IOL Options in 2005

With so many new IOL models either recently or soon to be available, cataract surgeons and their patients have more choices than ever to consider. Cataract & Refractive Surgery Today convened several experts from our editorial board to debate the merits and tradeoffs of these new technologies. As we all know, it will take time for evidence-based studies to settle the most controversial questions. In the meantime, clinicians need practical advice that we hope our panel can provide.

—David F. Chang, MD, Moderator

IOL haptic design
Dr. Chang: The most recent survey of ASCRS members1 showed that monofocal acrylic IOLs are still the most popular choice among ophthalmologists in the US and are preferred by 69% of respondents. Currently, surgeons have several different options when choosing a monofocal acrylic lens, such as varying haptic designs and a blue-light–blocking feature. Let's discuss IOL haptic designs first. Those of you using acrylic lenses, which haptic style do you prefer, and why?

Dr. Hill: I like the single-piece acrylic lens from a refractive point of view. Because it lacks any vertical (z-axis) forces, the capsular bag tends to “shrink-wrap” around this lens at the plane of the zonules. The result is a more quickly realized refractive stability than with a three-piece lens, in which vertical axis forces of the haptics tend to gradually decay over time and result in variable amounts of myopic shift.

Dr. Arbisser: I also prefer the single-piece IOL, for that reason as well as for its ease of insertion with traumatic cataracts and other difficult circumstances. In particular, the single-piece IOL releases no energy, and the fact that its forces are evenly distributed on the capsular bag eliminates the potential for a Maddox rod effect from posterior capsular wrinkles.

Dr. Chang: Interestingly, in the US, 85% of all Acrysof IOLs (Alcon Laboratories, Inc., Fort Worth, TX) implanted are single-piece, as are 50% of those implanted in Europe (Alcon representative, personal communication, September 2004.) The single-piece design has truly become the dominant preference among Acrysof users.

Dr. Arbisser: I recently conducted a study2 that examined the centration of the single- and three-piece Acrysof (Figure 1) lenses in both pseudoexfoliation and control patients. It produced interesting findings. Because all the patients in the study were 2 to 3 years out, I do not know the exact starting location of the implanted lenses. Remarkably, the statistically significant difference between the pseudoexfoliation and control patients was only 0.08mm from the eyes' geometric centers based on ultrasound examinations from the iris root. There was a statistically significant difference in multivariate analysis, but not univariate analysis, and the one-piece IOL centered 0.1mm farther from the geometric center of the eye than the three-piece lens. I am not certain whether this finding represents postoperative movement or whether I placed it originally in this location. One of the reasons I like using the one-piece lens is because my goal is to place the capsulorhexis' edge on the optic in all cases. Whereas the three-piece design autocenters based on the capsular bag and the haptic configuration, the surgeon is free to slightly move the one-piece. I believe that the one-piece Acrysof IOL stays where the surgeon puts it, which allows him to maximize centration under the capsulorhexis. The vast majority of those lenses in my study that were off center were nasal and inferior, which is where I would center my capsulorhexis.

Dr. Dick: I currently prefer the three-piece IOL design, primarily because of its 360º posterior sharp edge. To my knowledge, there is no evidence that the one-piece surpasses the three-piece IOL in terms of posterior capsular opacification (PCO) and other issues such as centration. Although centration with many foldable lenses is very good, the capsular C-design haptics, such as with the Ceeon and Tecnis IOLs (Advanced Medical Optics, Inc., Santa Ana, CA), provide superb centration and eliminate folds in the capsular bag. This is because of the broader area of contact between the haptic and the peripheral capsular bag, which gives a more uniform distribution to the capsular tensing forces. Of course, all haptics lose their memory within the first postoperative weeks, and the bag will have sealed around the IOL by then, regardless of whether it is a one- or a three-piece design. In cases of a compromised capsule, many three-piece IOLs perform better.

Dr. Kershner: Is the American interest in a one-piece IOL design due to a particular advantage of the haptic design, or is it because of the ease of implantation with the one-piece versus a three-piece lens?

Dr. Olson: I think US surgeons prefer the one-piece design because of its ease of insertion. Alcon Laboratories, Inc.'s AT design for both types of lenses, which includes an increased anterior curvature and a smaller, frosted peripheral edge, minimizes the glinting pupil and decreases unwanted images. I have statistical analyses soon to be published that support this finding. Regarding long-term data on centration and refractive stability, my colleagues and I did not find a difference between the one- and three-piece Acrysof lenses. We saw, however, a statistically significant increase in PCO in the one-piece lenses compared with the three-piece designs.3 We were able to see the lens epithelial cells protruding through the lens-haptic junction. Okihiro Nishi, MD, of Osaka, Japan, has also carefully examined PCO development with IOLs and has shown that, in the long term, the critical variable in PCO occurrence is whether the capsular bag can fuse around the single-piece IOL's haptic.4 The haptic creates an avenue through which lens epithelial cells will eventually enter the posterior capsular space. The real advantage of the single-piece lens is its ease of insertion and decreased dysphotosia profile, although it clearly will not perform as well in terms of PCO prevention as the three-piece design.

Dr. Dick: Do you think that a 360º sharp edge incorporated into a one-piece IOL would be beneficial?

Dr. Olson: David Apple, MD, of Salt Lake City, UT, and I have made that recommendation. Dr. Nishi, however, does not think that a 360º sharp edge would reduce the induction of PCO because he believes that the bulk of the haptics is the determining factor in this case. He says that having a sharp edge is insufficient and that rather, the IOL must produce a discontinuous bend. He feels that this capsular seal, which only a lens with small, thin haptics can create, is necessary for preventing PCO. Rupert. Menapace, MD, of Vienna, Austria, has stated that the best haptic design is that of the Ceeon 911, because it extends straight out from the optic and enhances capsular bag fusion. Eventually, if the regenerative cellular elements break the seal created by the fused bag and the tight overlap over the IOL's edge, then the incidence of PCO will rise. The single-piece IOL does not permit this seal. I believe that the rate of PCO, from our study published in the American Journal of Ophthalmology with a single-piece IOL,3 will be approximately twice as much as the Acrysof IOL with a three-piece design.

Dr. Kershner: My experience with PCO has been the same. On the Ceeon 911-A platform and the Tecnis Z-9000 and Z-9001 IOLs, capsular configuration does more than just ensure centration. The 90º take-off and 6º angulation of their stiff PVDF haptics press the optic against the capsule. Because the contact is minimal, the capsule can seal around the haptics. This effect can be seen in patients implanted with the Tecnis IOL by dilating their eyes at 1 to 2 weeks postoperatively. Clinically, I have not had to perform an Nd:YAG capsulotomy on those eyes.

Dr. Olson: According to the data, the only long-term, randomized clinical trial of an IOL that has shown superior results to the three-piece Acrysof BMA60 lens is that of the Ceeon 911, which had statistically better results at 18 months.5

Dr. Dick: The absence of early posterior capsular folds after the implantation of an IOL with a capsular C-design is also important for the prevention of PCO and dysphotopsias due to capsular folds in the visual axis.

Dr. Olson: Absolutely. Not only do the Ceeon 911 haptics come straight out, but they also have a very broad base of peripheral capsular contact that minimizes capsular folds. Any space that allows for lens epithelial cells to enter the barrier will increase PCO. Furthermore, silicone IOL material has advantages. The anterior capsular reaction we have been discussing enhances capsular sealing and posterior pressure on the IOL, so everything else being equal, silicone will perform better than acrylic every time in regard to PCO prevention. It is critical to compare similar features such as haptic design and a truncated IOL edge.

Dr. Chang: Regarding haptic tensile strength, a very interesting study was presented at the 2003 AAO meeting in Anaheim, California. The study was a large, retrospective comparison of the single- and three-piece Acrysof lenses.6 The single surgeon in the study used an identical capsulorhexis size and technique for the two groups. He found no cases of capsular contraction in the three-piece group, whereas patients in the one-piece group had a statistically higher incidence of anterior capsulorhexis contraction (4% of these patients required a YAG-relaxing incision to the phimotic capsulorhexis). Obviously, that percentage is quite small, and I believe that the single-piece Acrysof lens is appropriate for the majority of patients. In cases with potentially weak zonules, however, such as pseudoexfoliation and trauma (and other studies have shown a greater rate of capsular contraction in patients with uveitis and diabetes7,8), I believe we should select stiff haptics with the greatest tensile strength. I would choose three-piece haptic designs in these groups.

Dr. Hill: I've never seen anterior capsular contraction with the Acrysof SA60. I take care to make the capsulorhexis slightly smaller than the lens optic and remove most of the anterior subcapsular epithelial cells by I/A along the rim of the capsulorhexis.

Dr. Arbisser: Nor have I, not a single case. I make an effort to avoid creating a small capsulorhexis. In fact, I always enlarge small capsulorhexes so that they fit the optic more appropriately, and I've never experienced a capsular contraction in anything but a plate haptic silicone lens. No matter what I do with that type of lens, the capsule has the potential to contract. I suspect that surgeons might not take the time to enlarge the capsulorhexis if it is somewhat small.

Dr. Olson: Our study3 confirms that the Acrysof, especially the single-piece, induces minimal anterior capsular reaction, which directly correlates with anterior capsular contraction. It appears from this discussion, however, that the SA60 is not as forgiving of small capsulorhexes if the zonules are loose, which proves that haptic tension in the bag is also an important factor in bag contraction in some cases.

Blue-Blocking Technology
Dr. Chang: Let's move to the newest option for acrylic IOLs—blue-blocking technology. How many of you are using the Acrysof Natural IOL (Alcon Laboratories, Inc.), and what are your reasons?

Dr. Hill: I think that there is now a reasonable amount of convincing scientific evidence that the shorter, energetic wavelengths of light can place the pseudophakic eye at risk for an increased incidence of macular degeneration. I see absolutely no downside to implanting the blue-blocking IOL, and it has become my lens of choice.

Dr. Arbisser: I implant the blue-blocking lens in every patient who doesn't need a multifocal IOL. I also feel that, although there is no substantial, long-term evidence that blue-light filtering prevents age-related macular degeneration (AMD), most ophthalmologists accept that we should use operating microscopes with this filter. There is enough proof of acute damage as well as teleological and circumstantial evidence regarding pseudophakes' developing worse AMD in the eye that has an implant that it is worthwhile for us to use it.9,10 The reasoning against the use of blue-blocking lenses is so weak that I would prefer to do my patients a favor if I were right and not do them any harm if I were wrong.

Dr. Dick: I rarely use the blue-blocking lens, except for certain indications, such as in a patient who requires an IOL in one eye that suffers from excessive macular drusen or dry AMD when the other eye already has AMD. Some research justifies using blue-blocking lenses because of the observation that deep blue light is 50 to 80 times more efficient at causing receptoral damage than green light, despite the fact that it is efficiently absorbed.11,12 On a cautionary note, we should remember that the majority of these studies have been conducted with nocturnal rodents, and it has not been established that the same damage pathways have a significant role in diurnal species. These studies are animal trials, and to my knowledge there is no evidence-based proof of a direct benefit for the human retina from this specific lens.

Also, blue-blocking lenses have some potential drawbacks, depending on the concentration of the filter used. It is still unclear whether color perception is affected by blue-blocking lenses, especially at the blue end of the color spectrum. Many of the methods used to evaluate pre- and postoperative color perception in the clinical trials did not properly test the right parameter. In some studies, patient questionnaires addressed the postoperative change in color perception compared with the preoperative perception, which is not a valid test of the blue-blocker effect on color vision. Most investigators used the Farnsworth Panel D15 test to test pseudophakic color vision, but this test is inadequate for evaluating blue color perception. It is definitely not the right tool to measure the effect of blue-blocking lenses on color vision because blue is the color that is fixed in this test. Box 4 of the Farnsworth Munsell 100 Hue test would be the proper test (Box 4 tests blue). Interestingly, two researchers, Greg Jackson, MD, from the University of Alabama, and Dr. Olson, found a decrease in scotopic vision with blue-blocking lenses, because scotopic sensitivity (dim light, rods) is more dependent on violet and blue wavelengths than photopic sensitivity (bright light, cones) (Figure 3).13

In my own mind, there is no doubt that light plays a role in the pathogenesis of AMD, particularly blue light, which is a source of oxidative stress via its interaction with retinal chromophores. Therefore, a reduction in blue-light exposure might reasonably be expected to reduce the progression of AMD. However, because the research until now was somewhat faulty, I am reluctant to use the blue-blocking lens for all routine cases. For selective cases, the blue-blocking lens may have the greatest potential in elderly patients who are at greatest risk of AMD progression. However, without sufficient direct evidence that environmental light causes retinal damage, the benefit of blue-blocking filters is unclear. Because of the potential drawbacks, I do not recommend the widespread use of blue-blocking lenses in the elderly in order to avoid potentially harming some of my patients.

Dr. Kershner: I thoroughly agree with Dr. Dick that blue-blocking technology is not such a simple choice as deciding to use a UV-blocker. There is ample evidence that suggests that blocking UV is good, and, because we are not aware of any downside to using a UV-absorber, cataract surgeons for the most part have adopted this technology; virtually 100% of IOLs now contain UV-absorbers. My concern with using a blue-blocking lens is the potential downside of filtering light below a wavelength of 440nm. Without evidence-based studies demonstrating that blue-blocking lenses truly protect the eye, I cannot employ the technology with my patients because there is a potentially significant downside.

Before surgeons justify the performance of blue-light–filtering IOLs, they should read a recent article by Martin A. Mainster, MD, PhD, and Janet R. Sparrow, PhD, in the British Journal of Ophthalmology.14-16 We need to recognize the difference between filtering out blue light, which is important for night vision, and filtering out UV radiation, which is not useful for vision. We still lack knowledge about the role that blue-light phototoxicity plays in retinal aging, as well as how much blue light can be filtered before visual performance under scotopic conditions is compromised. The scotopic luminous efficiency of the human eye occurs at the precise wavelength that is absorbed by the Acrysof Natural IOL—a fact that cannot be good. Interestingly, clinicians' initial enthusiasm for using this IOL as a contrast-enhancing lens was tempered once they learned that the lens did not enhance contrast at all. Even if it can be demonstrated that the Acrysof Natural offers retinal protection, I think its potential drawbacks of decreased contrast, particularly at night, cannot be ignored. I feel that these concerns are significant enough for us to refrain from advocating the routine use of lenses with blue-blocking technology.

Dr. Hill: When the Acrysof Natural was first introduced, my staff and I gave the first patients implanted with this lens the Farnsworth-Roth-Munsell color-vision test. We found no abnormalities of color vision whatsoever.

Dr. Kershner: The D15 color tray of the Farnsworth-Munsell test shows no difference between pre- and postoperative or fellow eyes. Again, I agree with you. That screening test is not sensitive enough to show the color difference with a blue-blocking IOL.

Dr. Olson: The main argument here is whether blue light is related to AMD. If this correlation were unquestionably proven, blue-light filters would become the standard for all IOLs. I think that evidence that the technology will block AMD trumps all other issues. What evidence do we have? First, Dr. Mainster advocated using UV filters long ago, although erythropsia was the only obvious result of having no UV filter. Erythropsia occurred because patients exposed themselves to too much UV/blue wavelight, thus eradicating blue color from their vision. Now, most IOLs have UV filters.

There are two theories regarding light and AMD development: the blue-light toxicity theory and the blue/green-light toxicity theory.14 One or neither of these two pathways may be important in AMD. Unequivocally, using a significant amount of blue light is more toxic to the eye than blue-green light, following the electromagnetic spectrum. Eventually, all light is toxic to the eye, so we must decide exactly what to filter. There is just as much evidence of blue/green light's toxicity as for blue light. The big problem with all of the visible-light issues is epidemiological studies. We would expect something that is supposedly so important in the progression of AMD to appear in long-term epidemiological investigations. Seven studies looked particularly at this issue. Two of them (Maryland Waterman and Beaver Dam studies17,18) suggest that there is a relationship between visible light and AMD; one (Blue Mountains study19) suggests that the more blue light an eye receives, the less AMD it develops; and three investigations show no difference whatsoever between light exposure and AMD.

Almost all the studies conducted on AMD have shown smoking, diet, and genetics as factors in AMD development, so, if blue light is an important causative factor, it must be less important than those three. The evidence indicates that an abundance of blue light, particularly in cell cultures, can damage retinal cells and that blocking this light protects them. Is this type of acute damage really AMD? Answering this question will require a prospective, randomized clinical trial. Most retinal specialists and researchers say that the evidence that blue light increases the risk of AMD is exceedingly weak at this time.

Now for the good news: there is a multicenter study on blue-light toxicity, cosponsored by Alcon Laboratories, Inc., and the National Eye Institute, that will begin soon and be extremely important. Remember that the average age for a patient who undergoes cataract surgery is approximately 75 years. I think we are going to see some very good information regarding whether the blue-blocking IOL reasonably protects the eye. I agree that, if the technology poses no downside, then using it is not unreasonable. It is worth discussing its drawbacks, however, in light of the data available. Regarding photopic and mesopic vision and contrast sensitivity, I do not think there are any studies that show any downside. If anything, I think that the preponderance of studies suggests that these lenses may provide some advantages in visual acuity and contrast sensitivity under certain lighting situations. One fact is well known: trap shooters, hunters, and often professional athletes will use an amber-colored lens, because blocking blue light helps their acuity (a phenomenon with which photographers are also familiar). Thus, blocking some blue-wavelength light may offer a slight visual advantage to patients under certain lighting situations.

Regarding blue-blocking IOLs' effect on color vision, I've heard all of the arguments, and two stay with me. My colleagues have performed 100 hue tests in a group of patients who received an SA60 lens and were tested with and without a blue-blocking filter. They found no statistical difference. Jack Holladay, MD, of Bellaire, Texas, told me that, rather than score the entire 100 hue test, we should just score box four (which includes just the blue colors). Doing this, my colleagues did find a difference. Some patients do notice a slightly blue difference in color with the eyes that have the Natural lens, but the effect is not dramatic. I do not expect color to be a clinically significant issue.

There is one point of clinical significance that remains. I do not accept the argument that we do not use scotopic vision. For older patients to stumble and fall because of their poor scotopic vision can be lethal, and thus the problem is a major quality-of-life issue for them. If, as Dr. Mainster calculated, humans can lose almost one-third of their rod (scotopic) vision from a blue-blocking lens in comparison with a clear IOL, I suggest that this effect may be clinically important. My group tried to test this phenomenon with dark adaptation and could not detect any difference, but we have planned a more sensitive test that will assess threshold scotopic visual fields. Our preliminary results not only confirm Dr. Mainster's work, but suggest that those with AMD are even more at risk. If so, does the phenomenon have a clinical impact on the patient? My group's outcome study will explore a host of issues such as this one. Also, Dr. Jackson at the University of Alabama will test the practical impact of this scotopic vision loss. If patients cannot detect any difference in scotopic function with the Natural Lens, then I will agree that scotopic vision loss may not be clinically important. Until further study is conducted, however, I think that the problem of nighttime vision loss remains a concern, and it gives me pause. I agree, however, that using a blue-blocking lens makes sense if a prospective study can prove it helps prevent AMD. I think that summarizes the state of the science right now.

Dr. Kershner: I would like to raise one question regarding the “reasonableness rule.” Given the potential macular phototoxic injury theory, for which we have no conclusive evidence, wouldn't evolutionary pressures have selected against an animal whose predominant vision is sensitive to blue-green wavelengths of light? If these wavelengths were truly phototoxic in vivo, then the human animal would have had poor vision throughout its evolution and have not survived.

Dr. Olson: That's the teleological debate. Of all the arguments for the blue-blocker IOL (that the crystalline lens blocks blue light to progressively protect the macula as we age), this is the argument with which I disagree the most. I do not have one bodily process at age 57 that performs better than when I was 20, and I can't imagine that the crystalline lens is an exception. What is important, and I think Dr. Holladay is absolutely correct in this theory, is that teleologically, physical performance peaks during the period of time that we historically reproduce. Therefore, peak performance for the crystalline lens ought to fall between the ages of 18 and 25. Clearly, at this age, our eyes let in a lot more blue light.

Teleologically, AMD is a disease of old age, a factor that genetics disregards. Therefore, using teleology in this argument is a mistake. The real argument has to be whether blue light is important to AMD. I applaud the Alcon-National Eye Institute prospective study that I hope is forthcoming. We also need to ascertain whether this blue-blocking lens induces clinically important scotopic visual loss. If further study finds no downside, then it is not unreasonable for surgeons to use these lenses.

Dr. Arbisser: All of the arguments over color are illogical. The absorption curve of the plain UV lens indicates that that IOL lets in more blue light than the 4-year-old natural crystalline lens does, so we alter color every time we operate on the eye. What is real color? I think we've created an artificial “wow,” an unnatural increase in light by implanting a clear implant with UV protection. We know that young, healthy patients who underwent unilateral cataract surgery prior to the use of blue-filtered lenses would postoperatively remark on the yellowness of the fellow eye's vision. Now these patients, after receiving blue-filtered lenses, thank their surgeons for matching the quality of vision in their surgical eye to that of their nonoperated eye. I don't think that these arguments about color mean anything, because there is no absolute standard of what color is other than having your own natural, healthy lens in your eye as a young person.

Dr. Kershner: Interesting. Has anyone performed a Farnsworth-Munsell test on a patient who has one virgin eye and a mature cataract in the fellow eye in order to see if the patient could detect a difference in vision between the two eyes? I assume that most of the studies have compared one IOL with another.

Dr. Arbisser: On the other hand, the question about decreasing function in the dark would be important to study. If we are wrong about the preventative properties of blue-blocking IOL technology; then we will have only mildly affected patients' vision. If we are right, however, we may save their sight. The lens we put in our patients' eyes today will remain with them for the rest of their lives. If there's a chance that the blue-blocking lens is going to preserve their functional independence in terms of driving and reading, then that's what I'll use. When I first began implanting the Acrysof Natural IOL unilaterally, my patients could not notice any difference whatsoever from their other eye. From the moment it was available, I've used that lens in every eye that I could.

Dr. Kershner: All you're saying is that you restored the color distortion of their cataracts.

Dr. Dick: My question is, would you change your opinion of the lens if the IOL's chromophore spectrum and concentration matched the natural lens of a 20-year-old rather than that of a 55-year-old?

Dr. Arbisser: That would be great, wouldn't it?

Dr. Chang: Any pseudophakic patient could be given blue-blocking spectacles to wear outdoors. Such patients would know whether the blue-blocking filter were a disadvantage in certain situations, such as under scotopic conditions. If so, they would simply remove their blue-blocking spectacles.

TORIC IOLs
Dr. Chang: Before we finish discussing the topic of acrylic lenses, I want to ask Dr. Hill about the toric IOL platform that Alcon Laboratories, Inc., is studying. I've had a fair amount of experience with toric IOLs using the Staar toric lens (Staar Surgical Company, Monrovia, CA) (Figure 4). For those astigmatic eyes in which limbal relaxing incisions are less effective, either because the patient is too young or because the amount of astigmatism is very high, toric IOLs can produce dramatically better results. It is obvious that the adoption of the Staar toric lens has been weakened by its plate haptic design, limited power choice, and tendency toward early rotation, particularly if the shorter lens is used. I published a study20 that showed good rotational stability with the longer toric lens model, but the surgeon must have a perfect capsulorhexis with good cortical cleanup. Dr. Hill, tell us about your experience with Alcon's toric IOL.

Dr. Hill: As you mentioned, first-generation toric lenses have a limited power range and show frequent problems with rotational stability. Also, think about the predicted astigmatic correction and the axis at which you implant the toric lenses in your patients. Have you noticed that these rarely come out as predicted? This is because we have failed to take into account one very important factor: the wound.

Astigmatism is a vector quantity, which means it has both magnitude and direction. The moment that the cataract wound is created, the astigmatic characteristics of the cornea are changed. For example, to correct 1.25D of corneal astigmatism at 135º without taking into account the 0.50D of astigmatism induced by a temporal clear corneal wound would produce a postoperative angular error equal to approximately 0.50D at the corneal plane. For those who make a scleral tunnel, to correct 2.00D of corneal astigmatism at 135º without taking into account the 0.75D of astigmatism induced by a superior scleral wound would produce a postoperative angular error equal to approximately 0.75D at the corneal plane. At the plane of the capsular bag, this would be a 1.00-D astigmatic power error.

The next generation of single-piece acrylic toric IOLs will have companion software available that will allow the surgeon to more accurately calculate the resultant magnitude and axis of astigmatism to be corrected based on the typical amount of astigmatism induced by the phacoemulsification incision.

Dr. Dick: What are the powers available?

Dr. Hill: Right now, the recently completed phase III FDA study for the SA60 platform toric IOL was limited to astigmatic powers of up to 3.00D, but powers as high as 6.00D are being considered for future release.

Dr. Olson: R. Bruce Wallace, MD, of Alexandria, Louisiana, published an important study approximately 5 years ago in which he measured astigmatism three ways before surgery and then calculated subjects' refractions afterward to find the axis.21 He discovered that the three measurements often did not correlate with each other and that the final axis was dramatically different, especially with cylinder of 1.00D or less. Unfortunately, the best way to find the axis today remains taking the refraction after surgery. So, surgeons who are going to implant a toric IOL need an accurate axis. Higher levels of astigmatism make axis determination easier. Because many surgeons today want cylinder corrections down below 0.50D, determining the axis is a problem. The best IOL platform to date concerning IOL rotation over time is the SA60, to my knowledge.22 IOL rotation from contractional capsular bag forces is certainly another problematic variable when considering toric IOLs.

My biggest concern with the SA60 IOL is predicting the axis preoperatively, because having to perform secondary rotational procedures on this IOL (because of its inherent tackiness and bulky haptics) may be a problem. Rotating that lens and its bulky haptics around after the fact may not be so easy if the axis determination is off preoperatively, which commonly occurs. I applaud the toric lens, but the problem of finding the axis before surgery is important. Also, the incision induces a variable amount of astigmatism that cannot be accurately determined until after surgery. I think that the best toric solution is to accurately correct cylinder postoperatively. In my opinion, the Light Adjustable Lens (LAL; Calhoun Vision, Inc., Pasadena, CA) is going to be the best platform for correcting astigmatism. According to information reported at the company's medical advisory board meeting held at the 2004 ASCRS Meeting, no patient was more than 0.25D off after adjustment, and most were dead on. Toric adjustment ought to be as accurate, and the Calhoun Vision, Inc. lens allows the surgeon to readjust the toricity until it is correct. We clearly need such an approach. Astigmatic keratotomy is a good technique, but it isn't great, because it creates issues with healing as well as the issue of the axis preoperatively.

Dr. Hill: I think that we will see a significant improvement in our ability to predict both the axis and magnitude of the astigmatism