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Tips for Safe and Effective Hydrodissection

 
 
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EyeNet Magazine >> Ophthalmic Pearls

Ophthalmic Pearls/Cataract

Tips for Safe and Effective Hydrodissection

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).


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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.


 

 
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