Novel internal analysis of metal irrigation/aspiration tips could explain mechanisms of posterior capsule rupture

Introduction

Posterior capsule rupture (PCR) rates are used to measure cataract surgeons’ quality. We wished to evaluate the internal non-visible surfaces of metal irrigation/aspiration (I/A) tips to identify potential mechanisms for PCR via novel metallographic imaging.

Methods

Ten metal I/A instruments underwent metallographic preparation by fine sectioning to expose inner surfaces near the aspiration opening. Analysis of inner bore, lumen, and opening aperture of metal aspiration tips was performed by optical microscopy, scanning electron microscopy (SEM), and 3D volume X-ray computational tomography (XCT). Distances from external aperture to first sharp metal surface were obtained and compared with a silicone-tipped instrument.

Results

We identified metal burrs near the aspiration apertures and manufacturing defects within all tips. XCT confirmed optical and SEM findings of significant defects and metal irregularities within aspiration tips. Samples also showed variation in lumen size/thickness, rough surfaces and material inhomogeneity, most pronounced at the internal tip. Median distance from outer aperture opening to first metal burr was 30 microns (range 10–120) and to internal tip irregularity (manufacturing flaw) was 250 microns (range 100–350). By comparison, distance to metal from the silicone outer aperture opening was 850 microns.

Conclusions

We have demonstrated the hidden sharp metallic irregularities within commonly used metal I/A tips. If an aspirated capsule encounters these sharp metal flaws, PCR could result. Minimising this risk would require lengthening potential distance between capsule and bare metal (as with polymer/silicone tips). Our study provides unique imaging evidence endorsing this principle and illustrates a hidden mechanism contributing to PCR.

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Fig. 1: Macro-optical photograph demonstrating roughened (spectrum 1) and smooth (spectrum 2) external metal surfaces on a metal coaxial I/A.
Fig. 2: Cross-sectioning photography of (a) coaxial and (b) bimanual aspiration I/As.
Fig. 3: Composite of SEM images revealing sharp internal irregular metal surfaces, most pronounced at the internal tip (a–d).
Fig. 4: Composite of SEM images revealing hidden sharp metal burrs at the outer and inner aspiration openings of the metal I/As.
Fig. 5: XCT 3D volume renderings for both the bimanual and coaxial metal I/As revealed variability in the wall thickness, internal roughness and inhomogeneity at the internal tip.

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Acknowledgements

A version of this paper is a free paper presentation at the (virtual) 38th ESCRS Congress in October 2020.

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Correspondence to David Lockington.

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Nil relevant to this work. DL has received educational and KOL honoraria from Alcon, Bausch & Lomb, Santen and Thea. AM, TM, FS: nothing to declare.

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Lockington, D., Macente, A., Marrocco, T. et al. Novel internal analysis of metal irrigation/aspiration tips could explain mechanisms of posterior capsule rupture. Eye (2020). https://doi.org/10.1038/s41433-020-01181-7

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