24

Lens Quake Phaco

Jack A Singer

Introduction

Lens quake phaco utilizes a hexagonal or diamond-shaped phaco tip to induce a disturbance in the lens nucleus, which simulates a miniature earthquake called a lens quake. The lens quake can be propagated along nuclear fault lines that run from the y- sutures to the equator and posterior pole. Using this method, the nucleus can be cracked from the center to the periphery without the need to place a sharp chopping instrument near the equator of the lens.

TIPS

The Lens quake phaco cobra tip (Figs 24.1A to C) from surgical design has a modified hexagon shape, a 15-degree curve, a 15-degree bevel that faces up when the curve is pointing up, and a circular lumen (Fig. 24.2), which promotes occlusion. The hexagonal shape permits lens quake propagation without tilting or zonular stress, which can occur with a round phaco tip. Also, the additional mass in the head of the cobra tip focuses additional cavitation inside the tip that enhances the efficiency of both lens quake inducement and segment removal.

Mastel Precision Instruments can supply non-cobra hexagonal Lens quake phaco tips for various other phaco systems. However, the additional mass in the head of the cobra tip focuses additional cavitation inside the tip that enhances the efficiency of both lens quake inducement and segment removal.

The author has used the Storz Osher nucleus manipulator for years and finds it ideal for lens quake phaco. It has two blunt finger-like projections that can be used for a variety of maneuvers. However, any nucleus manipulator that provides a firm grasp on nuclear material will work. A sharp chopper is unnecessary but can be used for lens quake phaco.

FIGURES 24.1 A TO C Hard-Rock Lens quake tip, with double 15-degree bevel for enhanced cutting and gripping

Phacoemulsification 360

FIGURE 24.2 Singen Lens quake tip with external hexagonal shape and circular internal lumen

Mechanism

We are all familiar with the annular structure of a tree. Similarly, the human lens is composed of annular concentric layers of radial fibers, beginning with the fetal nucleus, which becomes the hard adult nucleus through the addition of radial fibers throughout life (Figs 24.3A to C). These radial lens fibers join at the anterior and posterior y-sutures, which are encountered at times during central sculpting or during slit lamp examination of the lens. These are natural fault lines in the lens corresponding to these radial layers that are added through life. So, the lens not only has concentric layers but also has radial cleavage planes, which can be used for lens quake propagation.

When the phaco tip is advanced into the center of the nucleus and is occluded, vacuum energy and the wedge shape of the tip induces stress and strain near the y-sutures resulting in lens quake induction.

Techniques

In order to perform lens quake phaco, set your machine at a low flow rate of 3 to 5 cc/minute and a vacuum limit of 200 mmHg. Rotate the infusion sleeve 90 degrees so that the infusion stream is

FIGURES 24.3A TO C Mechanism of lens quake phaco

Phacoemulsification 362

FIGURES 24.4A TO C Hard-rock lens quake tip, with double 15-degree bevel for enhanced cutting and gripping

directed sideways when the phaco tip bevel is sideways. Clean up the anterior cortex and epinucleus inside the anterior capsulotomy for better visibility.

Next, orient the phaco tip bevel sideways so that the points of its hexagon are facing up and down, and the flat areas are facing sideways. Then, place the tip just inside the capsulorhexis at an angle pointing towards the center of the nucleus and place your nucleus manipulator in a stand-by position about 90 degrees away (Figs 24.4A to C). Using U/ S, drive the tip into the nucleus at a slow pace, switching between foot switch positions 3 and 2 as needed but do not go into position 1. When the top of the hexagon is

completely buried, begin leveling off the entry angle and continue advancing until the port is at the central nucleus with its bottom point at half nuclear depth. Mute the U/S and stay in foot switch position 2 holding the phaco tip still while the vacuum builds.

One of the most common causes of lens quake inducement failure is releasing the vacuum after the tip is placed into position and occluded.

After the phaco tip is driven into position and vacuum is allowed to build, place the second instrument into the nucleus directly above the stationary phaco tip until it touches the tip. Now, hold it there for a second or two until you see a crack forming just in front of the tip. This is the induced lens quake!

A simple manipulation will propagate the lens quake to the posterior pole and to the equators. We need to mimic a strike-slip fault in which blocks of earth slide past each other horizontally during an earthquake in order to induce lens quake propagation in the lens nucleus.

Slide the nucleus manipulator downward along the side of the stationary phaco tip and then move the phaco tip slightly forward and the nucleus manipulator slightly backward to produce a strike-slip fault, sliding the nuclear segments past each other horizontally.

This will induce complete propagation of the lens quake to the posterior pole and to the equators. While sliding the nuclear segments past each other horizontally, the lens and phaco tip can be rotated into position for the subsequent lens quakes, which is performed in a similar fashion on each heminucleus.

Lens quake phaco can be used on any nucleus that is sufficiently firm enough to crack, and should not be used on soft lenses due to the risk of aspirating lens material distal to the tip down to and including the posterior capsule.

Summary

In summary, lens quake phaco is a significant advance in phaco efficiency and safety, which utilizes a hexagon-shaped phaco tip and high vacuum to induce a lens quake near the y-sutures. A simple manipulation that mimics earthquake movements will propagate the lens quake to the posterior pole and to the equators.