“We should anticipate refractive surprises when an eye is extremely myopic or extremely hyperopic, so in very large or very small eyes,” says Kevin M. Miller, MD, a professor of clinical ophthalmology at the Jules Stein Eye Institute at UCLA. “With conventional lens power calculations, even when the appropriate formula is used for extreme myopes and extreme hyperopes, patients can end up hyperopic. We have to adjust our calculations for extreme cases, targeting for a bit of residual myopia. For example, if the SRK/T formula predicts a negative power IOL in axial myopia, I will usually choose the IOL power that targets for -1.5 D of postoperative myopia, expecting to hit emmetropia by doing so. If the Hoffer Q formula predicts a 38 D IOL in axial hyperopia, I will often choose a 39 or 40 D IOL instead, expecting to achieve emmetropia by doing so.”
Dr. Miller also anticipates refractive surprises in patients who have previously undergone RK, PRK or LASIK. Additionally, there can be surprises in post-penetrating keratoplasty patients and in cases where the anterior segment of the eye is disproportionately sized compared to the overall length of the eye.
However, when refractive surprises occur with no warning after routine cataract surgery, it is important to stay calm. Dr. Miller says the best course of action is to remain the patient’s advocate and not to let the situation become adversarial.
Colorado Springs-based surgeon Steve Dewey, MD, notes that preoperative IOL counseling can help prepare patients for surprises. “I let the patient know that while this looks like we’re playing darts, it’s really horseshoes,” he says. “We’re trying to get patients as close as possible to their goal, but we won’t know exactly how close we’re going to be until after the surgery. I typically do the nondominant eye first if we are doing both eyes. I tell patients that I can adjust the implant power for the dominant eye and make their vision closer to our target. It is rare to find someone who doesn’t tolerate 1 D of myopic anisometropia, but it happens. Then, you have to discuss with the patient how she wants to proceed.”
Determining What Went Wrong
Once you realize that the patient’s vision is not what you expected, it is important to re-check and re-perform all of your calculations. “We need to go back and Monday night quarterback what happened to this eye,” says Lisa Arbisser, MD, adjunct associate professor at the University of Utah’s Moran Eye Center.
The first step is to make sure that the right patient has the right lens. “I had one instance where two patients’ lenses were switched,” says Richard S. Hoffman, MD, who is a clinical associate professor of ophthalmology at the Casey Eye Institute at Oregon Health & Science University. He is also in private practice at Drs. Fine, Hoffman & Sims. “Then, I make sure that the right data were put in the Holladay, and I make sure that the axial length and K readings were put in correctly. Little surprises are somewhat common, but when you get a huge 2 D to 3 D surprise, you want to know that the right patient got the right lens and that the data were put in correctly.”
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Dr. Arbisser notes that the refraction may not be stable immediately after surgery in some patients. “In a patient who has had RK, the refraction may not be stable for one to three months,” she says. “Patients with a one-piece acrylic lens are typically stable on day one. But, after implanting a Crystalens, the refraction can continue to change over two weeks or more. With a Crystalens, I would not consider correcting a refractive error for two weeks.”
In some cases, the residual refractive error may not be in the eye that was operated on. “Sometimes, the problem is that the eyes just don’t work together after you have operated on one. You have to consider the binocular situation and not just the monocular situation,” Dr. Miller says.
If the eye that just underwent cataract surgery has a bad refractive outcome, the options are limited to glasses or contact lenses, corneal refractive surgery, or a lens exchange or piggyback lens. “We can always fix refractive errors with glasses and contact lenses, so we have to be sure that that isn’t the patient’s choice because anything we do will carry some risk associated with it, and there will be a cost to someone, depending on how you structure your costs,” Dr. Arbisser says.
“If it is pure mixed astigmatism, we can perform peripheral corneal relaxing incisions,” says Dr. Miller. “For small amounts of spherical or spherocylindrical error, I use PRK or LASIK. For larger amounts, I would choose a lens exchange or piggyback IOL.”
Corneal Refractive Surgery
For small amounts of residual error or to finesse the results, PRK or LASIK may be the best choice. “There is more finesse with PRK and LASIK than there is with lens exchange or piggybacking,” Dr. Miller says. “With the latter options, the finesse is 0.4 to 0.5 D at best, and you can get down to 0.1 to 0.2 D with PRK and LASIK. In terms of optical outcomes, PRK and LASIK are the same. However, in the older patients who tend to fill the cataract ranks, I generally prefer PRK over LASIK because there are fewer dry-eye problems. For younger patients, I usually offer a LASIK enhancement.”
He notes that, if you are going to do a touch-up procedure, you have to make sure to wait long enough to achieve total refractive stability and an incision that’s very tight. “I would never consider doing LASIK sooner than one month after surgery, and, practically speaking, I almost never do PRK or LASIK until at least three months has elapsed,” says Dr. Miller.
PCRIs are a good choice for patients with up to 2.5 D of mixed astigmatism, as long as the spherical equivalent refractive error is 0.
Lens Exchange
According to Dr. Miller, lens exchange is reserved for patients who have one of two problems: Either they have a really significant refractive error or there is a problem with the lens itself. “I don’t typically exchange lenses for small refractive errors,” he says. “Sometimes, the new lens will have a different vertex or the actual powers of the old and new IOLs will be slightly different than the powers listed on the boxes. Unfortunately, the mentality of many patients is that if the problem is with the lens, then we should swap out the lens. In this situation, you have to explain that you can probably achieve a better refractive outcome by not swapping out the lens, but by performing keratorefractive surgery instead. If a patient has a multifocal in the eye and he or she has poor-quality vision or waxy vision, then it makes sense to do a lens exchange. In certain cases, the diffractive surface of the optic may have been damaged. If you give patients adequate time to recover their distance and near vision, and they don’t, it is probably a deformed diffractive optic. In this situation, I would go to a lens exchange before I would perform a keratorefractive procedure. That’s my general approach. However, some patients just want the lens out. I have done lens exchanges for less than 1 D of refractive error because a patient wanted a better refractive result but did not want corneal surgery.”
He notes that he always wants to have the option of a lens exchange, so he aggressively polishes the lens epithelial cells off the anterior lens capsule. “I try to get every last cell out; I never actually achieve that, but I try. As such, I can take out a lens five or six years later. It’s almost like re-opening a LASIK flap. I generally wait three months or so before I do touchups, unless it is a toric lens that is malpositioned,” he says.
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Dr. Arbisser agrees that subtle refractive errors are not well-addressed with lens exchanges. “If we have a larger refraction problem, then piggybacking can be an option,” she says. “If we are going to piggyback a lens, my choice is a Staar AQ series because it is 13.5 mm from haptic to haptic, so it fits every sulcus. It has a nice smooth anterior edge and a little bigger optic. For all those reasons, it is really made as a sulcus lens, and it is the best choice for a planned piggyback lens. It comes in +5 to -5.”
Piggybacking a lens is the easiest surgery, according to Dr. Arbisser, but it has the largest long-term potential risk, in that, despite using the best sulcus lens, it is possible to get pigmentary dispersion. Additionally, there is the cost of the extra lens.
Dr. Hoffman notes that piggyback lenses are usually covered by insurance, while corneal refractive surgery isn’t. “The piggyback lenses that we have in the United States won’t treat astigmatism, but corneal refractive surgery does treat the astigmatism, so my preferred method is to do the corneal refractive surgery,” he says. “However, patients have to pay extra to have that done. When I’m doing premium lenses, I make patients aware of that additional cost upfront. Some people just do it as an all-inclusive fee, and some people do it a la carte, which is my preferred method. Placement of a piggyback lens is a little bit more straightforward.”
Rotating a Toric Lens
For toric lenses, rotating the lens may fix the issue. “We have an astigmatic error calculator online,” Dr. Arbisser says. “We put in our preop and postop measurements, and the calculator tells us what we have to do to fix it, which is usually rotating the lens. If the lens was good on day one and then rotates, that’s another story. If it went in wrong, and you can see that you can rotate it back to where it ought to be, then I think that’s the thing to do.”
If the first eye has a toric that is a little bit off, the surgeon can compensate when she does the second eye. “I had a patient who was fine on day one but then rotated and had some residual astigmatism,” Dr. Arbisser says. “This was the eye that had the most astigmatism. He decided to save the money on the toric lens in the other eye, and we left both eyes with a little bit of residual astigmatism. He was very happy with the result.”
According to Dr. Dewey, correcting these surprises depends on the comfort of the surgeon, which IOL was used, and how long it has been since the lens was implanted. “If it’s as simple as a malrotated toric IOL, simply rotate it into place at an early stage,” he says. “These can be rotated months later, but the lens is going to want to go back into its little fibrosed space in the capsule, making precision a bit more challenging. If it is a perfectly rotated toric, or if it’s a simple myopic or hyperopic error several months or years later, I think a piggyback with the Staar AQ5010V makes the most sense.”
Dr. Miller adds, “The original incision should be reopened whenever possible and the malpositioned toric IOL should be aligned with the postoperative axis of corneal astigmatism, not the axis originally targeted by the toric calculator. These two axes will likely be slightly different. The goal is to have the toric optic aligned with the axis of steepest postoperative corneal cylinder.”
The Future
According to Dr. Arbisser, in the future, surgeons will have technology that theoretically will be able to touch up the refraction by changing the lens itself postoperatively, such as the Calhoun lens in FDA trials, for which Dr. Miller is an investigator. “The most exciting technology is using a femtosecond laser in a proprietary method that is being worked on at Rochester University to actually correct the prescription without wound healing issues by changing the refractive index of the cornea as well as any implant. It could be that, in the far future, we won’t need contacts or glasses or ever get a wrong implant,” she says. REVIEW
