Analysis of internal surfaces of metal irrigation/aspiration tips identifies intrinsic reasons for capsule rupture in cataract surgery
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First Author: D.Lockington UK
Co Author(s): T. Marrocco F. Sillars
Posterior capsule rupture (PCR) most commonly occurs during cortical clean-up in modern cataract surgery. There are a variety of co-axial and bimanual options for irrigation and aspiration (I/A), including metal, polymer and silicone tips. We wished to evaluate their internal openings and hidden surfaces to identify potential reasons for PCR.
Tennent Institute of Ophthalmology, Glasgow, UK, and the Advanced Materials Research Laboratory, University of Strathclyde, Glasgow, UK
Ten various metal I/A instruments (used and unused) were obtained. Silicone tipped I/As were examined for comparison. Metallographic preparation involved removal of side and back wall by fine sectioning to expose inner bore adjacent and opposite to aspiration opening. Cut edges were peeled back to reveal the hidden inner surface. Macro- and micro-photography was undertaken. Analysis of the inner bore, lumen and opening aperture was performed by optical microscopy, scanning electron microscopy (SEM) and 3D volume scan of aspiration tips by X-ray computational tomography (XCT). Distances from outer opening to the first sharp or irregular metal features were measured.
Optical micrographs before fine sectioning revealed sharp metal burrs visible at the aspiration apertures and irregular manufacturing defects on the external tips. XCT confirmed the optical and SEM findings of significant defects and metal irregularities within the aspiration apertures. Samples also showed variation in lumen size/thickness, rough surfaces and material inhomogeneity, most pronounced within the internal tip surface. Distance from outer aperture opening to first metal burr was 10 – 120microns. Distance from outer opening to internal tip irregularity (flaw) was 100 – 350microns. By comparison, distance to metal from the silicone outer aperture opening was 850microns.
We have demonstrated inherent irregularities hidden within commonly used metal I/A tips. If capsule is inadvertently aspirated and encounters these sharp metal flaws, PCR is likely to result. Through unique 3D scanning, we have clearly shown the intrinsic reasons responsible for PCR, by visually illustrating the inherent dangers of metal instruments having hidden sharp and irregular internal surfaces. Minimising this risk would require lengthening the potential distance between capsule and metal, as occurs with polymer or silicone tips. Publications suggest trainee silicone I/A tips result in reduction (even elimination) of PCR. Our analysis gives physical evidence to these clinical recommendations.
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