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Structural integrity of enVista MX60 eyelets

Watane, Arjun BS; Kalavar, Meghana MHS; Pollmann, André S. MD; Lewis, Darrell R. MD; Gupta, R. Rishi MD, FRCSC; Townsend, Justin MD; Patel, Nimesh A. MD; Sridhar, Jayanth MD; Yannuzzi, Nicolas A. MD

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Journal of Cataract & Refractive Surgery: May 2021 - Volume 47 - Issue 5 - p 677
doi: 10.1097/j.jcrs.0000000000000607
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We previously reported a series of 25 intraocular lens (IOL) displacements secondary to eyelet fractures in scleral-fixated enVista MX60 lenses.1 Notably, there were no reports of suture breakage or knot slippage, which suggests that the intact suture passed through the eyelet fracture, thereby allowing the displacement to occur. Potential explanations of eyelet fractures include improper surgical technique, increased suture tension, and lens fragility. In our series, 2 types of knot configurations were used to secure the suture to the eyelet—the simple-pass method and modified cow-hitch method. To further investigate the potential causes of eyelet fractures, we compared the tensile force needed to fracture the eyelet of enVista MX60 IOLs between these 2 knot configurations.

A benchtop model similar to the one used previously by Pollmann et al was designed to approximate suture geometry and force vectors present on the eyelet of a scleral-fixated IOL.2 A mounting platform and clamp (Thorlabs Inc.) secured the IOL in place directly after its retrieval from the supplied packaging to mirror hydration conditions present when used in vivo. Two suture configurations were tested. In the first method, the Gore-Tex suture (CV-8) was looped using a simple pass through the IOL eyelet. In the second method, the Gore-Tex suture was folded, and the folded end was passed through the eyelet. The folded end was then passed over the haptic, and the suture was then tightened so that it ultimately wrapped around the haptic and passed through the eyelet. In both configurations, both suture ends were passed through the plastic spacing unit and subsequently connected to an electronic force gauge (PCE-DFG N20, PCE Instruments GmbH). The gauge was then placed on a linear track system, allowing the gauge to accurately record the tension applied to the suture–eyelet complex in newtons (N). The ambient temperature and humidity were controlled at 75°F and 60%, respectively.

Eight trials for each suture configuration were completed. The mean force required to fracture the eyelet in the simple-pass suture configuration was 2.42 N (standard deviation: 0.11 N, range 2.25 to 2.55 N). In comparison, the cow-hitch suture configuration required significantly less force to fracture the eyelet at 1.40 N (standard deviation: 0.26 N, range 1.08 to 1.81 N) (P < .001).

Our experiments demonstrate that a greater force can be applied before the enVista MX60 eyelet fractures when using a simple-pass suture when compared with a cow-hitch configuration. One explanation for our finding is that the single point of contact of the suture to the IOL in the simple-pass method may allow greater flexibility of the eyelet arms. On the other hand, the multiple points of contact in the cow-hitch method may stress more fragile areas of the eyelet arms, allowing it to break at a lower tension. Although further biometric studies are needed to fully understand the physics behind IOL fractures, we recommend surgeons consider these findings when suturing enVista MX60 IOLs.

REFERENCES

1. Watane A, Botsford BW, Sood AB, Williams AM, Xu D, Gupta RR, Conner IP, Sivalingam A, Gupta OP, Ward MS, Mehta S, Del Cid M, Crossan A, Sierpina DI, Hwang FS, Rachitskaya A, Ehmann DS, Kovacs KD, Orlin A, Zhang AY, Patel U, Dubovy S, Klufas MA, Patel NA, Sridhar J, Yannuzzi NA. Scleral-sutured intraocular lens dislocations secondary to eyelet fractures. Am J Ophthalmol 2021;221:273–278
2. Pollmann AS, Lewis DR, Gupta RR. Structural integrity of intraocular lenses with eyelets in a model of transscleral fixation with the Gore-Tex suture. J Cataract Refract Surg 2020;46:617–621
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