Key Features
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The refinement of incision placement and architecture, as well as the reduction of final incision size occasioned by the implantation of a foldable, injectable intraocular lens, permits the reduction of postoperative astigmatism and enhancement of refractive cataract surgery.
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Continuous curvilinear capsulorrhexis facilitates sculpting techniques, such as divide and conquer, trending to today’s preferred horizontal and vertical chopping methods.
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Hydrodissection to lyse cortical–capsular connections.
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Hydrodelineation to permit phaco within the protective layer of the epinucleus improves the safety and efficiency of phaco.
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Power modulations, such as millisecond level control of ultrasound power application, allow for reduction of the energy required for cataract extraction, protection of the cornea from thermal injury, and enhancement of the rapidity of postoperative visual rehabilitation.
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Femtosecond laser-assisted surgery represents a relatively new technology that some surgeons have adopted for cataract extraction.
Introduction
The principal technical features of phaco include the following:
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Watertight, self-sealing corneal incisions.
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Intact, round, centered capsulorrhexis with a diameter smaller than that of the intended intraocular lens (IOL) optic.
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Efficient ultrasound power modulation and fluidics to protect the capsule, iris, and cornea.
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Fastidious cortical cleanup, resulting in a clean capsular bag.
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Atraumatic IOL insertion through an incision of 1.5–2.4 mm.
“Phaco” refers to the techniques and technology required for the fragmentation and extraction of the crystalline lens through a small corneal incision and the implantation of an intraocular lens (IOL), resulting in rapid visual rehabilitation and reduced need for optical correction.
Since the time of its introduction in the late 1960s, phaco has evolved into a highly effective method of cataract extraction. Incremental advances in surgical technique and the simultaneous redesign and modification of technology have permitted increased safety and efficiency. Among the advances that have shaped modern phaco are incision construction, continuous curvilinear capsulorrhexis, cortical cleaving hydrodissection and hydrodelineation, and nucleofractis techniques.
The United States patent #3 589 363, filed July 25, 1967, lists Anton Banko and Charles D. Kelman as inventors of “an instrument for breaking apart and removal of unwanted material, especially suitable for surgical operations such (as) cataract removal, including a handheld instrument having an operative tip vibrating at a frequency in the ultrasonic range with an amplitude controllable up to several thousandths of an inch.”
Even until recently, the fundamental mechanisms by which the system known as “phaco” operates has remained controversial. Although some authors have described the surgical advantages of a unique type of cavitational energy, others have denied any role for cavitational energy in phaco.
Incision Construction and Architecture
Since 1992, when Fine described the self-sealing temporal clear corneal incision (CCI), the availability of foldable IOLs has furthered the trend away from scleral tunnel incisions to clear corneal incisions. Rosen demonstrated through topographic analysis that CCIs 3 mm or less in width do not induce significant astigmatism. This finding led to increasing interest in T-cuts, arcuate cuts, and LRIs for managing pre-existing astigmatism at the time of cataract surgery. Surgeons recognized many other advantages of the temporal CCI, including better preservation of the conjunctiva, increased stability of refractive results because of decreased effects from lid blink and gravity, ease of approach, elimination of the bridle suture and iatrogenic ptosis, and improved drainage from the surgical field via the lateral canthal angle.
Surgeons originally adopted single-plane incisions utilizing a 3-mm diamond knife. After pressurizing the eye with viscoelastic through paracentesis, the surgeon placed the blade on the eye so that it completely applanated the eye, with the point of the blade positioned at the leading edge of the anterior vascular arcade. The knife was advanced in the plane of the cornea until the shoulders, 2 mm posterior to the point of the knife, touched the external edge of the incision. Then, the point of the blade was directed posteriorly to initiate the cut through Descemet’s membrane in a maneuver known as the dimple-down technique. After the tip entered the anterior chamber, the initial plane of the incision was re-established to cut through Descemet’s membrane in a straight-line configuration.
Williamson was the first to utilize a shallow 300–400 µm grooved CCI. Langerman later described the single-hinge incision, in which the initial groove measured 90% of the depth of the cornea anterior to the edge of the conjunctiva. Surgeons employed adjunctive techniques to combine incisional keratorefractive surgery with CCIs. Osher described the construction of arcuate keratotomy incisions at the time of cataract surgery for correction of pre-existing corneal astigmatism. Kershner used the temporal incision by starting with a nearly full-thickness T-cut, through which he then made his corneal tunnel incision. Finally, the recommendation of LRIs by Gills and Nichamin advanced what ultimately became most popular means of reducing pre-existing astigmatism.
Following phaco, lens implantation, and removal of residual viscoelastic, stromal hydration may be performed to seal the incisions by gently irrigating balanced salt solution into the stroma at both edges of the incision with a 26- or 27-gauge cannula. An intraoperative Seidel test may be used to ensure sealing. Studies of sequential optical coherence tomography of postoperative CCIs have demonstrated that the edema from stromal hydration lasts up to 1 week.
CCIs, by nature of their architecture and location, are associated with unique complications. Chemotic ballooning of the conjunctiva may occur as a result of irrigating fluid streaming into an inadvertent conjunctival incision. In this case, the conjunctiva may be snipped to permit decompression. Incisions that are too short can result in an increased tendency for iris prolapse and poor sealability. A single suture may be required to secure the wound. In contrast, a long incision may result in striae in the cornea that compromise the surgeon’s view during phaco. Coarse manipulation of the phaco tip may result in epithelial abrasions or tears in Descemet’s membrane, compromising self-sealability. Of great concern is the risk of incisional burns. When incisional burns develop in CCIs, rapid contraction of tissue and loss of self-sealability occur. Suture closure of the wound may induce excessive astigmatism.
The literature supports the view that suboptimal construction of CCIs may lead to poor coaptation, inadequate sealing, and ingress of bacteria, thereby increasing the risk of acute postoperative bacterial endophthalmitis. However, four large published series have found no greater likelihood of infection with corneal versus other types of incisions. Regardless of the type of incision, the principle to be followed is that appropriate incision construction and watertight closure are obligatory. Besides poor wound closure, other significant factors that have been associated with higher risk of postoperative infection include posterior capsule rupture, vitreous loss, older age, prolonged surgery, immunodeficiency, active blepharitis, lacrimal duct obstruction, inferior incision location, and male gender.
Continuous Curvilinear Capsulorrhexis
Implantation of the IOL in an intact capsular bag facilitates the permanent rehabilitative benefit of cataract surgery. For many years, surgeons considered a “can opener” capsulectomy to be satisfactory for both planned extracapsular cataract extraction and phaco. However, in 1991, Wasserman et al. performed a postmortem study that showed that the extension of one or more V-shaped tears toward the equator of the capsule produced instability of the IOL and resulted in malpositioning of the IOL. Gimbel and Neuhann popularized continuous curvilinear capsulorrhexis (CCC) in the later 1980s.
The basic principles of manual CCC include the following:
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The continuous capsular tear should be performed in a stable anterior chamber under pressurization by an ophthalmic viscosurgical device (OVD).
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The tear should be initiated at the center of the capsule so that the origin is included within the circle of the tear.
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The continuous tear may proceed either clockwise or counterclockwise in a controlled and deliberate fashion, the surgeon regrasping with the forceps or repositioning the point of the cystotome/bent needle on the inverted flap to control the vector of the tear.
A tear that begins moving peripherally or radially is a signal that an existing condition requires immediate attention. Further progress of the tear should be stopped and the depth of the anterior chamber assessed. Frequently, the cause of the peripheral course of the tear is shallowing of the anterior chamber. Adding more OVD to deepen the anterior chamber opposes the posterior pressure, making the lens capsule taut, widening the pupil, and permitting inspection of the capsule ( ).
One important technique for redirection of the capsulorrhexis has been described by Little. In this technique, to rescue the capsulorrhexis from a peripheral tearout, the force applied to the capsular flap is reversed but maintained in the plane of the anterior capsule. It is necessary to first unfold the capsular flap so that it lies flat against the lens cortex, as it did prior to being torn. Force can then be applied with the capsule forceps by holding the capsular flap as close to the root of the tear as possible and pulling backward in a retrograde direction along the circumferential path of the completed portion of the capsulorrhexis. Traction should be applied in the horizontal plane of the capsule and not upward. The initial pull should be circumferentially backward and then, while holding the flap under tension, directed more centrally to initiate the tear. The forward progress of the capsulorrhexis will uniformly and predictably redirect toward the center of the capsule ( Fig. 5.11.1 ). If the capsule will not tear easily and the entire lens is being pulled centrally, this rescue maneuver should be abandoned to avoid a wrap-around capsular tear or zonular dialysis. Other rescue techniques, such as completing the capsulorrhexis from the opposite direction or making a relieving cut in the flap edge and continuing in the same direction, represent reasonable alternatives.
The use of trypan blue to stain the anterior capsule in the absence of a good red reflex constitutes an important adjunctive technique for capsulorrhexis construction. The dye may be injected into the chamber through paracentesis under air. The air and residual dye are then exchanged for viscoelastic. Despite the absence of a red reflex, the capsule is easy to see.
The technique of CCC has provided important advantages both for cataract surgery and IOL implantation. Because endolenticular or in situ phaco must be performed in the presence of an intact continuous capsulectomy opening, capsulorrhexis has served as a stimulus for modification of phaco techniques. The edge of a well-constructed rhexis completely overlaps the edge of the IOL, ensuring positional stability and enhancing refractive predictability.
Hydrodissection and Hydrodelineation
Hydrodissection has traditionally meant injection of fluid into the cortical layer of the lens to separate the nucleus from the cortex and the capsule. Following the adoption of capsulorrhexis, hydrodissection became a critical step to mobilize, disassemble, and remove the nucleus. Fine first described cortical cleaving hydrodissection, which is designed to cleave the cortex from the capsule and leave the cortex attached to the epinucleus. Cortical cleaving hydrodissection often eliminates the need for cortical cleanup as a separate step in cataract surgery.
In this technique, the anterior capsular flap is initially elevated with a 26-gauge blunt cannula. Firm and gentle continuous irrigation results in a fluid wave that cleaves the cortex from the posterior capsule. The lens bulges forward because fluid is trapped by equatorial cortical–capsular connections. Depressing the central portion of the lens with the side of the cannula forces fluid around the equator and lyses the cortical–capsular connections. Adequate hydrodissection is demonstrated by rotation of the nuclear–cortical complex. The demonstration of free rotation of the lens within the capsule represents a critical step in phaco.
Hydrodelineation describes separation of the epinuclear shell from the endonucleus by irrigation. The epinucleus acts as a protective cushion within which phaco forces can be confined. Further, the epinucleus keeps the bag on stretch throughout the procedure, making capsule rupture less likely.
To perform hydrodelineation, a 26-gauge cannula is placed in the nucleus, off center to either side, and directed at an angle downward and forward toward the central plane of the nucleus. When the nucleus starts to move, the endonucleus has been reached. At this point, the cannula is directed tangentially to the endonucleus, and a to-and-fro movement of the cannula is used to create a tunnel within the epinucleus. The cannula is backed out of the tunnel approximately halfway, and gentle but steady pressure on the syringe allows fluid to enter the distal tunnel without resistance. A circumferential golden or dark ring will appear, outlining the endonucleus.
Occasionally, an arc, rather than a complete ring, will result, surrounding approximately one quadrant of the endonucleus. In this instance, the procedure can be repeated in multiple quadrants until a golden or dark ring confirms complete circumferential separation of the endonucleus from the epinucleus.
Nucleofractis Techniques
The recognition that the lens nucleus could be divided and removed from within the protective layer of the epinucleus while preserving the capsulorrhexis influenced the development of a plethora of phaco techniques.
Divide and Conquer
In the divide-and-conquer technique originally described by Gimbel, a deep crater is sculpted into the center of the nucleus, including the posterior plate. However, phaco fracture, described by Shepherd, is often referred to as a “divide and conquer” technique. In this technique, the surgeon sculpts a groove parallel to the incision one and a half to two times the diameter of the phaco tip, with the tip in a bevel-up position, using moderate power and low vacuum. Using the phaco handpiece and a second instrument, the surgeon then rotates the nucleus by 90° and sculpts a second groove perpendicular to the first. Sculpting continues until the red reflex is seen at the bottom of the grooves. A bimanual cracking technique is used to create a fracture through the nuclear rim in the plane of one of the grooves. The nucleus is then rotated by 90°, and additional fractures are made until four separate quadrants are isolated. A short burst of phaco power with increased vacuum then is used to embed the phaco tip into one quadrant, which is pulled into the center for emulsification. The second instrument can help elevate the apex of the quadrant to facilitate its mobilization.
Phaco Chop
Nagahara first introduced the “phaco chop” technique by using the natural fault lines in the lens nucleus to create cracks without creating prior grooves (Presentation at the American Society of Cataract and Refractive Surgery Film Festival, 1993). The phaco tip is embedded in the center of the nucleus after the superficial cortex is aspirated. In horizontal chopping, a second instrument, the phaco chopper, is then passed to the equator of the nucleus, beneath the anterior capsule, and drawn to the phaco tip to fracture the nucleus. The two instruments are separated to widen the crack. In vertical chopping, a sharp-tipped instrument is inserted directly into the nucleus beside the embedded phaco needle, and the two instruments are again separated as in horizontal chopping. The nucleus is rotated, and this procedure is repeated until several small fragments are created, which are then emulsified.
Divide and Conquer
In the divide-and-conquer technique originally described by Gimbel, a deep crater is sculpted into the center of the nucleus, including the posterior plate. However, phaco fracture, described by Shepherd, is often referred to as a “divide and conquer” technique. In this technique, the surgeon sculpts a groove parallel to the incision one and a half to two times the diameter of the phaco tip, with the tip in a bevel-up position, using moderate power and low vacuum. Using the phaco handpiece and a second instrument, the surgeon then rotates the nucleus by 90° and sculpts a second groove perpendicular to the first. Sculpting continues until the red reflex is seen at the bottom of the grooves. A bimanual cracking technique is used to create a fracture through the nuclear rim in the plane of one of the grooves. The nucleus is then rotated by 90°, and additional fractures are made until four separate quadrants are isolated. A short burst of phaco power with increased vacuum then is used to embed the phaco tip into one quadrant, which is pulled into the center for emulsification. The second instrument can help elevate the apex of the quadrant to facilitate its mobilization.
Phaco Chop
Nagahara first introduced the “phaco chop” technique by using the natural fault lines in the lens nucleus to create cracks without creating prior grooves (Presentation at the American Society of Cataract and Refractive Surgery Film Festival, 1993). The phaco tip is embedded in the center of the nucleus after the superficial cortex is aspirated. In horizontal chopping, a second instrument, the phaco chopper, is then passed to the equator of the nucleus, beneath the anterior capsule, and drawn to the phaco tip to fracture the nucleus. The two instruments are separated to widen the crack. In vertical chopping, a sharp-tipped instrument is inserted directly into the nucleus beside the embedded phaco needle, and the two instruments are again separated as in horizontal chopping. The nucleus is rotated, and this procedure is repeated until several small fragments are created, which are then emulsified.
Power Modulations
Fine described the “choo-choo chop and flip” technique in 1998 and subsequently correlated the reduction of ultrasound energy made possible by power modulations with superior uncorrected visual acuity on the first postoperative day. Effective phaco time (EPT), absolute phaco time (APT), and cumulative dissipated energy (CDE) have become standard metrics for the utilization of ultrasound energy. Although EPT, APT, and CDE cannot be compared across different machines made by different manufacturers, when using the same machine, they can be compared from one case to the next as a sign of surgical efficiency.
In Fine’s technique, a 30° straight phaco tip is used bevel down. After aspirating the epinucleus uncovered by capsulorrhexis, a horizontal chopper is placed in the golden ring by touching the top center of the nucleus with the tip and pushing the tip peripherally so that it slides beneath the capsulorrhexis. The chopper is used to stabilize the nucleus by lifting and pulling toward the incision slightly, after which the phaco tip “lollipops” the nucleus in either pulse mode at 2 pulses per second or at the 80-millisecond burst mode. Burst mode utilizes fixed power and duration with variable interval. In pulse mode, there is variable power with fixed duration and interval. These power modulations reduce total ultrasound energy and increase hold. Once the tip is buried in the center of the nucleus, vacuum is maintained in foot position 2. The nucleus is scored by bringing the chopper to the side of the phaco needle. It is chopped in half by pulling the chopper to the left and slightly down while moving the phaco needle, still in foot position 2, to the right and slightly up ( Fig. 5.11.2 ). Then, the nuclear complex is rotated by 90°. The chop instrument is again brought into the golden ring, the hemi-nucleus is lollipopped, scored, and chopped with the resulting wedge now lollipopped on the phaco tip and evacuated. The nucleus is rotated so that wedges can be scored, chopped, and removed by high vacuum assisted by short bursts or pulses of phaco. The size of the wedges is varied according to the density of the nucleus.
After evacuation of all endonuclear material, the epinuclear rim is trimmed in each of the three quadrants, mobilizing the cortex. As each quadrant of the epinuclear rim is rotated to the distal position in the capsule and trimmed, the cortex in the adjacent capsular fornix flows over the floor of the epinucleus and into the phaco tip. The floor is pushed back to keep the bag on stretch until three of the four quadrants of the epinuclear rim and cortex have been evacuated. The epinuclear rim of the fourth quadrant is then used as a handle to flip the epinucleus. As the remaining portion of the epinuclear floor and rim is evacuated from the eye, the entire cortex is often evacuated with it.
If there is remaining cortex after removal of all the nucleus and epinucleus, there are three options. The phaco handpiece can be left high in the anterior chamber while the second handpiece strokes the cortex-filled capsular fornices. Frequently, this results in floating the cortical shell as a single piece and aspirating it through the phaco tip (in foot position 2) because cortical cleaving hydrodissection has cleaved most of the cortical–capsular adhesions.
Alternatively, if one wishes to complete cortical cleanup with the irrigation–aspiration handpiece prior to lens implantation, the residual cortex can almost always be mobilized as a separate and discrete shell and removed without turning the aspiration port down to face the posterior capsule.
The third option is to visco-dissect the residual cortex by injecting a dispersive viscoelastic through the posterior cortex onto the posterior capsule. The viscoelastic material spreads horizontally, elevating the posterior cortex and draping it over the anterior capsular flap. At the same time, the peripheral cortex is forced into the capsular fornix. The posterior capsule is then deepened with a cohesive OVD, and the IOL is implanted, leaving anterior residual cortex anterior to the IOL. Removal of residual OVD material accompanies mobilization and aspiration of the residual cortex.
Nonlinear delivery of ultrasonic or sonic frequencies, such as torsional and elliptical phaco, has further improved operating efficiency. Chopping techniques in combination with power modulations and nonlinear ultrasound power delivery minimize morbidity and enhance the rapidity of visual rehabilitation.
Biaxial Microincision Cataract Surgery
Advances in ultrasound engineering during the late 1990s led to the application of millisecond-level control and variable duty cycles in phaco, vastly reducing the risk of thermal injury from the phaco needle and permitting removal of the irrigation sleeve. Separation of irrigation from aspiration during phaco came to be known as biaxial microincision cataract surgery (B-MICS) ( ).
The advantages of B-MICS include better followability because of the separation of infusion and aspiration, access to 360° of the capsular bag with either infusion or aspiration by switching instruments from one hand to the other, the ability to use the flow of irrigation fluid as a tool to move material within the capsular bag or anterior chamber (particularly from an open-ended irrigating chopper or manipulator), prevention of iris billowing and prolapse in cases of intraoperative floppy iris syndrome, and significantly decreased risk of vitreous prolapse in the case of a posterior capsular tear, zonular dialysis, or subluxated cataract, thanks to maintenance of a pressurized stream of irrigation.
Perhaps the greatest advantage of the biaxial technique lies in its ability to remove the subincisional cortex without difficulty. As originally described by Brauweiler, by switching infusion and aspiration handpieces between two microincisions, 360° of the capsular fornices are easily reached, and cortical cleanup can be performed quickly and safely.
Since dispersive OVDs do not easily extrude through these small incisions, the anterior chamber is more stable during capsulorrhexis construction, and there is much less likelihood of an errant tear. This added margin of safety is particularly noticeable in cases of zonular compromise, such as pseudo-exfoliation and traumatic zonular dialysis ( Fig. 5.11.3 ). The added chamber stability also can make a difference in control of the capsulorrhexis in both high myopia and high hyperopia with an extremely deep or a very shallow anterior chamber, respectively ( ).
B-MICS Vertical Chop Technique
After hydrodissection and hydrodelineation, the phaco needle is first embedded proximally with high vacuum and 40% power. In the other hand is a vertical chopper that will be used to split the nucleus. As vacuum builds to occlusion a rapid rise time enables the phaco needle to quickly grasp the endonucleus. At the point occlusion is reached, the aspiration flow rate drops to zero. The surgeon then moves into foot position 2 so that high vacuum is maintained and the power drops to zero. The blade of the irrigating vertical chopper is brought down just distal to the phaco tip. As a full-thickness cleavage plane develops, dividing the nucleus in two, the instruments are separated to insure a complete chop ( Fig. 5.11.4 ).
