Download Chang Right Angle Cannula for Hydrodissection

Hydrodissection – Pearls & Pitfalls
David F. Chang, MD
Although capsulorhexis is the most important step of cataract surgery, hydrodissection is probably
the most underrated. Hydrodissection produces 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. There are three
separate goals for hydrodissection: 1) endonucleus rotation, 2) epinucleus rotation, and 3)
loosening of the cortex.
Hydrodissection Goals:
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 upon the
zonules. If the fluid wave hugs the inner capsular surface, it will accomplish the first two goals by
separating the capsule from the epinucleus. As a result, both the epinucleus and endonucleus will
revolve together - even following subsequent hydrodelineation.
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 new 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
stationery, immobile epinuclear shell. However, because the epinucleus remains adherent to the
capsule, it becomes difficult to aspirate, mobilize, or flip as a unit.
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”, as described by Dr. Howard Fine, loosens the cortex so that it can be mobilized
in large sheets, rather than in thin adherent strips. This enhances the efficiency and safety of
cortical cleanup.
Hydrodissection Technique:
A rapid, instantaneous fluid wave that propagates without any resistance may be moving along too
central an anatomic plane. Unless it travels just along the internal capsular surface, the fluid wave
will not loosen the cortex effectively. 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
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have been achieved. Using a small gauge cannula that not only hooks the capsulorhexis edge, but
also indents the anterior capsule slightly upwards facilitates this. This makes it more likely that the
hydrostatic 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 (e.g. 30 Ga. or 27 Ga.) should be used. The increased flow resistance from a smaller
cannula maximizes the hydrostatic force that can be generated by a small volume of fluid. The
most effective fluid jet is one which is brief, sufficiently forceful, and oriented in a radial direction.
Hydrodissection Pitfalls:
(1) Insufficient injection force.
The fluid wave must have sufficient hydrostatic force to dissect through the path of greatest
resistance. This force must be generated quickly since there is a limited volume of fluid that can be
safely injected. Overly tentative and gradual injection may empty the syringe, but only produce
circulation of BSS within in 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. Continuing to inject fluid that cannot escape the capsular bag may over inflate and
rupture the posterior capsule. This is usually not appreciated until the phaco tip is introduced and
the nucleus abruptly drops posteriorly as the irrigation pressure and initial sculpting maneuvers
widen the posterior capsule defect.
If the nucleus suddenly elevates above the hydrodissection wave, the injection must be terminated,
and the nucleus should be depressed posteriorly with the cannula shaft. While it is a misconception
that this maneuver further loosens the nucleus, this will break the internal capsulorhexis seal so
that the ensuing hydrodelineation fluid is able to exit the bag.
(3) Over-filling the anterior chamber with viscoelastic.
The capsulorhexis step immediately precedes hydrodissection and is facilitated by a deep AC.
Since anterior capsular convexity associated with chamber shallowing will promote peripheral
extension of the capsular tear, abundant viscoelastic may be necessary 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.
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Chang Right-Angle Hydrodissection Cannula
There are many excellent designs for hydrodissection cannulae. My preference is to use a rightangled tip. While this can simply be fashioned by bending the tip of a disposable straight cannula,
the reusable Chang Cannula is commercially available through Katena Products, Inc. (No financial
interest). The 27-gauge cannula has a 1 mm right angle tip. The tip is flattened to produce a fanlike jet. Using a small disposable 3 cc syringe allows one to accurately gauge the plunger force.
Larger syringes do not provide enough kinesthetic or tactile feedback. Once the cannula tip is
radially oriented and properly positioned beneath the capsulorhexis edge, a sufficiently forceful
pulse of fluid is delivered.
K7-5464 Chang Hydrodissection Cannula, 27 gauge
Successful hydrodissection depends more on technique than on instrumentation. Nevertheless, the
small right angle design of this cannula provides several ergonomic advantages.
(1) 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 is done in the same
way that a right-angled I/A tip is used to access subincisional cortex. This preferentially loosens
the subincisional cortex.
(2) The 1 mm tip is small enough to flip around within the anterior chamber to sequentially
hydrodissect or hydrodelineate both lateral quadrants.
(3) 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.
(4) Like a hook, the short right-angled 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 45-degree
angle of the tip creates a point on the end that can be used to engage the anterior nuclear surface.
The cannula is in position for additional hydrodissection attempts if necessary.
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(5) This 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 ECCE.
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