8.3.5 Microincision Intraocular Lenses: Others

8.3.5Microincision Intraocular Lenses: Others

Richard S. Hoffman, I. Howard Fine,

and Mark Packer

Core Messages

ßCurrent limitations in the available IOL technology have impeded full utilization of a biax-

ial microincisional approach to cataract surgery by many surgeons.

ßThere are numerous IOLs available internationally that can be injected through 1.5–

2.2mm incisions.

ßIOLs that are multifocal and toric are being manufactured and implanted through sub-

2.0mm incisions.

ßInjectable polymer lenses hold the promise of making full utilization of a biaxial microincisional

technique without the need for incision enlargement, although further research and development needs to transpire.

Continuing advances in phacoemulsification technology have allowed for safer lens extraction through smaller and smaller incisions. Removal of the crystalline lens utilizing microincisions has improved our technique not so much because of the use of smaller incisions, but through the virtues of performing the lens extraction by means of a biaxial approach. In reality, reducing incision sizes below 2.5 mm has diminishing returns with regard to astigmatism reduction, since the induced astigmatism for these incision sizes is practically neutral. Although there may be some added safety inherent in smaller incisions with regard to incision trauma, incision leakage, and endophthalmitis, the true power in removing cataracts through 1.0–1.2 mm

R S. Hoffman ( )

Drs. Fine, Hoffman & Packer, LLC, 1550 Oak Street, Suite 5, Eugene, OR 97403, USA

e-mail: rshoffman@finemd.com

incisions lies in the added options inherent in a biaxial approach with separated infusion and aspiration.

A biaxial approach through microincisions allows the lens to be approached from two different directions by easily switching aspiration and irrigation handpieces between two microincisions. This has added safety for difficult and challenging cases such as eyes with weakened zonules resulting from trauma, pseudoexfoliation, or genetic diseases such as the Marfan syndrome. The biaxial approach has also been found to be helpful in reducing vitreous loss in the presence of ruptured posterior capsules and reducing the incidence of posterior capsule rupture in eyes with weakened or defective posterior capsules, such as posterior polar cataracts. Bimanual irrigation and aspiration of cortical material has also allowed for the safer removal of subincisional cortex, especially in the presence of a small capsulorhexis.

The advantages of a biaxial approach are numerous. Despite this, there has been a slow incorporation of this method, especially within the United States, because of perceived difficulties in achieving proficiency with this technique and perceived limited advantages without the access to microincision intraocular lenses (IOLs) that can be inserted through these microincisions. Currently available IOLs within the US require 2.0–3.0 mm incisions for implantation. Thus, in order to complete a biaxial microincision procedure, a third incision of the appropriate size would need to be created between the biaxial microincisions, or one of the microincisions would need to be enlarged to accommodate IOL insertion. Despite this current drawback, the benefits of a biaxial approach far outweigh the need for a larger incision for IOL insertion. This advantage is somewhat analogous to the advantages that were presented years ago with the introduction of 3.2 mm phacoemulsification that still required wound enlargement for 6 mm PMMA IOLs. It was not until the introduction of foldable IOLs that could fit through 3 mm incisions that the full benefits of 3 mm phacoemulsification could be realized.

IOL technology has tended to lag behind phacoemulsification technology, and the same is true for current microincision phacoemulsification. The microincision IOLs that are currently being produced and developed are such that they can be inserted into smaller and smaller incisions, taking us one step closer to the ideal IOL that can deliver the full benefit of a microincision technique, and especially a biaxial

microincision technique. Some of the lenses and lens technologies that may be instrumental in furthering the utility of microincision lens extraction are reviewed below.

8.3.5.1 ThinOptX®

The ThinOptX IOL is a hydrophilic acrylic IOL with a special annular ring design that allows the 5.5 mm optic of the lens to be no thicker than 300–400 mm [9]. The posterior surface of the lens has a 3 mm central optic surrounded by a series of concentric annular rings of increasing diameters (Fig. 8.53). The rings form optically cooperative image-forming sections that create a single well-focused image without significant optical aberrations. Each ring contains the desired refractive power and contains a step that leads into the next ring segment, minimizing the thickness of the refractive ring. Each step is perpendicular to the curve of the ring at that point allowing each ring to focus incoming images at the desired focal point, while maintaining the thickness of each ring to approximately 50 mm [24].

The rings of the ThinOptX IOL appear similar in design to that of a Fresnel lens. However, the lines on a Fresnel lens function as a series of prisms with a diffractive design that has multiple focal points. The ThinOptX IOL is refractive with the posterior surface designed to assist the front surface in focusing light at a single point. Thus, it is not a true Fresnel lens but does share the quality of an ultrathin structure by virtue of a concentric ring construction. This ultrathin

Fig. 8.53 The ThinOptX IOL demonstrating concentric annular rings of increasing diameters

design of the ThinOptX lens has been reported to yield modulation transfer function (MTF) that exceeds 100% when conventional testing methods are utilized. This is believed to be due to the limitations of current MTF devices that assume the presence of some optical aberrations that may not be present on the ThinOptx IOLs [24]. Other studies have confirmed excellent MTF in the ThinOptX IOL but found the results to be no different than conventional foldable acrylic IOLs [2].

The unique thin design of the ThinOptX lens has produced some interesting advantages and some potential drawbacks. A recent study by Ouchi demonstrated better contrast sensitivity and lower spherical aberration with the ThinOptX IOL compared to the Alcon AcrySof lens [20]. Dogru also demonstrated higher contrast sensitivities in the ThinOptX compared to the three-piece AcrySof IOL [7]. Pseudo-accommodation has also been demonstrated with the ThinOptX IOL. Vejarano measured over 2 D of accommodation with the push-up method and similar amplitudes with trial lenses [31]. In a pilot study of the IOL performed by Alio, ultrasound biomicroscopy revealed forward movement of the IOL during accommodation that may be contributing to improved near vision results [24].

Although none of the 10 patients in Alio’s study reported glare or halos, a larger recent study of 50 eyes by Prakash revealed a 61% incidence of colored halos around artificial lights and a 64% posterior capsule opacification (PCO) rate at 15 months postoperatively [21]. A greater tendency for PCO was also discovered when the ThinOptX was compared to the three-piece AcrySof IOL [11].

The greatest advantage of the ThinOptX IOL with regard to microincision surgery is the ability to implant the lens through incision sizes of 1.4–1.7 mm [9, 21, 24]. Secondary to the ultrathin construction of the IOL, it can be rolled and injected into the eye with gentle atraumatic unfolding within the capsular bag. An injector system is available that does not require a cartridge to be placed within the incision and scanning electron studies have demonstrated no signs of surface damage or alterations, after the IOL has passed through the dedicated injector [15]. Although the IOL has been shown to move forward during accommodation, none of the eyes in Alio’s pilot study were reported to demonstrate any permanent change in IOL position, significant decentration, or lens tilt, 1 year following surgery.

8.3.5.2 Smart IOL

One of the more interesting prospects for microincision IOLs involves a technology being developed by Medennium. The Smart IOL is a lens constructed of a thermodynamic hydrophobic acrylic material. Wax is chemically bonded to the acrylic in order to create a material that remains solid at room temperature [6]. At room temperature, the lens is packaged as a 2 mm wide × 30 mm long solid rod. When inserted into the eye and warmed to body temperature, the rod transforms into a soft elastic disc that has dimensions that closely mimic those of the natural crystalline lens (9.5 × 3.5 mm) (Fig. 8.54). Before the IOL is packaged as a rod, it is imprinted with a precise dioptric power and after 30 s at body temperature, it expands into an elastic lens with the desired lens power [34].

There are many potential advantages of the IOL design. In addition to allowing for implantation through a microincision, the lens completely fills the average capsular bag (Fig. 8.55). There should be no open space for cell growth, no edge glare, no spherical

aberration, and no decentration in the presence of an intact capsular bag. The hydrophobic acrylic material should promote adherence to the capsular bag, reducing the incidence of PCO. The acrylic is highly flexible (Fig. 8.56) and has a high refractive index of 1.47, thus, there is an anticipation that minute changes in lens shape through accommodative effort may result in significant changes in lens power shift-yielding high amplitudes of accommodation [34].

There is also the possibility of changing the current rod dimensions in order to facilitate IOL insertion through smaller microincisions. The Smart IOL is currently in the preliminary stages of development although cadaver studies and optical bench studies have been performed.

8.3.5.3Afinity™

The Staar Afinity IOL (Fig. 8.57) is a single piece plate haptic IOL designed to be injected through a 2.2 mm incision utilizing the Staar nanoPOINT™ injector

Fig. 8.55 The Smart IOL in situ (cadaver eye) fills the capsular bag completely (Courtesy of Nick Mamalis)

Fig. 8.56 Elastic quality of the Smart IOL

Fig. 8.57 Staar Afinity single piece plate haptic IOL (Courtesy of Staar Surgical)

system (Fig. 8.58). Collamer is a proprietary hydrophilic material made from a combination of collagen and Poly-HEMA hydrogel. A benzophenone chromophore is covalently bonded to the poly-HEMA copolymer to create the final UV filtering Collamer material.

Collagen within the Collamer material inhibits protein deposition. Shortly after implantation into the eye, the Collamer IOL is encapsulated with fibronectin, which protects the lens from the immune system in addition to acting as a bioadhesive that aids in the fixation to the capsular bag. Studies have demonstrated excellent biocompatibility of the Collamer material and it may represent the ideal lens material for IOL implantation in eyes with a history of uveitis or active uveitis [28, 30]. The Collamer IOL was also found to have excellent optical qualities with lower higher order aberrations compared to those induced with the AcrySof IOL [14]. One potential drawback of this IOL is its plate haptic design which has been demonstrated to develop hyperopic refractive shifts due to progressive posterior displacement of the IOL, secondary to capsule fibrosis [27].

8.3.5.4AcriTec

AcriTec (Carl Zeiss Meditec) has a large range of foldable acrylic IOLs and all of the lenses that utilize a single-piece plate design can be injected through 1.5 mm incisions (Table 8.7). The AcriTec IOLs are made from Acri.Lyc, a copolymer of hydroxyethylmethacrylate and ethoxymethacrylate with a UV absorber. The Acri.Lyc material is 25% hydrophilic but

Fig. 8.58 Staar Afinity being ejected from the Staar nanoPOINT™ injector system (Courtesy of Staar Surgical)

maintains a hydrophobic surface. The material has a strong memory that does not change its curvature or power after rolling and unfolding and no surface damage develops after microincision injection [15]. The IOLs can be injected through a 1.5 mm microincision utilizing the Acri.Smart Glide System (Acri.Shooter A2-2000 and Acri.Smart Glide cartridge). Extensive tests measuring point spread functions before and 120 min after injection through the cartridge system confirmed that optical performance of the IOLs was not altered. Initial studies of the Acri.Smart IOLs demonstrated good centration, absence of tilt, very low induced astigmatism, and low Nd:YAG capsulotomy rates [24].

The Acri.Smart series of Acri.Tec lenses were some of the earliest microincision IOLs developed in the world. The initial design utilized a 5.5 mm optic but this has now been replaced with three newer versions of the Acri.Smart IOLs that incorporate a 6 mm diameter optic – Acri.Smart 46S, Acri.Smart 36A, and Acri.Smart 46LC (Fig. 8.59). These three microincision IOLs basically have the same plate IOL design and are made from the same Acri.Lyc material. They differ only in the aspect that the Acri.Smart 46S lens is spherical while the Acri.Smart 46LC is aspherical, and the Acri.Smart 36A is “aberration-correcting,” in that it is designed to neutralize corneal spherical aberration.

Acri.Tec produces two bitoric IOLs designed to treat astigmatism. The Acri.Comfort 643TLC is a bitoric foldable IOL with a tripod design that can be injected through a 2.2 mm incision. The Acri.Comfort 646TLC (Fig. 8.60) is also bitoric and can be injected through a 1.5 mm incision utilizing the Acri.Smart Glide System injector. The cylinder correction is symmetrically distributed over the front and back surface of the IOLs. Due to the reduction of the difference in the radii of curvature, image quality is claimed to be superior to traditional monotoric IOLs. The truly remarkable feature of these toric IOLs is the range of cylinder correction. Spherical power ranges from −10.0 to +32.0 D and cylindrical power ranges from +1.0 to +12.0 D. Higher powers can also be manufactured with special request.

Acri.Tec has also released a new generation bifocal IOL – the Acri.LISA (Fig. 8.61). The Acri.LISA 366D is a biconvex diffractive-refractive single-piece IOL with a 6.0 mm aspheric optic. The aspheric profile is designed to neutralize positive corneal spherical aberration. The lens has an overall diameter of 11.0 mm with 0° angulation. The diffractive-refractive optic of the Acri.LISA is based on patented SMP technology (smooth micro phase). The SMP technology produces a lens surface that does not exhibit any square edges or right angles. This technology is claimed to produce ideal image quality with a marked reduction of scattered light unlike common diffractive IOLs that incorporate a saw-tooth design on the surface of the lens. Incident light is distributed 65% for distance and 35% for near focus and the bifocal optic functions independent of the pupil size. The IOL power ranges from 0 to +32 D and incorporates a

Fig. 8.61 Acri.LISA 366D biconvex diffractive-refractive single-piece IOL with a 6.0 mm aspheric optic (Courtesy of Carl Zeiss Meditec)

+3.75 D near add that corresponds to a +3.00 D add at the spectacle plane. Note: LISA is an acronym for (L) light distribution for 65% distance and 35% near, (I) independent of pupil size, (S) smooth micro phase refractive/diffractive optic, and (A) aberration cor- recting-optimized aspheric optic.

Recent studies of the Acri.LISA bifocal IOL have demonstrated good performance with a satisfactory full range of vision. Alfonso reported on 81 patients implanted bilaterally with the Acri.LISA and found mean binocular distance-corrected near vision of approximately 20/20. The mean binocular distancecorrected intermediate acuity ranged from 20/20 at 33 cm. to 20/40 at 70 cm. Contrast sensitivity was within normal limits under photopic and mesopic conditions and improved at all spatial frequencies with binocular testing [1].