David F. Chang, MD
In the quest to provide pseudophakic accommodation, one idea has always been to refill the capsular bag with a compressible, clear material. The goal would be to utilize the eye's natural accommodative mechanism according to the Helmholtz theory. Of course, there are many obvious obstacles to overcome. How can surgeons get this new lens material through a small capsular opening and confine it in the capsular bag? If the opening is tiny, how can they remove the cataract? How can a smooth anterior optical surface be created in the area of the capsulotomy? How can a surgeon prevent optical imperfections such as bubbles or crevices if a gelatinous material is injected? How can he obtain the proper dioptric power? Finally, how can he prevent or treat posterior capsular opacification?
The concept behind the Medennium Smart IOL (Medennium, Inc., Irvine, CA) may overcome many of the aforementioned obstacles. The lens is composed of a hydrophobic acrylic material with unique thermoplastic properties that permit a temperature-induced change in its shape. Chemically bonding wax to the acrylic polymer creates a “smart” material, which remains in a solid state at room temperature. Because the wax component melts at body temperature, adjusting the percentage of wax content produces a semisoft gelatinous polymer once the lens is in the eye.Insertion Technique
The concept of implanting the Smart IOL is first to create an optic that fills the bag with an appropriate shape and dioptric power. The lens is then heated and compressed so that a solid, thin, 50mm long rod results upon cooling. Next, the rod can be implanted through a small incision (about 3.5mm in width), through a standard capsulorhexis, and into the capsular bag. As the rod warms to body temperature, it changes back to a pliable lens measuring 10mm in diameter and 3.5mm in thickness (Figure 1). The lens fills the capsular bag as it recovers the predetermined shape and dioptric power. Using an injector system, Samuel Masket, MD, of Los Angeles has successfully implanted Smart IOL prototypes into human cadaver capsular bags (Figure 2). Model in vitro testing systems are being designed to determine how flexible the optic must be in order to be compressed by the capsular bag. The polymer's composition may be varied in order to titrate the optimum flexibility. The Smart IOL is still a long way from becoming a clinical option, but it represents an ingenious approach to reviving the natural mechanism of accommodation.Vision Membrane IOL
Lee T. Nordan, MD
The Vision Membrane (Vision Membrane Technologies Inc., Carlsbad, CA) is an anterior chamber phakic IOL that has a central thickness of 600µm for all refractive powers as a result of multiorder diffractive optics. The optic is 6mm in diameter, and the curve of the optic parallels the inner curve of the cornea (Figure 3). The Vision Membrane possesses a one-size-fits-all design that is unique for an ACIOL, and its concept overcomes the problem of improper IOL sizing, the greatest impediment to the use of phakic ACIOLs today.
Potential complications are minimized by the small incision size and the limited surgical manipulation necessary to implant this IOL. The vaulted optic precludes angle-closure glaucoma, and its capability to accommodate an eye of any size is very important in eliminating iris tuck. The shape and thinness of the Vision Membrane keep it away from the endothelium. The lens is designed specifically to eliminate the formation of synechiae by means of a hydrophobic material and wide haptics that the iris cannot encircle. Of course, only time will confirm the absence of synechiae.Method of Insertion
The surgeon implants the Vision Membrane IOL through a 2.5-mm limbal incision with an injector that does not require transportation or grasping of the multiorder diffractive lens by the scrub nurse. After the Vision Membrane is folded, the surgeon can perform the implantation in less than 2 minutes. The Vision Membrane offers a superlative combination of advantages when compared with other phakic and pseudophakic IOLs. Some of these benefits include the previously mentioned one-size-fits-all functionality, a constant thinness for all powers, diffractive optics without chromatic aberration, and ease of implantation and removal. In addition, there is no need for a peripheral iridotomy during implantation of the Vision Membrane, and the lens has no association with cataract formation. Six Vision Membranes of the final design have been implanted with a follow-up time of 2 months and no complications. Proof-of-concept trials of a bifocal optic, which is also based upon multiorder diffractive optics, are expected to begin within a few months.Conclusion
The Vision Membrane project has progressed rapidly thus far. The combination of advantages offered by the lens makes it a likely candidate for being the refractive IOL of the near future.
Lenstec's Kellan Tetraflex IOL
Robert E. Kellan, MD
The design of the Kellan Tetraflex IOL (model KH-3500; Lenstec, St. Petersburg, FL) is based upon the criteria for the ideal IOL as set forth by Charles Kelman, MD. The lens must (1) fit through a 3-mm or smaller clear corneal incision, (2) be composed of a 100% biocompatible material, (3) have no more than 1mm of anatomic touch at any of its fixating points, and (4) be as readily explantable as it is implantable.
The Tetraflex IOL features a square-edge design with a 5.75-mm optic, which may be inserted through a 2-mm incision. The lens is composed of PolyHEMA (hydroxyethylmethacrylate), a highly biocompatible material consisting of 26% water. The structural configuration of the Tetraflex is entirely different from that of the Crystalens (Eyeonics, Inc., Aliso Viejo, CA), which is a hinged accommodative lens designed to vault posteriorly against the capsular bag (Figure 4). This movement is dependent on positive vitreous pressure to shift the lens forward. The Tetraflex has no hinges. It is angulated forward (ie, away from the capsular bag) and, therefore, has a unique mechanism of accommodation independent of positive vitreous pressure. The haptic configuration of the Tetraflex allows the lens to move with the entire capsular bag (Figure 5).Insertion Technique
There is no learning curve for cataract surgeons implanting the Tetraflex IOL, because the lens is readily implantable from a 1.8-mm cartridge into any clear corneal incision of 2mm or longer. The ophthalmologist may use his standard phaco technique. Unlike with the Crystalens, no atropinization is necessary with the Tetraflex IOL.Calhoun Vision's Light Adjustable Lens
Arturo S. Chayet, MD
The Light Adjustable Lens (LAL; Calhoun Vision, Inc., Pasadena, CA) enables surgeons to adjust the lens' power in situ to correct for refractive errors occurring after the LAL's implantation. The three-piece IOL has modified C-loop, blue PMMA haptics and a 6-mm, square-edge optic. The lens is composed of a photosensitive silicone material that undergoes a controlled change in shape when exposed to a specific UV-beam intensity from the light-delivery device. The altered shape of the lens produces a corresponding power adjustment.Surgical Technique
I implant the LAL using standard techniques. Surgeons can achieve refractive corrections of 2.00D in myopic, hyperopic, and astigmatic eyes. A slit-lamp–based light- delivery device has been designed with a fixation light that ensures that the treatment is centered on the visual axis. Adjustments take less than 2 minutes, during which time surgeons can use a contact lens with Goniosol (Ciba Vision, Duluth, GA) to help stabilize the eye and maintain a smooth corneal surface. Of the 12 patients whom I have treated for spherical correction, all have achieved power corrections within 0.25D of the intended outcome (Figure 6).
I most recently performed implantation procedures with a digital light-delivery device designed and manufactured by Carl Zeiss Meditec AG (Jena, Germany). The light-delivery device is based upon a digital chip technology similar to those used in high-resolution digital televisions and projectors and is capable of generating treatment-beam profiles with a spatial resolution of less than 1µm. The advantage of this device to the LAL technology is its ability to create precise, reproducible patterns, thus enabling the fast generation of cylindrical irradiation patterns along any axis. Thus, surgeons can treat each patient with a customized astigmatic adjustment.Efficacy
To date, two patients have been treated for astigmatism with the new digital light-delivery device at the Codet-Aris Vision Institute in Tijuana, Mexico. Patients have achieved toric corrections of less than 1.00D and been stable at 1 month (Table 1). These initial clinical results demonstrate that LAL patients can attain a successful treatment for accurate toric adjustments along a predictable axis that frees them of spectacles for distance vision.AMO Tecnis Multifocal IOL
Robert M. Kershner, MD, MS, FACS
IOL design has advanced tremendously since the late Sir Harold Ridley invented the first IOL in 1949. Only recently have the optics of the IOL begun to change. The Tecnis IOL (Advanced Medical Optics, Inc., Santa Ana, CA) represents the first IOL that has a wavefront-designed, modified prolate, anterior-surface optic that neutralizes the positive spherical aberration of the human cornea.1 Its design is based on the average corneal-surface wavefront-derived spherical aberration in a group of patients, and the optic neutralizes this aberration.2 Spherical aberration is the single most significant aberration of the human optical system, and it increases throughout life to continually decrease visual quality. Implanting conventional spherical IOL optics not only fails to address this problem but also contributes to it. The implantation of the Tecnis IOL can significantly reduce spherical aberration in postoperative cataract patients.1,3
Most of the undesirable optical side effects of any single-optic bifocal IOL are due to spherical aberration. Using the highly successful and stable Tecnis platform, optical engineers added a diffractive multifocal optic to the posterior surface of the lens. The result is the modified prolate Tecnis Multifocal IOL (Figure 7).Insertion Technique
The Tecnis Multifocal IOL is easily handled and injected into the eye with the Silver Series IOL injector (Advanced Medical Optics, Inc.) (Figure 8).4 I have found that I can easily implant the Tecnis Multifocal IOL through a sub-3-mm incision.
I use a very small ribbon of viscoelastic, such as Healon, Healon GV, Vitrax, or Healon5 (all products of Advanced Medical Optics, Inc.), on the length of the hinge and sparingly in the troughs of the cartridge to ensure sufficient lubrication. After properly loading the IOL, I position its leading haptic at the 2-o'clock position and the trailing haptic at the 8-o'clock position. Using the forceps' blades, the surgeon should press the optic under the edges of the two wings of the cartridge and move the IOL back and forth along the edge of the hinge to ensure its free movement. While holding the optic in position to guarantee that it does not pop out of the grooves, I gently fold the cartridge's wings so that the optic assumes a concave configuration.
I manually position the leading haptic into the cartridge and visually confirm that the trailing haptic remains outside of the cartridge. After loading the cartridge into the handle, I advance the plunger while visualizing the optic and haptics moving together. I place a small bolus of Healon5 into the center of the capsular opening. Immediate insertion into the eye is best. The surgeon should position the injector's tip bevel down and pass it through the incision such that the tip overlies the center of the capsular opening. Next, I advance the plunger as the IOL unfolds. The leading haptic will position itself down and to the left of the injector's tip. By slightly rotating the barrel of the injector counterclockwise 90º, surgeons may facilitate the remaining unfolding process. Finally, I remove all
By neutralizing spherical aberration, one of the leading causes of patients' dissatisfaction with conventional IOLs, this multifocal IOL promises to be a successful means of restoring accommodation to the postcataract patient. The Tecnis Multifocal IOL is not yet FDA-approved for use in the US.
Visiogen Synchrony IOL
David F. Chang, MD
The Visiogen Synchrony IOL (Visiogen, Inc., Irvine, CA) is the first dual-optic accommodating IOL to undergo clinical trials. For any IOL design that relies upon a moving optic to produce near focus, the amount of accommodative shift is proportional to the dioptric power of the optic. Consequently, hyperopes who are implanted with high plus power IOLs should enjoy much greater accommodative amplitude than myopes. The principal goal behind the dual-optic system is to afford every patient a moving +34.00D optic. This aim is accomplished by pairing it with a variable minus power optic in order to provide each individual with the necessary net IOL power for emmetropia. The two silicone optics are connected by a system of spring-like struts that pushes the optics apart (Figure 9).
The Synchrony IOL is designed to utilize the natural mechanism of accommodation according to the Helmholtz theory. Made of the latest generation of silicone, the single-piece design is sized so as to distend and fill the capsular bag (Figure 10). With a relaxed ciliary muscle, the zonules become tense, and the taut capsular bag compresses the two optics together. As the ciliary muscle contracts, the zonules and capsular bag relax. This relaxation permits the +34.00D anterior optic to move forward. A small-diameter, 4.5-mm capsulorhexis is needed to confine the moving anterior optic (5mm diameter) to the capsular bag. An injector system has been developed to deliver the lens through a 3.5-mm incision.Clinical Results
To date, offshore clinical trials have evaluated several minor design modifications and power-calculation adjustments. At the recent AAO meeting in New Orleans, Ivan Ossma, MD, of Columbia, reported on 24 eyes with a minimum of 6 months follow-up that had received a newer generation design of the IOL.5 When tested with the distance correction, 23 of 24 eyes (96%) had at least J3 monocular acuity. Using defocus curves, the mean monocular amplitude of accommodation was 3.17D. High-definition ultrasound biomicroscopy (HF35-50 High Frequency Ultrasound; Ophthalmic Technologies Inc., Toronto, Canada) confirmed separation of the optics, with movement of up to 0.78mm when a near target was presented to the opposite eye (Figure 11).US FDA-monitored trials are scheduled to begin later this year.
David F. Chang, MD, is Clinical Professor at the University of California, San Francisco, and is in private practice in Los Altos, California. Dr. Chang is on the scientific advisory board for Medennium, Inc., but states that he holds no financial interest in the company or any of its products mentioned herein. He is also a consultant for Visiogen, Inc., and the medical monitor for the Synchrony IOL. Dr. Chang may be reached at (650) 948-9123; email@example.com.
Arturo S. Chayet, MD, is Director of the Codet-Aris Vision Institute in Tijuana, Mexico. He states that he holds no financial interest in any of the products or companies mentioned herein. Dr. Chayet may be reached at +52 66 4683 57 23; firstname.lastname@example.org.
Robert E. Kellan, MD, is Director of the Kellan Eye Center in Boston and Assistant Professor of Ophthalmology at Boston University. He is the inventor of the Tetraflex lenses. Dr. Kellan may be reached at (978) 682-8661; email@example.com.
Robert M. Kershner, MD, MS, FACS, is Clinical Professor, University of Utah School of Medicine, John A. Moran Eye Center, Salt Lake City, and Consultant Specialist–Ophthalmic Medical Device and Biomedical and Biotechnology Development with Eye Laser Consulting in Boston. The author states that he holds no financial interest in any of the products or companies mentioned herein. Dr. Kershner may be reached at firstname.lastname@example.org.
Lee T. Nordan, MD, is the CEO of Vision Membrane Technologies, Inc., in Carlsbad, California. He is the inventor of the Vision Membrane and holds a financial interest in the product and company. Dr. Nordan may be reached at (760) 431-1846; email@example.com.
1. Kershner RM. Retinal image contrast and functional visual performance with aspheric, silicone, and acrylic intraocular lenses. J Cataract Refract Surg. 2003;29:1684-1694.
2. Artal P, Berrio E, Guirao A, Piers P. Contribution of the cornea and internal surfaces to the change of ocular aberrations with age. J Opt Soc Am A Opt Image Sci Vis. 2002; 19:137-143.
3. Mester U, Dillinger P, Anterist N. Impact of a modified optic design on visual function: clinical comparative study. J Cataract Refract Surg. 2003;29:652-660.
4. Kershner RM. Tecnis IOL adapts well to injector system. Ocular Surgery News. 2004; 22:21:4,5-53.
5. Ossma IL. The Synchrony Accommodating Intraocular Lens: one-year results. Paper presented at: The annual AAO/ASOA meeting; October 22, 2004; New Orleans, LA.