After Chopping or Cracking a 4+ Nucleus, a Leathery Posterior Plate Still Connects the Fragments Centrally. How Should I Proceed?
The most challenging aspect of phacoemulsification of the 4+ nucleus is the resistance of the posterior nucleus to a clean cleavage of the cracked segments. This is true whether you are performing divide and conquer, horizontal chop, or vertical chop. To deal with the phenomenon, you have to understand its origin. By the time a cataract reaches the 4+ stage, the expansion of the nuclear hardening has incorporated the epinucleus. The posterior epinucleus is no longer a malleable separate cushion layer. Instead, it is firmer and adherent to the endonucleus. When you try to split the endonucleus, the posterior layer has bridging fibers that we have come to call “leathery.” Another analogy is the “greenstick fracture” phenomenon that occurs when you try to break a fresh tree branch. The fibers do not break cleanly, but rather flex and keep the 2 ends of the branch connected.
The net result is that you can separate the nuclear fragments you create, but when you try to engage and remove the fragment with vacuum, it will only come partially and then fall back. The phenomenon of the bridging posterior strands is maximal at the center of the posterior nucleus, which means that the apex of the nuclear fragment not only remains adherent, but also cannot be tilted to be engaged by the phaco tip. The result is a stranded posterior plate (Figure 26-1A).
Figure 26-1. (A) Strands of the leathery posterior nucleus are maximal at the apex. (B) The surgeon passes a chopping-type instrument behind the nuclear fragment parallel to the posterior capsule. (C) The chopping instrument snaps the bridging fibers that interfere with delivering and emulsifying the nuclear fragment. (Reprinted from Cataract Surgery, 2nd ed, Steinert RF, The dense cataract, © 2002, with permission from Elsevier.)
In theory, you might think that flipping the nucleus, so that the posterior portion is now anterior, is the answer. However, even for advocates of nuclear flipping, a 4+ nucleus is the most dangerous time to perform this maneuver. The nucleus is very large, and the capsule frequently is more fragile than usual because it is under tension. A very large capsulorrhexis would be needed to flip the nucleus, and even if this were acceptable to you with regard to later intraocular lens (IOL) implantation, phaco of a large hard nucleus in the anterior chamber will result in excessive endothelial damage.
In addressing these 4+ dense nuclei, begin with using trypan blue (VisionBlue, Dutch Ophthalmic Research Corporation [DORC], Rotterdam, Holland). This not only aids in performing an optimal capsulorrhexis, but also aids in keeping the edge of the anterior capsule visible during the case to avoid inadvertent damage to the rhexis and resultant capsular tear. Also, use a retentive viscoelastic liberally in the course of the surgery. You will be using a lot of phaco power and have prolonged phaco time, so protecting the endothelium is critical.
I suggest these specific steps, which have worked for me, to deal with the leathery posterior nucleus1:
* Bowl out the center of the nucleus. This spares the endothelium, and the large firm peripheral nucleus still provides plenty of material for the phaco tip to grab onto and hold.
* Use a chopping or finger-type instrument to break the leathery fibers. While I prefer the hook shape of my claw-shaped chopper (Rhein Medical, Tampa, Fla), there are many suitable choppers or nuclear-manipulating instruments. The maneuver is to rotate the instrument so that it is parallel to the posterior capsule. While the nuclear fragment is held by vacuum of the phaco tip and drawn partially toward the center, you pass the instrument posteriorly under the fragment, from the periphery toward the center, snapping the posterior strands (Figures 26-1B and 26-1C).
* As soon as you have any area with a visible red reflex, use this space to inject a dispersive viscoelastic behind the nucleus. This serves 3 purposes. First, it creates an artificial epinucleus to protect the posterior capsule. Second, it elevates the nucleus a little, making it easier to pass the instrument posterior to the nuclear fragments in order to snap the fiber strands. Third, it will stabilize the nuclear fragments, making it easier to position them optimally, avoiding tumbling. Do not forget to add some more viscoelastic anteriorly to protect the endothelium!
1. Steinert RF. The dense cataract. In: Steinert RF, ed. Cataract Surgery. 2nd ed. Philadelphia: WB Saunders; 2002.