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Pearls
Ophthalmic Pearls/Cataract
Tips
for Safe and Effective Hydrodissection
By David F. Chang, MD
Edited by
Ingrid U. Scott, MD, MPH, and Sharon Fekrat,
MD
Hydrodissection is probably the most
underrated step of cataract surgery. Hydrodissection imparts a
broad fluid wave that separates the epinucleus and the
capsule. Nucleus disassembly then commences with
hydrodelineation, whereby a second internal fluid wave cleaves
the epinucleus apart from the firmer endonucleus.
Three Goals to
Achieve
1. Endonucleus rotation. Because
the phaco tip is confined to one location, nuclear rotation is
integral to every phaco technique. Effective hydrodissection
allows the nucleus to rotate with minimal stress transmitted
to the zonules. (If the fluid wave hugs the inner capsular
surface, it will accomplish this and the next goal by
separating the capsule from the epinucleus. As a result, both
the epinucleus and endonucleus will revolve together, even
following subsequent hydrodelineation.)
2.
Epinucleus rotation. After the endonucleus has been
removed, it is much safer to aspirate the anterior shelf of
the epinuclear shell rather than the posterior portion that
remains adherent to the underlying capsule. If the epinuclear
shell is loosened enough to spin, it can be aspirated in this
way and flipped as a unit. At other times, as the
contraincisional epinucleus is being aspirated by the phaco
tip, the anterior shelf may break off. A loosened epinuclear
shell can simply be rotated until a fresh area of anterior
shelf is exposed.
Occasionally, an attempt at
hydrodissection results instead in hydrodelineation only.
Although a fluid wave is visualized, it has traveled in a
plane that cleaves the epinucleus from the endonucleus. This
occurs more frequently in softer lenses where the epinucleus
is proportionately larger. Hydrodelineation without
hydrodissection will allow the endonucleus to rotate within a
stationary, immobile epinuclear shell. However, because the
epinucleus remains adherent to the capsule, it becomes
difficult to aspirate, mobilize or flip as a
unit.
3. Loosening the cortex.
Finally, if a slow-moving fluid wave propagates along and
against the inner capsular surface, it effectively shears the
cortical-capsular attachments. This third goal of �cortical
cleaving hydrodissection� loosens the cortex so that it can be
mobilized in large, loose sheets, rather than in thin adherent
strips.1 This enhances the efficiency and safety of
cortical cleanup and can help prevent posterior capsule
opacification.2
Preferred Technique
Optimal
hydrodissection produces a slowly propagating wave that has
scalloped advancing borders because it is plowing through the
cortex as it hugs the inner capsular surface. Observing this
type of wave gives advance confirmation that all three goals
have been achieved. Using a small-gauge cannula that not only
hooks the capsulorhexis edge but also tents the anterior
capsule slightly upward facilitates this. This makes it more
likely that the wave will follow the inside contour of the
capsule.
Since the volume of fluid that can be injected
into the capsular bag is limited, a small-diameter cannula
(30- or 27-gauge) should be used. The increased flow
resistance from a smaller cannula maximizes the force that can
be generated by a small volume of fluid.
The most
effective fluid jet is one that is brief, sufficiently
forceful and oriented in a radial direction. A 3-cc syringe is
recommended, as a tuberculin syringe contains insufficient
volume and larger-volume syringes do not provide enough
tactile feedback as the plunger is
advanced.
Three Pitfalls to
Avoid
1. Insufficient injection force. The
wave must have sufficient force to dissect through the path of
greatest resistance. Overly tentative and gradual injection
may empty the syringe but only produce circulation of balanced
salt solution within the anterior chamber.
2.
Injecting in the presence of �capsulo-lenticular
block.� With proper hydrodissection, the nucleus will
elevate away from the posterior capsule. A large, brunescent
nucleus may rise enough so that it apposes and internally
blocks the capsulorhexis opening.3 Continuing to
inject fluid that cannot escape the capsular bag may
overinflate and rupture the posterior capsule. If a firm
nucleus suddenly elevates above the hydrodissection wave, the
injection must be terminated, and the nucleus should be
depressed posteriorly with the cannula tip. This will break
the internal capsulorhexis seal so that any ensuing
hydrodelineation fluid is able to exit the
bag.
3. Overfilling the anterior chamber with
viscoelastic. Since anterior capsular convexity
associated with chamber shallowing will promote peripheral
extension of the capsular tear, generous amounts of
viscoelastic are often used to compress and flatten the
anterior capsule profile. However, downward compression of the
nucleus is counterproductive for hydrodissection because it
increases the resistance that a posteriorly dissecting fluid
wave must overcome. Once the capsulorhexis is complete,
burping out enough viscoelastic to shallow the anterior
chamber will facilitate the hydrodissection step. This
intraocular �decompression� expedites elevation of the nucleus
away from the posterior capsule upon
hydrodissection.
Preferred
Cannula
There are many excellent designs
for hydrodissection cannulas. My preference is to use a
right-angled tip. While this can simply be fashioned by
bending the tip of a straight cannula, the reusable Chang
Right-Angled Cannula is commercially available from several
manufacturers.4 The 27-gauge cannula has a
1-millimeter right-angle tip. The tip is flattened to produce
a fan-like jet.
Successful hydrodissection depends more
on technique than on instrumentation. Nevertheless, this
cannula provides several ergonomic advantages:
-
By angling the shaft within the tunneled
incision, one can pass the 1-mm tip just under the proximal
capsulorhexis edge�either slightly left or right of the
incision. This preferentially loosens the subincisional
cortex.
-
The tip is small enough to flip around
within the anterior chamber to sequentially hydrodissect or
hydrodelineate both lateral quadrants.
-
Because the tip is at a right angle,
rotation of the shaft will angle the tip so that it points
either slightly above or below the plane of the
capsulorhexis. By initially angling it slightly upward, the
undersurface of the anterior capsule is tented so that the
ensuing hydrodissection wave hugs the capsule. By then
angling it slightly downward, the tip rotates into the
proper cleavage plane for hydrodelineation.
-
The tip can be used to spin the nucleus
by engaging the anterior surface peripherally and pulling
with a rotational motion. This repetitive raking motion
manually breaks the remaining capsular adhesions and
confirms successful hydrodissection. The cannula is in
position for additional hydrodissection attempts if
necessary.
-
The right-angle design keeps the shaft
out of the way as fluid is injected behind the nucleus. This
can facilitate efforts to prolapse the endonucleus out of
the capsular bag. This maneuver is used in supracapsular
techniques such as phaco flip or for manual small-incision
extracapsular cataract extraction.
________________________
1 Fine, I. H.
J Cataract Refract Surg 1992; 18(5):508�512.
2
Peng, Q. J Cataract Refract Surg
2000;26:188�197.
3 Miyake, K. et al. J Cataract Refract
Surg 1998;24(9):1230�1234.
4 Katena, Mastel, Oasis
(disposable).
________________________
Dr. Chang
is clinical professor of ophthalmology at the University of
California, San Francisco, and in private practice in Los
Altos, Calif. He has no financial interest in any instrument
mentioned.