnis Multifocal is pupil independent.
We have implanted more than 400 zonal aspheric ReZoom and diffractive silicone Tecnis Multifocal IOLs as part of a multicenter study on mixing and matching. In the future, we will also use the acrylic Tecnis Multifocal.
In group 1, 108 patients underwent bilateral Tecnis Multifocal IOL implantation. In group 2, we performed staged and customized implantation in 102 eyes, according to patient selection. We determined the dominant eye and performed IOL implantation in this eye first. The second surgery was performed within 2 weeks. If the patient's major activities were distance dominant, we implanted the ReZoom in the dominant eye; however, if the major activities were near dominant, we implanted the Tecnis Multifocal in the dominant eye.
Information from a patient questionnaire and psychometric test will be correlated with the outcomes and the degree of satisfaction several months after surgery.
Results with the ReZoom and Tecnis Multifocal have been excellent. We found that the combination of a ReZoom and Tecnis Multifocal IOL enhances spectacle independence. To date, all ReZoom/Tecnis Multifocal patients reported being 100% spectacle independent, while 90% of the bilateral patients reported the same result (Figure 1).
All patients in the mix-and-match group were spectacle independent. Furthermore, distance and reading vision improved (Figures 2 and 3). Subjective complaints were minimal, with only six of 51 patients voicing concerns. Their results improved over time with neural adaptation. Patient satisfaction was high, with most noting that they would undergo the same procedure again and would recommend it to friends.
OPTIMAL NEURAL ADAPTATION STRATEGIES
Careful patient screening—including determining if the patient wishes to be spectacle independent—is imperative. We ask if the patient is willing to accept some optical compromises, such as glare and halo, and consider his lifestyle needs in respect to his career and hobbies. Assess the patient's personality: Is he a perfectionist or someone with an obsessive personality? Perfectionists often make demanding and hypercritical patients. Caution should be used when patients are over-concerned about possible side effects. We also discuss the possibility of laser enhancement with the patient before the procedure is performed.
The ideal candidate for multifocal IOLs is one who desires less spectacle dependence and is willing to be patient with the process. It is important for the patient to recognize that it may take time to adapt to the new visual system. Generally, cataract patients are less demanding and hyperopic patients are most strongly motivated to reduce spectacle dependence.
Understanding and explaining the neural adaptation process to patients is critical. Spending extra time counseling patients preoperatively will lead to less postoperative counseling time. Although I never promise patients that they will be free of spectacles, I do explain they will me more independent after multifocal IOL implantation—and in most cases, patients are eventually spectacle independent.
Frank J. Goes, MD, is the Medical Director and a Senior Surgeon at the Goes Eye Centre, Antwerp, Belgium. Dr. Goes states that he receives travel support from Advanced Medical Optics, Inc., and Carl Zeiss Meditec AG. Dr. Goes may be reached at tel: +32 3 2198491; fax: +32 3 2196667; e-mail: frank@goes.be.
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