6.7Biaxial Microincision Cataract Surgery: Techniques and Sample Surgical Parameters

Mark Packer, I. Howard Fine,

and Richard S. Hoffman

Core Messages

ßEach step in cataract surgery builds on the preceding step.

ßThe clear corneal incision should be sized correctly for instrumentation.

ßThe capsulorhexis should be centered, round and slightly smaller than the optic of the

intraocular lens to be implanted.

ßEndo lenticular nucleofractis techniques protect both the capsule and the cornea.

ßSeparation of infusion and aspiration facilitates the removal of the lens material and has

advantages in difficult and complicated cases.

To begin the bimanual vertical chop technique for a moderate 2+ nuclear sclerotic cataract in a patient with asteroid hyalosis, a paracentesis type of incision is made to the left, constructed with a trapezoidal diamond blade. This incision measures 1.2 mm internally, which is precisely the size required for 20 gauge instrumentation such as the one used for bimanual microincision phacoemulsification. The anterior chamber is filled with a dispersive viscoelastic which remain in the eye during the high flow, high vacuum chop technique. The capsulorhexis is initiated centrally with a pinch and pulled with a counterclockwise motion.

The microincision forceps (MST, Redmond, WA) allow excellent control of the capsulorhexis and in addition, the small incisions also facilitate the control of the capsulorhexis because the viscoelastic does not exit the eye. This means that the chamber remains stable. Pressure in the anterior chamber on the anterior lens capsule helps to control the capsulorhexis. It is well

known that the loss of chamber stability will cause the capsulorhexis to run out towards the periphery. One of the advantages of microincision technique is that the chamber remains stable during the completion of the capsulorhexis. This allows better control of the size, the diameter, and the position of our capsulorhexis. Newer technology IOLs, which prevent posterior capsular opacification with a square edge or facilitate accommodation with axial movement, are dependent upon accurate sizing and position of the capsulorhexis. A capsulorhexis, which is smaller in diameter than the lens optic, such as 4mm in the case of a 4.5mm accommodative IOL or 5mm in the case of a standard 6mm multifocal or single vision lens, is needed.

Cortical cleaving hydrodissection is preformed by tenting up the anterior capsule and injecting the balanced salt solution under the rim of the capsule, and watching the fluid wave advance completely across the posterior capsule. The fluid wave is trapped temporarily between the lens and the posterior capsule, causing the lens to prolapse anteriorly. Repositioning the lens by pushing it posteriorly with the cannula in the center decompresses the fluid that is trapped, forcing it around the equator and lysing the corticocapsular connections. The lens is then rotated to make sure that it is free. Hydrodelineation can be carried out by embedding the tip of the cannula in the center of the lens and advancing it until the resistance of the endonucleus is encountered. A slight to and fro motion of the cannula will create a small space into which the balanced salt solution is injected. The fluid flows between the endonucleus and the epinucleus, forming the golden ring as seen in Fig. 6.55.

M. Packer ( )

Oregon Health & Science University, Drs. Fine, Hoffman and Packer, 1550 Oak Street, Suite 5, Eugene, OR 97401, USA e-mail: mpacker@finemind.com

Fig. 6.55 The 20 gauge phaco needle is embedded in the endonucleus as the irrigating chopper is prepared to incise and split the lens

The phaco needle is now embedded proximally with high vacuum and 40% power (Table 6.4). The vertical chopper, which will be used to split the nucleus into two, is held in the left hand. As vacuum builds to occlusion,theCASEsoftware(SovereignPhacoemulsification System; Advanced Medical Optics, Santa Ana, CA) enables a rapid rise time and the endonucleus is firmly grasped on the phaco needle. At the point where the

occlusion is reached, the aspiration flow rate drops to zero. This is followed by the movement into foot position two so that a high vacuum is maintained and the power goes to zero (Fig. 6.55). The blade of the irrigating vertical chopper is brought down just distal to the phaco tip by slightly lifting up with the phaco needle. As a full thickness cleavage plane develops, which divides the nucleus into two, the surgeons separate

Fig. 6.56 The nucleus is divided to the right and the left. In this case, a posterior shelf has developed; it is particularly important to separate the instruments fully to insure a complete chop in this situation

Fig. 6.57 After the second chop has divided one of the heminuclei, the first quadrant is mobilized

their hands to insure a complete chop (Fig. 6.56). In this case, the heminucleus to the left is larger and is therefore addressed first.

The lens can then be rotated with the irrigating chopper so that the first heminucleus can be chopped and consumed. If there is a disparity in size, the larger half is moved distally. The phaco needle is now embedded to the right using high vacuum and low levels of power. A quadrant size piece is chopped off and consumed (Fig. 6.57). The remaining quadrant of the first heminucleus is then impaled with the phaco tip and aspirated (Fig. 6.58). Total Effective Phaco Time (EPT) to this point is less than half a second. EPT is a useful parameter for surgeons to follow. It can not be compared across different machines made by different manufactures, however, when using one machine, it can be compared from one case to another case as a sign of surgical efficiency. EPT is the amount of time for which ultrasound would have been turned on if it had been running on 100% continuous power. This means that about half a second has been used, out of the maximum ultrasound power that the machine can produce, to remove half the nucleus. Continuous power can produce thermal energy, but using WhiteStar Technology, or micropulsed phaco, avoids any risk of wound burn. Despite the tightness of the incisions, minimal incisional outflow is present and has a cooling effect around the phaco needle.

To address the second half of the nucleus, it is first rotated with the irrigating chopper so that it is in the distal capsule. The phaco needle is embedded in the smaller heminucleus and it is subdivided with the irrigating chopper, again using high vacuum and low levels of power (Fig. 6.59). As the final quadrant is grasped and pulled centrally for aspiration, the sharp

Fig. 6.60 As the final quadrant is aspirated, the chopper is turned sideways and the flow of the irrigation fluid is directed posteriorly to keep the posterior capsule at a safe distance

Fig. 6.62 The capsule is clean; asteroid hyalosis is visible in the vitreous cavity

blade of the irrigating chopper is turned sideways as a safety precaution (Fig. 6.60).

When addressing the epinucleus, the settings are reduced, the vacuum and flow rate are turned down and rim of the epinucleus is trimmed, disallowing the epinucleus from flipping into the phaco needle with the stream of irrigation fluid or the irrigating chopper itself. The advantage of the trimming procedure lies in the aspiration of cortical material from behind the epinuclear shell. In most cases this step eliminates the need for I/A prior to IOL insertion. Once three quadrants of the epinuclear shell have been rotated and trimmed, the final quadrant is used to flip the epinuclear bowl into the phaco needle (Fig. 6.61). Following aspiration of the epinucleus, the capsule is entirely free

of cortex (Fig. 6.62). The asteroid hyalosis in the vitreous cavity is obvious.

The incision for the lens is constructed with the differentially beveled 3D Blade (Rhein Medical, Tampa, FL) which reproducibly creates a 2.5mm incision at the shoulders. The relatively larger incision (approximately 2.5mm) which is constructed for IOL insertion seals quite well because it has been only minimally disturbed. Stromal hydration is performed at all the incisions and Seidel test is performed at the conclusion of the case. Careful attention to sealing clear corneal incisions may be critical for the prevention of post operative infection.

Bimanual phaco with a vertical chop technique allows efficient lens extraction with rapid visual rehabilitation. This case demonstrates some of the tangible benefits of separating inflow from outflow such as enhanced cortical cleaving hydrodissection, use of irrigation fluid as an instrument to mobilize material, and reduced EPT.

Fig. 6.61 The epinucleus is grasped with the phaco needle at reduced power, flow and vacuum and flipped

Take Home Pearls

ßReduction of ultrasound energy improves the rapidity of postoperative visual rehabilitation.

ßThe stream of irrigation fluid from the irrigating chopper can be used as a gentle instrument

in the eye to move material, keep the posterior capsule on stretch, and maintain the volume of the anterior chamber.

ßSpecific instrumentation for micro incision surgery has allowed the development of improved

surgical technique.