Refractive
Spring 2024

by Ellen Stodola
Editorial Co-Director

There has been controversy around ICL sizing and vault for a long time, said Mark Packer, MD. Even around 20 years ago, there were proponents of using ultrasound to look at the distance across the sulcus, which is where the lens is going to go, and saying that is really more appropriate compared to using surrogate measures of corneal white-to-white and anterior chamber depth, which are the key elements in the approved nomogram that STAAR has in their labeling.

The EVO ICL (STAAR Surgical) comes in four sizes: small (12.1 mm), medium (12.6 mm), large (13.2 mm), and XL (13.7 mm), Dr. Packer said. “I think one of the other interesting things we learned in the clinical trial is people tend to want to avoid extra-large.” People tend to want to avoid the extremes, because they are wary of high and low vault, he said. However, in the clinical trial, the highest vault was not with a 13.7 lens; it was with a 13.2 lens, Dr. Packer added.

Neda Nikpoor, MD, said the size of the EVO is decided during preop testing. In addition to typical refractive screening tests, Dr. Nikpoor also uses IOLMaster (Carl Zeiss Meditec), Pentacam (Oculus), a digital caliper for primary white-to-white measurement, and UBM (Sonomed). She will also do a contact lens over refraction for high myopes. 

Dr. Nikpoor uses the Dougherty nomogram for UBM to measure sulcus to sulcus. “I find that tells me a lot more than just ‘white-to-white,’ she said. “I look at white-to-white and see where that lands on modified nomogram.” If the white-to-white is on the border between two sizes, then I favor whatever the UBM is going to tell me and let that be a tiebreaker. If they disagree completely, I’ll still use the UBM with a little bit of caution, she said. “I’m looking at the sulcus and where it will sit.” As another tie breaker, I will look at lens rise on the UBM, and if it’s more than 0.75, then I would favor sizing up, Dr. Nikpoor added. If white-to-white and sulcus-to-sulcus are very much in the middle of the size range and lens rise is over 0.75, Dr. Nikpoor won’t change from the recommended lens, using those two nomograms that agree. She uses lens rise as tiebreaker or third data point. 

The other important data point, she said, is anterior chamber depth (ACD). It is CE marked down to 2.8 in Europe, so Dr. Nikpoor will often go down to 2.8 or even 2.75. “If I have someone who has less than a 3-mm ACD, if the sizing looks like it’s going to be tight, I’ll downsize because I’d rather have lower vault and a shallower anterior chamber depth,” she said. “If I have something that’s really borderline between two sizes and have 3.5 anterior chamber depth, I’m more comfortable bumping up a size.” If she’s between two sizes, in a normal 3–3.2 ACD with everything else average, she tends to size down. 

For a deep dive on ACD on EVO see “Clearing up the confusion: get the right anterior chamber depth for ICL” on page 76.

The rate of cataracts with EVO is very low, Dr. Nikpoor said, lower than it was with Visian (STAAR Surgical). “I was a lot more willing to size up with Visian, but now we have 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 postop 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 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 vault, the problems due to 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 incidence of cataracts with EVO is so much lower. Exchanging these patients is just not necessary, in my opinion.”

With 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 non-central 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 between two sizes in the nomogram, if it’s non-toric, dropping down a size is almost never a problem, Dr. Packer said. But if it’s a toric lens, going to the larger size is probably a better move because you don’t want a toric lens to rotate, especially a higher power toric. “A lot of EVO surgeons I talk to don’t use toric if it’s under 2 D; they perform an arcuate incision or on-axis incision instead. They’d rather avoid the issues of the lens potentially rotating unless they need 3 or 4 D.”

Many surgeons are using artificial intelligence to improve sizing, Dr. Packer said. Roger Zaldivar, MD, is doing just that. “The last few years, we’ve finally realized the role and importance that UBM has on ICL selection.” While he’s had UBM in his clinic for some time, he said that there are difficulties in applying UBM to every single patient and lack of standardization. “Today, since we are living a true AI revolution, there are different means to standardize what we’re doing and improve and get the best images,” he said. “We’re now understanding exactly what we have to measure, and we’ve trained a deep learning model based on UBM, and we are using different brands of UBM, not just one.”

Dr. Zaldivar’s method—ICL Guru on the Revai platform—processes different videos and clips, extracting the best images automatically selected by the algorithm. That fits the algorithm to give you a recommendation based on the whole eye configuration, he said. “We have trained the model with more than 12,500 images, which is very robust, and we are putting thousands of images in each week,” he said. “Each time, we are getting less and less outliers. The level of predictability is impressive. We’ve never experienced this amount of predictability.” For example, he said roughly 100% of patients with the 13.7 ICL size, the most difficult ICL because it’s the biggest, were within 250 microns of predictability, with an absolute error around 83 microns. 

Dr. Zaldivar said the main concept of this method is that it’s a deep learning algorithm that still uses some parameters of anterior chamber OCT to double check. “It’s the combination of the two that allows us to be so sharp,” he said. 

It’s important to also consider the concept of a safe vault, he said. “We have been insisting in this concept for a long time. Finally, we are happy with everyone else understanding this complexity,” he said. While many publications note a safe vault of 250–750 microns, Dr. Zaldivar said a safe vault absolutely depends on each patient and each eye configuration. “If you have a big eye, the margins are much higher. You could have 1,000 vault, and it could be perfect. It would be absolutely depending on the angle of the anterior chamber and lens rise,” he said, adding that vault is also considered in his nomogram. 

Dr. Zaldivar has extensive experience with using ICLs and said he hasn’t explanted one for many years. “With this methodology, we’re getting predictability in numbers that are really impressive.” He’s also noticed a change in comfort with the procedure. “What has changed is the behavior of how we analyze which patient can get an ICL,” he said. “We’re using every single power of ICL. We don’t even hesitate with PRK; we just put in an ICL. We’re so comfortable using this as a standard procedure.”

Many physicians have experience in this area, Dr. Zaldivar said, and experience helps to deal with outliers, but he said his predictability method could prove very beneficial in the future. 

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About the physicians

Neda Nikpoor, MD
Aloha Laser Vision
Honolulu, Hawaii

Mark Packer, MD
Fort Collins, Colorado

Roger Zaldivar, MD
Instituto Zaldivar
Mendoza, Argentina

Relevant disclosures

Nikpoor: STAAR Surgical 
Packer: STAAR Surgical
Zaldivar: STAAR Surgical

References

1. Packer M. Meta-analysis and review: effectiveness, safety, and central port design of the intraocular collamer lens. Clin Ophthalmol. 2016; 10:1059–1077.
2. Yiming Y, et al. Evaluation of ciliary body morphology and position of the implantable collamer lens in low-vault eyes using ultrasound biomicroscopy. J Cataract Refract Surg. 2023; 49:1133–1139.
3. Packer M. The Implantable Collamer Lens with a central port: review of the literature. Clin Ophthalmol. 2018; 12:2427–2438.

Contact 

Nikpoor: drneda@alohalaser.com
Packer: mark@markpackerconsulting.com
Zaldivar: zaldivarroger@gmail.com