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.
Contingency
Plan
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.