How Your Patients Will Benefit From the Latest Lens Technology
How Your Patients Will Benefit From the Latest Lens Technology
MARC R. BLOOMENSTEIN O.D., F.A.A.O. Scottsdale, Ariz.
Laser-assisted in situ keratomileusis (LASIK) is a surgery that is safe and predictable for excellent candidates. Yet, the intraocular lens (IOL) is still evolving for cataract patients. Additionally, the IOL is filling a niche for those patients who aren't LASIK worthy, whether they undergo refractive lens exchange (RLE) or a phakic IOL — the choices have become copious.
Much like the parent who can't help but provide the best for his child, optometrists need to find the IOL that will best suit their patients. Knowing your patient's needs, occupation and expectations will lead you to the right decision.
Here, I'll discuss the various IOLs currently available on the U.S. market, how you can determine which one will best suit your patient and the future of this important device.
Three lenses are currently approved by the Food and Drug Administration (FDA) to provide presbyopic relief:
■ ReZoom (Advanced Medical Optics). This is AMO's second generation multifocal IOL. The ReZoom is based on the Sensar AR40e platform with a hydrophobic acrylic optic, poly-methyl methacrylate (PMMA) haptics and OptiEdge triple-edge design that the company says reduces internal reflections, edge glare and posterior capsular opacity formation. The OptiEdge is made with the same principle used in AMO's ClariFlex three-piece silicone IOL and acrylic Sensar lens. The ReZoom is a 6.0mm optic and blends five concentric zones throughout the entire optic portion of the lens. Termed "Balanced View Optics Technology" by AMO, each zone is proportioned to provide good vision across a range of visual demands and lighting conditions.
ReZoom is a second generation multifocal IOL.
For example, the large central zone at the optical center of this IOL is designed for distance vision and bright-light conditions. The outermost zone is the thinnest and designed for distance vision in low-light conditions, in which the pupil is maximally dilated (such as when driving at night). The reconfigured thickness of the edge helps to reduce any internal reflections and thus reduce glare and halos. In total, this IOL has three distance zones and two near-point zones, with intermediate vision coming from the interfaces between each zone.
The ReZoom provides a natural range of vision, with very good distance and intermediate ranges overall. I've found that most ReZoom patients can work spectacle-free at a computer terminal.
A caveat: While the near acuity of this lens is good, an effective add of approximately 2.75D at the spectacle plane, may not be enough for some patients to see fine detail at near. This is something you need to discuss with the patient prior to making a recommendation on a presbyopic IOL.
|Non-FDA-Approved Presbyopic IOLs
|■ Tetraflex (Lenstec). This lens is made of a poly-hydroxyethyl methacrylate (HEMA) acrylic material with 26% water content and a 5.75mm optic. The Tetraflex is based on the same principles of the Crystalens, in that it uses the forces of vitreal displacement to shorten the focal length of the visual system.|
Surgeons can insert this IOL into the posterior chamber with an injector through a 2.5mm-incision. Currently, the lens is in phase-III FDA clinical trials in seven centers in the United States. Of the 140 eyes that have reached the six-month follow-up period, 58% have an uncorrected visual acuity (UCVA) for distance of 20/20 or better, and 98% achieved a UCVA of 20/40 O.U. or better. UCVA for near was 20/50 (want-ad size print) in 59% of cases and 20/63 (telephone-directory size print) in 83% of cases.1
Tetraflex is based on the same principles as the Crystalens.
■ Synchrony (Visiogen) This lens is a dualoptic accommodating IOL that features two optical segments connected by haptics that have a spring-like action. The IOL works on the Helmholtz theory of accommodation. The theory: As the eye responds to a near target, the ciliary muscle contracts, which in turn releases the tension in the zonules allowing the two optics to come apart and thus increase the positive power of the system. The optical power of the anterior optic is within the range of +30.00D to +35.00D, and the posterior optic is assigned a variable diverging power in order to produce emmetropia for a given eye.
Synchrony works on the Helmholtz theory of accommodation.
This lens design relies on axial displacement of the anterior optic, similar to that of other pseudo-accommodating IOLs, in the range of 0.25- to 1mm to achieve the accommodative effect.
The results of a prospective, noncomparative, pilot clinical trial of the Synchrony dual-optic IOL suggest that this implant may provide pseudophakic patients with better accommodation than standard monofocal IOLs.2 The investigators compared the postoperative visual acuities (distance and near) and the accommodative range (based on defocus curves) of 24 eyes of 21 patients implanted with the Synchrony IOL with the same parameters in 10 eyes implanted with a monofocal, single-optic IOL. All patients were examined one day, one week and one, three, six and 12 months after the IOLs' implantation.
All study eyes achieved a distance best-corrected visual acuity (BCVA) of 20/40 at all visits, but the investigators noted a difference in near visual acuity between the groups. Six months postoperatively, the Synchrony eyes had a better accommodative range (mean: 3.22 ±0.88 D; range: 1.00D to 5.00D) than the eyes with a monofocal IOL (mean: 1.65 ±0.58; range: 1.00D to 2.50D). All the eyes in the Synchrony group tolerated the implant, and the investigators didn't observe any capsulerelated complications.3 In January, Visiogen announced that the FDA had granted it permission to expand its ongoing phase-III clinical trial of the Synchrony IOL to further evaluate the implant's safety and effectiveness in pseudophakic patients.
■ AcrySof ReSTOR (Alcon). This lens has a 6.0mm optic that is primarily distance-oriented in the main refractive region. The company uses a patented process called apodization to create a diffractive central 3.6mm optic zone. The apodized diffractive zone is made up of a series of apodized concentric steps. Apodization, a gradual decrease in step heights from center to periphery, creates a smooth transition of light between the distance, intermediate and near focal points.
ReSTOR uses apodization to create a diffractive central 3.6mm optic zone.
The apodization process is also meant to reduce the amount of perceived glare and halos, as it creates a very slow and gradual diffraction of entering light. This process creates approximately +4.00D of near-point add, equivalent to about a +3.20D at the spectacle plane.
The AcrySof ReSTOR is designed for patients who demand a very high degree of spectacle independence at near. This lens also offers an intermediate range of vision, though this range is not as clear as the lens' near vision.
A caveat: For some patients, the +3.20D effective add may be too much. So, patients with this lens may need to reduce their usual working distance to see clearly at near. Discuss this with patients prior to making an IOL recommendation.
■ Crystalens 5-0 (Eyeonics). This lens is an accommodating IOL made of the proprietary material Biosil, which is incorporated incorporated into a biconvex silicone plate with a square-edge design. The IOL incorporates a hinge into the plate design, allowing the optic portion of the lens to move in the eye in a way analogous to that of the natural crystalline lens, the company says.
Crystalens 5-0 is designed to mimic the movement of the natural crystalline lens.
During near-point activities, accommodation causes ciliary body contraction, and ciliary body mass distribution forces vitreous displacement, allowing the optic to move forward (as observed in A-scan technology).
The anterior-posterior movement of the optic and lens flexure, or "bowing" of the lens, provides the near-point vision for the patient, without loss of contrast sensitivity. The subjective quality of vision usually offers glare- and halo-free vision, which is sometimes not the case with multifocal IOL designs.
Also, the crystalens provides a continuous range of vision by projecting a single image to the back of the retina, instead of the multiple images from individual focal points of the multifocal IOL designs. Crystalens doesn't split light rays, allowing full vision under mesopic and scotopic conditions. The single point of focus allows smooth transition of ranges for the presbyope. The Crystalens enables patients to begin using their ciliary muscles again, as they did in their youth, the company says.
At present, other lenses are in clinical trials attempting to match the accommodative system of the natural crystalline lens. (See "Non-FDA-Approved Presbyopic IOLs," page 34.)
While all three of the aforementioned presbyopic IOLs will induce clearer near vision, they don't correct for astigmatism. Therefore, patient selection for these lenses is critical, as astigmatism could derail the results of these lenses.
I have found that any patient with more than 0.75D of corneal astigmatism will require some form of surgical intervention prior to IOL implantation. This could be a limbal relaxation incision, photorefractive keratectomy (PRK) or LASIK.
Biometry is another critical step in the implantation of all these lenses. This is because the ReSTOR functions best at a plano to small amount of hyperopia. In other words, since the lens has a strong central add, leaving the patient slightly hyperopic is beneficial, versus a patient with some mild myopia, which would decrease the effects. Also, the Crystalens works best slightly myopic, and any amount of hyperopia can take away from the IOL's visual function at near. There is no general rule for adjusting Biometry in fitting of the Re-Zoom lens.
Because not every patient is a great candidate for corneal solutions to problems of astigmatism, a lenticular option may be better for some of these patients. This is where toric IOLs come in handy. Currently, two toric lenses are on the market:
• STAAR Toric (STAAR Surgical). This lens is a plate haptic silicone lens with a 2.00D cylinder that corrects 1.40D at the corneal plane or a 3.50D cylinder that corrects 2.30D at the corneal plane.
• AcrySof Toric (Alcon). This lens is available in cylinder powers of -1.50D, -2.25D and -3.00D and has a more traditional haptic design, which may reduce lens rotation.
A caveat: Toric IOLs have the potential to rotate in the capsular bag after implantation, causing a reduction in, and possibly complete neutralization of, the astigmatism-correcting effect. When this occurs, the patient may need to undergo a second surgery to rotate the lens back into its proper position. Discuss this with patients prior to IOL selection.
Phakic IOLs not only benefit patients incapable of undergoing LASIK, they can also benefit children who have neuro-behavioral disorders, such as mental retardation and autism. For instance, a recent study presented at the American Association for Pediatric Ophthalmology and Strabismus Meeting, April 2007 in Seattle, showed ametropic children who had high myopia and neuro-behavior disorders did better with LASIK than with spectacle correction. Researchers examined 20 eyes of 12 ametropic children and found these patients tended to refuse spectacle correction or look around the edges or over the top of their spectacles. The researchers then decided to try an IOL, of which the children seemed more accepting. At 11 months post-op of phakic IOL implantation, 17 of the 20 eyes were within +1.00D of target refraction.
Two phakic IOLS are currently available:
■ Verisyse (AMO). This lens is an iris-fixated anterior chamber IOL and is available in two optic sizes: -5.00D to -20.00D in the U.S. with an overall correction range of -4.00D to -23.00D.
Verisyse is an iris-fixated anterior chamber IOL.
To implant this non-foldable IOL, the surgeon must make a 6mm-incision. Once inserted, the lens is clipped (enclavated) into the peripheral iris fibers.
The visibility of the lens in the anterior chamber is a huge benefit for the surgeon for reasons of centration and gross complications. The large incision, however, requires sutures and can induce astigmatism.
Currently, a foldable version of this lens is available in Europe and may be available in the United States in the near future.
Visian ICL rests in the ciliary sulcus.
■ Visian ICL (STAAR Surgical). This lens is a foldable posterior chamber lens composed of the company's proprietary Collamer material and requires a 3.0mm- to 3.2mm-incision. It's available in four lengths with sizing based on anterior chamber depth and the horizontal white to white measurement of the patient's eye. It rests in the ciliary sulcus. The surgeon delivers the lens into the anterior chamber and then places its four footplates behind the iris to rest in the ciliary sulcus. A caveat: The surgeon can have difficulty visualizing the lens in the ciliary sulcus.
|A toric-phakic IOL will eliminate the need for a separate surgery for astigmatism control.|
With the introduction of other lenses, our assortment of phakic IOLs will continue to grow. The most anticipated addition: the first toric-phakic IOL — eliminating the need to do a separate surgery for astigmatism control.
These lenses are designed to decrease the amount of unwanted aberration that follows standard IOL surgery. The young, healthy eye (birth to age 40) has a balance of positive spherical aberration on the cornea with that of negative spherical aberration in the lens. As the eye ages, an increase in the magnitude of positive spherical aberration on the lens leaves the eye with unwanted spherical aberration.
Positive spherical aberration is responsible for common night-vision distortions, such as glare, halo and poor contrast sensitivity. Putting a traditional spherical IOL into an older (presbyopic) eye compounds the problem by further increasing the amount of positive spherical aberration. Wavefront IOLs have aspheric or modified prolate surfaces to minimize this distortion by better imitating the curvature of the cornea.
Currently, three Wavefront IOLs are available:
• Tecnis (AMO). This lens comes in both silicone and acrylic platforms and has a prolate surface that induces negative spherical aberration, thereby reducing or eliminating total spherical aberration. The Z-sharp optic technology, which is incorporated to flatten the curvature in the anterior surface of the lens, produces the modified prolate surface, and in turn creates negative spherical aberration. The introduction of Z-sharp technology into the IOL necessitates the correct centration and tilt of the Tecnis to avoid inducing new aberrations. The surgeon must center the lens on the pupil. Any tilting of the lens or positioning off-center will cause aberrations.
• AcrySof IQ (Alcon). This lens incorporates the foldable acrylic material used in the original AcrySof lens and contains the same blue-light filtering chromophores as the original. The back aspheric design, much like the front surface design of the Tecnis, however, is intended to reduce the positive spherical aberration of the cornea. This IOL boasts a 9% reduction in central lens thickness (less aberration), according to Alcon.
• SofPort AO (Bausch & Lomb). This aspheric lens is aberration-neutral, meaning it doesn't have a negative or positive aberration. The uniform center-to-edge power for optical performance, that is unaffected by pupil size or location of the optic, serves to make the SofPort lens aberration-free. Without a specific aspheric design, practitioners can consider the lens free of tilt or decentration issues.
On the horizon
Calhoun Vision, of Pasadena, Calif. (www.calhounvision.com), is currently working on an intriguing lens material. Using a light-sensitive polymer imbedded with macromers, surgeons can alter this new lens material in vivo. In other words, surgeons can insert this light-adjusted IOL into the capsular bag (in whatever form the IOL is designed) and can take the patient's refraction one to two weeks post-op.
Using a proprietorial laser, the lens can alter its refractive shape up to 4.00D (hyperopic, myopic or astigmatic). You can recheck the refraction, and when the surgeon determines the lens is stable, another blast of the laser will "lock-in" the correction. This material allows any lens implanted into the eye to be "finetuned" without further surgical intervention.
As comanaging practitioners in IOL implantation, it's essential for us to have up-to-date knowledge on the latest lens technologies offered and which patients fit the profile of a specific product. Armed with this information, we can educate our cataract and non-LASIK candidates on the benefits and risks of each lens and ensure that the IOL selection and implant process is a mutually comfortable one. OM
References furnished upon request.
|Dr. Bloomenstein is director of Optometric Services at Schwartz Laser Eye Center in Scottsdale, Ariz. E-mail him at email@example.com.|
Optometric Management, Issue: June 2007