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Up Front | Jul 2008

New Microincision IOLs Expand Surgeons’ Options

CRST Europe invited two cataract surgeons to select and review a sampling of IOLs that can be inserted through incisions of 2.5 mm or less.

The growing desire among ophthalmic surgeons to perform cataract surgery through incisions smaller than 2.5 mm introduces several challenges for IOL implantation. In recent years, we have observed two approaches to IOL selection for ultrasmall or microincision cataract surgery (MICS).

The first approach is to use an acrylic one-piece IOL. Although designed for larger incisions, with some adaptation they may be implanted through smaller incisions. By using a cartridge with a smaller tip and by applying it only to the outside of the incision istead of entering it (wound-assisted implantation), IOLs designed for 3-mm incisions can be implanted through 2.2- to 2.4-mm incisions.1,2

The Akreos Adapt (Bausch & Lomb, Rochester, New York), the AcrySof SA60 series (Alcon Laboratories, Inc., Fort Worth, Texas), and the Xcelens Idea (Xcelens, Croma-Pharma, Leobendorf, Austria) are a few examples of IOLs for which this approach can be used.

Additionally, aspheric designs and the high refractive index of some IOL materials allow some thinning of the optic center, thus reducing the diameter of the IOL when folded.

The advantage of this approach lies in the ability to implant standard high-quality IOLs. The disadvantage is that none of these IOLs can be safely implanted through incisions of 2 mm or less throughout the whole dioptric range.

The second approach is to design smaller and thinner IOLs that can be implanted through sub–2-mm incisions; however, such IOLs cannot simply be smaller versions of a larger IOL. The introduction of the Thinoptx lens (Abingdon, Virginia) opened the discussion on how to manufacture the IOLs to reach the incision size objective, although it compromised on optical quality. The Acri.Tec Acri.Smart IOL (Carl Zeiss Meditec AG, Jena, Germany) has obtained wide acceptance in Europe. More recently, other microincision IOLs with different designs have been introduced, and the impression is that we are facing a further evolution of cataract surgery.

This article reviews the qualities and characteristics of a number of recently introduced microincision IOLs selected by the authors, who have no financial interest in any of the lenses discussed.

ACRI.SMART SERIES
The design of the Acri.Smart IOL series is simple: It is a one-piece, plate-haptic, foldable acrylic IOL with a water content of 25% and with hydrophobic surfaces. These lenses can be considered an evolution from older silicone models, with the acrylic material favoring better and more stable fixation. The refractive index is 1.46, the central thickness is approximately 0.7 mm, the edge thickness is 0.25 to 0.27 mm (similar to standard IOLs), and the diameter of a 19.00 D rolled lens is 1.3 mm.3 The lens can be implanted through a sub–2-mm incision,3 and it has been demonstrated to provide visual results equal to those of standard IOLs in implanted eyes.3,4,5

Because of its efficacy and success, several modifications were implemented with the purpose of meeting specific needs: the toric model, Acri.Comfort 646 TLC (Figure 1A), and the multifocal, Acri.LISA 366D. Most recently, a combination of these two variations has been launched: the Acri.LISA Toric 466TD (Figure 1B). This lens has a toric anterior surface and a diffractive design 3.75 D add on the posterior surface, providing a 2:1 ratio of light focused to distance and near (Table 1). Microincision IOLs are perfect platforms for toric and multifocal designs because MICS does not impair the corneal surface.

AKREOS MI60 MICROINCISION IOL
Although presented by the manufacturer as an evolution from previous models, the Akreos MI60 IOL is a completely new IOL (Figure 2). The material is hydrophilic acrylic with 26% water content, the total length is 10.5 to 11 mm, and the optic diameter is 5.6 to 6.2 mm, depending on the dioptric power. The optic design is neutral aspheric equiconvex.

This lens has several innovative features that indicate improved understanding of ultrasmall-incision IOL design. The aspheric optic ensures high-quality image transmission even in the case of lens decentration or tilt, which may occur in the case of complications. The four-haptic design increases resistance to vitreous pressure and anteroposterior lens stability. Additionally, this thin-haptic design provides four zones for capsule sealing around the optic, thus promoting early and stable centration. The progressive resistance of the haptics prevents capsular bag contraction from displacing the optic, a concept derived from car-safety studies.

The problem of providing this thin lens with a double square edge was solved with a special fish-tail design of the peripheral optic and by limiting the polishing process. As a result, our experience with posterior capsular opacification (PCO) has been good.

When implanted in normal eyes, the Akreos MI60 IOL provides results similar to larger acrylic IOLs, with equal or better centration compared with the Akreos Adapt. Although it is thin, the lens demonstrated no pseudoaccommodation (Figure 3), indicating good anteroposterior stability.

The results in terms of refraction and optical aberrations have also been good. With this neutral aspheric microincision IOL, postoperative higher-order aberrations are the same as the preoperative corneal surface aberrations in uncomplicated eyes. We call this condition aberration-free cataract surgery, a technique of special interest for eyes that have previously undergone corneal refractive surgery.6

The four-loop design with progressive loop resistance offers distinct advantages in complicated surgeries. When a posterior capsular tear involving less than one quadrant of the capsule occurs, the lens can still be implanted into the capsular bag without dilating the capsule equator or late decentration (Figure 4).

OTHER MICROINCISION IOLs
Several other microincision IOLs have recently been introduced to ophthalmic surgeons (Table 1). They can be divided into two main types depending on whether they have a plate or closed-loop haptic.

Plate-haptic. This design offers better stability against posterior vitreous pressure, and it can therefore be of advantage in avoiding lens displacement after implantation. An example of this design is the WaveLight L303 (Alcon Laboratories, Inc.), an interesting hydrophilic acrylic IOL 11 mm long with a full 6-mm optic (Figure 5). Although an incision of 2.2 to 2.6 mm is recommended for implanting this lens, it can be injected through a sub–2-mm incision using a Medicel 1.8 Viscojet cartridge (Medicel AG, Wolfhalden, Germany), currently the smallest cartridge available for MICS IOL implantation.

Closed-loop haptic. This design has been implemented in the MicroSlim IOL (PhysIOL, Liege, Belgium), which is currently the microincision IOL with the largest optic diameter, 6.15 mm. Currently, the new Micro AY IOL (PhysIOL) is the only microincision lens with a blue-light–blocking filter (Figure 6).

AN ACCOMMODATING MICROINCISION IOL
In developing MICS IOLs, manufacturers can strive for lens stability or they can strive for lens movement due to posterior vitreous pressure and ciliary muscle contraction (ie, pseudoaccommodation).

To achieve forward displacement of the optic, the haptic should offer little resistance in the sagittal plane, and the best way to achieve this is with a closed-loop haptic design. The leading lens in this regard is the Tetraflex IOL (Lenstec, St. Petersburg, Florida). This is an anteriorly vaulted flexible acrylic lens with a 5.75-mm optic. It has a posterior square edge to reduce the occurrence of PCO (Figure 7).

Because of its weak closed-loop haptics, this lens is anteriorly displaced by ciliary muscle contraction and by posterior vitreous pressure, demonstrating an accommodative amplitude as high as 2.40 ±1.00 D, and more than 2.00 D in 100% of eyes in a clinical trial.5 Although experience to date is limited, results reported in implanted eyes are exciting.7

CONCLUSION
Microincision IOLs were developed to help surgeons reduce incision size for phacoemulsification. With increased experience in manufacturing and implanting these IOLs, we now are realizing that they are not simply reduced versions of standard IOLs. Microincision lenses are an entirely new type of IOL, with several relevant features that must be studied, discussed, and developed.

Generally speaking, these lenses are perfect for high-quality cataract surgery because of the small incision size. Additionally, they offer new possibilities in refractive cataract surgery, namely the incorporation of toricity and multifocality.

As for stability after implantation, they have the potential to head in two directions. One possibility is to aim for lens stability to ensure a stable refraction and to incorporate special optical designs; this necessitates thicker or highly technological haptics. The second possibility is to aim for lens movement to offer pseudoaccommodation, and the closed-loop design is showing promise as a way to achieve this goal.

Roberto Bellucci, MD, is Chief of the Ophthalmic Unit at the Hospital and University of Verona, Italy. Dr. Bellucci states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: roberto.bellucci@azosp.vr.it.

Simonetta Morselli, MD, is Chief of Anterior Segment Surgery at the Hospital and University of Verona, Italy. Dr. Morselli states that she has no financial interest in the products or companies mentioned. She is a member of the CRST Europe Editorial Board. She may be reached at e-mail: morselli.simonetta@azosp.vr.it.

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