This article is from March 2005 and may contain outdated material.
The brunescent nucleus challenges every phaco surgeon. Successful management requires that surgeons first understand and then employ specific strategies to overcome these intimidating obstacles.
Multiple Challenges of the 4+ Nucleus
Virtually every step of cataract surgery is more difficult in the setting of a mature, brunescent nucleus. The lack of a good red reflex certainly impedes the capsulorhexis step. However, without a red reflex, even a successfully completed capsulorhexis remains difficult to see during nuclear emulsification, which increases the risk of disrupting the edge with the chopper or phaco tip.
Other challenges to consider:
Capsular-lenticular block. During hydrodissection, an elevating brunescent nucleus is more likely to seal the capsulorhexis from below. Because it cannot escape the capsular bag, any additional fluid injected at this point will distend and eventually rupture the posterior capsule. The surgeon may not recognize a problem until the nucleus suddenly descends through the torn posterior capsule following the first sculpting stroke.
Incisional burns. If the overlying viscoelastic is not initially aspirated away, 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 stromal whitening and heat shrinkage can result from the higher levels of continuous phaco power typically employed for 4+ nuclei. It is the combination of longer phaco time and greater phaco needle stroke length that generates excessive heat compared to routine cases.
Endothelial cell loss. As evidenced by increased corneal edema on the first postoperative day, endothelial cell loss is much greater with 4+ nuclei. 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, there is poor followability and much greater chatter occurring at the phaco tip. This produces excessive particulate turbulence within the anterior chamber, which traumatizes the endothelium.
Posterior capsule rupture. There is proportionally more endonucleus and less epinucleus with brunescent cataracts, which can double the volume of solid material requiring emulsification. This also forces the phaco tip to work much closer to the peripheral and posterior capsule, particularly when sculpting a deep central trough. Unlike a softer nucleus, which absorbs instrument pressure like a pillow, a dense nucleus is as rigid as a wooden board. As such, it more directly transmits all of the instrumentation forces directly to the posterior or peripheral capsule.
Weak zonules. Ultra-brunescent nuclei are often associated with weak zonules. I have often wondered if this comorbidity is 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 there is little or no epinucleus 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 more 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.
10 Pearls and Strategies for the 4+ Nucleus
1. Capsular dye. Now that trypan blue 0.06 percent (VisionBlue) is approved for capsular staining in the United States, this should be the agent of choice for the mature nuclear cataract. Indocyanine green produces a weaker staining that adequately contrasts the capsule against white cortex, but not against a dark brown nucleus. Trypan blue provides a more intense and persistent coloration, which enhances visibility of the capsulorhexis edge during 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 capsulorhexis. One must avoid the temptation to continue injecting until the migrating posterior fluid wave completely crosses behind the nucleus. Instead, tap the center of the elevated nucleus 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. While advantageous under ordinary circumstances, these phacodynamic parameters become particularly important in managing the dense cataract. Burst mode and high vacuum combine to provide a maximal grip. Inadequate holding power makes it more likely that the vertical chopper will dislodge pieces from the phaco tip, and makes it more difficult to elevate large fragments out of the bag. Particularly with a brunescent lens, continuous mode cavitation cores out the firm material surrounding the phaco tip. This facilitates sculpting but prevents total tip occlusion by eroding the seal. Because high vacuum levels require a well-occluded phaco tip, burst mode is particularly advantageous for the dense lens.
4. Sculpt a central pit prior to diagonal phaco chop. By reducing phaco power and time as well as stress on the zonules, chopping is a superior phaco technique for the brunescent nucleus. In the absence of an epinuclear shell, horizontal phaco chop is contraindicated, and vertical chop also is better able to transect the leathery posterior plate. Sculpting a deep pit in the central anterior nucleus allows the surgeon to penetrate the bulky nucleus more deeply and peripherally with the phaco tip than if the nucleus was impaled without this step. Louis D. Nichamin, MD, has named this strategy “crater-quick chop.” To better impale the nucleus, one should maximally retract the irrigation sleeve and bury the tip to the hilt. A very sharp vertical chopper will best incise into the dense nuclear face without displacing it. I like to first place the chopper peripherally beneath the blue-stained anterior capsule, and then chop in a diagonal direction toward the buried phaco tip. This adds a slight horizontal vector force that compresses the fragment against the phaco tip during the vertical chop.
5. Subchop brunescent fragments. Regardless of whether the initial nuclear fragmentation is accomplished by divide-and-conquer, stop-and-chop or pure chopping methods, the resulting fragments are much larger and denser than those encountered with typical nuclei. One can employ horizontal chopping to subdivide these large fragments into smaller, bite-sized pieces. 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 lessened.
6. Hyperpulse technology. Originally introduced as WhiteStar technology with the AMO Sovereign, hyperpulse power modulation is now available from a number of companies. The widely recognized advantages of hyperpulse are a dramatic reduction in heat and energy production, and improved followability because of decreased chatter of fragments at the phaco tip. The combination of subchopping and hyperpulse mode can significantly reduce particle turbulence within the anterior chamber, which I believe is the most important factor in decreasing endothelial cell loss with brunescent cataracts.
7. Maximally retentive viscoelastics. With the prolonged operative times associated with brunescent nuclei, viscoelastic washout is a far greater problem than with most typical cases. Dispersive viscoelastics, such as Viscoat and Vitrax, or the viscoadaptive Healon 5, if utilized properly, are able to coat and protect the endothelium for longer periods than their cohesive counterparts. As all viscoelastics eventually wash away, consider stopping to replenish the protective endothelial layer midway through the nuclear removal step.
8. “Viscoelastic vault.” Roger F. Steinert, MD, has coined this term to describe a technique for deploying a dispersive viscoelastic as an artificial epinucleus for the brunescent nucleus. In cases where the epinucleus is scant or absent, one should temporarily stop phaco before removing the last remaining fragments. A generous amount of dispersive viscoelastic is injected in front of and behind the fragments in order to partially fill the capsular bag. Because dispersive viscoelastics better resist aspiration by the phaco tip, they will better restrain the lax and exposed posterior capsule from trampolining toward the phaco tip. This viscoelastic layer also cushions the capsule from being poked by 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. This $15 disposable, flow-restricting device from Staar Surgical decreases postocclusion surge and is adaptable to the aspiration tubing of any phaco machine. While minor degrees of surge are generally not problematic with routine cases, they can pose significant risk if the capsule is lax, or if there is no epinucleus to restrain the exposed posterior capsule. For challenging cases, the Cruise Control device greatly reduces the risk of postocclusion surge, without having to sacrifice the advantages of high vacuum.
10. Capsular tension rings and capsule retractors. Capsule retractors can stabilize a wobbly nucleus with weak zonules during phaco. Their insertion is again dependent upon effective staining and capsulorhexis visualization. I prefer to use retractors such as the Mackool Cataract Support System instead of capsular tension rings (CTRs) to stabilize the lens during phaco. CTRs impede cortical cleanup, and they don’t provide the anterior-posterior support or torsional stability for the bag that the capsule retractors do. However, CTRs are certainly invaluable for stabilizing a moderately weakened capsular bag for IOL implantation and longer-term centration.
Despite these helpful devices and strategies, individual surgeons must assess their personal limit in terms of how brunescent a lens they can safely emulsify. It is far better to accept the larger incision of a standard extracapsular cataract extraction than to have a dropped nucleus or decompensated cornea.
Even when proceeding with phaco, the surgeon must have a contingency plan for unexpected problems such as weak zonules or poor visibility. For the most challenging cases, consider administering a regional anesthetic block—and have a contingency kit of instruments needed to convert to a standard ECCE readily available.
Dr. Chang is clinical professor of ophthalmology at the University of California, San Francisco, and in private practice in Los Altos, Calif. He is a consultant for AMO but has no financial interest in any product mentioned in this article.