22 EyeWorld Asia Pacific | June 2024 EVO, and the lens floats, with the aqueous circulating through the holes. I’m more willing to size down, and I am comfortable monitoring a really low vault.” Dr. Packer published a meta-analysis of over 20 papers in 2016.1 Inclusion requirements for the meta-analysis were: papers had to explain/describe sizing methodology and they had to measure postoperative vault using OCT. “What was fascinating to me was that it didn’t matter which method was used. The results were similar,” he said. “Mean vault was always around 400–500 microns, and the standard deviation of the vault was always around 200 microns, no matter what they did. I thought that was interesting because, in a lot of articles, people were claiming their method was superior, but when looking at the results, they were all the same.” Dr. Packer continues to look at the literature as it comes out, and the findings are consistent with the meta-analysis. You can vary the mean vault a little bit, but there’s always a variation of approximately plus or minus 200 microns in terms of the standard deviation, he said. The recent approval of EVO, Dr. Packer said, was based on 6-month data. But the 3-year trial is ongoing, he said. The investigators in that clinical trial were using STAAR’s nomogram, and you see the same kind of mean and variability in the 6-month data, he said. Lens vault is variable due to how the lens sits in the ciliary sulcus, Dr. Packer said. If you think about the footplates of the ICL, he said, they’re soft pliable collamer material, and sometimes they’re lying flat, but sometimes they’re up on tippy toes, and sometimes on zonular fibers. “Recently, there was a publication2 showing all these positions using high resolution ultrasound, which shows that the lens sits in different ways, and there’s no way to control that when you’re putting it in the eye. Even if you could, the haptic positioning could change with natural movement of the ciliary body and iris.” So, where does that leave us? In a good place, Dr. Packer said, because even though we see variability in the vault, the problems related to the vault have almost disappeared with the central port design, so it’s not so much about the vault; it’s more about aqueous flow. Even if you have a very low vault, because aqueous is flowing over the top of the crystalline lens and out the port, the crystalline lens is protected. In the published literature, there’s close to zero incidence of anterior subcapsular cataract,3 Dr. Packer said. The other potential problem is angle closure glaucoma due to excessive vault. That has virtually disappeared as well, he added. “What we do see still is that surgeons may be uncomfortable with an extremely high vault, and they may decide to exchange a lens,” Dr. Packer said. When you look at the angle with gonioscopy or OCT, it might look disturbingly narrow. The good news with the central port design is that adverse events or complications due to extremes of vault have virtually disappeared. He said he thinks the mindset of trying to fix the problem of vault, however, persists. A safe vault, Dr. Nikpoor said, is between 250–750 microns. “Even if it’s less than 250, I’m usually not so worried about it with an EVO. I’ve had maybe one high vault, hovering around 1,000 or 1,500, that I’m observing because they tend to drop back over time.” High vault by itself isn’t a reason to exchange, she explained, but a high vault with a sign of high IOP or intermittent angle closure is. “With a low vault, as long as it’s not zero, as long as there’s some space between the lens and the crystalline lens, then I think you’re safe to just observe, and I observe those patients because the risk is that they could develop a cataract,” Dr. Nikpoor said. “In my opinion, if you go in and are trying to exchange a low vault lens for another lens, you have a risk of inducing a cataract just from exchanging that lens, and it can be hard to get that low vault lens elevated up and untucked. I would just leave that alone, especially knowing the incidence of cataracts with EVO is so much lower. Exchanging these patients is just not necessary, in my opinion.” With a high vault, Dr. Nikpoor is more concerned and more likely to follow the patient frequently and check the IOP and angles for signs of glaucoma. If their pressure is high or the angle is intermittently closed or too narrow or closed, then I’d consider exchanging that high vault lens, she said. “I think there’s a lot more tolerance and forgiveness because people are using so many different sizing methods and so many different nomograms and having good success, so there must be some tolerance built into this, otherwise there would be one method better than the other,” Dr. Nikpoor said. “I think people worried about sizing are warranted because the last thing you want to do is have a super high vault and some emergent problem, but I think that’s why I generally tend to size down. I think people can rest assured that if you just got a digital caliper and measured your white-to-white and did nothing else, you’d probably be fine the majority of the time.” Low vault is not as scary as it used to be with the noncentral port design, Dr. Packer said, so undersizing is not that big a deal, except with the toric because if you have an undersized lens it might rotate. When you find yourself REFRACTIVE SURGERY
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