Premium Lenses in Problematic Patients

Transcription

1 Premium Lenses in Problematic Patients How to be successful with presbyopic lenses in eyes that have already had LASIK surgery. Walter Bethke, Managing Editor If implanting a monofocal intraocular lens in a post-lasik patient is like shooting at a moving target, then implanting a presbyopic lens in such a patient is like hitting a moving target with a moving gun. There are issues with the loss of contrast sensitivity, the compounding of LASIK-induced spherical aberration and the possibility of errors in predicting the effective lens position with an accommodating lens. These issues are in addition to the perennial difficulty of calculating the right IOL power in the post-lasik eye. However, despite these problems, surgeons say presbyopic lenses such as the ReSTOR, ReZoom and Crystalens can be implanted in post-lasik patients successfully. Here are helpful tips from several surgeons. Patient Selection Setting aside the issue of proper lens power calculation for a moment, surgeons say there are certain criteria that need to be met for a post-lasik patient to be a good candidate for a presbyopic lens. Nashville surgeon Jeffrey Horn is mindful of all the same issues that go into determining a candidate for a presbyopic lens in a non-post-lasik eye, in addition to a couple of others. Someone with irregular astigmatism, a decentered ablation, astigmatism you can t reduce to 0.5 D or less after the surgery and/or severe ocular surface disease wouldn t be a good candidate, he says. The last factor, dry eye, is increased in the post-lasik population, so you also have to treat it aggressively if you eventually perform the surgery. If they have tear-film problems afterward, they won t get good results with a multifocal lens. Also avoid someone with any pre-existing condition that would reduce contrast sensitivity, such as significant corneal guttata, epiretinal membrane, significant macular drusen or age-related changes, significant diabetic retinopathy or glaucoma. You also have to factor in how the LASIK may have affected the corneal optics, Dr. Horn continues. Post-LASIK patients who are now coming in for cataract surgery

2 may have had their LASIK five or 10 years ago with older technology that may have affected their corneal optics more than our current lasers do. These patients can have corneal curvature changes that reduce their contrast sensitivity, and now we re implanting a [multifocal] lens that can reduce it further. In addition, the constant refrain of the surgeons is be prepared to have to perform an enhancement on these patients. This influences another patient selection factor: There must be enough residual tissue, and the cornea can t be too flat or too steep, for you to do laser vision correction enhancement postop. I ll bring the patient to my refractive surgery colleague to find out if it s possible for him to have another refractive surgery after the lens implantation, says Sao Paulo, Brazil, cataract surgeon Leonardo Akaishi. He says another factor may be multiple past refractive surgeries that make it too difficult to calculate the lens power. In terms of residual tissue, however, surgeons note that if there s a problem with a thin cornea, you could always exchange the lens postop if you had to, so it may not be a deal-breaker. As you consider these factors, surgeons say it s important to have a good discussion with the patient about the surgery. These patients present a situation that s a double-edged sword, says Indianapolis surgeon Kevin Waltz. As people who have had LASIK in the past, they re defining themselves as individuals whose vision is very important to them, so they become prospective premium lens candidates automatically, and are interested in the technology. However, getting good refractive results is going to be harder, so they need a clear, realistic discussion of what you can do for them. Let them know that it may be a two-step process. They re often comfortable with that, because their initial LASIK was most likely a two-step process 10 or so years ago. Warn them that, for premium IOLs, there s an enhancement rate of x percent even if the patient never had LASIK previously, and that, for them, it s probably double that. Though there have been no large-scale studies of presbyopic lenses in post-lasik patients, some surgeons estimate the enhancement rate in these cases to be around 20 percent, so patients need to accept this risk before going any further with the surgery. Patients with unrealistic expectations, who expect to see at all distances without compromise, probably shouldn t have the procedure either, says Dr. Waltz. Choosing a Lens

3 Certain attributes of the presbyopic lenses may lead you toward a particular lens for individual post-lasik patients. The kind of refractive error the patient had before his LASIK colors the discussion a bit, says Dr. Waltz. Someone who had LASIK for myopia will have a relatively flat central cornea with a peripheral cornea that s relatively steep, so they ll have an excess of positive spherical aberration. A former low myope has a little extra, but a previously high myope will have a lot. So, it s helpful if you can treat that or at least try not to add to it. The ReSTOR aspheric has about -0.2 µm of negative spherical aberration, so it s an attractive option for these former myopes, because it can treat some of the excess positive spherical aberration in their corneas. The Crystalens doesn t have negative spherical aberration, but it doesn t add to the positive spherical aberration much because its optic diameter is limited to 5 mm. The ReZoom has essentially zero spherical aberration. Dr. Waltz notes that the Tecnis Multifocal, the data for which has been submitted for approval to the U.S. Food and Drug Administration, may be able to treat even more positive spherical aberration once it s approved, as it has µm of spherical aberration. In a twist of fate, the old ReSTOR lens, the original design before the asphericity was added, may be better for patients who had undergone LASIK for hyperopia than the new aspheric version, say several surgeons. If a patient had hyperopic LASIK, I prefer the old ReSTOR for him, because it is spherical, says Dr. Akaishi. This is because the post-hyperopic LASIK patient doesn t have the surgically induced positive spherical aberration that the post-myopic LASIK patient does, and if you implanted an aspheric lens, you could increase the negative spherical aberration the post-hyperopic LASIK eye has. I have a stockpile of old ReSTOR lenses at the hospital in which I operate. Dr. Horn agrees, saying that, depending on a patient s visual needs, he d prefer to implant an original ReSTOR or a Crystalens in the post-hyperopic LASIK patient, since the latter is spherical, as well. Not all surgeons, however, think a multifocal lens is the right choice for the post-lasik eye, and instead would opt for the pseudo-accommodative Crystalens. When discussing presbyopic IOLs, I lean more toward accommodating lenses because of quality of vision issues, says Minneapolis surgeon Y. Ralph Chu, who

4 consults for AMO. As we all know, especially with the higher degrees of myopic and hyperopic correction, there s some loss of contrast due to the shape change of the cornea. Whether this is detectable by the patient or not, there s still a subtle loss there. I m concerned about compounding this by putting a multifocal lens in the eye, which I ve found can cause some further loss of contrast and quality of vision. St. Louis surgeon and Bausch & Lomb consultant Jay Pepose also prefers to use a Crystalens if the patient is a good candidate. I know some surgeons will place an aspheric lens with negative spherical aberration in an effort to counter the positive spherical aberration of the post-myopic LASIK patient s cornea, but if the lens alignment is decentered with respect to the corneal ablation, you can induce a lot of coma, he says. Though he acknowledges a spherical lens might be better in a patient who had hyperopic LASIK, he still would be wary of placing a spherical multifocal like the old ReSTOR. Whatever photic complaints the patient has could be compounded in an already highly aberrated eye, he says. Even though the Crystalens has some positive spherical aberration, I don t feel as if I m adding to an already complicated wavefront with it. In addition, if the intended target turns out to be a little off, a small amount of postop hyperopia can be offset by the Crystalens accommodative function. It should be noted that all of the previous lens recommendations depend on patients occupations and hobbies, and what visual distances are more important to them. Is it someone who s going to be upset if he doesn t have excellent intermediate vision? asks Dr. Horn. If so, the ReSTOR may not be quite as good, for example. Dr. Waltz concurs, saying, The biggest thing you run into with patients, I ve found, is the need for good vision at the computer. And, depending on what distance they work at, the Crystalens probably gives the best vision at the computer, but maybe not as strong near vision as the ReSTOR, ReZoom or Tecnis Multifocal. If someone tells me he needs really sharp near vision, he needs a ReSTOR or a Tecnis Multifocal [when approved] in one eye, Dr. Waltz says, alluding to the practice of mixing lens types to maximize a patient s visual range. If he needs clear distance vision in all lighting conditions, he needs a Crystalens in one eye. You can implant another lens in the other eyes of these examples, but those lenses are sort of the givens in those cases.

5 Calculating Lens Power Surgeons say this is the main challenge when implanting a presbyopic lens in the post-lasik patient, because the lens power has to be very accurate for the lens to have its best effect, yet the post-lasik eye confounds this attempt at accuracy since the ratio of anterior:posterior corneal curvature that keratometry instruments assume to be normal has actually been altered. Here s a review of some of the more popular formulas for corneal and IOL power calculation, and a discussion of the methods several surgeons prefer. Estimating corneal power and performing biometry. If you ve got the pre-lasik corneal power and the patient s spherical equivalent refraction pre- and post-lasik, you can plug them into the following formula to estimate the post-lasik K: Kpre + (SEpre - SEpost). This is the clinical history method, and it s widely known. One of the limiting factors of this technique is that some of the change in the measured postop SE refraction could come from the cataractous lens, however. If you know the preop and postop patient data, you can also use the so-called double-k formulas, which use the preop K to calculate where the lens will sit in the eye and the postop K to help calculate the current corneal power. These formulas include the Double-K SRK/T and the Holladay II in the Holladay IOL Consultant. You can also use the Haigis L formula, notes Dr. Pepose, which estimates the position of the lens without using the Ks as a predicting value. The Haigis L requires data from the IOLMaster, however.

6 Unfortunately, in many cases, you won t have access to the patient s pre-lasik data, and will have to estimate the corneal power. For this, surgeons say you might try the contact lens overrefraction method, which, like the clinical history method, is widely known. As a quick review, in the CLO method, the corneal power is the sum of a rigid contact lens s base curve, power and overrefraction minus the eye s manifest SE without the lens.1 Several other formulas for the estimation of corneal power appear in Figure 1. In our practice, to get the proper K reading, we use the Pentacam and topographic Ks, says Dr. Chu. We re not using the sim Ks, but instead we re looking for the power in the area of the ablation zone that makes the most sense. That power is different for myopes or hyperopes. In myopes we re looking for the lowest K value in the axis, but in hyperopes I think it varies. I ve found that using a standard keratometer at a 3-mm zone seems to give the most accurate measurement in patients who underwent a standard hyperopic treatment [from +1 D to +3 D]. Dr. Horn measures the Ks at least three ways, sometimes four: manual keratometry; topography; wavefront aberrometry with the Nidek OPD-Scan and the Pentacam. If he doesn t have access to the patient s pre-lasik data, Dr. Pepose uses the Orbscan to measure the total optical power of the central 4 mm of the cornea. In a poster he presented at the 2007 meeting of the American Academy of Ophthalmology, he and his colleagues found that method to deviate by only -0.1 D

7 ±0.56 from back-calculated K values. The latter K values were those calculated post-implantation to determine what K should have been entered pre-implantation to hit the target. Calculating IOL Power. Though there are many formulas for getting the lens power, several surgeons say the post-lasik IOL calculator on the website of the American Society of Cataract and Refractive Surgery s website ( has become very useful to them. Other websites that offer multiple-formula calculations, some for a fee, are ocularmd.com and eyelab.com. If the patient had myopic LASIK, you select that calculator and then fill in the biometry that you have, says Dr. Waltz, who beta-tested the ASCRS calculator. If you have enough data, it will give you IOL powers from six to eight formulas. You ll only get one formula s results if you just have enough data for that. The site also has formulas for patients who had hyperopic LASIK previously. As to how he gets his data, Dr. Waltz gets the K readings from the IOLMaster, and compares them to those from the Zeiss-Humphrey Atlas topographer s central ring. Also, he feels the IOLMaster gives the most accurate biometry. The other issue you can run into, especially in hyperopes, and which is still not well-understood, is that all the formulas attempt to estimate effective lens position, which depends on anterior chamber depth, Dr. Waltz continues. About 20 percent of hyperopes, though, have a normal chamber depth, meaning the effective lens position is more posterior and they therefore need a stronger lens. The problem is you have to include that in your formula to adjust for it. Older formulas, like the Holladay I, don t account for it, so you have to use a modern formula, such as the SRK/T or the Holladay II. Not every surgeon accounts for this in his normal cataract surgeries, and may be able to do them all right, but the penalty for not doing it is much greater when you re implanting a presbyopic lens. Dr. Horn says he s recently been using the Pentacam and the Holladay equivalent K determined by the device. We then use the Holladay II program and enter the Holladay equivalent K as the surgeon-entered K in the area of the program designated for patients who have had refractive surgery, he explains. If we have the historical data, we ll enter that, as well, since it tends to tighten the vergence calculations. Then, the Holladay II does a double-k kind of calculation that takes into account that there s one K that s good for effective lens position and one that s good

8 for the power. However, I ll still go to the ASCRS site and plug in the data to see how the formulas there compare to my result. I find it tends to be closest to the Haigis L. The process becomes more art than science when there s a discrepancy between the Haigis L and my method, however. Dr. Horn says that, in a study of 20 eyes he did at his practice using this method, he was within approximately ± 0.3 D of his target on average, with a range of 0.03 D to 1 D. Only one eye required lens exchange and no other enhancements were needed. After Dr. Pepose gets the corneal power with his Orbscan, he also calculates the IOL power with the Holladay IOL Consultant, using its prior refractive surgery mode as Dr. Horn does. If he has the patient s pre-lasik data, he ll enter that in to calculate the effective lens position. If the data s unavailable, he uses the system s default K of to estimate the ELP. I then use the ASCRS website and look at a number of the formulas to find the mean and see where the results cluster, Dr. Pepose adds. I then make my final IOL decision based on that.

9 In his study of his method, Dr. Pepose says he got 72 percent of the patients within a diopter of their intended refraction, and 42 percent within 0.5 D. His average deviation from the true IOL power (as back-calculated ) was ±0.56 D. Dealing with Enhancements More frequent enhancements are a fact of life when implanting presbyopic IOLs in patients who ve had LASIK, say surgeons. Fortunately, if you ve already had a clear

10 preop discussion with the patient about the possibility of enhancement, he will be ready for it, and you get down to the business of sharpening his vision. Here s how several surgeons approach these secondary procedures. If the refractive error is small, some surgeons will lift the flap and re-lase. Others, however, think PRK is a better option. I think PRK is better afterward because it removes less tissue, says Dr. Akaishi, who says if a patient is myopic after lens implantation, it s usually less than -1.5 D. For hyperopic errors postop, if the error s less than +2 D, I perform a procedure in which I push the optic of the lens forward in front of the capsulorhexis. Depending on the power of the lens, it s possible to correct 1 D of hyperopia this way. If patients have more than 2 D of error, I prefer a piggyback lens implant. Interestingly, Dr. Akaishi says if he has to err on one side or the other when choosing a lens power preop, he errs on the hyperopic side. I like to make a mistake for hyperopia, he says, because it s better for my refractive surgery colleague. In most of these patients, the corneal curvature is very low to begin with, and if you have to do a PRK and make it lower, that s not good. However, as a counterpoint, Dr. Horn points out that performing a hyperopic laser vision procedure afterward might negate some of the asphericity of an aspheric lens such as the ReSTOR aspheric. Dr. Chu also prefers a surface procedure. I really lean toward a surface procedure after the lens, even after previous LASIK, he says. Usually it s a small correction, and these patients who are getting implants are typically older, so they have more chance for epithelial defects with LASIK.

11 Surgeons warn, however, that the laser procedure you perform may have to be a conventional one, depending on which lens you implanted, due to some lenses effect on wavefront aberrometers. If you need to do laser vision correction at all with these lenses, you can often do a custom procedure with a diffractive lens, like the ReSTOR, and with an accommodative lens, says Dr. Horn. But you can t get a good wavefront with a refractive lens like the ReZoom. Dr. Pepose keeps both the PRK and the LASIK option on the table. Most of the time there s enough tissue to lift the flap and re-lase, he says. If there s not enough tissue, or the patient has dry eye that s significant, sometimes we ll do a surface treatment with mitomycin-c. I treat each patient s situation as unique, Dr. Pepose continues. I make my decision based on a number of factors. Maybe the eye s really dry or the cornea s already had a lot of surgery and is really thin. In that case, sometimes putting in a piggyback IOL might be the better part of valor, and you don t risk breaking the capsule as you might with a lens exchange I try to be open-minded and not rule anything out of the armamentarium. So, for me, if I can t do laser, piggybacking is the first choice, and the more extreme option is lens exchange. If it s necessary, he usually does an

12 intraocular procedure in the first couple weeks postop, if possible. Dr. Horn also takes several factors into account. The questions arise: Is it better to do the laser, which entails waiting a bit longer postop because I like to do a YAG before the laser procedure; or is it better to do the lens exchange? The answer depends on what you and your patient are comfortable with, and there may also be cost issues involved with taking him to the OR vs. to the laser. However, when we re talking about putting in an aspheric lens and then reducing the asphericity with a hyperopic LASIK, for example, I d just as soon do a lens exchange or a piggyback. Dr. Horn explains the use of the pre-laser YAG: I find that, sometimes, especially with the Crystalens and sometimes with the ReSTOR, the YAG actually changes the refraction and negates the need to do the laser enhancement or changes what enhancement is needed, Dr. Horn says. So, I tend to wait several months before doing a laser enhancement, because I don t want to have to do a YAG unless I have to. However, I like to do the lens exchanges or piggybacking earlier, in a matter of weeks. Despite the hurdles, Dr. Horn says presbyopic lenses can be effective, even in these more complicated eyes. The bar s clearly raised with these patients, and you have to make sure you can clear it, he says. But if you can, and the patients are appropriate candidates, they can be some of the happiest patients in your practice. 1. Wang L, Booth M, Koch D. Comparison of intraocular lens power calculation methods in eyes that have undergone laser-assisted in-situ keratomileusis. Trans Am Ophthalmol Soc 2004;102: Vol. No: 15:07Issue: 7/1/2008