David F. Chang, MD
A brunescent nucleus challenges every phacoemulsification surgeon. Successful management of a rock-hard cataract requires that each surgeon first understand and then use specific strategies to overcome these intimidating obstacles.
The Challenges of a 4+ Nucleus
Virtually every step of cataract surgery becomes difficult in the setting of a mature, brunescent nucleus.1 The lack of a good red reflex impedes the capsulorrhexis step. However, without a red reflex, even a successfully completed capsulorrhexis remains difficult to see during nuclear emulsification, which increases the risk of disrupting the edge with the chopper or phaco tip.
During hydrodissection, an elevating brunescent nucleus is likely to seal the capsulorrhexis from below, causing a capsular-lenticular block. Because it cannot escape the capsular bag, any additional fluid injected at this point will distend and eventually rupture the posterior capsule. Surgeons may not recognize a complication until the nucleus suddenly descends through the torn posterior capsule following the first sculpting phaco stroke.
Incisional burns are also likely to occur with brunescent nuclei. If enough overlying viscoelastic is not initially aspirated, it can mix together with the brunescent nuclear emulsate to clog the phaco tip. Absent any exiting fluid, there can be no gravity-fed irrigation inflow, and a burn immediately develops as ultrasound commences. Particularly with a clear corneal incision, moderate whitening and heat shrinkage can result from the higher levels of continuous phaco power typically used for 4+ nuclei. The combination of longer phaco time and greater phaco needle stroke length generates excessive heat compared to cases that were not rock hard.
As evidenced by increased corneal edema on the first postoperative day, endothelial cell loss is greater with 4+ nuclei than with cases without a rock-hard nucleus. The increased density and volume of nuclear material necessitates greater ultrasound power and time. Because of the increased stroke length, and because rigid nuclear fragments do not mold as well to the phaco tip, poor followability and greater chatter occur at the phaco tip. This produces excessive particulate turbulence within the anterior chamber, which traumatizes the endothelium.
Posterior capsule rupture is likely with 4+ nuclei for several reasons. Proportionally, more endonucleus and less epinucleus exist with brunescent cataracts, which can double the volume of solid material requiring emulsification. This also forces the phaco tip to work closer to the peripheral and posterior capsule, particularly when sculpting a deep central trough. Unlike a softer nucleus that absorbs instrument pressure like a pillow, a dense nucleus is as rigid as a wooden board. As such, the dense nucleus transmits all of the instrumentation forces directly to the posterior or peripheral capsule.
Ultra-brunescent nuclei are often associated with weak zonules. The author has often wondered if this is comorbidity associated with advanced age, or whether the greater mass of the lens imparts more force against the zonules with each ocular saccade, producing a cumulative zonular weakening over time. Weak zonules are particularly problematic if little or no epinucleus is present. Normally, the soft epinuclear shell restrains a lax posterior capsule from trampolining toward the phaco tip as the last nuclear fragment is removed. Without the epinucleus, the exposed posterior capsule is likely to billow toward the phaco tip with even the slightest degree of postocclusion surge. The sharp edges of the brunescent fragments and the greater capsular laxity caused by weak zonules further increase the risk of capsular puncture. If one reacts defensively by emulsifying the last fragment closer to the cornea, then one further heightens the risk of endothelial cell loss.
Ten Pearls and Strategies for the 4+ Nucleus
1. Capsular dye
Now that trypan blue has been approved by the Federal Drug Administration (FDA) for capsular staining, it should be the agent of choice for removing a mature nuclear cataract (Slide 1).2 Indocyanine green produces a weak coloration that makes the capsule visible against white cortex, but which is not intense enough to contrast the anterior capsule from a dark brown nucleus. Trypan blue produces an intense and persistent coloration, which enhances visibility of the capsulorrhexis edge during nuclear emulsification.
2. Avoid capsular block during hydrodissection
To avoid capsular-lenticular block, one should terminate hydrodissection as soon as the solid nucleus elevates against the capsulorrhexis. One must avoid the temptation to continue injecting until the migrating fluid wave completely crosses behind the nucleus. Instead, the center of the elevated nucleus is tapped to dislodge it posteriorly before resuming hydrodissection from the opposite quadrant. A right-angled hydrodissection cannula facilitates the latter step.
3. High vacuum and burst mode
Although advantageous under ordinary circumstances, phacodynamic parameters become particularly important in managing a dense cataract. Burst mode and high vacuum combine to provide a maximum grip (Slide 2).3 Inadequate holding power means that the vertical chopper will
dislodge pieces from the phaco tip, or that a surgeon may be unable to elevate fragments out of the bag without “dropping” them. Particularly with a brunescent lens, continuous mode cavitation cores out the firm material surrounding the phaco tip. This facilitates sculpting but prevents tip occlusion by eroding the seal. Because high vacuum levels cannot be reached without a well-occluded phaco tip, burst mode is particularly advantageous for a dense lens.
4. Sculpt a central pit prior to diagonal phaco chop
5. Subchop the brunescent fragments
Regardless of whether the initial nuclear fragmentation is accomplished by divide-and-conquer, stop-and-chop, or pure chopping, the resulting fragments are larger and more dense than those encountered with typical nuclei. One can use horizontal chopping to subchop these large fragments into smaller pieces (Slide 3C).4 This reduces the tendency for oversized fragments to deflect away from the vibrating phaco tip. By reducing particle chatter and turbulence within the anterior chamber, endothelial cell loss can be further minimized.
6. Hyperpulse technology
First introduced as WhiteStar technology with the Advanced Medical Optics (AMO) Sovereign in 2001, hyperpulse is now available with the Infiniti (Alcon, Fort Worth, TX), Legacy (Alcon), and Millennium (Bausch & Lomb, Rochester, NY) machines, as well. The widely recognized advantages are a dramatic reduction in heat and energy production, and improved followability due to reduced chatter of fragments at the phaco tip.3 Both of these benefits contribute to decreasing endothelial cell loss. By combining sub-chopping with hyperpulse mode, the author believes that reducing chatter and particle turbulence within the anterior chamber is the most important factor in decreasing corneal edema.
7. Maximally retentive ophthalmic viscodevice (OVD)
With the prolonged operative times associated with brunescent nuclei, OVD washout is a more significant complication than with most typical cases. Dispersive [Viscoat (Alcon) and Vitrax (AMO)] or viscoadaptive
8. Viscoelastic vault
Steinert recently coined the term viscoelastic vault to describe a technique for using a dispersive OVD, such as Viscoat or Vitrax, as an artificial epinucleus.1 In patients where the epinucleus is scant or absent, one should temporarily stop phaco before removing the last remaining fragments. A generous amount of dispersive OVD is injected in front of and behind the fragments to partially fill the capsular bag (Slide 3B). Because a dispersive OVD better resists aspiration by the phaco tip, it will restrain the lax and exposed posterior capsule from trampolining toward the phaco tip. This OVD layer also cushions the capsule from being poked by the sharper contours of the brunescent fragments. With less concern about proximity to the posterior capsule, the surgeon is less likely to phaco the last fragment too close to the endothelium.
9. Cruise Control
Cruise Control, the disposable $15 device from Staar Surgical (Monrovia, CA) is adaptable to the aspiration tubing of any phaco machine,1 and serves as a flow restrictor to decrease postocclusion surge. While minor degrees of postocclusion surge are not generally problematic with routine cases, they can pose a major danger if the capsule is lax, or if there is no epinucleus to restrain the exposed posterior capsule. Cruise Control can give the surgeon a greater safety margin with respect to postocclusion surge, without sacrificing the advantages of high vacuum.
10. Capsular tension rings (CTRs) and capsule retractors
A capsule retractor can stabilize a wobbly nucleus with weak zonules during phaco.1 Insertion of a capsule retractor is dependent upon effective staining and capsulorrhexis visualization. The author prefers to use retractors, such as the Mackool Cataract Support System (Impex, FCI, Duckworth & Kent, St. Louis, Mo.), instead of CTRs to stabilize the lens during phaco. CTRs impede cortical cleanup and do not provide the anteroposterior support or torsional stability of the capsule retractors. However, they are invaluable for stabilizing a moderately weakened capsular bag for IOL implantation and long-term centration.
Contingency Plan
Despite these helpful devices and strategies, all surgeons must assess their personal limit in terms of how brunescent a lens they can safely emulsify. It is better to accept the larger incision of a standard extracapsular cataract extraction (ECCE) method than to have a dropped nucleus or decompensated cornea. Even when proceeding with phaco, a surgeon must have a contingency plan for unexpected complications such as weak zonules or poor visibility. For the most challenging patients, consider administering a regional anesthetic block and having a contingency kit of instruments needed to convert to a standard ECCE readily available.5
References
- Chang DF. Phaco strategies for complicated cataracts. In: Phaco Chop: Mastering Techniques, Optimizing Technology, and Avoiding Complications. 2004.
- Pandey SK, Werner L, Vroman DT, Apple DJ. Dye-enhanced anterior capsulorrhexis: Surgical techniques, guidelines, and recommendations for surgeons. Comp Ophthalmol Update. 2003; 4:179.
- Chang DF. Optimizing machine settings for chopping techniques. In: Phaco Chop: Mastering Techniques, Optimizing Technology, and Avoiding Complications. 2004.
- Chang DF. Phaco chop techniques: Comparing and integrating horizontal and vertical chopping. In: Phaco Chop: Mastering Techniques, Optimizing Technology, and Avoiding Complications. 2004.
- Chang DF. Strategies for managing posterior capsule rupture. In: Phaco Chop: Mastering Techniques, Optimizing Technology, and Avoiding Complications. 2004.