A Survey of IOLs for Refractive Lens Exchange

Numerous companies are hard at work on IOLs that could improve the surgical outcomes of refractive lens exchange. This article provides an update on the lenses currently and those not yet available in the US that have or could have a special application for this procedure.

CURRENT IOLS IN THE US

The Array
Three FDA-approved IOLs spring to mind as particularly useful for refractive lens exchange. The Array lens (Advanced Medical Optics, Inc., Santa Ana, CA) has a proven track record of freeing patients from spectacle-dependence. This is the primary lens that I and many other surgeons use for refractive lens exchange, because it suits most patients undergoing the procedure who are generally aged 40 years or older, interested in distance vision, and concerned about near vision. A study in which I was involved included several patients who were nearly emmetropic and underwent refractive lens exchange primarily to address their presbyopia.1 Each subject has been well satisfied with his surgical outcome. Virtually all of the patients in whom I have implanted the Array have been able to drive and read the newspaper without glasses.

The lens is not for everyone, however, so patient selection is critical. Poor candidates for the lens generally include individuals who express concern about the prospect of seeing halos at night, are particularly demanding of their vision (eg, engineers, architects, and artists), or frequently drive at night. Nighttime driving, however, is not an absolute contraindication, in my experience. A patient of mine who received the Array is a truck driver and has been very satisfied with his vision. I attribute his success to an accurate refractive result; patients who are emmetropic postoperatively see well at near and are satisfied with their outcomes.

Patients' pupils must be larger than 2.8 mm when reading in order to be able to use the near-vision portion of the Array. I have had to perform photomydriasis on a few Array patients in order to enlarge their pupils. I performed this procedure with a diode laser (Oculight GL; Iris Medical, Mountain View, CA). Described in 1984 with an argon laser,2 the technique places multiple broad spots circumferentially around the pupil.

The Array is also very sensitive to slight defocus and astigmatism, and refractive surgery patients tend to be more demanding of their visual outcome than cataract surgery patients. For that reason, I use several techniques to enhance patients whose postoperative UCVA is less than 20/20 after their refraction has stabilized: (1) I perform LASIK for residual sphere and cylinder; (2) in cases of residual sphere only, I implant the AQ-2010V lens (STAAR Surgical Company, Monrovia, CA) as a piggyback IOL; and (3) I have found that limbal relaxing incisions or an astigmatic keratotomy are often better options than LASIK for cases of residual cylinder only.

The STAAR Toric IOL
This silicone plate haptic lens is available in 2.00 and 3.50 D. At the corneal plane, these sizes correct 1.54 and 2.30 D, respectively. I use the STAAR Toric IOL (STAAR Surgical Company) for eyes with astigmatism of 6.00 D or more, because they cannot be corrected by limbal relaxing incisions, LASIK, or an astigmatic keratotomy. For higher degrees of astigmatism, I use limbal relaxing incisions in conjunction with the IOL.

The lens is easy to implant, but rotation has been an issue. The approach I have found most effective for minimizing this problem is implanting the lens upside-down. Stephen Bylsma, MD, a consultant for STAAR Surgical, reported his success with this technique at this year's Royal Hawaiian Eye Meeting,3 but this method constitutes an off-label usage of the product. The toric surface is on the lens' anterior surface, which is therefore shaped like a cylinder. Implanting the lens so that its cylindrical surface contacts the posterior capsule limits rotation. Of all the IOLs I have implanted in this manner, I have only had to reposition one.

Of course, this lens does not address presbyopia. Surgeons need a manufacturer to produce a multifocal IOL of zero power that they can implant in the sulcus on top of the STAAR Toric IOL. This option would benefit both highly astigmatic patients and individuals who underwent cataract surgery 10 or more years ago and now desire multifocality.

The Tecnis Lens
I recently began using the Tecnis lens (Pharmacia Corporation, Peapack, NJ) for refractive lens exchange. When performing indirect ophthalmoscopy, ophthalmologists use aspheric lenses because they produce a crisp image across the lens. Similarly, the aspheric Tecnis lens produces higher optical quality than do standard, spherical, monofocal lenses. The Tecnis is a good option for patients who desire refractive surgery but are not candidates for LASIK due to their high hyperopia of +4.00 D or more. Additionally, the lens works well for patients who would be bothered by the unwanted visual phenomena associated with the Array. I have also used the Tecnis lens in combination with a piggyback IOL for patients who have required more than 30.00 D of correction. Initially, I was concerned that contact between the two IOLs might change the surface curvature of the aspheric Tecnis, but, because the sulcus lens is +4.00 D at most, it leaves adequate space between the IOLs. Like the STAAR Toric IOL, the Tecnis does not address presbyopia.

IOLs IN THE WORKS

The CrystaLens
C&C Vision (Aliso Viejo, CA) has submitted all the data on its CrystaLens to the FDA. Outside the US, the lens already has a substantial track record. This accommodative, silicone IOL features a 4.5-mm optic and hinged haptics (Figure 1). It may be implanted through a 3.5-mm incision without an injector or through a smaller incision with one, but the injector was not part of the FDA study. Although it is a single-vision IOL, the CrystaLens moves in an anterior-to-posterior direction in the eye. It achieves accommodation via this axial movement, the amount of which depends on the individual's accommodative effort. At my practice, we have implanted 96 of these lenses, and, without correction, all patients have been able to see 20/30 or better at distance and J3 or better at near; more than 70% are 20/20 and J1 or better uncorrected.4 Our patients are satisfied with their visual outcomes and have experienced no optical side effects. Because the optic is essentially the same as that of a monofocal IOL, patients' contrast sensitivity with the CrystaLens is equivalent to that obtained with a monofocal IOL.

One advantage of the CrystaLens over a multifocal lens is that it is not preset to a particular distance. For instance, the near portion of the Array provides a static 2.30 D of addition. With the CrystaLens, patients can focus at distance, intermediate, and near simply by making a greater accommodative effort. My colleagues and I have found that patients experience slightly better acuity with this lens at intermediate distance (32 inches), perhaps because it requires less accommodative effort than near distance (16 inches).

I believe that, once available in the US, the CrystaLens will initially become the primary lens for refractive lens exchange, although that application is not part of the FDA-approval process. I would note, however, that some of our patients have difficulty maintaining the level of accommodation I described earlier. Whereas a multifocal IOL simply presents images, a patient must exercise his ciliary muscle in order to move the CrystaLens. Some of our patients implanted with this IOL wear low-powered (eg, 1.25 D) reading glasses when they want to read a book by the fire for a few hours. We have also observed a somewhat higher rate of PCO with this lens than with square-edged monofocal lenses. Patients are visually symptomatic, but we have found that performing an Nd:YAG capsulotomy actually improves their near vision. Accommodation may be compromised by fibrosis of the capsular bag, but the accommodative effect of the lens is enhanced by an Nd:YAG capsulotomy.

The 1CU
Already available in Europe, the 1CU Akkommodative IOL (HumanOptics AG, Erlangen, Germany) may come to the US as well. Like the CrystaLens, it features an axial-movement design but is slightly bulkier. The lens features four haptics, and surgeons working with the IOL have been satisfied by its performance. Using wavefront measurements, H. Burkhard Dick, MD, of Mainz, Germany, demonstrated approximately the same amount of accommodation between the 1CU Akkommodative IOL and the CrystaLens.5

A Multifocal Tecnis Lens
Pharmacia Corporation has already designed a multifocal version of its Tecnis lens. It shares the diffractive design of the company's 811e PMMA lens, which is available in Europe. Pharmacia has placed this diffractive design on the posterior surface of the modified prolate foldable IOL, which will probably be implanted through a 3.5-mm incision with a forceps or a 2.5- to 2.8-mm incision using an injector (Figure 2). A study of the 811e diffractive IOL found it superior to the Array in terms of reading performance.6

Pharmacia plans to initiate FDA-monitored trials of their multifocal Tecnis lens in the fall. The improved optical quality provided by the lens' modified prolate anterior surface should theoretically counterbalance the decrease in optical quality inherent to multifocality. As a result, this lens should offer optical quality like that of a standard, spherical, monofocal IOL, and it should outperform both the Array and spherical diffractive IOLs. I think that this IOL will compete with accommodative IOLs for preeminence in the field of refractive lens exchange.

The MA60D3
The multifocal IOL from Alcon Laboratories, Inc. (Fort Worth, TX), is currently in FDA-monitored clinical investigations. The study lens is similar to the company's three-piece Acrysof lens, but its central 3-mm zone features diffractive optics (Figure 3). Because the near-vision portion of the IOL is in the center of the optic, small pupils when reading are not the potential problem that they are with the Array lens. Locating the distance portion of the lens beyond 3 mm on the optic means that patients also should not experience as much image degradation when driving at night as with the Array.

The Light Adjustable Lens
Data from the first implantations of the Light Adjustable Lens (LAL) (Calhoun Vision, Inc., Pasadena, CA) in human subjects will be presented at this year's ASCRS annual meeting. The molecules in the 6-mm, silicone LAL are not polymerized and are sensitive to UV light. As a result, the IOL's power may be adjusted postoperatively. Although surgeons attempt to perform accurate IOL power calculations, the final position of a lens in the eye determines its refractive power, and predicting that position depends on basically empirical formulae. Surgeons will be able to modify the LAL's power postoperatively as necessary. For instance, if the IOL proves to be slightly underpowered after it has stabilized in the eye, the surgeon can irradiate the center of the lens. Polymerizing the light-sensitive molecules in that area creates a concentration gradient that prompts the remaining, unirradiated molecules to diffuse across the lens. This action thickens the lens and increases its power. The surgeon can treat astigmatism by applying UV light in a cylindrical pattern across one axis.

Beyond power adjustments and the treatment of astigmatism, it is also possible to apply wavefront corrections with the LAL. In a collaborative effort with Calhoun Vision, Inc., Carl Zeiss Meditec Inc. (Jena, Germany) has created a digital light delivery system that allows the measurement and correction of higher-order aberrations such as coma and quadrafoil. In the laboratory, the companies have shown that these applications of light are on an order of magnitude to make these corrections. For instance, an aberration on the order of 0.1 µm can be effectively corrected on the lens' surface.

The SmartLens
Medennium, Inc. (Irvine, CA), is conducting laboratory studies of a lens made of the same thermoplastic acrylic as its SmartPLUG. The SmartLens is currently compacted into a rod that is 2 mm in diameter, although the manufacturer can now reduce the rod's size to 1 mm. Once inserted through a small incision into the eye, the IOL warms to body temperature, at which point it opens into a full-sized lens that fills the capsular bag. This is the largest IOL ever implanted through a sub–2-mm incision.

In the optical lab, the SmartLens has provided good optical quality as measured by modulation transfer function, a standard measure of a lens' efficiency. It seems as if the lens will function well in vivo, and it is possible that the SmartLens will allow some accommodation because the lens material remains slightly pliable, like a soft gel. In addition, because the lens leaves no empty space in the capsular bag, it may cause pressure necrosis of any lens epithelial cells present and thereby have a reduced incidence of PCO compared with other IOLs. Performing an Nd:YAG capsulotomy is possible if it becomes necessary, however; the lens will remain in a stable position even if the capsule is opened.

Because it is the same size as the crystalline lens, the SmartLens does not cause vitreous traction, which can be a significant problem in highly myopic, young patients. As a rule, lenticular surgery (whether cataract or refractive) should be performed cautiously in high myopes unless they have already experienced a vitreous detachment, are asymptomatic, and have undergone treatment for any existing high-risk lesions such as lattice degeneration. The SmartLens may eliminate our concerns about inducing a retinal tear or detachment in these patients. Although the technology is promising and designed with refractive lens exchange in mind, the IOL is several years away from clinical use.

CONCLUSION
Despite the good news about the many current and pending IOL options for refractive lens exchange, we should not forget the idea of an injectable polymer, which has been almost the Holy Grail for cataract surgeons. Okihiro Nishi, MD, of Osaka, Japan, has worked extensively with injectable polymers, and several companies are conducting investigations of the technology. Injectable polymers would involve minimally invasive surgery and allow surgeons to adjust the material's refractive power intraoperatively. By completely filling the capsular bag, the pliable material would restore functional accommodation.

At present, we cannot know which IOL technology will prove to be the best option for refractive lens exchange. The ideal refractive lens surgery would likely involve (1) a simple needle puncture, (2) aspiration of the lens through a tiny capsulorhexis, (3) removal and/or destruction of lens epithelial cells, and (4) injection of a flexible, accommodating polymer that leaves the patients with a plano postoperative refraction and minimal higher-order aberrations. Today, we ophthalmologists can remove the crystalline lens through two paracentesis incisions sized 1.4 mm or less via bimanual phacoemulsification, but we must enlarge the phaco incision in order to implant an IOL. We create a capsulorhexis that is smaller than the lens optic with complete 360º overlap of the anterior capsule on the optic, and we rely on careful cortical cleanup, as well as IOL design, to inhibit PCO.

We are approaching the ideal, and the next few years are bound to offer exciting results, both successful and unanticipated. The long-term beneficiaries of this technological innovation will be our patients.

Mark Packer, MD, is Clinical Assistant Professor at the Casey Eye Institute, Department of Ophthalmology, Oregon Health and Science University, and is in private practice at Drs. Fine, Hoffman & Packer, LLC. He is a consultant for Pharmacia Corporation, VisionCare, and iScience; he has received honoraria and travel expenses from Medtronic Solan, Carl Zeiss Meditec, Advanced Medical Optics, Inc., and Alcon Laboratories, Inc.. Dr. Packer may be reached at (541) 687-2110; mpacker@finemd.com.

1. Packer M, Fine IH, Hoffman RS. Refractive lens exchange with the Array multifocal lens. J Cataract Refract Surg. 2002;28:421-424.
2. Thomas JV. Pupilloplasty and photomydriasis. In: Belcher CD, Thomas JV, Simmons RJ, eds. Photocoagulation in glaucoma and anterior segment disease. Baltimore: Williams & Wilkins; 1984:150-157.
3. Bylsma S. Reversing the Toric IOL: Stabilizing rotation and other pearls. Paper presented at: The Royal Hawaiian Eye Meeting; January 20, 2003; Maui, Hawaii.
4. Packer M. The AT-45 CrystaLens Accommodating Intraocular Lens. In: Khoo CY, dir. Javal Lectureship—Fresh ideas about corneal shape and structure. Presented at: XXIX International Congress of Ophthalmology; April 25, 2002; Sydney, Australia.
5. Dick HB. Current status of accommodating IOLs. Instructional course offered at: XX Congress of the ESCRS; September 8, 2002; Nice, France.
6. Richter-Mueksch S, Weghaupt H, Skorpik C, et al. Reading performance with a refractive multifocal and diffractive bifocal intraocular lens. J Cataract Refract Surg. 2002;28:1957-1963.