Very high frequency ultrasound improves the precision of ICL sizing – Tips & Results

The implantation of an intraocular collamer lens (ICL) is reversible, protects the cornea from permanent changes and expands the treatment range up to -20 D for myopes and up to 6 D for astigmatic myopes. Additionally, in Food and Drug Administration clinical studies of Visian Toric ICL (STAAR) in patients with mean myopia of -9.37 D and mean astigmatism of +1.95 D, 82% of eyes 20/20 or better were uncorrected and 54 % of eyes were 20/16 or better uncorrected.1 In a recent retrospective study of my Toric Visian ICL patients, 87% of the eyes achieved a postoperative spherical equivalent of 0.5 D or less.

Related: IOLs offer excellent vision and a low risk profile for presbyopia

These features and results are one of the reasons I am an avid ICL advocate and why I recommend these implantable lenses even for myopic people, unlike many of my colleagues who refer them to patients who fall outside of approved LASIK parameters.

ICL sizing

Despite over a decade of excellent results, the ICL acceptance rate is not as robust as expected. Many consider lens size limitations to be one of the factors responsible for underutilization. The most common ICL sizing method is to obtain white-to-white (WTW) measurements and plug the data into the online pricing and ordering system. This combination results in correctly sized ICLs in most cases, but is also associated with rare, risky, outlier results.2

Phakic lenses occupy the space between the posterior surface of the iris and the anterior surface of the lens of the eye. Due to the limited space here and the need to allow aqueous humor to pass through, it is crucial to accurately measure this area preoperatively. Exact sizing of the ICL is critical as it affects the vault. Ideally, the vault size should be around 250 to 750 μm. If any vault is less than 250 μm, there is a risk of anterior subcapsular cataract formation. With a curvature of more than 750 μm, there is a risk of pupillary block glaucoma and narrowing of the corner of the eye with possible chafing of the iris and resulting pigment loss.2

Very high frequency ultrasound

My practice is among the first in the US to use an innovative Ultra High Frequency Ultrasound (VHFUS) device – the ArcScan Insight 100 (ArcScan, Inc) – which, among other things, improves the precision of ICL sizing. The device can image behind the iris and clearly show the sulcus space. Although conventional ultrasonic biomicroscopy (UBM) can also image this space, the Insight 100 achieves exceptional resolution and repeatability. The device maintains consistent perpendicularity and distance to the eye with a robotically controlled 50MHz ultrasonic transducer and automatic focus depth adjustments. The calipers on the Insight 100 are accurate to within 0.12mm on the side behind the iris. Each preoperative imaging scan set includes 7 meridians to cover the desired area of ​​lens base position. In addition to determining the exact lateral distance, the resulting images can be used to detect the presence of ciliary cysts or other pathologies, aiding in surgical planning.

High-risk outcomes are rare in refractive surgery practices, but because of the size challenges and the unlikely — albeit possible — event of pupillary block glaucoma or cataract formation, the first 24 hours after ICL implantation can be stressful.

Surgeons like me who perform many ICL procedures have had the experience of implanting a lens that is too small or too large and then had to remove the lens or perform an ICL exchange. The ArcScan system essentially eliminates these concerns and allows me to offer my patients this excellent option of refractive surgery with a high level of confidence in its effectiveness and safety.

Eliminate outliers

As I mentioned earlier, external eye measurements are still the most commonly used criteria for determining ICL size. In addition to the WTW measurements, however, many other factors must be taken into account. For example, in addition to sulcus-to-sulcus measurements, the Insight 100 can measure anterior chamber depth, anterior chamber angle, angle-to-angle, anterior chamber width, measured scleral spur to scleral spur, depression-to-angle angle of depression lens rise, sulcus-to-sulcus lens rise, and inner diameter of the ciliary body (illustration 1).

The aim of these measures is to reduce lens changes to a very rare occurrence. Once we have secured the detailed intraocular measurements and entered them into the digital ArcScan template, we upload the data to the London Vision Clinic’s free online ICL size calculator (www.iclsizing.com), which uses a dedicated nomogram to calculate the Predict vault size for each ICL (figure 2). This process allowed us to eliminate the outliers. The nomogram takes into account the inner ciliary body diameter as well as the lens pitch, the scotopic pupil size and the lens power. If we have those 4 measurements, we can reduce the scatter of the postvault by a factor of 4, according to Dan Reinstein, MD, who is responsible for the ICL size nomogram and much of the research for the ophthalmic VHFUS measurement technology.

The Insight 100’s ICL sizing feature eliminates the risk of size-related complications by selecting a lens based on direct measurements of the posterior chamber. By creating VHFUS images instead of images acquired by analog UBM systems or WTW measurements, an accuracy of 1.0 µm at the cornea and 0.12 mm laterally behind the iris is ensured.3

retrospective study

We conducted a retrospective study examining our ICL patient cohort to assess the accuracy and predictability of using the Insight 100 in conjunction with the online London guide. Analysis of the first 86 eyes from 160 ICL patients identified for this study revealed that we were within 300 μm – half the thickness of a cornea – of the predicted ICL bulge size with the ArcScan system 97% of the time could come.

The elimination of outliers has further increased our confidence in this procedure, and we believe that surgeons who have previously been hesitant to offer ICLs to their patients will be more likely to add these lenses to their toolkit once concerns about high-risk outliers are resolved . Surgeons often only use ICLs when a patient is not a LASIK candidate, but we offer ICLs to any myopic or astigmatic myope who falls within the approved treatment parameters—even those who have lower prescriptions. We are not afraid of risky results because we are confident in the accuracy and precision we achieve with the Insight 100.

Based on my experience with the ArcScan Insight 100, I believe VHFUS will become the gold standard for ICL sizing. And with our ability to predict the ICL vault with this level of accuracy, I expect ICLs will continue to be adopted by refractive surgeons.

Brett Mueller II, DO, PhD

E: bmueller@nuvisiontx.com

Mueller is a cataract refractive surgeon at Parkhurst NuVision in San Antonio, Texas. He did not provide any information about the content.

references

1. STAAR Visian Toric ICL Post-Registration Study (TICL-PAS). ClinicalTrials.gov. Updated August 20, 2020. Accessed October 15, 2021. https://clinicaltrials.gov/ct2/show/NCT04516772

2. Packer M. The implantable central port collamer lens: review of the literature. Clin Ophthalmol. 2018;12:2427-2438. doi:10.2147/OPTH.S188785

3. Reinstein DZ, Archer TJ, Silverman RH, Coleman DJ. Accuracy, Repeatability and Reproducibility of Artemis High Frequency Digital Ultrasonic Arc Scan Side Dimension Measurements. J Cataract refractive surgery. 2006;32:1799-1802. doi:10.1016/j.jcrs.2006.07.017

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