The aim of microincision (ie, bimanual phacoablation performed through two 1.5-mm incisions or smaller) and mini incision (ie, coaxial performed through a 2.2-mm incision) phacoemulsification is to reduce surgically induced trauma and astigmatism. Each technique is becoming more reliable and reproducible, due partly to the developments in phacoemulsifiers and instruments. Two options are currently available for implanting an IOL during phacoemulsification: (1) An IOL suitable for microincision phaco is implanted with an injector. One of two microincisions is enlarged to 1.8 mm, without compromising the water-tightness of the incision, or (2) a traditional flexible IOL is implanted with an injector through a 2.2-mm mini incision.
New developments are the result of approximately 30 years of technical and clinical experience—occurring at a slower rate than developments in phacoablation instruments. Bimanual microincision phacoemulsification implants have been available for 6 years.1 IOLs suitable for an incision of less than 2 mm must comply with technical specifications. The injector cartridge determines the incision size, particularly the internal diameter at the tip of the cartridge for a peripheral injection (ie, at the edge, without introducing the bevel into the anterior chamber). Generally, a corneal incision of less than 2 mm requires an internal cartridge diameter of less than 1.4 mm. Avoid possible cartridge damage (eg, splitting, stress-whitening, or microfracture of the tip) as well as the fish mouth phenomenon (ie, widening of the cartridge tip). A damaged cartridge may have a particularly adverse affect on implantation; it may cause small linear tears in the optic, leading to loop ruptures that may combine with a wide optic tear.
WITHSTAND PRESSURE
The IOL material must withstand considerable pressure that is placed on it during injection. Deformability and resistance to tearing are more important than the refractive index, even though this enables reduction of optic thickness. All microincision IOLs are currently made of hydrophilic acrylic material, because hydrophilia is one key factor in its deformability. The optic zone diameter should be approximately 6 mm at 20.00 D to avoid the risk of optic aberrations due to decentration, which causes patient discomfort. Moreover, aspheric optics reduce the peripheral thickness, and therefore, the IOL's volume during injection.
The IOL haptics must accept a certain degree of compression in the capsular bag without decentering the optic, as postoperative capsular bag retraction always occurs—even if it is unpredictable and varies between implants and patients. Reducing IOL thickness actually significantly changes the stability of the implant, and suitable loops must be designed to avoid decentration or tilting to ward off early posterior capsule opacification (PCO). Wider loops with four footplates for even distribution of force are angled to increase pressure on the posterior capsule and thus reinforce the anti-PCO barrier effect. The fragile PMMA haptics of three-piece IOLs mean that a single-piece IOL, easier to inject, is preferred.
Implantation of this new type of IOL requires specific conditions: a 6-mm–wide capsulorrhexis and a bag opened wide using a viscoelastic solution. Implantation is performed with a single-use injector through a 1.8-mm incision. The plunger of the injector contains a foam tip, avoiding damage to the IOL when depressed. This is combined with a winged top-load cartridge that folds the IOL into a U-shape. Viscoelastic is injected into the cartridge injection tunnel, and the IOL is placed in the loading chamber. After folding, the viscoelastic is injected into the back of the loading chamber. The silicone tip of the plunger is carefully inserted into the loading chamber, and the IOL is pushed to the cartridge bevel with the plunger. To position the IOL, the injection cartridge is placed parallel to the extension of the incision edges, which act as a support. The injection is performed at the edge of the incision by applying firm pressure to the plunger so that the IOL slides into the incision. Correct lens position in the bag should be checked as the haptics are unfolding in the posterior chamber. The optic should be flat against the posterior capsule, avoiding any viscoelastic residue under the IOL at the conclusion of the procedure. This principle of viscoinjection (ie, peripheral injection) combines a flexible silicone-tipped plunger and a viscoelastic solution. Several companies that claim to use the microincision procedure employ viscoinjection. This device enables the viscoelastic and IOL to be constantly kept at the front of the plunger to protect the haptics during injection. The haptics cannot be jammed by the tip. The device also allows for easier depression of the tip in the case of very small diameters. Injections are thus easier and safer.
MICROINCISION IOLs
New-generation IOLs are single-piece hydrophilic acrylic lenses that allow the biomaterial to be sufficiently compressed and injected through a microincision. Currently, eight microincision IOLs are available:
•Acri.Smart IOLs (Acri.Tec GmbH, Henningsdorf, Germany);
•ThinOptX UltraChoice (ThinOptX, Abingdon, Virginia);
•Akreos AO Micro Incision (Bausch & Lomb, Rochester, New York);
•IOLtech MICS microincision lens (IOLtech, La Rochelle, France; and Carl Zeiss Meditec, Stuttgard, Germany);
•TetraFlex KH-3500 (Lenstec, St. Petersburg, Florida);
•AcriFlex MICS 46CSE IOL (Acrimed GmbH, Berlin);
•CareFlex IOL (W20 Medizintechnik AG, Bruchal, Germany); and
•SuperFlex and C-Flex IOLs (Rayner Ltd, East Sussex, UK).
Clinical research is only available for the first four IOLs listed, which we have used and will discuss below.
Acri.Smart. The 48S and 46S (Figure 1) are single-piece, biconvex, nonangled, square-edged, oval-shaped IOLs, made of 25% hydrophilic acrylic with a hydrophobic surface. The diameter of the optic is 5.5 mm and 6 mm for the 48S and 46S, respectively. The total diameter is 11 mm with full haptics. It is equiconvex, biconvex, and nonangled; it may be positioned on both sides. Both IOLs have an optical power range of 0.00 D to 35.00 D.
Kanellopoulos2 first implanted this IOL for a clinical trial in 2000, and Wehner carried out the first prospective multicenter study with the Acri.Smart 48S on 100 eyes (98 patients) with a 6-month follow-up.3 There was no implant decentration or tilt. Two cases of PCO were observed, but they did not require Nd:YAG capsulotomies. Only four eyes had a visual acuity lower than 0.40, and each was associated with a preexisting pathology. In 2003, Wehner also studied 100 eyes with Acri.Smart 48S implants and a preexisting pathology such as cornea guttata, diabetic retinopathy, or maculopathy.4 Two early Nd:YAG capsulotomies in 6 months, no aggravation of the preexisting pathology, and average BCVA of 0.82 were recorded. Koch5 conducted a study on 100 eyes implanted with the Acri.Smart 48S through a 2-mm microincision. Results showed 5% early capsulotomy, 1% halos, no decentration, and no loss of BCVA.
Alió presented 6-month visual results on 45 eyes (23 patients) who underwent microincision cataract surgery and Acri.Smart 48S implantation in the posterior chamber.6 This oval-shaped implant (ie, total diameter, 11 mm and optic zone, 5.5 mm) has a hydrophilic acrylic center and a hydrophobic acrylic surface. It was inserted—with a cartridge injector—through a 1.5-mm microincision in most cases (ie, less than or equal to 1.5 mm for two-thirds of the patients, enlarged to 1.7 mm for 10 patients, and 1.9 mm for three patients).
After 6 months, 71% of patients had an uncorrected far visual acuity greater than or equal to 0.6, and 99% had a BCVA greater than or equal to 0.7. The average residual spheroequivalent ametropia was -1.10 ±0.90 D. In 70% of patients, the average near vision addition was less than or equal to 1.50 D, and 26% of patients achieved an average addition of 2.00 D, suggesting the possible existence of pseudoaccommodation. No change in implant position or significant decentration was recorded. There did not appear to be postoperative space between the IOL and the posterior capsule, and the capsule subsequently adhered to the posterior IOL surface. No early capsular fibrosis was noted. Patients were very satisfied and did not report any reflections or halos. Overall, this implant seems highly suitable for microincision cataract surgery, due to its easy implantation through an incision of approximately 1.5 mm.
ThinOptX UltraChoice. This full oval-shaped and angled IOL (Figure 2), made with 18% hydrophilic acrylic, has an A-constant of 118.9. It has an optical power range of 15.00 D to 35.00 D. The diameter of the confocal optic zone is 5.5 mm, and the total diameter is 11.2 mm. The optic has a refractive-diffractive design that is based on the Fresnel prisms principle. The implant thickness is reduced to 300 µm at the periphery and 50 µm at the center of the optic, due to the five concentric diffractive segments of the posterior surface. These rings form individual images that combine to create a single focused image, which in theory has no aberration. Each ring functions as an independent optical unit, but when positioned together on the optic, they form a focused image.
The IOL is stabilized in the capsular bag, because the full haptics have four small bulges at each tip. This ultra-thin implant may therefore be rolled into the injector cartridge and inserted through a 1.8-mm incision using the Thin-Roller injector (ThinOptX). This is a specific, single-use, syringe injector. When the injector is assembled, the loading chamber is screwed to the tip. The injecting tunnel—very short and flexible—is submerged into the irrigation solution, and the hydrated implant is introduced into a slit. Applying pressure to the cap causes the implant to roll up in the loading chamber of the cartridge. This is the only implant that is rolled instead of folded into a U- or M-shape. This pressure must be maintained for 10 seconds. No viscoelastic solution is necessary. Once the implant has been rolled, check that it is unfolding in the right way, which is indicated by the direction in which the small openings are facing. The device is injected rapidly through an 1.5- to 2-mm incision, depending on the optical power.
Dogru7 first studied this implant by comparing 16 eyes implanted with the ThinOptX UltraChoice at 6 months with 20 eyes implanted with AcrySof MA60MB (Alcon Laboratories, Inc., Fort Worth, Texas). There was no difference in visual acuity, sensitivity to contrast, halos, surgically induced astigmatism, and loss of endothelial cells. No early PCO was noted in either group.
The modulation transfer function of microincision implants was compared on 30 eyes that received microincision cataract surgery without incident:8 10 eyes received a posterior chamber implant with the ThinOptX UltraChoice 1.0 IOL that was rolled and injected through a 1.6- to 1.8-mm incision; 10 eyes received a posterior chamber implant with an Acri.Smart 48S, injected through a 1.6- to 1.8-mm incision; and 10 eyes received the AcrySof MA60BM, injected after enlarging the incision to 3.2 mm. Patients' BCVA was greater than or equal to 20/25 at 3 months. Optic quality was studied objectively using the Optical Quality Analysis System, (Visiometrics S.L., Terrassa, Spain), which projects a modulation transfer function point source onto the center of the macula and analyzes the contrast of this projected image. The system measures loss of contrast of the light rays, after a double pass of the ocular diopters with a 5-mm pupillary diameter, independent of residual ametropia. While there is a correlation in vitro between the best posterior chamber implants and the best modulation transfer function results, the 30 eyes did not show any significant difference between the IOL types.
Akreos AO MI60 Micro Incision. This IOL (Figure 3) is 26% hydrophilic acrylic, a material already well proven on the Akreos Adapt (Bausch & Lomb). This material offers high resistance to stress and excellent deformability. The optic measures 6 mm and has a 360º posterior ridge to prevent PCO. It contains four fixation points angled at 10º to ensure early flattening of the optic against the posterior capsule. Fusion of the capsular flaps may occur in four areas during the first postoperative weeks. These haptics are directly inserted onto the optic, and the optic zone varies slightly—depending on the optical power—allowing a reduction in implant volume and a relatively constant section to be obtained. This lens is unique in that it contains a rigid proximal portion for stability and angulation and a flexible distal portion to cushion the compression of the capsular bag by fitting closely to the equator. The A-constant is 118.4.
The Akreos MI60 is injected with an injector and a 1.8 Viscoglide cartridge (Medicel, Widnau, Switzerland). A flexible silicone-tipped plunger is employed. Amzallag9 studied 20 patients divided into two groups according to injection technique. In one group, the injector bevel was introduced into the anterior chamber (ie, in group). In the second group, the injection was performed at the edge (ie, out group). The minimal incision sizes after injection were 2.2 mm for the in group and 1.8 mm for the out group. For the out group, a significant reduction in incision size with experience (ie, 2 mm to 1.8 mm) was noted. No complications were recorded after a follow-up period of 6 months.
IOLtech MICS microincision. The hydrophilic implant has an overall diameter of 12 mm, a 5.5-mm optic with square edges to limit PCO, and haptics angled at 13º. The A-constant was estimated at 119.3 for an anterior chamber depth of 5.77 mm. The IOL is available between 5.00 D and 36.00 D, in increments of 0.50 D. Implantation is performed with a single-use injector, through a 2-mm incision.
Verges10 studied 48 patients aged between 55 years and 73 years who underwent bimanual microincision phacoemulsification. Implantation was performed through a 2-mm incision. After 1 year, 96% of the patients had a BCVA of 20/25. Three cases of glare and two Nd:YAG laser treatments for early PCO were noted. Two patients presented with haptics that folded under the optic, due to retraction of the capsular bag. There were no repercussions on visual acuity.
MINI INCISION IOLs
Even though microincision IOLs for 1.8-mm incisions exist, the majority of IOLs currently require the enlargement of one incision. Nevertheless, certain traditional implants may be injected through microincisions that are moderately enlarged to 2.2 mm. They offer all the advantages of the traditional range (eg, square edges, haptic-optic angulation, and a low rate of PCO), and they are inserted through a mini incision.
Slimflex. The Slimflex (Physiol, Belgium) is a 6-mm, 26% hydrophilic acrylic, square-edged, biconvex optic with four haptics that are made thinner and angled at 5º. It may be injected through a 2.2-mm incision due to its design, which avoids any blockage effect in the injector cartridge and provides high resistance to compression.
AcrySof 30 AT. Made of hydrophobic acrylic with a 5.5-mm optic, the AcrySof 30 AT (Alcon Laboratories, Inc.) is injected through an enlarged incision.
Quatrix Aspheric. This single-piece hydrophilic acrylic IOL (Figure 4) made by Corneal Laboratories (Pringy, France) is an 11-mm, 360º, square-edged IOL with a 6-mm optic and 6º haptic angulation. This range of aspheric IOLs varies between 10.00 D and 30.00 D for an A-constant estimated at 119.6. Viscoinjection allows the implant to travel down the corneal tunnel and is inserted through a 2.2-mm mini incision.
Helping pave the way toward less invasive phacoablation surgery, microincision phacoemulsification is of great interest to 30% of European surgeons who wish to use this technique this year.11 For 6 years, suitable implants have been not just available, but used with increasing interest by ophthalmologists. The optical qualities of these microincision implants are identical to those of traditional implants, however, care must be taken to observe the stability in the capsular bag and their rate of secondary capsular opacification, something that new studies with a significant follow-up period will be able to assess fully.
J.C. Rigal-Sastourné, MD, practices at the Val de Gr‚ce Hospital, in Paris, and is the editor of the www.phacobimanuelle.net, a Web site dedicated to teaching ophthalmologic surgeons bimanual phaco technique and style. Dr. Rigal-Sastourné states that he has no financial interest in the products or companies mentioned. He may be reached at jcrigal@phacobimanuelle.net.
Up Front | Mar 2007
Assessing Microincision IOLs in 2007
The optical quality of these lenses is identical to that of traditional implants.
J.C. Rigal-Sastourné, MD
