One-Year Results With the CrystaLens
The results from our clinical trial involving the CrystaLens accommodative IOL (C&C Vision, Aliso Viejo, CA) have been uniformly excellent. We began implantations of the lens in March of 2001. In the initial phase we enrolled just 25 patients, and we were only allowed to implant the lens in one eye. Because many of the patients in the study had bilateral cataracts, they received a standard IOL in the other eye. From the beginning, we were surprised to find that these patients were able to read with the CrystaLens implanted in just one eye. With the Array multifocal lens (Allergan, Inc., Irvine, CA), which we still use extensively, patients require implantation in both eyes for a good reading effect (I feel that comparing the CrystaLens to the Array lens is natural because the Array is the only lens we have had available so far that provides both distance and near vision). In addition, the CrystaLens patients did not experience any of the optical side effects that we have seen with the Array lens. Often, initial patient experience with the Array lens includes halos around lights and some loss of contrast sensitivity, so we were very pleased to see that with the CrystaLens there were no side effects at all—no halos, no glare, and no difficulty with night driving. In fact, contrast sensitivity studies have shown that the CrystaLens is comparable to a standard monofocal IOL, so there is no additional downside in terms of lost contrast sensitivity or optical side effects.
BILATERAL IMPLANTATION
We have now moved on to bilateral implantation with the CrystaLens. We have implanted a total of 96 eyes at our office, almost one quarter of the study total, which includes 425 eyes. We are still very pleased that the patients are seeing well at distance and are able to read. In fact, every one of our patients is able to read at a minimum of 20/30, and at least J3, without correction. A significant number of the patients are seeing even better; there are many who are 20/20 and J2, which is excellent distance and near vision. I believe that the CrystaLens implant is certainly headed for approval. We have not had any significant problems with it at all, so I believe the FDA will approve this lens once the data are in.
THEORY OF ACCOMODATION
The theory regarding how this lens functions dates back to the work conducted by D. Jackson Coleman, MD, in the 1980s. He showed that vitreous pressure increases during accommodation. The idea is that the ciliary body increases its mass during accommodation, thickening as it flexes, and in doing so, it decreases the volume of the vitreous cavity so that the vitreous bulges forward and pushes the lens forward. We were concerned that following a capsulotomy, perhaps the vitreous would not push in the same way, because of the opening in the posterior capsule, or that maybe the vitreous would come around the side of the lens, which would hinder accommodation. This has not been the case, however, and the few eyes that have undergone laser capsulotomy still accommodate well.
Will Accommodative Ability Change Over Time?
We are still waiting for long-term results to determine whether there will be a change in accommodative ability as the capsular bag continues to fibrose at 2, 3, or even 5 years after surgery. If we look at autopsy eyes with implants, such as those collected by David Apple, MD, there is a great weight of lens epithelial cells that often builds up in the capsular bag. The sheer weight of those cells, in addition to the weight of the collagen (the fibrosis) that they produce, could eventually hinder accommodation somewhat, in theory. We do not know how this issue might develop in the long term, but for now, we have more than a year of follow-up for these patients, and they are continuing to accommodate well.
Will Accommodation Change Following YAG Capsulotomy?
We have not had to explant any of the lenses from our study patients; however, three patients in our practice underwent YAG laser capsulotomy because of posterior capsular opacification. Surprisingly, one of these patients actually saw better at both distance and near after the capsulotomy than he ever had previously, even before he developed opacification. There seems to be no loss of accommodation following YAG capsulotomy with the CrystaLens, although this was a concern of ours.
Will Patients With Previous Surgeries Be Able to Use This Lens?
One other question to which we do not yet know the answer is how the CrystaLens will perform in an eye that has undergone surgery previously. For example, what will be the outcome in a patient who has undergone a vitrectomy, will they be able to accommodate with this lens? We will not know the answer to this question until we have a chance to implant the lens in that type of patient. In the study, all the eyes on which we operated were healthy, other than having cataracts, and they did not have diabetic retinopathy or anything that would cause them to undergo a vitrectomy, so there have not been any vitrectomies performed yet with this implant in place.
What About Unwanted Side Effects?
Surgeons may also wonder about glare or unwanted optical effects with the CrystaLens due to the size of the optic. The optic is 4.5 mm, which is a smaller size than most surgeons are used to implanting. Many of the silicone or acrylic foldable lenses are 6-mm or 5.5-mm diameter lenses, and many surgeons are used to this size. Because the CrystaLens' optic is only 4.5 mm, it seemed possible that it might allow stray light rays around the periphery of the lens, or that light rays could hit the edge of the lens, which would cause an unwanted effect. Our patients have not experienced these side effects at all. Their contrast sensitivity is equivalent to that of patients with a standard IOL implant, and we have not had any patients complain about glare, halos around lights, or anything similar. We believe the reason is that this lens, because of its hinges, sits very far back in the capsule. When we place the CrystaLens in the capsule, we push the optic all the way back against the posterior capsule. We then give the patient atropine, which paralyzes the ciliary muscle for a period of time following surgery so that the lens can settle in a very posterior position. Because it is so far back against the pupil, the lens is closer to the nodal point of the eye where all the light rays converge to a single point, and so all the light is entering through a much narrower diameter. I believe this is the reason that CrystaLens patients are not experiencing unwanted side effects, although this issue was a concern for us initially, and I know that it may be a concern for other physicians. However, it has not proven to be a problem at all.
CALCULATING LENS POWER
Because we are trying to decrease patient dependence on glasses, part of the challenge of this lens is achieving very good uncorrected vision, which really depends on accurate lens power calculation. Therefore, much of our effort in this study has focused on accurate lens power choice, beginning with biometry. We used the Quantel Axis II Ultrasonography Unit (Quantel Medical, Boseman, MT), which was something new for us because we had previously been using the IOLMaster (Zeiss Humphrey Systems, Dublin, CA), which is a partial coherence interferometry measurement for optical length, as well as applanation ultrasound, which, I think, is the most commonly used method. We found that using the immersion method greatly improved our accuracy in lens power choice, and I believe that others involved in the study have found this also to be the case. We recently published a study in the February 2002 issue of the Journal of Cataract and Refractive Surgery comparing our results with the immersion and partial coherence interferometry (although not in conjunction with the CrystaLens study), and found that those two methods are virtually identical in terms of accuracy. We were excited about that result because when our goal is independence from glasses for the CrystaLens patients, we must be accurate in calculating the power of the implant we use. The wrong power would limit the efficacy of a lens such as this. Accurate lens power calculation is a major part of using the CrystaLens effectively.
THE QUEST TO PROVE THE ACCOMODATIVE THEORY
So far, we have had this theory regarding how the lens moves in terms of increased vitreous pressure. Although it makes sense on a theoretical level, and we have been able to utilize the Wavefront Power Map (Tracey Technologies, Inc., Bellaire, TX) to show that there is accommodation of approximately 2.25 D, what has been missing to this point is pictorial evidence that this lens is actually moving inside the eye. Using a magnetic resonance image scanner, we will soon be studying several of the CrystaLens patients. This scanner has a special surface coil that allows very high resolution imaging, so that we will actually be able to see the changes in the ciliary body and the movement of the lens inside the eye. At the level at which this implant is in the eye, the lens provides one-half diopter of accommodation for every 400 µm of movement, which is multiplied by 1.3 to give the equivalent at the spectacle plane. Therefore, we expect that the lens is moving approximately 1 mm, which is approximate to the 2.25 D that we believe it moves. This new imaging system should help us to not only understand how this lens works, but also to understand the mechanisms of accommodation in general, which are still controversial even at this late date.
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