Material Plus Design Equals Excellent Results

Surgeons discuss the unique attributes of the Akreos MICS Lens.

R. Bruce Wallace, III, MD (moderator): Although the concept of microincisional cataract surgery (MICS) was first introduced in the 1990s, surgeons in the United States weren't able to take full advantage of its potential benefits until 2009. That was the year in which the Akreos AO Micro Incision Lens (model MI60L, Bausch + Lomb), known as the Akreos MICS lens, became available. The Akreos MICS lens can be implanted through an unenlarged sub-2-mm incision, 1.8 mm to be exact, and it has other unique design elements as well.

I would like to talk with the panel first about the lens material, which is hydrophilic acrylic, how it differs from hydrophobic materials, and the advantages and disadvantages of these materials. Dr. Silverstein, you were involved in some of the early work with the Akreos MICS lens, including the clinical trials. Describe what you consider to be the important advantages of the hydrophilic material.

Steven M. Silverstein, MD, FACS: The current generations of both hydrophilic and hydrophobic materials yield excellent results and have really advanced our optical outcomes dramatically. However, what I like most about the hydrophilic platform is the dependable unfolding characteristics. This includes the ease of implantation, the memory of the lens that allows the unfolding process to guide it consistently at the point of the leading haptic, and the fact that very little manipulation is needed to get the lens into the capsular bag with one motion. In other words, the material is user-friendly.

Dr. Wallace: What about the material from the standpoint of biocompatibility?

Boris Malyugin, MD, PhD: A study by Ursell and colleagues¹ compared the number of cells on the surface of hydrophobic and hydrophilic IOLs, including patients with uveitic cataracts and diabetic cataracts. They observed a considerably higher amount of cells on the surface of hydrophobic lenses, which they thought indicated better uveal biocompatibility with hydrophilic material vs. hydrophobic material. Other studies have shown a greater tendency of hydrophobic acrylic IOLs toward higher incidences of late foreign-body cell reaction.^2,3 In my opinion, hydrophilic material is much better suited for MICS because we have to squeeze the lenses through a small cartridge. Hydrophilic material has a water film on the surface, which is why it glides through the small-bore cartridge easily. We usually can't squeeze hydrophobic material through the same cartridge as easily. I know IOL manufacturers have been trying to solve this problem by using special lubricants on the inner surface of the cartridge, which helps to make passage of the lens easier to some extent. However, hydrophilic material has natural lubricating properties, which is one reason why it is more suitable for MICS.

Dana J. Weinkle, MD: Clinically, some eyes implanted with hydrophobic IOLs occasionally show epithelial cell migration onto the anterior lens surface from the edge of the capsulorhexis. I have not seen this with the Akreos MICS lens.

The Akreos material is a combination of polymethylmethacrylate (PMMA) and hydroxyethylmethacrylate (HEMA), the latter being a soft and flexible material. Combining the two materials maximizes the benefits of each. HEMA allows increased water content of the lens to approximately 26% compared with a hydrophobic acrylic lens, which typically has a water content of less than 1%. This allows for compressibility, which, as Dr. Malyugin mentioned, makes it much easier to implant the lens. The PMMA component provides the lens with excellent memory. As a result of these material characteristics, the Akreos MICS lens compresses and folds well. It unfolds in a smooth manner, and regains its original shape because of the PMMA component. These are important advantages.

Moderate Index of Refraction Facilitates MICS

N. Timothy Peters, MD, FACS: The Akreos MICS lens also has a moderate index of refraction of 1.46, which is lower than some hydrophobic acrylics, which tend to be at or around 1.55. When you combine the moderate index of refraction with the higher water content, it eases implantation through the microincision and allows the lens to regain its shape after unfolding, as has been mentioned. The moderate index of refraction may also help to limit dysphotopsias, mainly those caused by internal reflection.^4,5 The Akreos MICS lens has an aspheric optic all the way out to its 360° square edge, and dysphotopsias around that edge are limited because of the moderate index of refraction.

Dr. Malyugin: The moderate index of refraction also has a cosmetic benefit, in particular for younger patients. With hydrophobic IOLs, we often see what is referred to as a “cat's eye” effect or a “blinking lens.” There are two reasons for this. One is the less curved shape of the anterior surface of the hydrophobic lenses, and the other is their higher index of refraction. With hydrophilic material, these effects do not occur.

Dr. Peters: I haven't seen any glistenings in the Akreos MICS lenses. Has anyone else?

Dr. Malyugin: Absolutely not.

Dr. Wallace: Those are two good points. All of us, in our experience to date, have found the Akreos MICS lens to be glistening free. Also, it provides the cosmetic benefit, not only for younger patients but also for older patients, of not causing that “glint” in the eye. With today's refractive cataract surgery, we're reducing our patients' need to wear eyeglasses, which makes it more difficult to hide the appearance of the pupil.

Dr. Weinkle: With regard to the 1.46 index of refraction of the Akreos MICS lens, it's very similar to that of the natural crystalline lens. At the slit lamp postoperatively, the IOL remains crystal clear and virtually indistinguishable from surrounding aqueous.

Dr. Wallace: The Akreos MICS lens has a 360° square edge. What is the value of that aspect of the design?

Dr. Malyugin: A square edge has become the standard in modern intraocular lenses. It is a must for creating a barrier to help keep the posterior capsule clear. I doubt any of us would implant a lens with any other kind of edge design.

The Impact of Four-Point IOL Fixation

Dr. Wallace: The Akreos MICS lens has a four-haptic design, which some surgeons aren't accustomed to using. What has been your experience with this characteristic? Does it affect implantation, centration or stability?

Dr. Silverstein: My response to that question is an enthusiastic one. I love the novel 4-haptic design. It has such a natural fit in terms of equal compression and stretch on the capsular bag. It self-positions with virtually no learning curve for the surgeon, and it helps the lens remain in place.⁶ I was involved in the studies of this lens from the earliest days, and now that we're years out from that time, I've seen that the lens has no movement other than what would be associated with capsular phimosis or capsular contraction where the entire capsular bag/lens complex moves as one. Because of the equal tension, I don't see the tension lines within the posterior capsule that are sometimes seen with other lenses and can cause dysphotopsias. As far as user-friendliness in guiding and facilitating implantation and selfstabilizing and centering, in my opinion, this lens has no equal.

I would advise surgeons not to associate this IOL's novel footplate design with the behavior of the old plate silicone lenses that came shooting out of the plunger-style injectors, rarely but occasionally puncturing the posterior capsule after an otherwise perfect phaco. That issue doesn't exist with the Akreos MICS lens. It releases and unfolds more quickly than a hydrophobic IOL, thankfully, but in a very predictable and very well-controlled fashion. There is nothing sudden or springy about it. I believe surgeons will be pleasantly surprised by how easily controlled this lens is and how “well-behaved” it is relative to the direction of the injector.

Dr. Weinkle: Like the Akreos MICS lens, the four-loop haptics of the Akreos AO lens also provide four-point fixation. The haptics are so easy to maneuver that a lens hook can be used to gently push them into the capsular bag. Because the lenses are flexible and so easy to manipulate, the irrigation/aspiration (I/A) tip is easily maneuvered underneath to remove viscoelastic. Both lens models center beautifully. They tend to stretch the capsular bag slightly because the four haptics create two axes of fixation. Therefore, as Dr. Silverstein pointed out, the striae often seen with a standard 2-haptic design are rarely visible.

Dr. Peters: Before I began implanting the Akreos MICS and Akreos AO lenses, I was concerned that they were so flexible that when the typical capsule contraction or fibrosis occurred, the lenses would vault anteriorly and change the refraction or erode refractive stability over time. I suspect other surgeons who have not used these IOLs have that concern as well. However, I haven't seen that happen at all, and I think it's because the four haptics have flexible junctions at the ends, which allow for capsule contraction without malpositioning of the lens. I haven't seen any refractive drift in my patients over the years either.

Dr. Weinkle: Also, there is a little cleavage point at the tip of each haptic. Some of the force that is applied when the capsule contracts is absorbed by these tips, thereby eliminating anterior or posterior vaulting or displacement.

Dr. Malyugin: Surgeons who have not had experience with four-haptic IOLs may expect to have to double their efforts as they are inserting the lens inside the bag because instead of two haptics they have four. That is not the case in my hands. I just press lightly with the instrument on top of the optic, and the trailing haptics go automatically into the bag. No special maneuvers are needed when dealing with these haptics. This is likely one of the biggest concerns surgeons may have when they are considering adopting the Akreos lenses, so it's an important point that no extra effort is required for implantation.

MICS Lens Insertion Techniques

Dr. Wallace: Yes, one of the most welcome surprises with the Akreos MICS lens is the ease of insertion. What I've been doing is using a blunttipped cyclodialysis spatula through the side port incision and once I put in the leading haptics, I use the spatula and the inserter to place the other haptics. Then, I like to put the lens in a vertical position, and as Dr. Weinkle said, remove the viscoelastic from underneath. I typically remove the viscoelastic from beneath first and then from above, and the IOL moves very little.

What is your preferred method of lens insertion through a 1.8-mm incision? What instruments do you use in addition to the insertion device that make this work well for you?

Dr. Peters: I routinely implant the Akreos MICS lens through a 1.8-mm incision, although to be fair, I measured my incisions for a while in the beginning and post-phaco/pre-implant, most were 1.9 mm. They had stretched a little bit. When I implant the lens, I put a Kelman forceps in the paracentesis as a fixation device, and I dock the cartridge into the incision. At first, I was really pushing and twisting to make sure it was in, but as I became more comfortable, I found it's only necessary to insert it into the incision. The cartridge doesn't go through the incision; it goes in the incision. Once I put the leading haptics into the capsular bag, the trailing haptics go into the anterior chamber. After that, I typically go through the main incision and tuck them in. It is a simple one-step tuck. I push on the optic and both haptics simultaneously go in. I've done that step with a second instrument and I've done it with just the I/A handpiece, and it is easy either way. As long as I push on the optic, the trailing haptics both just slip in.

Consider, too, that we're not implanting a MICS lens in every single case. In situations in which we need to enlarge our incision to place a presbyopia-correcting or toric IOL, we can go ahead and do that when we're finished with our 1.8-mm cataract surgery. The enlarged wound hasn't been operated through, so it's a virgin, pristine wound. It has not been stretched at all. The sealing and closure of the enlarged wounds for the other lenses is unlike anything else I've seen.

Dr. Malyugin: I typically use a wound-assisted insertion technique, and when I do, I prefer that the eyeball be a little bit harder so I have some resistance from the globe when I'm injecting. Therefore, I have a tendency to fill the chamber with viscoelastic very tightly. I'm not concerned, however, about overfilling the chamber because when I inject the lens, I'm usually using an instrument through the sideport incision. This stabilizes the eye to help with injection and it also opens the paracentesis, which serves as a valve for excess viscoelastic to go out. I've never had a problem with the anterior chamber being overfilled.

There are some differences between using a wound-assisted vs. a standard insertion technique, but they aren't dramatic nor do they cause any kind of problem. For example, in my hands at least, with the wound-assisted technique, the leading haptics can sometimes go over the capsular bag and onto the top of the iris rather than into the bag. This is because the tip of the injector isn't located in the center of the anterior chamber as it is with larger incisions. However, this is not a big issue because all it takes to get the lens inside the bag is pressing on the optic with the second instrument.

Dr. Wallace: I agree. With a wound-assisted technique, I rely more heavily on a second instrument because the leading haptics seem to want to float anteriorly. As I mentioned previously, the second instrument I typically use is a blunt-tipped spatula, which allows me to press posteriorly.

It's important to point out that for surgeons who have not used the Akreos MICS lens, the inserter is a syringe style. Only one hand is needed to insert the lens — a second instrument just helps to guide it into the capsular bag.

Dr. Weinkle: As an alternative to wound-assisted insertion, I use a “patient-assisted” technique. Prior to lens implantation, I remind the patient to fixate on the microscope light. The fixation creates counter-pressure during insertion.

Also, I try to eject some of the viscoelastic from the injector cartridge, so the lens is positioned approximately one quarter of an inch from the tip. With that small amount of viscoelastic remaining, the Akreos lens advances easily and never gets wedged in the incision. These small incisions require much less hydration at the end of the case, and less hydration helps to reduce corneal edema and foreign body sensation postoperatively.

Dr. Silverstein: Echoing the comments of the other panelists, I use the lens manipulator in the paracentesis for wound-assist. With two simple corkscrew maneuvers, I wedge the injector into the main wound.

Unlike some of the other IOL injector systems — that necessitate entry all the way into the anterior chamber to ensure the leading hapticoptic junction makes it into the capsular bag consistently — the Akreos MICS lens self-directs through the wound and into the anterior chamber. With downward angulation, the lens goes under the anterior capsular leaflet. Once it's there, the injector can be removed and either a second instrument through the paracentesis or the I/A tip can be used to gently tap the trailing haptics under the subincisional capsular leaflet.

Dr. Malyugin: Another important point about 1.8-mm cataract surgery is that it allows us to easily make truly square incisions, which we know from the work of Paul Ernest⁷ are the bestsealing and therefore the safest wounds. In contrast, when we're using a larger blade, such as 3 mm, we never have a square incision because it has to be too long and close to the center of the cornea. ■