State of the art: Aspheric lens implants in cataract surgery

George Beiko, BM, BCh, FRCSC, details some of the available lenses and how they are used.

John A. Hovanesian

John A. Hovanesian, MD, FACS: Today we are speaking with Dr. George Beiko, who is in private practice in St. Catharines in Ontario. Dr. Beiko, thanks for joining us.

George Beiko, BM, BCh, FRCSC: Thank you for having me.

Dr. Hovanesian: We are talking today about the use of aspheric lens implants in cataract surgery. Why should a surgeon who is not currently using them consider the use of aspheric lenses?

Dr. Beiko: I think the most important thing for our patients is not only to try and get them 20/20 vision, which is the parameter that we use, but try to get them the highest quality vision that we can, and aspheric lenses give us that opportunity.

Dr. Hovanesian: What types of lenses are available?

Dr. Beiko: There are a number of lenses that are available to us. Let’s start off with the standard lens, which is not aspheric. This lens tends to have a positive spherical aberration component to it. Some of the older lenses that have been around for a while tend to have a value of about 0.24 to 0.3 in terms of the positive spherical aberration.

There are also some lenses that were made initially that did not have a positive spherical aberration or very low spherical aberration, such as the Abbott Medical Optics Clariflex.

And then we get into the new generation of lenses. These include those that have no spherical aberration whatsoever, which are primarily made by Bausch & Lomb and include the Akreos and the SofPort AO. Those that have some negative spherical aberration include the lenses made by Alcon — its IQ lens, which has a value of about –0.17, and the aspheric multifocals in that line can have a value of –0.1 to –0.17.

And then we have the AMO line of lenses, which includes the Tecnis, Tecnis multifocal acrylic and Tecnis multifocal silicone lenses, which have a value of –0.27. So we have a full range of values that are available to us, and hopefully we can use those in different patients to achieve the best vision for them.

Dr. Hovanesian: How do you evaluate a patient to decide which lens is best?

George Beiko

Dr. Beiko: Both the clinical data and laboratory data show us that there are different amounts of impact that you can have on the modulation transfer function. If we look at laboratory data and simulate various corneas and simulate the various lenses, and there are software packages out there that the industry uses to evaluate that, what tends to come out is that if you target a plano refraction and a zero spherical aberration for a patient, that you get the best outcome for them.

Now the other factor that comes into play is pupil size. If you have small pupils, then essentially spherical aberration has no impact on that. Once you get a pupil size of about 3 mm, 4 mm and 5 mm, then you see a progressively increased amount of effect of modulation transfer function from those pupil sizes.

Dr. Hovanesian: How do you measure the preoperative pupil sizes? In dim light or in bright light?

Dr. Beiko: Again, it depends on what the patient’s primary function is. For most of our patients, their preference is to have good vision in typical-lit conditions. But for some of our patients who are long-distance drivers or patients who are airplane pilots, they work under fairly mesopic conditions and you may want to measure the pupil under those conditions. So, again, it depends on the patients.

For the majority, photopic conditions would be ideal. I tend to prefer a device that gives me a value, so something like the Colvard pupillometer or the NeurOptics pupillometer. NeurOptics, my favorite instrument, will give me a value. And I have my staff evaluate the pupil under mesopic and photopic conditions and then go on from there.

Dr. Hovanesian: So then with the pupil area size information and the patient’s preoperative asphericity, you make a decision on a lens.

Dr. Beiko: That’s right. That’s something we have not covered, but you can use corneal topography to measure the patient’s asphericity. We know that in an aphakic individual, so that would be the goal of our cataract surgery, in essence that the majority of the aberrations come from the anterior corneal surface. We also know that with small-incision cataract surgery our impact on this value is minimal. So if you measure the patient’s preoperative corneal spherical aberration at 6 mm using one of the available topographers, most of them have software now embedded that will allow you to have the spherical aberration at that value. So you have that value and you have the pupil size and you go forward.

Dr. Hovanesian: Are there any downsides to the use of these aspheric lenses?

Dr. Beiko: Primarily the downside would be under conditions in which you have some sort of complication during surgery or in conditions in which we have an unstable bag; decentration or tilt of these lenses can lead to decrease in vision. However, to have a significant impact, you have to have a tilt more than 10° and a decentration more than 0.8 mm. Currently, in cataract surgery that is done with a capsulorrhexis that overlaps the lenses, the chances of having this condition are less than six cases per 1,000. So it has to be the rare case in which these lenses would not be indicated.

Dr. Hovanesian: Do you typically come to the OR prepared with a non-aspheric lens in the event that one of those adverse events happens?

Dr. Beiko: We do, and in my case, we have the Clariflex as a backup, which has almost zero spherical aberration. In the other OR, we have access to the SofPort AO, which can be used as a backup lens as well.

Dr. Hovanesian: Finally, what impact has the use of aspheric lenses had on your practice as a cataract surgeon? What would a typical cataract surgeon expect the use of these lenses to have on his or her practice?

Dr. Beiko: From the literature, what we find is that surgeons struggle with the concept of using these lenses because when they typically ask a patient who has an aspheric lens in one eye and a non-aspheric lens in the other eye to discern which eye is better, they find that the patients are not able to tell them which one is better. However, we know when we do contrast sensitivity testing that the eye with the aspheric lens always outperforms the eye with the standard lens. We also know that when we do things such as vision simulation studies for nighttime driving, that the patients perform much better with these. And thirdly, when you look through an aspheric lens compared with a standard lens, you get a better view of the retina. So we know that they have a higher quality of vision. And it is this quality of vision that I am very happy to give to my patients, and my patients are able to respond to it.

I think the other thing that is interesting right now is that when we look at the lenses, we have the variability to have two of the lenses in a single-piece profile. There have been very good studies done by Prof. Ulrich Mester in Germany, and he has looked at the Tecnis one-piece. What he has shown is that the lens, when it is finally set in the capsule, that its tilt and decentration actually mimic that of a young individual in their 20s. So we know that these lenses are sitting in-the-bag and not only are they providing patients with good vision, but they are actually restoring the position of the lens of a young individual.

Dr. Hovanesian: Dr. Beiko, thanks very much.

• George Beiko, BM, BCh, FRCSC, can be reached at Niagara Health Centre, 180 Vine St. South, Suite 103, St. Catharines, Ontario, Canada L2R 7P3; 905-687-8322; fax: 905-687-8766; e-mail: george.beiko@sympatico.ca.
• John A. Hovanesian, MD, FACS, can be reached at Harvard Eye Associates, 24401 Calle De La Louisa, Suite 300, Laguna Hills, CA 92653; 949-951-2020; fax: 949-380-7856; e-mail: drhovanesian@harvardeye.com.