Torsional ultrasound

May 1, 2006

Wound distortion by manipulation of two rigid cannulas during bimanual phaco through tight corneal incisions has been shown to be significant.

Here, Tjia provides an update on this new technique and the technologies that go hand in hand with it. By allowing us to tap into his knowledge and practical experience, he invites you to consider rethinking your surgical approach to cataract surgery.

Recently, torsional ultrasound phacoemulsification with the OZil™ handpiece has been introduced to the market as a new energy delivery modality to the Infiniti Vision System (Alcon, Fort Worth, USA). The oscillatory motion at the hub and shaft of the phaco tip is similar to that of the NeoSoniX™, but torsional has approximately half of the oscillation amplitude when compared with the NeoSoniX™ handpiece and the frequency is ultrasonic (32.000 Hz for OZil™ versus 100 Hz for NeoSoniX™).

Why do we need torsional ultrasound?

Torsional ultrasound addresses the two main drawbacks of traditional ultrasound. Firstly the traditional method is associated with excessive heat production at the incision site, which carries with it the potential danger for wound burn. Torsional ultrasound, on the other hand, generates two to three times less heat at the same power level. Secondly, the repulsion by the forward movement of the phaco tip results in chatter and a decreased efficiency. Torsional ultrasound has a greatly reduced repulsion and nuclear quadrants appear to be 'glued' at the tip.

The side-to-side movement of torsional ultrasound is 100% effective, whilst traditional ultrasound is only 50% effective, because the backward stroke does not come into contact with lens material. Sculpting through very hard nuclei is markedly easier, faster and more efficient with torsional ultrasound. With a greatly reduced repulsion, fluid turbulence in the anterior chamber is significantly reduced. Protective viscoelastic substances are better retained and corneal endothelial cells are better protected.

Fluid dynamic settings can be adjusted to much lower levels, resulting in an increased safety margin level. The efficiency of torsional ultrasound with low fluid dynamic settings is still extremely good.

Catering for the complicated case

This technique is also beneficial in the treatment of the most challenging of cases, such as:
– Zonular weakness
– Posterior polar cataracts
– Posterior capsular rupture
– Corneal endothelial dystrophy
– Floppy iris syndrome
– Posterior vitreous pressure

Low fluid dynamics settings are mandatory for a successful outcome in these cases. Whilst a low aspiration flow of 20 ml/min or less and a low bottle height help to prevent vitreous or iris being caught by the phaco tip, a low vacuum setting of 250 mmHg with the low compliant FMS cassette of the Infiniti machine produces no significant surge flow on occlusion break.

These low parameters, however, will not provide sufficient holding power with traditional longitudinal ultrasound during quadrant removal. The settings would lead to repulsion and scattering of nuclear pieces in the anterior chamber; hence, a great deal of manipulation would be required, though this carries with it an increased risk of complications.