IOLs: The Innovation Continues
IOLs: The Innovation Continues
Understanding the latest IOL offerings is key to comanaging cataract and refractive surgical cases.
BY JUSTIN HOLT, O.D., & DANE DANSIE, O.D.
Since November 29, 1949 when Dr. Harold Ridley, M.D., implanted the first intraocular lens (IOL) at St. Thomas's Hospital in London, IOL developers and clinicians have aggressively researched and improved upon cataract surgery and IOLs. Today, there are more innovative IOL designs both in use and in development than ever before. Here is a look at the state of IOL design, by category, including those lenses approved by the Food and Drug Administration (FDA) and those in the pipeline.
► TECNIS Multifocal (1-Piece) (Abbott Medical Optics)
The most recent addition to the U.S. multifocal market is the Tecnis Multifocal released in January 2009. It is an aspheric, diffractive lens, with a near add of +4.00D. The lens' excellent near vision is primarily due to the diffractive optics that cover the entire posterior surface of the optic. Thus, even eyes that have large pupils can achieve good near acuity.
The Tecnis uses 50% of light for near vision, and 50% of light for distance vision at all pupil sizes and in all lighting conditions. Therefore, patients have simultaneous reading vision independent of the amount of light present. This independence from pupil size seems to provide enhanced reading speed in patients.
AMO introduced the latest generation of this lens, the Tecnis 1-piece IOL to the U.S. market in March of this year. The optics remain unchanged. However, this new IOL features a ProTec 360° edge and TriFix design. The new edge minimizes cell migration by having an uninterrupted barrier edge as well as an uninterrupted barrier edge at the haptic-optic junction. In addition, the edges of this IOL are frosted to minimize glare. The TriFix design allows for stability by providing a three-point fixation.
► ReSTOR 3.0 (Alcon)
The original AcrySof Re-STOR received FDA approval in March 2005. The latest generation of the lens, The AcrySof IQ ReSTOR +3.0D, received approval in February 2009. This lens now incorporates a +3.00D correction at the lenticular plane (approximately +2.50D at the spectacle plane), for improved near and intermediate vision vs. the original AcrySof IQ ReSTOR IOL +4.0D, which would tend to require the patient to hold objects closer than was desired for comfortable near vision.
Like its predecessor, this lens is an apodized diffractive optic IOL. Apodization gradually blends the diffractive step heights, effectively managing the light that's delivered to the retina. Thus, it improves vision quality while minimizing visual disturbances. The apodized diffractive optics are found within the central 3.6mm optic zone of the lens. This area comprises nine concentric steps of gradually decreasing step heights (from 1.3μm to 0.2μm) that allocate energy based on lighting conditions and activity, creating a full range of quality vision — near to distant. The factors that provide enhanced contrast and image quality improvements include an aspheric optic, balanced use of optical power, number of diffractive rings, step height and ring width.
► ReZoom (AMO)
The second-generation Re-Zoom IOL — an acrylic, threepiece lens with a 6mm optic — received FDA approval in March 2005. While AMO introduced the Tecnis Multifocal IOL last year, the ReZoom still enjoys popularity among surgeons.
AMO built the ReZoom lens on the platform of the company's first-generation multifocal IOL, the Array. It improved the design of the Array, through the company's "Balanced View Optics" technology. This technology utilizes five optical zones proportioned to provide good visual function across a range of distances in varying light conditions. Zones 1 (1 being the center of the optic), 3 and 5 are distance-dominant, while zones 2 and 4 are near dominant.
AMO created an aspheric transition between each zone, to provide the patient with balanced intermediate vision. This is particularly useful to patients who spend a great deal of time at the computer.
In addition, AMO has altered the size of the rings in proportion to those used in the design of the Array lens.
The result of these modifications is that complaints of dysphotopsia have greatly decreased when comparing the Array to the ReZoom. The ReZoom typically provides very good distance and intermediate vision. Patients may occasionally need to use reading glasses for very small print with this IOL. Typical near vision tends to be around 20/30. Though the add measures 3.50D, the effective add at the corneal plane ends up at about 2.25D.
► Crystalens AO (Bausch + Lomb)
Because a phakic lens is about 5mm thick and an IOL is about 1mm thick, early researchers hypothesized that there may be space in which an IOL could move, thus providing a level of accommodation. The Crystalens is designed to provide accommodation up to 3.33D via dynamic retinoscopy.
The FDA approved the original Crystalens IOL in November 2003. The new generation, the Crystalens AO (aspheric optic) was approved in October 2009. It's a fifth-generation Crystalens and remains the only truly accommodating (rather than pseudo-accommodating) IOL available on the U.S. market. The lens features a hinged plate-haptic with a newly designed 5.0mm silicone anterior optic that is aspheric on both the anterior and posterior surfaces.
When the patient attempts to accommodate, the ciliary body contracts, and the tension on the capsular bag diminishes. The increased pressure within the vitreous body then allows the lens to vault forward at the hinges, resulting in near focus.
The optic of the Crystalens is monofocal. Research measuring contrast sensitivity indicates that multifocal design intraocular implants can slightly decrease the level of contrast sensitivity that a patient experiences after cataract surgery. With the Crystalens design, patients can maintain levels of contrast sensitivity. In previous versions of the Crystalens, the limited excursion of the lens optic during accommodation provided an average amplitude of 1.00D to 1.50D. With the Crystalens AO, early clinical results show a total accommodation of approximately 1.70D.
► Synchrony (AMO)
The Synchrony (AMO) is a silicone, single-piece, dual optic, foldable lens. It has a +32.00D anterior optic and a variablepowered, negative posterior optic connected to one another by a spring system. When the ciliary body is at rest, the two optics are close together and are set for distance vision. When the ciliary body contracts, reducing capsular bag and zonular tension, the front lens moves forward, moving the eye's focus to intermediate and near vision. This allows the patient more accommodation with less movement of the optic. Studies indicate an accommodative amplitude of 3.00D with this IOL.
Dual optic accommodating IOL designs have shown less potential for glare and halos because they contain no refractive diffractive zones.
Although not currently available in the United States, the Synchrony has been available commercially in Europe since January 2009. The lens also is currently under review by the FDA. It is anticipated that the lens will obtain FDA approval sometime this year.
► Tetraflex (Lenstec)
The Tetraflex (Lenstec), available in Canada and undergoing FDA review, is a single-optic accommodative lens with a hinged haptic. The lens is vaulted anteriorly to begin with and with accommodative effort, the optic is pushed forward.
Clinical studies show the lens provides good reading speed. Initial FDA studies show 100% of patients had 2.00D of accommodative amplitude, and 69% had 3.00D of accommodative amplitude.
► Akkommodative 1CU (HumanOptics)
Akkommodative 1CU is another accommodating IOL currently being used in Europe. Like the Tetraflex, it's optic vaults forward during accommodation. It differs, however, from the Tetraflex in the design of its haptics. Specifically, at the optic-haptic junction, its four haptics taper to act as hinges.
► Visian Implantable Collamer Lens (ICL) (Staar Surgical)
The Visian ICL was FDA approved for use in the United States in December 2005. Its design allows the lens to be positioned in the sulcus between the iris and natural lens. This lens is ideal for those patients who desire refractive surgery but whose correction falls outside the treatment parameters available with LASIK. This lens maintains all the patient's accommodation, and the surgeon can easily explant it if and when cataract surgery is ever necessary. The Visian ICL offers a treatment range of myopia from −3.00D to −20.00D.
► Akreos (Bausch + Lomb)
The Akreos AO Micro-incision monofocal lens was given FDA approval in September of 2008. Through the use of a haptic design and the fact that it's 30% thinner than its parent lens, it can be implanted through a 1.8mm incision and has an aspheric optic with uniform power. Among the many advantages of implanting a lens with such a small incision are: increased wound sealability and a reduction in both endothelial cell loss and surgically induced astigmatism.
► Light-Adjustable Lens (Calhoun Vision)
Available in some countries outside the United States, such as England, the light-adjustable lens (LAL) can be altered for better vision correction even after it has been surgically implanted. Adjustments are made through an ultraviolet light delivery device developed by Calhoun Vision, of Pasadena, Calif.
In one study, Calhoun Vision states that of 110 LALs implanted, 86% of patients saw 20/20 or better one-year post operatively. Based on first bringing the patient to emmetropia, which the manufacturer says the LAL can do predictably, a small zone in the central part of the LAL can be modified with increased power, while not modifying the power of the lens outside this region. Customizing the zone size to a specific diameter and power add has the effect of enhancing near and intermediate vision.
Light-adjustable IOLs are now undergoing FDA clinical trials.
► AcrySof IQ Toric (Alcon)
The FDA approved the Acry-Sof Toric IOL in 2005. In March of 2009, the FDA approved the latest evolution of the AcrySof Toric IOL. Incorporated into the same platform that has been proven successful in earlier generations, the AcrySof IQ Toric IOL offers an enhanced aspheric optic that improves image quality and increases contrast sensitivity. It can correct 1.50D to 3.00D of astigmatism.
► Visian Toric ICL (Staar Surgical) The first phakic IOL for correcting myopic astigmatism, the Visian Toric ICL is the toric version of the Visian ICL. Currently under review by the FDA, the Visian Toric ICL is available internationally.
In addition to the features listed above for the Visian ICL, the sulcus location of the phakic IOL allows for the toric option to be designed and used for treatment of myopic patients who have astigmatism.
The IOL is available for patients who have myopia between −4.00D and −20.00D and astigmatism of 1.00D to 4.00D.
► Acri.LISA Toric 466 TD (Carl Zeiss Meditec)
The Acri.LISA Toric 466 TD, available outside the United States, features a diffractive optic that also corrects for astigmatism. It's a biconvex diffractive lens with a diffractive, aspheric posterior surface and a toric, aspheric anterior surface. It's available in a range of powers for sphere (− 10.00D to + 32.00D) and cylinder (1.00D to 12.00D), and the near add is 3.75D. A foldable lens, it can be implanted though a 1.5mm incision, according to the manufacturer.
This lens appears very promising, as it may correct myopia, presbyopia and astigmatism with just one procedure.
More to come
There is clearly considerable interest in developing new and innovative IOL designs. Several others not mentioned in this article are in the very early stages of development and will be brought to market in the coming years. In order to discuss surgical options with patients, it's important you're familiar with emerging IOL technologies Stay tuned, things are just getting interesting� OM
||Dr. Holt is in group practice at the Mount Ogden Eye Center and Bountiful Hills Eye Center. He completed a residency at the University of Utah Moran Eye Center and Veterans Hospital. He can be reached at firstname.lastname@example.org.||Dr. Holt is in group practice at the Mount Ogden Eye Center and Bountiful Hills Eye Center. He completed a residency at the University of Utah Moran Eye Center and Veterans Hospital. He can be reached at email@example.com.|
Optometric Management, Issue: June 2010