David F. Chang, MD, has no financial interest in this product.

Introduction

Although capsulorrhexis 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 in which 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.

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 I. Howard Fine, MD, 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 irrigation and aspiration (I&A) whether performed with the phaco handpiece or with the conventional I&A handpiece. Drs. Fine, Packer, and Hoffman describe this technique in greater detail in the tutorial Cortical Cleaving Hydrodissection.

Hydrodissection Technique

Slide 1

Slide 1
Slide 2

Slide 2

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 (Slide 1, Slide 2 and Slide 3). Observing this type of wave provides advance confirmation that all three goals have been achieved. A slowly propagating wave can be achieved by using a small-gauge cannula that not only hooks the capsulorrhexis edge but also indents the anterior capsule slightly upwards. This makes it more likely that the hydrostatic wave will follow the inside contour of the capsule.

Slide 3

Slide 3

Since the volume of fluid that can be injected into the capsular bag is limited, a small-diameter cannula (e.g., 30 gauge or 27 gauge) 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 that 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 because 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 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 larger nucleus may rise enough so that it apposes and internally blocks the capsulorrhexis. 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. Although it is a misconception that this maneuver further loosens the nucleus, it will break the internal capsulorrhexis seal so that the ensuing hydrodelineation fluid is able to exit the bag.

3. Overfilling the anterior chamber with viscoelastic.
The capsulorrhexis step immediately precedes hydrodissection and is facilitated by a deep anterior capsule. 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. Burping out enough viscoelastic to shallow the anterior chamber will facilitate hydrodissection. This intraocular "decompression" expedites elevation of the nucleus away from the posterior capsule upon hydrodissection.

The Chang Right-Angle Cannula

Slide 4

Slide 4

There are many excellent designs for hydrodissection cannulas. My preference is to use a right-angled tip (Slide 4). Although this can simply be fashioned by bending the tip of a straight cannula, the reusable Chang Right-Angled Cannula is commercially available through Katena (Denville, NJ) and Mastel (Rapid City, SD). The 27-gauge cannula has a 1-mm right-angle tip. The tip is flattened to produce a fan-like 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 capsulorrhexis edge, a sufficiently forceful pulse of fluid is delivered.

Successful hydrodissection depends more on technique than on instrumentation. Nevertheless, the small, right-angle design of this cannula provides several ergonomic advantages.

Slide 5

Slide 5
Video 1

Video 1
Video 1

Video 2