Mixing Similar Technologies
Much has been made of mixing and matching presbyopia-correcting IOLs to take advantage of the strengths of two IOL technologies. In my hands, the most successful lens strategy has been bilateral use of the AcrySof Restor lens (Alcon Laboratories, Inc., Fort Worth, Texas). I have not found a mixing option that improves on the performance I achieve implanting this lens bilaterally. However, this may change with the recent introduction of a version of the Restor with a less powerful near add.
My experience with presbyopia-correcting IOLs includes hundreds of Array IOLs (Advanced Medical Optics, Inc., Santa Ana, California; no longer available) implanted from 1998 to 2003 with only one explant. Much of my success with the Array lens can be attributed to identifying patients with a real desire for spectacle independence. Patient selection is one of the most important factors in successful use of presbyopia-correcting IOLs.
When the Restor became available to me in October 2003, I moved away from Array because of the advantages that the apodized, diffractive optic provided. I have implanted more than 700 Restor lenses. Now, my lens of choice is the aspheric version of the lens, launched in late 2007, because of the improvements in distance image quality this lens brings. Most of my patients now receive this lens, unless they are hyperopic post-LASIK patients.
Two concerns expressed with bilateral implantation of the Restor IOL are that the patient might find the near point too close and that intermediate vision may not be sufficient. These are the reasons usually given for choosing an IOL mixing strategy. I have tried several mixing strategies in the past. However, it was my experience that mixing often increased visual disturbances and that the tradeoffs were not sufficient to offset the image quality provided by bilateral Restor lenses. Additionally, these two concerns did not appear to be long-term issues for patients.
LONG-TERM RESULTS
Long-term follow-up is crucial to understanding how a lens will perform once a patient is out of our care. In 2007, I located 18 bilateral Restor patients who were 3 or more years postimplant. Ninety percent (16/18) of these patients reported not requiring glasses for any activity. Binocular UCVA averaged better than 20/20 at distance and near, and the mean UCVA was 20/25 at 50 cm and 20/30 at 60 cm. At 3 years follow-up, 94% of these patients said they would recommend this lens option to their friends.1 The rate of spectacle freedom noted by these patients exceeded the rate reported in the clinical trial for US Food and Drug Administration (FDA) approval of the lens (80%).2
I believe the success of these patients is a function of bilateral implantation. We know that binocular summation provides improvements in visual acuity; this has been demonstrated in phakic patients in general and with the bilateral Restor lens over time,3 but not with mixed lens combinations. There also appears to be neural adaptation in patients with presbyopia-correcting IOLs, so that the degree of visual disturbances over time seems to lessen and acuity seems to improve. Again, this has not been demonstrated with mixed lens combinations but has been reported for bilateral Restor patients.4
LOWER NEAR ADD
Thus, the rationale for mixing IOL technologies does not appear to hold in the long term. The spectacle independence seen with bilateral Restor implantation in my patients is such that I did not expect mixing lens styles could improve it much. However, recently I began to reconsider this position with the introduction of the aspheric +3.0 Add Power AcrySof Restor apodized diffractive lens.
The Restor +3.0 Add Power lens addresses two of the supposed drawbacks of the Restor +4.0 Add Power lens. This new lens has a 2.25 D add at the corneal plane, smaller than the approximately 3.20 D add of the Restor +4.0. My clinical results with bilateral patients who have received this lens (n=20) indicate a near point of 40 cm, and their intermediate vision is correspondingly improved. The distance between the near and far focal points is less, so there is less vision change between the two points. Additionally, US FDA and European trial data show no increase in visual disturbances with the new lens model relative to the Restor +4.0 aspheric lens.5 My results to date are consistent with this.
It appears now that I have the opportunity to mix lenses. I anticipate considerable use of the new +3.0 Add Power AcrySof Restor lens bilaterally, but if I need to combine lenses to provide better vision very close up for a patient, a combination of the +3.0 and +4.0 Add Power lenses is an option. The difference between this type of blending and the usual strategy of mixing a diffractive IOL with a zonal refractive IOL is that the two lens types share the same optic technology so that the signal to each eye is similar.
The potential for binocular summation and neural adaptation would seem to be higher with this type of combination. However, clinical results will indicate the optimal solution. Clinical results are the key to appropriate IOL selection for our cataract patients desiring presbyopia correction at the time of surgery.
Robert A. Kaufer, MD, is the Medical Director of Kaufer Cl'nica de Ojos, Buenos Aires, Argentina. Dr. Kaufer states that he is a consultant to Alcon Laboratories, Inc. He may be reached at tel: +54 11 4733 0560; e-mail: robert@kaufer.com.
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