1.
Viscoat posterior-associated levitation to
bring the nucleus up and away from the posterior segment.
2.
“Viscoat trap” to lift residual material as
anteriorly as possible and to keep it there.
3.
Vitrectomy through the pars plana with a separate side
infusion, staying in the posterior chamber to avoid
evacuating the Viscoat trap.
4.
Bimanual irrigation and aspiration to remove
remaining cortex through tighter clear-corneal stab
incisions.
“Because of our relative unfamiliarity with pars
plana sclerotomy, we are underutilizing an important option,”
Dr. Chang said. “A pars plana sclerotomy gives us the proper
angle to get behind the nucleus for levitation and allows us
to prevent vitreous loss through the phaco wound during the
vitrectomy. This is a vastly superior approach.”
Stop and
Stay
-
First, surgeons must know the subtle warning signs
of capsular break:
-
Any change in the fluidic environment or increase
in space.
-
A deepening of the posterior chamber, then of the
anterior chamber.
-
Loss of followability or holdability.
-
Loss of ability to rotate the lens.
-
Loss of rebound elasticity in the capsular
zonular structure.
As
soon as one suspects a breach in the capsular zonular
integrity, stop working, Dr. Nichamin advised, but do not exit
the eye. Instead, place a viscoelastic through the side-port
incision and fill the anterior chamber. This permits removal
of the phaco or irrigation and aspiration instrument without
triggering sudden hypotony. The viscoelastic also tamponades
the anterior hyaloid face and stabilizes any remaining lens
material.
Dr.
Nichamin places viscoelastic above the remaining lens material
to protect the cornea and below it to support the lens
material and to tamponade the vitreous face. A low-viscosity,
less-cohesive, highly dispersive viscoelastic such as Viscoat
works well in this situation, he said. Alternatively, the
viscoadaptive Healon5 may be useful.
Up and Away
As a means of preventing a dropped nucleus,
Charles D. Kelman, MD, first described the use of
posterior-assisted levitation—that is, inserting a metal
spatula through a pars plana sclerotomy to prop up the nucleus
from below.
“Compared with the phaco incision, the pars plana
sclerotomy gives us a much better angle for getting a
supporting instrument tip underneath the nucleus,” said Dr.
Chang.
Subsequently, Richard B. Packard, MD, proposed
using Viscoat instead of a metal spatula to support the
nucleus. In this variation, single or multiple nuclear pieces
can be levitated into the anterior chamber through a
combination of the Viscoat injection and manipulation of the
cannula tip, Dr. Chang said.
Again, the pars plana approach is advantageous.
“With a regular cataract incision, you are coming from above
and trying to inject viscoelastic below the nucleus, which is
mobile and moving away from you,” Dr. Chang said. “A small
pupil or capsulorhexis further complicates this.”
Addressing Residual
Nucleus
The
next step is to assess the anatomy and choose a strategy for
removing the remaining nucleus.
If
conversion to a standard, large-incision extracapsular
procedure is needed, generously enlarge the incision. Address
astigmatic concerns at a later time, Dr. Nichamin said.
To
avoid pressure on the globe when removing lens material, he
prefers viscodissection and instrument-aided removal. At other
times, he inserts a modified lens glide (Visitec) underneath
the lens material to both support and aid in removal.
Alternatively, the lens glide may be used as a
“pseudoposterior capsule,” to allow further
phacoemulsification, he said.
If
phaco is chosen, lower the flow rate and vacuum and work in
slow motion. Work from the outside in on the remaining nucleus
to avoid creating additional nuclear fragments that could fall
posteriorly.
“During normal phaco, we try to chop into little
pieces. Now we strive to do the opposite,” Dr. Nichamin said.
Dr. Chang added, “When continuing phaco over a Sheet’s glide,
try to keep the phaco tip positioned as centrally as possible.
Instead of chasing peripheral nuclear material, use a second
instrument to position pieces in front of the stationary phaco
tip.”
Vitrectomy and Lens Cleanup
As soon as vitreous begins to prolapse forward,
one must stop the phaco or the irrigation and
aspiration step to avoid aspirating vitreous,
Dr. Chang advised.
Both
Drs. Nichamin and Chang advocate using a bimanual vitrectomy
technique.
“Many authors have advocated a bimanual, two-port
vitrectomy, yet most cataract surgeons still rely on the
unimanual, coaxial vitrectomy instrument,” Dr. Nichamin
reported. “Unfortunately, this approach is inefficient,
potentially more dangerous, and much more likely to enlarge
the capsular rent.”
In a
bimanual anterior vitrectomy, the vitreous cutter is separated
from the infusion line to avoid creating unnecessary
vitreoretinal traction forces. For infusion, Dr. Nichamin
designed a blunt-ended 21-gauge infusion cannula (Storz). The
standard infusion line connects to this instrument and is
placed through the side-port incision in the limbus.
Lower the infusion rate to a level that simply
maintains volume as material is removed, Dr. Nichamin
explained. Then make a separate incision through the pars
plana to permit placement of a 20-gauge, posterior segment,
high-speed vitrectomy cutter.
Pars Plana
Advantage
Dr. Chang also favors a pars
plana incision for the vitrectomy cutter if lens material
remains in the eye. He places the separate, self-retaining
infusion cannula through a limbal port. Typically, surgeons
insert the vitrectomy cutter through the phaco incision
“because it is convenient, and because they aren’t comfortable
working through a pars plana sclerotomy,” he said.
“However, unlike the latter, the phaco incision is
too large for the vitreous. This causes more vitreous to
prolapse forward and out of the incision alongside the
vitrectomy shaft,” he said. “As more formed vitreous escapes,
the residual lens material loses its support and starts to
drop posteriorly,” Dr. Chang added. “We have all seen this
happen.”
“When we place the cutter through the limbus, we
often continue to pull up vitreous from the posterior segment,
and it is difficult to find an endpoint,” Dr. Nichamin
added.
With
the pars plana approach, one can efficiently remove anterior
chamber vitreous by drawing it down posteriorly, limiting the
total amount of vitreous that is removed.
It
is also easier to access the subincisional area where residual
lens material often resides, Dr. Nichamin continued. Through
the pars plana, one can use the vitreous cutter to remove the
remaining soft- and medium-density lens material for 360
degrees, leaving subluxated material for the posterior segment
surgeon to remove at a second sitting, if necessary.
Making the
Cut
The
pars plana is unfamiliar territory for many anterior segment
surgeons, but this incision is safe and straightforward to
make:
1. After a small conjunctival
peritomy, use calipers to carefully measure 3 to 4 millimeters
posterior to the limbus, depending upon total axial
length.
2. With a 19- or 20-gauge
microvitrealretinal blade, make a stab incision, keeping the
blade perpendicular to the eye wall.
3. Visualize the metal tip of the
blade through the pupil to ensure that entry is
complete.
4. Confirm that all incisions are
snug and watertight.
Then, remove vitreous at low (50 to 100 mmHg)
vacuum settings with high (400 to 1,500 cpm) cutting rates. To
remove lens material, reduce the cutting rate, and carefully
and gradually increase vacuum, Dr. Nichamin explained.
Finally, free the pars plana incision of any remaining
vitreous and close it with a suture.
“The
bimanual pars plana vitrectomy technique requires practice,
but it is a better, safer technique for patients, and surgeons
need to take the plunge and become familiar with it,” Dr.
Nichamin said.
The Viscoat
Trap
Dr. Chang employs a second maneuver to
avoid losing lens material posteriorly as the vitrectomy is
performed, a technique he has named the “Viscoat trap.”
Once
vitreous has prolapsed forward and prevents continued phaco or
irrigation and aspiration, Dr. Chang uses Viscoat to levitate
any free-floating lens material—nuclear pieces, epinucleus or
cortex—as far forward as possible, almost up against the
cornea. The Viscoat injection is continued until most of the
anterior chamber is filled. “In this way, the Viscoat layer
partitions and traps the material in the anterior chamber, so
that it can’t fall posteriorly,” Dr. Chang said.
Next, Dr. Chang inserts the vitrectomy
cutter through the same pars plana sclerotomy used for the
posterior-assisted levitation technique. However, he performs
the anterior vitrectomy in the plane just behind the pupil or
residual posterior capsule. “The goal is to sever any
transpupillary bands of vitreous, so it isn’t necessary to
place the vitrectomy tip in the anterior chamber,”
he
said. “In this way, the Viscoat ‘trap’ layer, which is
supporting the residual lens material, is not evacuated.
Viscoat is ideal in that it resists aspiration more than the
cohesive agents.”
Wrapping
Up
Finally, one can perform cortical cleanup, insert
the implant and constrict the pupil. Use bimanual
irrigation and aspiration rather than the typical
coaxial setup, and work at a lower flow and a
lower vacuum than you would with an intact capsular
bag, Dr. Chang suggested.
Remove viscoelastic with the vitrectomy instrument,
with meticulous attention to the pupil and wounds.
To avoid shallowing of the anterior chamber, temporary
air injection followed by a gradual fluid-air
exchange may be useful, Dr. Nichamin said. Postoperatively,
use vigorous steroid and nonsteroidal anti-inflammatory
drugs and consider cycloplegic and antihypertensive
agents.
______________________________________________
Drs. Chang and Nichamin have no financial
interest in any products mentioned.
___________
Save the
Date
Drs.
Chang, Kelman and Nichamin will discuss different aspects of
managing posterior capsule rupture during the special
“Spotlight on Cataract Surgery” symposium at the Annual
Meeting in Orlando. The symposium will be held Monday, Oct.
21.
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