Preoperative Considerations
Chicago surgeon Louis Probst says that there are aspects to correcting residual refractive error that the surgeon may not have considered. Here are several issues Dr. Probst says are worth thinking about:
• Who was the original surgeon? “The cases differ depending on who did the initial cataract surgery,” Dr. Probst says. “If it’s your patient, it’s your responsibility to make him happy and follow through as you see fit. But if it’s not your patient, be aware that there’s a kind of false assumption out there that the patient already had his main procedure and that these are simple ‘touch-up’ cases to make his vision a little better. However, these situations can get very complex, and these enhancements are far more difficult than PRK or LASIK on a virgin eye, for a host of reasons. If you didn’t do the original cataract surgery and this isn’t your patient, by agreeing to enhance him you’ll be suddenly adopting all the issues and concerns of the patient who had a less-than-ideal outcome, and he’ll become your problem. In such a situation, ask yourself if it’s something you want to get involved in.”
• Complications and/or ocular pathology. One of the factors that can make these cases more complex is a complication from the cataract procedure. “Though IOL surgery is very effective, it does have a complication rate,” says Dr. Probst. “If the patient had a complication during his cataract procedure, this could affect his final outcome from his postop enhancement. He may not have the potential to see 20/20, yet his expectation for the enhancement is that he will see very well, if not perfectly, so this sets the bar high. However, talking to him about this before surgery can be tricky because of the lofty image of laser vision correction and LASIK in society, which leads many to believe they will see very well. You can try to counsel him otherwise, but he will still have the hope that he’s going to see very well.”
The same goes for situations where the patient has ocular pathology that prevents her from reaching 20/20. “For example,” says Dr. Probst, “if someone’s uncorrected vision is 20/40 after IOL surgery, but a retinal exam reveals that at least half of that decreased uncorrected vision is probably due to some macular pathology, and her final best-corrected vision might be 20/30, you don’t want to do an LVC procedure to improve vision by just one line in the best case, while undergoing all the risks of another procedure.”
• YAG laser. The possible effect of a YAG capsulotomy needs to be accounted for, say surgeons. “Once someone’s had an IOL procedure, one of the reasons his vision is decreased might be because he has an opacified posterior capsule,” says Dr. Probst. “If that’s the case, it might be more appropriate to have the YAG performed first before doing any refractive procedure to determine whether that can improve the patient’s vision.”
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• Multifocal and accommodative lenses. “I think the multifocal IOL patient with an error is the best indication for laser refractive surgery postop,” says Tucson, Ariz., surgeon William Fishkind. “A multifocal patient who comes out a little off, maybe 0.5 to 0.75 D hyperopic or 0.75 D myopic, and can’t stand it, is a candidate. The lens won’t work as intended and he’s unhappy, and he’s spent a lot of money to get that multifocality.”
Of course, surgeons say that the irony is that even though the multifocal patient can be helped the most by sharpening his vision, he’s also the most challenging because his vision is now multifocal.
“You’ll see a higher frequency of patients needing refractive touch-ups from the multifocal group,” says Nashville, Tenn., surgeon Ming Wang. “For instance, if you don’t clean up a -1 D error in a multifocal patient, not only will he be nearsighted due to the error, but the myopia will prevent the lens from working as it’s intended. Once you correct the refractive error, something new comes out of the lens that isn’t present in a monofocal patient: the intrinsic multifocality.”
So, surgeons agree that multifocal IOL patients with postop refractive error need correction, but this gives rise to another question: What refractive target do you aim for?
“A multifocal patient doesn’t have a firm target,” says Dr. Probst. “He has multifocal vision with distance and near targets, so picking an endpoint becomes a delicate matter. The patients themselves are also more challenging because they have more complex expectations than a single-vision patient. They’re looking for distance and near vision, so you have the opportunity to fail at both. Multifocal patients require extensive discussion about what their expectations are for the enhancement: emphasis on reading or on distance?”
To help zero in on the endpoint, surgeons use the tools usually associated with preop refractive surgery: manifest refractions; anterior and posterior corneal topography and wavefront imaging. They say to discount wavefront a bit, however, since the multifocality of the lens may render it less than perfectly accurate.
Dr. Probst says the process involves a lot of discussion of the patient’s activities and expectations. “Let’s say we do a WaveScan on a patient with a multifocal lens and it reads a refraction of -1.5 D,” he says. “Then, we do a manifest refraction and find that the patient gets his best distance and near vision with -0.75 D. This makes it a little tricky determining what the target should be. It’s through the trial lenses and having him look at distance and at near that you determine which correction is ideally suited to that patient’s expectations. This could take multiple visits to sort through. What also bears some discussion with the patient is that the multifocal lens has already induced some loss in quality of vision, so the patient will be starting a step or two behind the virgin refractive surgery eye. If you don’t explain this to him, he may attribute a loss of quality in his final vision to the enhancement rather than the original IOL surgery.”
If possible, some surgeons like to do a contact lens trial. “If the patient will do it, a contact lens trial for a week or two allows him to try the corrected vision at distance and near in different situations, such as leisure, work and sports,” explains Dr. Probst. “He can then identify the areas where it was good and not so good and you can adjust the target. One of the great things about this is he’s participated in the decision, which he’ll appreciate. Also, if the postop vision isn’t 100 percent crystal clear, he’ll also realize he shares some of the responsibility for it, which can be helpful at times.”
As an alternate approach, Dr. Wang says he’s found that multifocal lenses and the Crystalens actually need slightly different refractive targets for postop laser enhancements. “For ReSTOR, we’ve found it’s best to target plano in both the dominant and non-dominant eyes,” he says. “This truly gives two focal points for each eye, one at distance and one at about 33 cm. For Tecnis, however, we’ve found that it’s slightly different. The distance vision is the same as ReSTOR, but the near point is a little too close for most patients, sitting at about 25 cm, or 4 D. So for Tecnis I intentionally target a little plus in the non-dominant eye, making it around +0.5 D, the goal being to move this 25-cm focal length slightly out nearer to 33 cm.
“For Crystalens, it’s different still,” he adds. “When the Crystalens eventually settles into position, we’ve found it comes forward a little bit due to capsular contraction, so if you aim at plano you’ll probably end up slightly minus. We’ve found the average accommodation in these patients is about +0.75 D, but for people to use a computer, which is sort of in the intermediate distance, they need maybe +1.25 D. So, in the dominant eye, I aim for +0.25 D, and in the non-dominant eye I’ll aim for -0.5 D due to the 0.75 D average amount of accommodation the lens gives.”
• Toric IOLs. Errors after toric lens implantation are somewhat less involved than after multifocal procedures, but still involve some diagnostic work. Dr. Fishkind says a list of pertinent questions can help home in on the problem. “Did the lens rotate or not?” he says. “What’s the effective lens position? Where is the final astigmatic refractive axis? How much is the astigmatic error? Can it be corrected with a limbal relaxing incision or a laser or does the lens need to be re-rotated back into position?”
When facing a toric lens enhancement, Dr. Probst first compares the preop and postop cylinder. “If there was a change in axis but there is still a significant amount of astigmatism, that suggests that perhaps the lens wasn’t implanted in the correct axis or it rotated,” he says. “Then, a lens rotation might be more appropriate. But, if it’s a toric patient with little residual astigmatism who’s now myopic, then LVC on the cornea would be appropriate.”
Choosing a Procedure
Once you and the patient have determined that an enhancement is necessary, surgeons advise trying to wait at least 90 days before performing it, to allow any postop inflammation and residual astigmatism to resolve, and to ensure you know the exact amount of error you’re dealing with. At that point, surgeons say the procedure you choose depends on which potential complications you’d rather avoid.
Some surgeons, like Dr. Wang, prefer PRK. “I typically do PRK because it avoids LASIK’s issues with diffuse lamellar keratitis, dry eye and flap complications,” he says. “It’s an overall better procedure except in one category: delayed gratification. LASIK heals in days, PRK heals in weeks. However, the post-cataract patient is older than the typical refractive surgery patient, so their eyes are drier to begin with, and I don’t want to induce more dry eye by doing LASIK.”
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Whichever procedure is chosen, surgeons say that, when faced with enhancing a multifocal IOL patient, it’s probably best to avoid custom ablations and perform a conventional procedure instead.
“By their very design, multifocal IOLs are supposed to cause some higher-order aberrations,” says Dr. Wang. “The lenses intentionally generate some spherical aberration to cause axial dispersion, or the existence of two images, one of which is focused closer to the retina and one away from the retina. Though, classically, ophthalmology has always tried to reduce spherical aberration and axial dispersion, they are the essence of the multifocality of the IOL. Also, these lenses are almost always slightly decentered a little bit which, because of their rings, will cause a little higher-order aberration, too. If we do a custom treatment in these cases, it will erase some of the multifocality of the lens by erasing some of the higher-order aberrations. Also, the cornea is regular in these patients, so we shouldn’t make it irregular by putting reverse aberrations on it to compensate for minor ones generated by the lens.”
Ultimately, Dr. Probst says that, no matter how you approach these cases, they will still be challenging. “I’m a 100-percent corneal refractive surgeon,” he says. “But I really try not to do too many of these cases. Many surgeons have come to me with the idea that these cases are a great opportunity to do more LASIK but, in fact, this is a very complex area that’s riddled with potential pitfalls. I’m not saying you shouldn’t do these cases, particularly if they’re your own patients and you feel that you could help them see better, but be warned that they can turn out to be far more complex than they first appear.” REVIEW
1. Solomon R, Donnenfeld ED, Holland EJ, et al. Microbial keratitis trends following refractive surgery: Results of the ASCRS infectious keratitis survey. J Cataract Refract Surg 2011;37:7:1343-50. doi: 10.1016/j.jcrs.2011.05.006.
