Nucleofractis Techniques

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Nucleofractis techniques

All modern day phaco techniques depend on nuclear disassembly (subdividing the nucleus into smaller pieces) for efficient emulsification. This allows for the wide nucleus to be efficiently removed from the capsulorhexis opening which is approximately half of the size of nucleus. Classical techniques for nucleofractis include divide and conquer, stop and chop and phaco chop. In 1991, Gimbel introduced divide and conquer, a nucleofractis technique that involved dividing the nucleus into four quadrants by sculpting, thereby giving it the appearance of a cross. As the phaco handpiece is quite active during this procedure and performs much of the lamellar dissection of the nucleus, there is far less dependence on bimanual dexterity and instrument coordination. Due to the safety and efficacy of this method, it has become the standard technique taught to novice surgeons.[1] Nagahara followed in 1993 by introducing the concept of phaco chop, which involved manually fragmenting the nucleus without sculpting. This resulted in a significant reduction in phaco energy required. Koch merged between the two and published his variation, stop and chop, in 1994. He described first dividing the nucleus with the traditional groove followed by subsequent chops of each heminucleus into smaller fragments, thus efficiently marrying between the two techniques. Stop and chop gained popularity as it bypassed the first step of chopping the nucleus in half which many surgeons found difficult. However due to the ultrasonic energy utilized during grooving, it did not match the same results as the chopping technique.[2] Since then many variations have been described, and the advent of the prechopper and femtosecond laser have evolved cataract surgery in the modern world.

Sculpting techniques

Divide and conquer

Described by Gimbel in 1991, the phaco probe is used to sculpt a deep trench from 11 o'clock to 7 o'clock for right-handed surgeons by gradually shaving the nucleus within the capsulorrhexis margin. This is similar to how a log is sawed and requires passing the probe back and forth multiple times. The trench can be widened if need be to accommodate the irrigation sleeve along with the phaco tip. The depth of the groove is around 80% or more and should be constantly assessed by observing the changes in the red reflex. Grooving should be halted when the pink reflex indicating cortex is seen.[3] The nucleus is then rotated 90° and the second trench is sculpted perpendicular to the initial one. The probe and the chopper are then inserted deep into the trenches and lateral forces are applied on the walls of the trench to divide the nucleus into four quadrants. These quadrants are then held with vacuum and emulsified within the bag by bringing them centrally or within the iris plane. The space created by the trenches allows maneuverability of the nucleus and avoids bringing the fragments into the anterior chamber for phacoemulsification. Although this technique requires longer phacoemulsification time and higher power, it is still the preferred technique for novice surgeons as it doesn’t utilize chopping maneuvers.[4]

[Video Credit-Uday Devgan MD -]

Stop and chop

Described by Koch in 1994, an initial deep trench similar to the description of the previous technique is created. The nucleus is then fractured into two heminuclei. The nucleus is then rotated 90° so that the heminucleus lies in front of the phaco probe. Gentle ultrasound power is used to bury the phaco tip into the nucleus. The chopper is then placed at the peripheral edge usually at the capsulorhexis margin. Placement of the chopper underneath the capsulorhexis margin can be required if the capsulotomy is small but great care is required so as to avoid capsular tear. While the probe is holding the nucleus with aspiration, the chopper is brought towards the probe resulting in linear cut within the nucleus. When the chopper is near the probe, the chopper and the probe are moved laterally to each other resulting in a crack and separation of one nuclear piece. The chopped-off piece can then be emulsified or the process can be repeated to chop the nucleus into multiple pieces before removal. Softer cataracts are usually chopped into four quadrants while the denser nuclei may require more. In denser cataracts the nucleus is initially chopped into the desired number of fragments and left for later emulsification in order to reduce the risk of posterior capsular rent by keeping the bag stretched.[5] Although this technique is less efficient as compared to the chopping methods, the central groove provides a favorable working space for aspiration and subsequent emulsification of the fragments as compared to the immobile tightly fit nuclear pieces after phaco chop.

[Video Credit-Uday Devgan MD -]

Chopping techniques

Horizontal or Nagahara phaco chop

Introduced by Nagahara in 1993, the chopper is used to fracture the nucleus without sculpting a trench. The chopper is slid under the anterior capsulorrhexis margin and peripherally hooks the equator of the nucleus. This step poses the biggest hurdle to novice surgeons transitioning to chopping maneuvers as sometimes the chopper is placed on the anterior capsule and can result in zonular tear of several clock hours when pulled. This can be avoided if the chopper is in constant contact as it is moved peripherally from the center. The phaco tip then impales the nucleus subincisionally near the wound with its direction towards the optic nerve head and is buried up to the sleeve. The two instruments are brought together and then moved slightly apart. In soft nuclei, there is minimal resistance felt in the chopper movement but in hard nuclei, the mechanical force required causes whitening of the nuclear tissue. The harder the nucleus, the more compressive force required. The initial fracture occurs distal to the phaco tip and the separating motion allows it continue through the proximal part. To remove the first nuclear fragment, the nucleus is rotated 30-45 degrees, the chopper is placed into the peripheral part of the nucleus and phaco tip holds the heminucleus through the initial split. The pie shaped segment is removed from the bag using high vacuum and emulsified in the iris plane. The chopper is used to crush and push the segment into the probe. The rest of the nucleus is chopped in a similar fashion with the harder nuclei requiring more chops as smaller fragments are easier to emulsify. Chop techniques require lesser amounts of ultrasound energy and time and also place lesser stress on the zonules. During the process of grooving, the capsule and the zonules grip and keep the nucleus immobile while in the phaco chop, the phaco tip braces against the chopper with the direction of the forces away from the zonules towards the center.[6] [Video Credit-Uday Devgan MD -]

Vertical chop

Fukasaku, and contemporaneously other surgeons, conceived of a variation to the traditional chop which involves vertical opposing movements of the chopper and probe as compared to horizontal. This technique does not require the chopper to be moved to the periphery of the equator but remain within the safe central margins of the capsulorrhexis. The phaco tip is deeply buried into the central nucleus followed by chopper placement just in front or to the side of the needle. Retracting the sleeve allows for deeper penetration of the nucleus as the needle tip is more exposed. The depth of the phaco tip is the key to achieving a successful chop contrary to the depth of the chopper tip in horizontal chop. The chopper is then depressed while simultaneously lifting the nucleus slightly upward creating a partial split. The instruments are then spread apart and the crack is propagated to its entirety. The nucleus is rotated and the process repeated until sufficient cleavage planes are achieved. Preferably, the nuclear fragments aren’t removed until the entire nucleus is chopped as the adjacent pieces provide stability during the vertical chop. The remainder of the procedure is completed as described in the previous section. Vertical chop is the preferred technique in dense cataracts and small pupils.[7] [Video Credit-Uday Devgan MD -]

Double-chop and cross-chop

Brian Kim conceived of a novel technique that does not require the use of high vacuum and power for holding the lens thus bypassing the limitations of traditional chopping. The chopper is slid and placed around the peripheral endonucleus in a similar fashion as described in the horizontal chop. The phaco tip now goes bevel down subincisonally and is placed in the soft epinucleus around the endonucleus at the equatorial level without burying it. The phaco tip essentially acts as a second chopper placed directly opposite to the chopper. Horizontal forces are used to bring the two instruments together and then laterally separated. The phaco tip is now placed deeply between the two heminuclei and the chopper is slid across the handpiece around the equator creating an “X” configuration. Without using ultrasound or vacuum the chopper is pulled centrally towards the phaco probe to fracture the heminucleus. This technique is termed as the cross-chop technique.[8] Ultrasound and vacuum are now applied to emulsify the fragments while keeping the tip in the central zone. The second hemiucleus is now rotated, chopped and emulsified. In dense nuclei, as the epinuclear layer required for the phaco tip to bury into is absent, downward force is applied by the tip on the lens surface while the chopper applies upward force while being pulled centrally. The direction of the forces is diagonal. The double chop is also effective in small pupils.[9]

Soft chop

Similar to the double-chop, Oetting described a technique to chop soft cataracts without using ultrasound and vacuum. While the double chop requires the probe to slide underneath the anterior capsule in the subincisional equatorial endonucleus, the needle is placed centrally in the soft chop. The chopper is passed underneath the anterior capsule and brought centrally towards the needle. It is essentially a horizontal chop without the use of ultrasound or vacuum. This technique can only be applied on soft cataracts. [Video Credit-Uday Devgan MD -]

Crater and split

Vanathi et al. introduced a technique for hard cataracts with a leathery posterior plate. A central crater of approximately 6 mm and 90% depth is created within the capsulorrhexis margin. The remaining nucleus is then cracked by horizontal chopping maneuvers with high vacuum and emulsified in the crater space.[10] Aslan et al modified this technique by reducing the crater size to 3 mm. This modification catered for nuclei of softer density along with the dense cataracts. The splitting of the soft nuclei can be done without vacuum and of dense nuclei with low vacuum.[11] [Video Credit-Dr. Soosan Jacob]

Decrease and conquer

Hong Kyun Kim described a technique for dense cataracts that comprises of 3 steps: separation of the epinucleus from the endonucleus, emulsification of the endonucleus followed by the removal of the epinucleus. After hydrodissection, the nucleus is centrally impaled by the phaco tip and held similar to a lollipop. The chopper is then introduced and impales the nucleus near the capsulorrhexis margin in front of the needle. Staying on the left side of the phaco tip, it is first pulled toward and downwards towards the needle achieving a cleavage plane and then laterally away from the tip separating the endonucleus from the core. This step is difficult to perform on very dense nuclei but can be done by holding the nucleus with high vacuum and deeper impalement of the chopper into the endonucleus. The same maneuver is repeated circumferentially until complete separation of the endonucleus from the dense core is achieved. Emulsification of the dense core is done with the help of the chopper. The epinuclear rim is then removed by low energy setting or aspiration depending on its density. In dense cataracts, the radial suture plane is dense at the posterior endonucleus. Traditional chopping techniques require complete fragmentation of the nucleus but the decrease and conquer technique bypasses this requirement because the separation of the epinucleus takes place in the lamellated zone which is loosely adherent. This also reduces the risk of posterior capsular rent as the posterior epinuclear shell acts as a shield while the central dense core is being emulsified. There is also reduced stress on the zonules as the movements of the chopper and the phaco tip are minimized.[12]

Pocket chop

Described by Braga-Mele for soft nuclei, a central pocket is sculpted by the phaco tip. The phaco tip initiates grooving near the capsulorrhexis edge similar to the trench in stop and chop but instead of passing through to the opposite edge, the tip is passed till the center of the nucleus. The depth of this pocket is a third of the nucleus and the length is 2 to 3 mm. The chopper is then placed in the nucleus near to the capsulorrhexis margin and a horizontal chop is performed. The buried phaco tip inside the pocket provides the counter force for the chopper. Due to the firmness of the counter traction provided by the phaco tip, the chopper does not necessarily have to be placed underneath the capsulorrhexis margin as required in traditional chopping. Other than soft nuclei, this technique can also be used to create space so that the rest of the maneuvers can be done optimally.[13]

Submarine chop and consecutive drilling

Hard cataracts pose a challenge due to their dense nuclear core accompanied by a thick posterior plate. Mohanta demonstrated a technique that debulks the central part of the nucleus resulting in a successful fracture. The phaco tip is buried into the subincisional nucleus bevel up. It then goes deep within the nucleus to the opposite equator. The chopper is then placed subincisonally and the two instruments are brought together and an initial semi fracture is achieved. The nucleus is rotated and held by the phaco tip and the chopper used to propagate the crack. The heminuclei are then divided in the same manner. The deeply buried phaco tip resembles a submarine hence the name. Following the same principle of debulking the densest central core in order for the crack to propagate completely, Chen et al. described a technique inspired by mining techniques. Akin to how miners crack a rock by initially drilling multiple holes and then applying inside-out forces, two to three consecutive drillings are done starting subincisionally progressing to the geometric center of the nucleus. The depth of the drilling is approximately two third of the nucleus and the angle of the tip is sixty degrees. The drilling subincisonally is relatively superficial as the subsequent drills as the nucleus is thicker in the center as compared to the periphery. Phaco tip is preferably bevel down. High ultrasound and power should be used to avoid causing stress on the zonules. The phaco tip impales the nucleus and the chopper is taken behind the capsulorrhexis and the two instruments are brought together resulting in a full thickness crack. The subsequent steps are similar to the previous technique. Both these techniques are highly efficient for hard cataracts as the entire nuclear structure is initially weakened before performing the chop.[14] [Video Credit-Uday Devgan MD -]

Two hole assisted phaco chop and Rotary chop

Despite the benefits of phaco chop over the sculpting techniques, many surgeons, especially residents, shy away from employing this technique because the chopper has to be passed underneath the anterior capsule and deep in the capsular bag which is outside the visual area obstructed by the iris. Novice surgeons tend to either tear the capsulorrhexis margin by the sharp edge of the chopper or the zonules if the chopper is erroneously placed on top of the anterior capsule when initiating the first chop. Miyamoto reported a new technique that employed similar use of the mechanical forces of horizontal chop but in a safer zone. This was done by creating a lens equator within the capsulorrhexis margin by drilling two holes which makes the first chop easier to perform. For the two hole assisted phaco chop, the phaco tip will be buried into the endonucleus about 3/4th depth anterior to the capsulorrhexis margin. The nucleus will be rotated 180° and the phaco tip will be impaled into the nucleus in a similar manner described previously. The chopper will be placed into the hole previously created on the opposite side and horizontal force will be applied similar to the horizontal chop. After the first crack the remaining steps will be done as described in the traditional chop technique. Mastering the two hole assisted phaco chop would make the transition of resident surgeons from divide and conquer to phaco chop smoother and more efficient.[15] Ifantides et al. presented a similar technique and named it rotary chop based on the appearance of the holes to the rotary phone dial.[16] [Video Credit-Uday Devgan MD -]

Supracapsular technique for soft cataracts

Lindstrom described a technique for the safe and effective emulsification of soft cataracts. Hydrodissection is performed in a slow and continuous manner until the nucleus tilts out of the bag. The nucleus is then positioned in front of the incision. While the nucleus is supported on the iris plane, it is emulsified until half of it is removed. The other half is then tumbled upside down and emulsified at the iris plane.[17] [Video Credit-Uday Devgan MD -] Harsh modified this into the tilt and crush. Hydrodissection is performed with the cannula 90 degree to the axis of the wound until the nucleus is prolapsed out of the bag from the opposite pole. High vacuum is used to hold the hold the nucleus vertically and the chopper is placed behind the erect lens. The nucleus is crushed between the instruments using mechanical forces and divided into two pieces. The upper piece is emulsified in the supracapsular space either only with vacuum or low ultrasound settings. The lower piece is then pulled out of the bag and similarly emulsified. This technique is safer and more efficient than other techniques described for the removal of soft cataracts such as tilt and tumble and hydro chop.[18] Uday Devgan demonstrates a similar technique where instead of crushing, chopping maneuvers are performed. [Video Credit-Uday Devgan MD -]

Prechopping techniques

The prechop technique described by Akahoshi in 1998, decreases the ultrasound used during phacoemulsification but may cause zonular stress. Many prechop techniques have since then been described using specialized instruments. The combo prechopper introduced by Akahoshi is inserted into the central nucleus and the blades are separated to fracture the nucleus. Zonular stress is induced when using this prechopper in hard nuclei.[19] [Video Credit-Uday Devgan MD -] A surgeon bent cystotome along with the nagahara chopper is used in the cystotome assisted prechop technique. The chopper is placed underneath the capsulorrhexis while the cystotome is embedded into the subincisional endonucleus just inside the capsular rim. Oblique forces are applied to pull the chopper while the cystotome is pushed until the two instruments meet and laterally separated resulting in a fracture.[20] [Video Credit-Uday Devgan MD -] A reverse prechopper has the advantage of decreased zonular stress and can be used for dense nuclei but their placement can be difficult in deep anterior chambers, very dense cataracts due to lack of space and also soft nuclei. The inverted semi-circular arc like reverse prechopper is introduced subincisionally around the lens equator and the nagahara chopper at the opposite equator. Mechanical forces are used to bring the two instruments together and fracture the nucleus. [21] [Video Credit-Uday Devgan MD -] Braga-Mele et al. described the hydro chop in which a hydrodissection cannula is used for prechop in soft cataracts by passing it multiple times back and forth within the central nucleus while simultaneously irrigating to create a groove half to two-thirds thick. The phaco tip is buttressed against the proximal aspect of the groove and the chopper is drawn towards the tip within the groove and then laterally to crack the nucleus.[22] In the Drill and crack technique for hard cataract, the phaco probe creates a deep central hole followed by placement of Akahoshi prechopper within this hole to crack the nucleus.[23] Microfilament snares such as miLOOP (Iantech Inc) are slid around the nucleus and then tightened to bisect the nucleus by inward forces. This technique does decrease the phaco energy required but its incorrect placement may cause total lysis of the zonular apparatus.[24] [Video Credit-Uday Devgan MD -]

Femtosecond-laser-assisted cataract surgery

Femtosecond-laser-assisted cataract surgery (FLACS) was introduced in 2008 and automated some of the important steps of cataract surgery, namely three, precise corneal incisions with minimal astigmatism, perfectly centered and reproducible capsulorrhexis and nuclear fragmentation reducing ultrasound requirements. Femtosecond laser incises tissues by causing photodisruption resulting in formation of a plasma of free electrons. The rapid expanse and collapse of the electrons generates microcavitation bubbles resulting in target tissue separation.[25] Similar to refractive surgery, the eye is docked into the laser system for stabilization resulting in temporary rise in intraocular pressure. Corneal incisions constructed by the femtosecond laser are precise, stable and reproducible although slower improvement of the anatomy was observed compared to manual incisions. Capsulorrhexis by the femtosecond laser is precisely positioned and perfectly sized aiding in cases where perfect centration of the lens is key to visual rehabilitation such as toric, multifocal and presbyopic IOLs.[26] Laser pretreatment by nuclear fragmentation reduces the required cumulative dissipated energy and phacoemulsification time. Different patterns are employed and the laser beam is propagated from posterior to anterior while maintaining a safety distance from the bag so as to avoid the shielding effects caused by the bubbles created.[27] The drawbacks of FLACS include higher cost, intraoperative miosis associated with the release of prostaglandins and capsulotomy complications.[28] [Video Credit-Dr. Soosan Jacob]


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