Cataract surgery has gone through a tremendous growing process during the last several years. Patients now have greater demands and expectations for not only anatomical but also optimal refractive results. Cataract surgeons have become more refractive oriented, a testimony to the merger of the cataract and refractive subspecialties. The latest generation of IOLs, which provides multiple focusing distances, has increased surgeons' and patients' interest in refractive lens exchange as a procedure able to correct both spherical ametropia and concomitant presbyopia.
These IOLs may be divided into two groups: (1) accommodative monofocal IOLs, which move within the capsular bag and thus change the refraction of the eye, and (2) multifocal IOLs, which either refract or diffract the light passing through them into two or more focusing distances. This article shares my comparative experience with the Crystalens (Eyeonics, Inc., Aliso Viejo, CA) and a new apodized diffractive IOL, the Acrysof Restor (Alcon Laboratories, Inc., Fort Worth, TX).
Although explaining the principle of action for an accommodative IOL is not the purpose of this article, the concept of a monofocal IOL's moving within the capsular bag—thanks to the physiological accommodative process for providing multiple focusing distances—is theoretically perfect. These IOLs are supposed to perform like monofocal IOLs at any distance. In other words, compared with multifocal IOLs, they should provide a wider and more effective defocus curve, better contrast sensitivity, and fewer side effects in terms of night vision and visual disturbances. Accommodative IOLs' performance should also depend less on pupil size. My clinical series of implanted eyes showed otherwise, however.
Visual Acuity Results
When evaluating how effectively accommodative and/or multifocal IOLs allow patients to focus at different distances, emmetropia is mandatory. I should also note that all of these IOLs perform better when implanted bilaterally. Figure 1 summarizes the results of the first 82 Crystalens IOLs that I implanted bilaterally. I examined patients 2 years after surgery and tested their distance visual acuity, corrected with spectacles when necessary (20/20 or better in all eyes). Basically a monofocal IOL, the Crystalens provides the same quality of vision and performance as any traditional IOL for distance vision.
Figure 1 shows that, although my patients' intermediate vision (measured at 65cm) was effective, their near vision (measured at 35cm) did not really allow them independence from spectacles when reading. Thirty-four percent of my patients saw 20/20 or better uncorrected at distance and J2 or better uncorrected at near and intermediate. According to a survey administered to my patients, 74% wore spectacles for reading, either occasionally or always, and 7% wore glasses for intermediate distance.
Side Effects and Visual Symptoms
None of my patients complained of severe visual symptoms or nighttime visual disturbances, although 10% reported some halo effects and slight visual disturbances at night. Most noticed a significant fluctuation in the IOL's accommodative performance, both daily and during longer periods of time, and 74% reported a reduction of accommodation between the first and second postoperative years. Posterior capsular opacification was sufficiently clinically significant in 18 eyes (22%) to require an Nd:YAG capsulotomy.
THE ACRYSOF RESTOR
This article will not describe the optical design of the Restor IOL. It is worth mentioning, however, that the
3.6-mm, central apodized, diffractive pattern (which splits light energy into two main focal points, distance and near) is intended both to improve image quality by reducing the optical disturbances typical of other multifocal IOLs and to transfer more light energy for distance vision as the pupil dilates. In a laboratory setting, like all multifocal IOLs, the Restor must perform worse in terms of the quality of the focal image(s) it generates compared with monofocal IOLs. It also cannot produce an intermediate focal image as good as that of a monofocal IOL. The real question is whether these issues really make a difference in a clinical setting. In other words, does the Restor provide unsatisfactory visual acuity and induce meaningful visual disturbances? Following are the 6-month results from my first 80 Restor IOLs implanted bilaterally.
Visual Acuity Results
I tested patients' distance BCVA and found it to be 20/20 or better in all eyes under normal, photopic conditions. Figure 2 shows patients' intermediate and near distance visual acuities. The outcomes were opposite to those with the Crystalens: patients could read with no correction in most cases, but they had more difficulty at intermediate distance. Eighty percent of patients saw 20/20 uncorrected at distance and J2 or better at near, and 48% of those individuals also saw J2 or better at intermediate. According to a survey, 4% and 18% of patients used spectacles for reading and intermediate distances, respectively.
Side Effects and Visual Symptoms
One Restor patient complained about visual symptoms, both in bright and dim light, that were severe enough to require the IOL's explantation from both eyes. Forty-nine percent of patients reported mild night vision symptoms at 1 week postoperatively versus 13% at 6 months.
No one complained of a significant fluctuation in the IOL's pseudoaccommodative performance, either daily or within longer periods, but 10% reported poor reading performance under mesopic lighting conditions. The follow-up period was too short to report the number of cases of posterior capsular opacification.
MY POINT OF VIEW
Although my results speak for themselves, I would like to add a few comments, because these two IOLs differ significantly in their performance. First, although the Crystalens seemed to provide slightly better UCVA at intermediate distance, the Restor was definitely more effective at providing satisfactory unaided reading vision. My Restor patients could easily and quickly read after surgery. The slight drawback with this IOL is that reading vision requires bright light, but that may be easily addressed by patients. Because intermediate distance is less important than reading vision to the vast majority of my patients, the Restor delivers spectacle independence to more of them than the Crystalens.
Second, the Crystalens was effective only in those eyes able to increase intravitreal pressure and thus move the IOL forward, whereas the Restor's add power is related to its optic and not the eye. Unfortunately, there is no way to predict a person's ciliary muscle activity before surgery, so results are more predictable and stable with the multifocal IOL.
In the Restor group, complaints regarding their quality of vision mainly occurred during the first postoperative weeks, a period during which patients' brains learn to disregard the second, out-of-focus image that the apodized diffractive optics generate. I only heard occasional, mild complaints 6 months after surgery.
Finally, but most importantly, my patients' subjective feedback revealed far greater satisfaction with the Restor, under all circumstances, than with the Crystalens. Patients' preference is the main reason that I choose the Restor.
Francesco Carones, MD, is Cofounder and Medical Director of the Carones Ophthalmology Center in Milan, Italy. He is a paid consultant to Alcon Laboratories, Inc. Dr. Carones may be reached at +39 2 76318174; email@example.com.
Both the Acrysof Restor IOL (Alcon Laboratories, Inc., Fort Worth, TX) and the Crystalens (Eyeonics, Inc., Aliso Viejo, CA) performed well in FDA clinical trials. Neither technology has the pedigree of laser vision correction to date, because LASIK has set the bar very high for refractive correction. The product labeling for each IOL demonstrates excellent outcomes (Tables 1 to 4 ).1,2
Currently, we do not have commercial, clinical US data on the Restor, whereas the Eyeonics IOL Registry (administered by Surgivision Consultants, Inc. [Scottsdale, AZ]) indicates that the Crystalens has performed quite well since its approval. This registry serves as a voluntary, on-line reporting system for surgeons to track and benchmark their outcomes. Table 5 demonstrates that trained surgeons can achieve similar, if not better, results with the Crystalens than in the FDA clinical trial (data on file with Eyeonics, Inc.). It also demonstrates that patients' near acuity improves with time and does not degrade. Additionally, as would be expected, the percentage of patients achieving the specified acuity levels is markedly better when patients receive the lens bilaterally versus monocularly (Table 3).
What are the purported shortfalls of the Crystalens? Some patients may not achieve their desired unaided near acuity immediately, but the FDA clinical trial data reveal significant improvement in near acuity from 3 months to 3 years (Table 5). From a surgical standpoint, because the Crystalens is in an entirely new device category, ophthalmologists implanting the lens must master new technical skills. It is very clear from the FDA and Eyeonics Registry data that an emmetropic result permits patients excellent intermediate and near visual function.
Capsular Contraction and Opacification
The biggest technical difficulty to date with the Crystalens has been capsular contraction syndrome,3 reported at a rate of 0.3% in the first 14,000 implants (data on file with Eyeonics, Inc.). Recent recommendations from the Eyeonics Medical Advisory Board have resulted in a marked reduction in the incidence of capsular contraction syndrome (data on file with Eyeonics, Inc.). These recommendations include a 5.5-mm circular capsulorhexis, compulsive removal of lens epithelial cells and cortical material, at least 90º of IOL rotation within the capsular bag to dislodge any covert cortical material, and at least 4 weeks of a postoperative topical corticosteroid, tapered to prevent inflammation that can trigger capsular contraction syndrome.
The Acrysof Restor has a higher documented incidence of Nd:YAG laser posterior capsulotomy compared to 11% for the Acrysof single-piece IOL.2,4 The posterior capsulotomy rate of the Crystalens in the FDA trial was 13.7% (57/415 eyes; data on file with Eyeonics, Inc.).
Competitors of Eyeonics often fault the Crystalens for being made of silicone. Regarding dysphotopsia, however, biconvex IOLs with a low refractive index (n = 1.43, similar to the Crystalens) provide the least reflected surface glare and unwanted optical imagery, whereas unequal biconvex lenses of a higher refractive index (n = 1.55, similar to the Acrysof [Alcon Laboratories, Inc.] and the Acrysof Restor) create the highest incidence of retinal intensity and the potential for glare.5
STEAK VERSUS SIZZLE
In refractive surgery, patients' expectations should not exceed realistic, documented outcomes. I am concerned that the current marketing copy for the Restor is inconsistent with the physician labeling. The printed marketing message is “a revolutionary new way to leave glasses behind.” Patients reading this slogan are imagining a 100% guarantee of not wearing glasses postoperatively, an unrealistic expectation.
I believe the promotional marketing data of the Restor and the physician-labeling literature should agree. The four main issues are (1) dysphotopsia (specifically, night vision problems, glare, and halos), (2) intermediate vision, (3) mesopic reading function, and (4) a night driving warning.
As noted in Table 4, the combined rates of severe and moderate dysphotopsia are markedly higher with the Restor than either the Acrysof monofocal control2 or the Crystalens.1 By design, multifocal lenses split light and thus negatively affect contrast sensitivity and scotopic imagery.6 It therefore should not be surprising that patients in the FDA trial of the Restor reported a 30.4% rate of severe-to-moderate halo complaints with the single-piece design of the Restor. In the grand scheme of things (patients' happiness and perception), it is irrelevant except from a marketing perspective that this multifocal optic is apodized and diffractive.
Intermediate vision is an issue with the Restor. Based on a defocus curve, this IOL functions like a standard bifocal spectacle6 (Table 2 and Figure 1). Additionally, the Restor offers the same if not slightly less intermediate function as the Acrysof monofocal IOL (Figure 1). To compensate, the surgeon must target a postoperative refraction of +0.25 to +0.50D to move the Restor's curve to the left in the defocus diagram. Doing so creates trade-offs. The patient's distance vision decreases (Table 3), and his reading near point moves farther away.
Physicians should address mesopic reading vision with each patient. The mean spherical add power required to achieve near BCVA was 2.50D in mesopic conditions versus a mean value of 0.09 to 0.16D in photopic conditions.2 Patients may notice this difference in their daily lives. Obviously, not all reading conditions will be ideally photopic, and patients should understand that preoperatively. Moreover, I should note that the average distance of best focus for near vision was approximately 31cm (12.2 inches) in the Restor's FDA trial,2 and many patients may find this distance too close for comfort.
Night driving vision remains a concern with multifocal optic designs, and the Restor is no different. The warning label for this IOL reports a reduction in contrast sensitivity for some patients as compared to the monofocal Acrysof control. Because this loss may be accentuated in low-lighting conditions, the physician labeling recommends patients exercise caution when driving at night or in conditions of poor visibility.2
Current IOL designs to treat presbyopia are very good, but they will not achieve perfect distance, intermediate, and near vision in every patient. Because these lenses represent an elective procedure for many individuals, surgeons should deliver cautious and realistic consultative instructions to prospective patients. The growth of this surgical category requires compulsive preoperative counseling, the highest level of biometric accuracy, flawless intraoperative technique, and the astute postoperative management of patients. Only through these steps will surgeons guide patients to a satisfactory outcome.
John F. Doane, MD, FACS, is a refractive and corneal surgeon practicing at Discover Vision Centers in Kansas City, Missouri, and he is Clinical Assistant Professor for the Department of Ophthalmology at Kansas University in Kansas City. He is on the Speaker's Bureau and Medical Advisory Board for Eyeonics, Inc. Dr. Doane may be reached at (816) 478-1230; firstname.lastname@example.org.
1. Crystalens [physician labeling]. Aliso Viejo, CA: Eyeonics, Inc.; 2003.
2. Acrysof Restor [physician labeling]. Fort Worth, TX: Alcon Laboratories, Inc.; 2005.
3. Davison JA. Capsule contraction syndrome. J Cataract Refract Surg. 1993;19:582-589.
4. Lane SS. Foldable hydrophobic acrylic IOLs. Ophthalmic Hyperguide. Thorofare, NJ: Slack, Inc. Available at: http://www.ophthalmic.hyperguides.com/default.asp?section=/tutorials/cataract/list.asp. Accessed May 6, 2005.
5. Erie JC, Bandhauer MH, McLaren JW. Analysis of postoperative glare and intraocular lens design. J Cataract Refract Surg. 2001;27:614-621.
6. Schwiegerling J. Optics of intraocular lenses. Ophthalmic Hyperguide. Thorofare, NJ: Slack, Inc. Available at: http://www.ophthalmic.hyperguides.com. Accessed May 6, 2005.