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E. A. Olson, M. S. Tsipursky, P. J. Bryar, W. G. Myers; The Effect of Using Transverse Ultrasound and Different Vacuum Settings on Nuclear Fragment Size Following Phacoemulsification: In Vitro Study. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6107.
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© ARVO (1962-2015); The Authors (2016-present)
Transverse ultrasound is a new alternative to traditional longitudinal ultrasound during phacoemulsification. With transverse US the repulsion from the phaco tip and the friction inside the incision are greatly reduced. The goal of the present study is to determine whether or not using transverse US and different vacuum settings will have any effect on the size of the aspirated nuclear fragments. This would be useful to know because larger fragments can cause line occlusion.
Two machines were made available for participation in this study: Advanced Medical Optics WhiteStar Signature and Bausch & Lomb Stellaris. The lenses of 12 eye bank eyes were extracted in the extracapsular fashion and graded according to nuclear density. Six lenses were randomly assigned to each machine. The lenses in the B&L group were each cut in half to allow for a cross-matched comparison using either a constant high vacuum (350mmHg) or low vacuum setting (200mmHg). Because the AMO WhiteStar Signature has both transverse and longitudinal US, the six lenses in this group were each cut into quarters so that the effects of US modality could be investigated concurrently with the high and low vacuum settings. Other settings were kept at constant values throughout all experiments, with phaco power at 40% and flow rate at 35cc/min. Each divided lens segment was phacoemulsified individually in an artificial chamber. Following each procedure, the aspirate was filtered and decanted. The leftover nuclear fragments were measured under a light microscope. The size distributions of each group were compared using one-tailed, independent samples t-tests.
Following each procedure, an average of 225 fragments were recovered and measured. The average fragment in the longitudinal US group was 12.7% larger than the average fragment in the transverse US group (p<0.01). This trend was significant in low grade (<3) and high grade (3+) lenses. The high vacuum group had 2.5 times more fragments than the low vacuum group that were >1mm in largest dimension. Likewise, the longitudinal US group had 3.5 times more fragments than the transverse US group that were >1mm in largest dimension (p<0.05).
Transverse US and low vacuum settings both lead to the aspiration of significantly smaller fragments than longitudinal US and high vacuum settings during phacoemulsification. This is important in the intraoperative setting where larger fragments are more likely to lead to occlusion with potential for wound burns and surge. Transverse US can be combined with low vacuum settings to allow for much more stable anterior chamber fluidics.
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