The thermodynamic hydrophobic acrylic material of the SmartLens (Medennium, Inc., Irvine, CA) makes it a stable, flexible, gel polymer that can be made into any size, shape, and dioptric power the physician desires (Figure 1). In this way, the lens may be customized to each individual patient. At room temperature, this material can be formed into a 2.0-mm rod and injected into the patient's eye through a normally sized capsulorhexis. Once the IOL reaches body temperature, it reconfigures into the initial shape, size, and dioptric power to which it was created and fills the entire capsular bag.
IMPLANTATION AND ACCOMMODATION
Although the SmartLens is still in the early stages of development and has yet to be implanted, I think it is interesting and important technology. Once implanted, the lens' material quickly becomes coated with fibronectin, as do other hydrophobic acrylic materials. The fibronectin bioadhesive causes the lens to stick to the capsule, which we expect will prevent the migration of cells and therefore PCO. Also, because the SmartLens fills the capsular bag, it cannot decenter, nor will it produce glare from any edge effect. The lens' elasticity makes it assume a rounder shape with accommodation and behave just like the human lens when the patient accommodates. It also has a high refractive index, so small changes in shape will result in significant changes in plus power, and there should be a large amplitude of accommodation.
We will be able to document that the SmartLens indeed accommodates using a variety of measurement techniques: (1) ultrasound biomicroscopy studies, so we can show the change in the shape of the lens; (2) MRI, which also shows the change in the shape of the lens; and (3) retinal wavefront power mapping, demonstrating the change in the power of the eye. Of course, we will also be able to perform cycloplegic and pilocarpine refractions to show an increase in plus sphere, as well as a decrease in sphere with atropine.
SURGICAL BENEFITS
The most exciting feature of this lens compared to all other injectable flexible polymers is that it is a stable gel rather than a fluid. Fluid lenses must be injected through a tiny capsulorhexis, and they limit surgeons to performing cataract extraction through a 1- or 2-mm capsulorhexis. Surgeons will have to refill the capsular bag with exactly the right amount of polymer and then seal the capsulorhexis site. Afterward, the possibility of the polymer leaking into the vitreous cavity will prohibit them from performing a YAG laser capsulotomy. The SmartLens allows us to create a regularly sized capsulorhexis. It fills the entire bag when inserted, and its stable gel material will permit a YAG laser capsulotomy without extrusion to the vitreous cavity. I believe it will overcome many of the problems associated with injectable flexible polymers.
CURRENT STATUS
The current issue regarding the SmartLens is whether it will pass the optical bench studies and toxicity studies, which I believe it will. Medennium has already made one lens and found that its optical properties are excellent, and I cannot imagine that the toxicity studies will pose any problem, because the lens is made of a material that has already been approved for use in the human body and is currently being implanted in patients' lacrimal canaliculi in the form of Medennium's SmartPlug.
Although at this time the SmartLens is reducible only to a 2.0-mm rod, the company is quite certain that shortly it will be reducible to a 1.0-mm rod, which will enable surgeons to insert this lens after performing bimanual microphaco through a 1.2-mm paracentesis. Another benefit of this lens is that it eliminates questions about implant size, because it allows surgeons to measure the phakic patient preoperatively in order to determine the size, shape, and dioptric power needed. We will also be able to imprint technology such as wavefront optics and toric optics onto the front of the lens.
To put the importance of this lens in perspective, if we look at cataract surgery over the last 30 years, there are three major leaps; everything else is an incremental step: Phaco is one, IOLs are the second, and I believe the SmartLens is the third.
I. Howard Fine, MD, is a founding partner of the Oregon Eye Associates in Eugene, Oregon, as well as former President of ASCRS. He does not hold a financial interest in any of the products mentioned herein. Dr. Fine may be reached at (541) 687-2110; hfine@finemd.com.
Part 2: Clinical Experience with the CrystaLens
BY D. MICHAEL COLVARD, MD
In a substudy of the FDA clinical trial of the CrystaLens implant, my colleagues and I compared 125 primary CrystaLens IOLs implanted in 125 pa-tients to 63 standard, 6.0-mm monofocal implants in 63 patients. The study was performed between February 2001 and October 2002. We conducted the study in order to answer two questions: (1) Does the CrystaLens technology do what it is intended to do (reduce dependency on spectacles relative to standard monofocal IOLs)?; and (2) Does the smaller optic of the CrystaLens decrease patients' quality of vision relative to standard IOLs? The inclusion criteria were the same as for the FDA Investigational Device Exemption protocol: Participants were required to demonstrate a visual potential of 20/40 or better by potential acuity meter, no significant preoperative pathology, and corneal astigmatism of 1.00 D or less.
Visual Acuity and Contrast Sensitivity
The patients displayed equally good uncorrected distance acuity of 20/40 or better with the CrystaLens (93.1%) compared with the standard IOL group (90.6%). The CrystaLens patients also exhibited better uncorrected near vision of 20/40 or better (85.1%) compared with the standard IOL group (47.2%).
Interestingly, the percentage of patients with postoperative near vision of 20/40 or better improved in the CrystaLens group to 92.1%, while that of the monofocal group worsened to 34% when we measured the reading vision with the distance correction in place. This is because some of the CrystaLens patients were hyperopic postoperatively. Without the distance correction in place, they were using their accommodation to correct their hyperopia. Once the full distance refractive error was corrected, the CrystaLens patients' near visual acuity improved, much like ordinary prepresbyopic hyperopes. On the other hand, the uncorrected near visual acuity of the standard IOL group grew worse when we corrected the distance refractive error. This is because some of the patients were myopic. The near vision with distance correction in place that was seen in the standard IOL group was consistent with that of a previously published series of standard monofocal IOLs.1,2
Our study also examined contrast sensitivity between the two groups of patients at both photopic and mesopic levels of illumination. We used the sine wave grating Stereo Optical device (Stereo Optical Company, Chicago, IL) and found no difference in visual quality as measured by contrast sensitivity between the two groups. Subjectively, the patients with the CrystaLens implants did not report nighttime glare symptoms more frequently than the patients in the standard IOL group.
Patient Satisfaction
Patient satisfaction has been very high with the CrystaLens. I realized that this IOL had a positive impact on patients after implanting my first 10 lenses for the phase I FDA study, which is concerned with safety. We followed those 10 patients for 1 year before we could implant any more CrystaLens IOLs. Every patient in this group who had a cataract in the fellow eye wanted to wait for the phase II study in order to receive the CrystaLens in the second eye as well. The mean age of this group was 73. These patients were thrilled to be able to see well at distance and read well without glasses for the first time in 30 years.
Accommodative Effect
My patients appear to have approximately 1.75 to 2.00 D of accommodative facility (Figure 2).
From a practical standpoint, this means that most patients can read their computer screens and magazine print easily, and they can read a restaurant menu without spectacles. Patients are very pleased to be free of spectacles in social situations.
Implantation Pitfalls
Precise biometry is critical with the CrystaLens. Pa-tients experience the full benefits of this IOL only if there is little or no postoperative refractive error at distance. Virtually all of my CrystaLens patients have gained greater independence from spectacles. Those whose A-scans have been absolutely on target, however, have fared wonderfully. Obviously, if patients are left myopic postoperatively, they can read well, but their uncorrected distance vision suffers. If patients are hyperopic postoperatively, they use the accommodative effect of the IOL to improve their uncorrected distance acuity at the expense of their near vision. Therefore, careful biometry is the key to success with this IOL.
Patient Selection
My experience is largely with patients who are older; the mean age of my series is approximately 73 years. All of my clinical experience with this IOL has been in cataract patients without preoperative pathology. When the IOL is released for use, I would expect that patients with pseudoexfoliation might be poor candidates for the lens because insufficient zonular support could reduce the effectiveness of the IOL.
Intriguing Observations
We have learned a few interesting facts about the CrystaLens implant. For instance, patients' reading ability improves even when only one eye is implanted with the CrystaLens IOL. Their near-vision performance is further improved when the IOL is implanted in both eyes.
Another remarkable observation with this lens is its success in restoring accommodative facility in older patients. Before commencing the study, I considered it unlikely that we could resurrect accommodation in a group of people who have lived without an effective accommodative effort for years. The performance of this IOL in this older group of individuals suggests that loss of accommodation is largely due to enlargement and stiffening of the crystalline lens with aging. The ciliary body must still be active even in the elderly. Helping to restore accommodation in this group of patients has been the most professionally satisfying aspect of participating in this study.
A third important observation from this study is that the CrystaLens does not seem to lose its effectiveness over time. I have more than 2 years of follow-up data in many of my patients, and they show no sign of regression of their initial results. Many physicians feared that the IOL might lose its accommodative effectiveness as the posterior capsule contracted, but so far this has not happened. I was also concerned that capsular contraction over time might increase myopia, but this also has not occurred. I also wondered whether the accommodative facility of the CrystaLens would be lost after a posterior capsulotomy. Fortunately, postoperative capsulotomy seems to have no effect on the near-vision performance of this lens.
Finally, perhaps my greatest concern with this lens was that its smaller optic would be associated with poor visual quality in low levels of illumination. Fortunately, visual-quality complaints have not been an issue with the patients in our series, and contrast studies have shown that the IOL performs at least as well as other monofocal IOLs in this cohort.
D. Michael Colvard, MD, is in private practice at the Colvard Eye Center in Encino, California, and is Assistant Clinical Professor at the University of Southern California. He is a consultant for C&C Vision. Dr. Colvard may be reached at (818) 906-2929; eyecolvard@earthlink.net.
1. Lindstrom RL. Food and Drug Administration study update. One-year results from 671 subjects with the 3M multifocal intraocular lens. Ophthalmol. 1993;100:91-97.
2. Steinert et al. A prospective comparative study of the AMO ARRAY zonal-progressive multifocal silicone intraocular lens and a monofocal intraocular lens. Ophthalmol. 1999;106:1243-55.
Part 3: THE 1CU AKKOMMODATIVE IOL
BY H. BURKHARD DICK, MD
The 1CU Akkommodative IOL (HumanOptics AG, Erlangen, Germany) was developed to allow the transmission of the contracting forces of the ciliary body into anterior movement of the lens optic to achieve pseudophakic accommodation. This focus shift principle should allow a defined amount of accommodation, theoretically 1.60 to 1.90 D per 1.0 mm of anterior movement of the IOL optic. The posterior chamber IOL is a one-piece lens made of hydrophilic acrylic with an ultraviolet inhibitor. The biconvex implant has an optical diameter of 5.5 mm, with an overall diameter of 9.8 mm. Its refractive index is 1.46; its estimated
A-constant is 118.1. The Akkommodative 1CU is available in +16.00 D to +26.00 D powers; further powers are available with special ordering. This IOL is intended to allow accommodation by anterior movement of the optic (focus shift) secondary to the contraction of the ciliary muscle. To achieve this aim, the lens haptics are modified with transmission elements at their fusion with the lens optic. The 1CU IOL is CE-approved. It was implanted for the first time in June 2000 at the University Eye Hospital of Erlangen-Nuremberg University. Since then, more than 1,200 patients have received the lens in Italy, Japan, Greece, Finland, the United Kingdom, and Germany. To date, all patients have reported satisfactory results, according to HumanOptics. The following data are from our study of 52 patients conducted at the University Eye Hospital in Mainz, Germany. I was the only physician performing the surgeries.
The Surgery
Initially, I made a 2.8-mm superior or temporal corneal tunnel incision. After creating a continuous curvilinear capsulorhexis with a diameter of 5.0 mm, I phacoemulsified the nucleus, removed the residual cortex, and vacuum-cleaned the posterior capsule. I then filled the capsular bag with a hyaluronic, acid-based, ophthalmic viscosurgical device and enlarged the incision to 3.0 mm. I folded and implanted the 1CU into the capsular bag using an injector (Advanced Medical Optics, Inc., Santa Ana, CA). After placing the IOL optic, I carefully unfolded the haptics with one of the bimanual I/A devices within the peripheral capsular bag and rotated the lens to a horizontal position. Afterward, I completely aspirated the ophthalmic viscosurgical device. All corneal incisions were self-sealing. Following surgery, I treated all patients with combined antibiotic and corticosteroid eye drops (prednisolone acetate and gentamicin sulfate 0.3%) q.i.d. After 5 days, I discontinued the antibiotic eye drops and prescribed prednisolone acetate 1% eye drops t.i.d. for 4 weeks. I used no atropine.
Postoperative Outcomes
The differences between the 1CU group and the control group were statistically significant for distance-corrected near visual acuity, subjective near point, accommodative range, and decrease of anterior chamber depth following pilocarpine eye drops. No statistically significant difference was observed for best spectacle-corrected distance visual acuity.
At the 2001 AAO meeting in New Orleans, I presented the first dynamic wavefront of pseudophakic elderly patients with the Akkommodative 1CU. The WASCA Analyzer (Carl Zeiss Meditec AG, Jena, Germany) enabled us to define the range of pseudoaccommodation accomplished by these elderly patients following cataract surgery. For example, during accommodation in a 72-year-old subject following implantation of the 1CU, the dynamic wavefront sphere and cylinder parameter plot clearly showed the change in sphere of the eye from -2.00 D to approximately -3.00 D (Figure 4). Data were acquired for 30 seconds. The cylinder also appeared to change marginally during accommodation in this eye.
Discussion
To date, I have not encountered any complications with the 1CU. The lens appears to be intraoperatively safe, and the data give the first subjective and objective indications of pseudophakic accommodation, which confirms the focus shift concept of this new IOL design. The 1CU IOL showed significantly more pseudophakic accommodation as indicated by near visual acuity, near point, accommodative amplitude, and anterior movement of the optic following pilocarpine eye drops. Other factors of pseudoaccommodation (such as increased depth of focus by pupillary constriction and spherical aberration, and multi-focality of the IOL and the cornea) may also contribute to or further increase the quality of distance-corrected near vision.
The accommodative mechanisms of the 1CU IOL are based on true capsule constriction, secondary to contraction of the ciliary muscle, and thus rely on elasticity of the lens capsule. Therefore, the fibrosis and shrinkage of the anterior and posterior lens capsule may potentially interfere with the focus shift action of the 1CU. I did not observe that the marked fibrosis of the lens capsule impeded the action of the 1CU IOL. I will continue to follow these 1CU patients to analyze the degree and possible consequences of late capsular fibrosis.
Additional studies are necessary to further analyze the 1CU with regard to long-term biocompatibility and accommodative properties. These studies should include longer follow-up, more patients, and preferably a multicenter design with prospective randomization, masking, and control groups.
H. Burkhard Dick, MD, practices at the Department of Ophthalmology at the University of Mainz in Mainz, Germany. He has no direct financial interest in the products mentioned herein, nor is he a paid consultant for any companies mentioned. Dr. Dick may be reached at +49 61 31 1751 50; dickburkhard@aol.com.
