Pre-Phacoemulsification
Before performing any initial incision (scleral tunnel, corneal scleral, or a clear corneal), the paracentesis port should be made approximately 70° from the center of the planned surgical wound. This provides optimum positioning for pivoting the second instrument or irrigation cannula within the eye. When topical anesthesia is used, lidocaine 1% (nonpreserved) is irrigated into the anterior chamber through the paracentesis site, which will also firm up the eye for the incision.
After the incision is complete, the viscoelastic is instilled and a continuous curvilinear capsulorrhexis (CCC) is performed. The tear is begun by making a single puncture in the center of the capsule with a closed forceps. By lifting the tip of the forceps, a slit or triangular tear is propagated. The edge of the capsule near one point of this tear is grasped and the tear is turned by appropriate vector forces and guided radially out to the appropriate diameter at 3 o'clock or 9 o'clock. The tear is then guided around the capsule to achieve a relatively small (approximately 5.5 mm) circular anterior capsulectomy. Keeping the CCC smaller than the optic of the IOL so that no part of the CCC edge will fuse to the posterior capsule reduces the risk of fibrosis and striae on the posterior capsule and makes decentration of the IOL less likely. When completing the tear, it is important to avoid any tags or nicks that can extend to an unintentional radial tear during lens manipulation. During the capsulorrhexis, the surgeon should grasp the developing capsular flap with the desired instrument close to where the capsule is tearing to ensure control. With more experience, the surgeon may grasp the flap closer to the center of the radius which will create a smoother tear faster, but with some loss of control. Also, by folding the capsule flap and placing the tip of the instrument slightly ahead of the advancing tear, the surgeon may direct it more centrally. Conversely, placing the instrument slightly behind the tear will direct it toward the periphery. If the tear begins to extend too far peripherally, it can usually be redirected centrally by releasing some of the anterior zonules in that area with a cystotome and then using an elongated Kelman-McPherson forceps or Kraff-Utrata forceps to pull directly toward the center or almost 180° away from the point of tearing. A viscoelastic agent is required to maintain the anterior chamber and neutralize the pressure on each side of the anterior capsule while redirecting these peripheral tears. A highly viscous cohesive viscoelastic will be more effective than a dispersive viscoelastic in flattening the anterior capsule and maintaining pressure against it to safely complete the CCC.
Many variations of the the CCC technique have been developed. In special cases, a two-stage CCC is performed (e.g., CCC in intumescent cataracts if stains are not available; small pupil, inadvertently small CCC, eccentric CCC, or positive vitreous pressure without ideal viscoelastics to safely perform a 5.5 mm CCC). After the initial small anterior CCC is made, the second stage is started with a short tangential snip on one side of the opening with capsule scissors. Additional viscoelastic may be injected into the anterior chamber and under the lens capsule to isolate and expose the edge. To prevent a V-cut that may destroy the integrity of the continuous tear, the capsule opening must not fold over or under the scissors as the capsule is cut. After the tangential cut is successfully performed, the second continuous tear is extended using Kelman-McPherson or Kraff-Utrata forceps to complete a larger or appropriately centered circle.
Another technique incorporating the principles of CCC is reversing the direction of a tear that may develop in the CCC from instruments snagging the capsule. These can be redirected back into the CCC if the tear has not radialized beyond reach. It may also be used to restart a tear that has radialized during CCC. This new start may be made across the radial tear or elsewhere on the circle depending on access through the incision.
Hydrodissection Technique
After a successful CCC is achieved, hydrodissection is performed. In cases of zonular weakness, complete hydrodissection will minimize zonular stress caused by nuclear rotation and will promote separation of cortex from the capsule. Complete hydrodissection facilitates the utilization of divide and conquer techniques requiring nuclear rotation. Hydrodissection should be performed with care in soft cataracts. Hydrodissection should be avoided in cases of posterior lenticonus because of the increased risk of central posterior capsular rupture.
Hydrodissection is achieved using a 26-guage cannula on a 3-cc syringe of balanced salt solution. The capsule should be lifted carefully off the cortex with the cannula so that the stream starts to achieve a clean dissection just under the anterior capsule. A bent cannula is used to start the dissection subincisionally because the fluid wave, when it reaches the posterior pole of the lens where the lens fibers join, may develop a new dissection plane within the cortex rather than between cortex and capsule because of the way that lens fibers join at the center as they are laid down. A straight 26-guage cannula is then used to complete the hydrodissection from the opposite meridian. If the direction was incomplete in the meridian opposite the incision and cortex remains attached to the capsule, it is easy to engage with the irrigation and aspiration (I&A) handpiece.
After hydrodissection, the cannula is imbedded into the epinucleus and hydrodelineation is performed. A golden halo may be seen. If only a crescent of fluid cleft is formed, injection on the opposite side should complete the ring of hydrodelineation. Completeness of hydrodissection and hydrodelineation is verified by easy rotation of the nucleus and epinucleus within the capsular bag using the cannula. If needed the cannula may be introduced through the paracentesis site to reach the 12 o'clock area for complete hydrodissection and to assist in rotation to break any remaining interdigitation of lens fibers.
Divide and Conquer Phacoemulsification
Five basic steps are involved in divide and conquer phaco:
- Deep central sculpting (trench or crater)
- Downslope sculpting
- Nucleofractis (radial fracturing of the nucleus)
- Piece-meal emulsification of nuclear wedges
- Rotation of the nucleus
Deep Central Sculpting
First, the lens is stabilized with the second instrument via the paracentesis port. Then, the phaco tip shaves across the lens
surface centrally or slightly to the right of center (approximately 11 o'clock to 7 o'clock) for right-handed surgeons. Linear,
surgeon-controlled power is essential for this technique, as well as the use of minimal effective vacuum to clear the debris. The
surgeon should continue to shave across the lens to form a trench wide enough to accommodate not only the phaco tip but also the
accompanying irrigation sleeve.
Downslope Sculpting
While forming the initial trench, it is important to understand the concept of downslope sculpting. The key to this technique is
to nudge the lens away from the incision with the second instrument, which results in exposure of the proximal part of the nucleus for
sculpting. A useful analogy to this technique is manipulating batter in a mixing bowl. By tipping the bowl up on one side, the batter
will shift downward, creating a deeper concentration of batter and easier accessibility with a spoon. Similarly, with the lens nucleus
nudged away, the surgeon can sculpt very deeply down the slope of the posterior curvature of the lens. Downslope sculpting has made
any pregrooving out to the edge of the nucleus unnecessary. Initial sculpting is stopped just past the center of the lens and then
shorter passes are made until one is deep into the posterior pole of the lens where instruments can be used to obtain the first fracture.
This technique ensures that the trench is deep centrally rather than deep beyond the center of the lens as is often found in traditional
sculpting techniques. Also, the technique ensures a trench deep enough to allow complete nucleofractis through the entire nucleus,
which is imperative for efficient lens removal, as will be discussed in the following section.
The risk of posterior capsule perforation during sculpting may be reduced by maintaining a shaving action and avoiding an impaling action with occlusion of the phaco tip, which could lead to unpredictable breakthrough. Furthermore, the thickness of the remaining nucleus can be gauged by observing the change in red reflex shining through the progressively thinning nuclear material. A brighter retinal reflex indicates close proximity to posterior cortex.
Nucleofractis
Although mechanical separation of the fibers of the lens nucleus occurs most easily as an "onion peel" type of separation exemplified
by the ease of hydrodelineation of nucleus from epinucleus or hydrodissection of epinucleus from cortex, the lens can also be separated
radially along radial cleavage planes that can be well seen in some zonular cataracts.
Nucleofractis is accomplished with a two-instrument approach. The phaco tip is placed against the nucleus deep in the right-hand side of the trench and centrally near the posterior pole of the nucleus. The second instrument is placed against the left-hand side of the trench, opposite the phaco tip; both are deep in the center of the nucleus. Next, with only irrigation, the phaco tip is pushed toward the right as the second instrument is pushed to the left taking caution not to extend the force posteriorly. Only slight pressure is necessary to crack the nucleus and remaining posterior plate of the epinucleus starting from the center and extending the fracture to the periphery in both directions.
Piece-Meal Emulsification of Nuclear Wedges
After the initial nucleofractis, the phaco tip is moved to engage the nuclear material to the left of the fracture and with a short burst
of ultrasound, the tip is burrowed into the tissue slightly. Next, the second instrument is placed 3 mm to 8 mm to the left of the initial
fracture and with gentle pressure in opposite directions, sideways and downward, another fracture is created. If the nucleus is dense, a
chopper or cleaver instrument may be used to chop or slice to start the second fracture, and then separate with sideways and vertically
opposite movements of the instruments. The chopper or cleaver must be placed carefully under the capsule, through the cortex and epinucleus,
out to the equator of the nucleus and over the edge to engage the edge of the nucleus. By pulling toward the center of the nucleus against
the resistance of the phaco tip, the radial fracture is begun. The separating and shearing movements are then added to more effectively
separate. This fracture creates an isolated wedge-shaped section of nucleus.
Next, under suction only, this wedge-shaped section of nucleus is brought into the center of the pupil. If it does not separate and tumble, further thinning of the posterior central nucleus may be required. The edges of each wedge may have been weakened but not completely broken during the cracking procedure and may need additional separation.
Once in the center of the pupil, but still posterior to the plane of the iris, the wedge of nucleus is safely emulsified. Therefore, throughout phacoemulsification, the tip of the phaco probe and thus the majority of the ultrasound energy and fluid turbulence are directed posteriorly toward the lens material and kept within the capsular bag. This maneuver also keeps the phaco tip away from the iris, which is essential in small pupil cases. Throughout phacoemulsification, the second instrument can be used to lift small pieces of nucleus up to the port of the phaco tip. The second instrument should also be used to stabilize the nuclear sections to keep them at or beneath the pupillary plane and prevent endothelial touch. The second instrument can also be placed just under the phaco tip so that it will hold the posterior capsule back during aspiration and phacoemulsification in the event of anterior chamber shallowing (e.g., positive posterior pressure, surge after vacuum break, or flaccid posterior capsule). This maneuver is also of importance because as more of the lens tissue is removed, the endoskeleton effect of the lens nucleus and epinucleus that keeps the posterior capsule from collapsing anteriorly is lost.
Rotation
After isolation of the first wedge-shaped section of nucleus, the nucleus is rotated clockwise within the capsular bag and the cracking
maneuver is repeated as described in the previous section. Sections may be removed as they are separated, or some or all of the sections
may be left in place until all the fracturing is completed. After removal of the nucleus, a thick bowl of epinucleus may remain. This bowl
is usually easily aspirated with the phaco tip from the part of the lens capsule opposite the incision but may require the assistance of the
second instrument entering through the paracentesis port to tease the epinucleus away from the subincisional area. If the epinucleus proves
resistant to this maneuver, additional hydrodissection may be necessary at this juncture. The I&A probe may also be used to pull the
subincisional epinucleus to the center of the capsule by dragging it ahead of cortex that is being stripped.
Cortex Removal
After all nucleus and epinucleus is removed, any remaining cortex is engaged subincisionally with low aspiration flow rates so that the vacuum rise time is long. This allows time for the surgeon to turn the port away from the capsule as the vacuum rises after cortex occludes the port so that the capsule is not also engaged. Circumferential stripping may be more effective than centripetal movements. Surgeon control of aspiration flow rate with a preset high maximum vacuum is used for easily reached cortex. After engaging cortex, the port is turned up while the vacuum builds and the section of cortex is aspirated, thereby avoiding the risk of aspirating and tearing the posterior capsule. After all cortex is removed, the posterior capsule is thoroughly polished with slow movements of the phaco tip using a flow rate of 5 cc/min and vacuum of 5 mm Hg. However, very loose posterior capsules cannot be vacuumed without puckering and a high risk of tearing. Gentle polishing without vacuum power can also be effective.
Variations on Basic Technique
The "trench" technique has been shown to be useful for lenses of moderate density and lenses with a soft epinucleus. These lenses require a narrow central sculpting to leave enough nucleus to allow the force of the two instruments to effectively achieve nucleofractis. However, in denser nuclear material including brunescent nuclei, it may be necessary to sculpt a crater and use a variation of the divide and conquer technique. One must sculpt widely and deeply to achieve a central crater through the nucleus. Variations of divide and conquer nucleofractis are described for soft lenses, grade 1 to 2 nuclear sclerotic lenses, grade 3 to 4 nuclear sclerotic lenses, brunescent lenses, and intumescent lenses.
Soft Lenses
The nucleofractis technique is not applicable with very soft nuclei, such as in the cataracts in young patients and middle-aged adults. Instead,
it is preferable to first aspirate or emulsify the equatorial epinuclear and cortical material from the part of the lens opposite the incision.
Then, with more resultant room for rotation and less resistance to rotation, the remaining lens material laterally is moved centrally from the
subincisional fornix and removed. If the epinucleus proves difficult to remove at the 12 o'clock position, more hydrodissection will be helpful.
In soft lenses, the adhesion between nucleus and epinucleus and between epinucleus and cortex is not strong and creates little stress to the
zonules when broken even without hydrodissection. The greatest stress to the zonular fibers occurs during the stripping of the residual cortical
fibers from the equatorial capsule.
The central nuclear material and a bit of epinucleus may be left in place so that the posterior capsule is protected from rupture in cases with positive posterior pressure. The spatula is used to stabilize and maneuver the remaining nuclear disc and epinucleus, which is emulsified as a final step by conventional techniques.
Grade 1 to 2 Nuclear Sclerotic Lenses
In cases of grade 1 to 2 nuclear sclerotic lenses, the trench should be made through the soft nucleus to the epinucleus at the posterior pole.
These lenses may be thin as well as soft so sculpting must be performed with caution not to occlude the phaco tip and penetrate through cortex
and engage the capsule. It is necessary that the sides of the trench retain enough nuclear material to accomplish nucleofractis. The epinucleus
will prove soft in these cases and will aspirate easily but will not fracture.
After the initial nucleofractis, the second instrument stabilizes the nucleus and the phaco tip engages the left-hand hemisection at 5 o'clock, breaks away a quadrant, and emulsifies it. The nucleus is rotated and the maneuver is repeated leaving the other half of the nucleus intact to be rotated to the left side, fractured and emulsified in sections, or brought to the capsule center and fractured by chopping.
With this variation, the main principle is to create two hemisections with the sculpting of the trench. These hemisections are then divided into smaller sections by nucleofractis rather than by additional sculpting. With increasing nuclear density, it is recommended to break away smaller sections at a time.
Grade 3 to 4 Nuclear Sclerotic Lenses
In grade 3 to 4 nuclear sclerotic lenses, thorough hydrodissection is imperative to minimize zonular stress during nuclear rotation and while
sculpting a crater. Although it is true that hypermature lenses usually have soft or liquid cortex, dense brunescent cataracts usually have normal
cortical adhesions. Complete hydrodissection is verified by rotating the nucleus within the capsule. If the nucleus cannot be rotated easily with
the cannula, hydrodissection should be continued.
Because fracturing the peripheral nuclear material in these cases is more difficult, it may be necessary to sculpt a deep and wide central area or "crater." A shaving action is used to sculpt away central nuclear material. The initial trench is widened using the second instrument to displace the nucleus inferiorly to thin the superior part and then leftward to extend sculpting toward the right. When deep central nuclear material is no longer within reach of the phaco tip, the nucleus is rotated clockwise and additional shaving is performed. This procedure is repeated until as much central core of nuclear material as necessary is removed to facilitate fracturing the nuclear rim. As a rule, the denser the peripheral nuclear material is, the wider the central coring should be. However, enough dense material must be left to allow the second instrument and phaco tip to engage the rim and fracture the nucleus into sections. Using a chopper or cleaver as the second instrument is most effective in dense nuclear rim situations.
Although some experience is required to judge how deep this central sculpting can safely proceed, there is a safety factor inherent to this technique. The presence of the peripheral rim places the entire capsule under tension and prevents the posterior capsule from suddenly protruding anteriorly.
After the deep central crater has been formed, a modified divide and conquer technique is performed. With a harder nuclear rim, it is necessary to form smaller wedge-shaped sections that are more manageable and less likely to escape the phaco tip. Instead of emulsifying sections as they become available, they may be left in place within the nuclear ring so the ring will remain stable. This keeps the capsular bag well formed and keeps the posterior capsular bag on stretch and away from the phaco tip. One small section of nucleus can be removed initially to allow space for maneuverability which ensures more complete fracturing to the apex of each wedge-shaped section. Once all nuclear material has been fractured, each wedge-shaped section is removed using the aforementioned techniques.
Brunescent Lenses
It is commonly recommended that patients with brunescent lenses are not candidates for phacoemulsification. Surgeons who are in the early stages of
learning the technique should avoid using endolenticular phacoemulsification for these lenses. However, with sufficient experience and knowledge of
the characteristics unique to these lenses, the majority of brunescent lenses can be safely removed using the divide and conquer technique.
It is important to realize that brunescent lenses have a very dense nucleus that is structured as successive thin "shells" with natural radial cleavage planes corresponding to the orientation of the lens fibers, culminating in the Y suture lines. Also, a thick softer shell of peripheral nuclear material often separates from the denser nucleus. This tissue, which is often called epinucleus, is sometimes transparent but often too firm to aspirate efficiently through the 0.3-mm port of the I&A handpiece. Furthermore, some lenses are actually not as dense as their color suggests and can be emulsified in a fashion similar to moderate nuclear sclerosis.
The criteria for determining use of endolenticular phacoemulsification are the thickness and consistency of the peripheral cortex and outer nucleus which can be determined during anterior capsulotomy. Movement of the lens upon puncture of the anterior capsule with the cystotome or forceps indicates a very hard peripheral nucleus and epinucleus. If the instrument makes only shallow cuts through cortex, the peripheral cortex is likely very thin and would make phacoemulsification difficult and risky. Therefore, in these cases it may be advisable to use the extracapsular cataract extraction approach.
Generally, the denser the nucleus, the more hydrodissection is needed to ensure the safety of the necessary rotational maneuvers. Hydrodissection should be continued until the nucleus can be rotated freely within the lens capsule with the tip of the irrigation cannula. Next, the "crater" method of the divide and conquer technique as previously described should be performed for lens removal. Sometimes, a peripheral firm shell of nuclear material remains close to the capsule, taking on the appearance of cortex. This should be loosened and folded into the center of the pupil using the spatula and phaco tip without suction.
Finally, during emulsification of the last few fragments of nuclear material, ultrasound power should be kept low so the small, hard pieces of nucleus are not bounced away from the phaco tip toward the corneal endothelium.
Intumescent Lenses
Intumescent lenses present a challenge during CCC due to the minimal fundus reflex and the liquid cortex that exudes from the lens capsule after it
is punctured upon anterior capsulotomy. Using indocyanine green or other stains under an air bubble or very viscous viscoelastic to stain the capsule,
the surgeon can perform a CCC as routinely as when a red reflex is present.
Intumescent lenses typically have a uniform density and fracture well even with shallow central sculpting. The trench technique usually is sufficient when there is no epinucleus and little cortical material remaining due to liquefaction. The nuclear material may aspirate freely and rapidly even without the use of ultrasound power. Therefore, it is advisable to keep the phaco tip in the center of the anterior capsulotomy and let the material come to the port. There is usually little if any cortical material to remove in these cases.
Some lenses may have a hard nucleus and intumescent cortex and epinucleus. In these cases, after successful CCC and cortex aspiration, it is recommended that a dispersive viscoelastic be used in the capsular bag to surround the hard nucleus to protect the capsule during nucleofractis in the same way that the epinucleus and cortex ordinarily protect it.
Summary
Lamellar and radial separation and fracturing of the epinucleus and nucleus of cataractous lenses allow disassembly of the lens and removal of even dense cataracts through small pupils and CCC openings small enough to have anterior capsule cover all of the optic of the IOL.
Bibliography
Gimbel HV. Divide and conquer nucleofractis phacoemulsification: Development and variations. J Cataract Refract Surg. 1991;17:281-291.
Gimbel HV. Down slope sculpting. J Cataract Refract Surg. 1992;18:614-618.
Gimbel HV. Two-stage capsulorhexis for endocapsular phacoemulsification. J Cataract Refract Surg. 1990;16:246-249.
Gimbel HV, Neuhann T. Development, advantages, and methods of the continuous circular capsulorhexis technique. J Cataract Refract Surg 1990;16:31-37.