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CONTENTS |
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CHAPTER HIGHLIGHTS |
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Introduction
When one considers that biaxial phacoemulsification was first described in 1985 and, therefore, has been one of the options available to cataract surgeons, it remains interesting that the approach can be viewed with some suspicion. Each time a particular surgeon has advocated the approach, interest was raised and then seemed to drift away. This was due, in part, to a lack of equipment and instrumentation to facilitate the technique. In fact, it has only been in the past 3 years that improvements in instrumentation and phacoemulsification equipment have enabled cataract surgeons to fully explore a biaxial approach and sub-2mm incisions. Today, a growing number of cataract surgeons are becoming converts to the biaxial technique for phacoemulsification. This chapter will explore the evolution of biaxial microsurgical phacoemulsification, as well as the current technique, instrumentation and software available.
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Terminology
The term bimanual phacoemulsification does not appropriately describe noncoaxial phacoemulsification. Arshinoff recently observed that even with coaxial phacoemulsification, because most surgeons have been operating for many years with both hands, the standard coaxial procedure has been bimanual (Figure 19-1).[1]
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Figure 19-1 Bimanual, coaxial phacoemulsification using a sleeved phaco tip and a chopper in the second hand. |
Since the new technique of unsleeved phacoemulsification has been introduced, it has been referred to by various names by various surgeons, including cold phacoemulsification. The new nonsleeved phacoemulsification procedure has enabled surgeons to perform phacoemulsification through a smaller incision. If phacoemulsification and aspiration are considered as one axis and the now-separated irrigation a second axis, then biaxial (as proposed by Arshinoff) is an appropriate term for the procedure. Biaxial is simply what is different from coaxial in biaxial phacoemulsification (Figure 19-2). The naming should be “biaxial” phacoemulsification, because it clearly refers to the fundamental difference in the procedure separating it from coaxial phacoemulsification. Biaxial makes no specific reference to incision size, although this may change over time.
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Figure 19-2 Bimanual non-sleeved phacoemulsification: aspiration is considered as one axis and the separated irrigation (chopper) as a second axis. With this configuration, biaxial phacoemulsification is the appropriate term for the procedure. |
To emphasize the smaller incision (1.5mm as opposed to 2.8 mm), the new procedure could appropriately be called microincision phacoemulsification (or MICS – microincision cataract surgery). When discussing incision length, Grabow recently suggested distinguishing the various lengths by the following terms:
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Long incision for extracapsular cataract extraction/intracapsular cataract extraction (10mm incision) |
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Small incision for phacoemulsification with a poly(methyl methacrylate) intraocular lens (6mm incision) |
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Mini-incision for phacoemulsification with a foldable intraocular lens (IOL) (3mm incision) |
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Microincision for phacoemulsification with a foldable IOL (≤1.5mm incision).[2] |
As the procedure is still in evolution, some cases are performed using nonsleeved phacoemulsification through two 1.5mm incisions with IOL implantation through an enlarged (or separate) incision. In this case, one could describe the procedure as biaxial phacoemulsification or microincision phacoemulsification, but could not truly call the whole procedure microincision, as only the phacoemulsification portion would have been performed through a microincision. Only when both phacoemulsification and IOL implantation are performed through 1.5mm incisions can we truly call the entire procedure microincision. But even this might be questionable to some extent, as previously pointed out by Osher. If two 1.5mm incisions (totalling 3mm of incision length) are used, is it still microincision surgery?[3]
If one incision is enlarged to 2.8mm and the other is left at 1.5 mm (totaling 4.3mm), it would be mini-incision surgery. Surgery using a 1.7mm (mini-incision) sleeved coaxial phacoemulsification with IOL implantation through a 1.8mm incision would be called coaxial mini-incision surgery. It seems to be appropriate to describe our procedures using both, the phacoemulsification technique (coaxial or biaxial) and the incision size, such as coaxial miniincision or biaxial microincision.
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Benefits of biaxial
The outcomes achieved with standard phacoemulsification techniques are quite good, making it a procedure that is difficult to improve upon. Still, there are some quantifiable benefits to using a biaxial approach:
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Greater anterior chamber stability – owing to microincisions limiting wound leakage and collateral fluid egress |
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Closed environment – reduced risk of infection |
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Corneal endothelial cell protection – due to less flow volume |
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Safer procedure in challenging cases – such as in eyes with compromised zonules and post-vitrectomy cataract removal |
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Minimal induced astigmatism. |
Biaxial phacoemulsification separates irrigation and phacoemulsification for cataract removal, through micro incisions that range from 1.2mm to 1.5mm in size, although it is possible to perform through incisions of less than 1mm. Irrigation is typically accomplished with an irrigating chopper, while the cataract is emulsified and aspirated using a sleeveless phaco needle.[4] The biaxial approach provides surgeons better visualization and maneuverability due to smaller instrumentations and can be a safer procedure in complicated cases. Further, various clinical studies have shown that biaxial phacoemulsification can be used on any grade of cataract.[5–17] Although there was a large degree of skepticism about the safety of removing cataracts through a microincision with a sleeveless phaco tip, a variety of advancements in phacoemulsification power modulation along with improved understanding of fluid dynamics have removed many of the perceived barriers to biaxial phacoemulsification.
Compared with coaxial phacoemulsification, biaxial phacoemulsification can lower mean phacoemulsification time, mean total phacoemulsification time and surgically induced astigmatism.[18] A number of studies also show that the two techniques are, substantially, equivalent in terms of endothelial cell loss and visual outcomes.[7,][19–21]
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Historical perspective
Introduced by Kelman in 1967, phacoemulsification has evolved to become safe and highly successful.[22] As mentioned, the first attempts of biaxial phacoemulsification through a 1mm incision were described in 1985 by Shearing.[23] However, attempts to separate aspiration and irrigation from ultrasound were first described in the 1970s by Girard.[24] He made a number of attempts at ultrasound and aspiration infusion separation but was unsuccessful, abandoning his efforts because of extensive thermal corneal damage.[24–26] Shearing and his colleagues continued where Girard left off and succeeded in performing biaxial phacoemulsification through two 1mm incisions, concluding that the technique was feasible.[23,][27]
The biaxial approach has since evolved to become safer and more successful, with a published report of the advantages specifically related to the biaxial technique in 1997 by Colvard, which states the benefits of the two-needle technique for irrigation–aspiration (I–A) in comparison to the aspiration of subincisional cortical material with a standard I–A handpiece.[27] In Japan, Tsuneoka et al. successfully performed cataract surgery through an incision of 1.4mm with a 20-gauge sleeveless ultrasound tip, avoiding thermal burns at the incision site by maintaining a level of leakage through the incision for cooling purposes.[28]
One of the critical components in the success of the biaxial approach is incision creation, with a number of surgeons advancing their level of knowledge of the optimal incision for this microsurgery. Ernest, developer of the sutureless technique, performed studies of wound geometry on cadaver eyes to conclude that wound leakage could be avoided, despite any internal or external pressure, through a square wound and an internal corneal lip of at least 1.5mm.[29,][30] Fine introduced temporal self-sealing clear corneal incisions, which significantly lessened surgical time, reduced the risk of induced astigmatism and promoted quicker postoperative recovery.[31,][32] Fine also developed several phacoemulsification techniques, including the crack and flip, chip and flip, and the choo-choo chop and flip techniques. Agarwal introduced the concept of Phakonit (Phako with Needle Incision Technology) in 1998 where the lens was emulsified through a clear corneal incision of 0.9mm, using a bare phaco needle and an irrigating chopper.[10]
In terms of instrumentation development, the goal was to create instruments capable of maximum efficiency through these microincisions. An infrared laser device for cataract removal was developed by Dodick in the early 1990s, evolving to become the Dodick photolysis system, which claimed safe operation within the capsular bag, reduced heat release and intraocular energy and clear corneal incisions of under 1.5mm.[33–35] Agarwal developed instrumentation for his Phakonit technique, including the irrigation chopper and the Phakonit knife, and Fine developed numerous instruments and implants including lens insertion forceps, bimanual handpiece sets and irrigating choppers.[16,][36,][37] The ‘tilt and tumble’ phacoemulsification technique was developed by Lindstrom, which was a variant of supracapsular phacoemulsification where a beveled phaco tip was used with the superior pole of the nucleus tilted above the capsule.[38]
The drawbacks to the biaxial phacoemulsification technique revolve mainly around the risk of thermal damage to the cornea and wound leakage, which can potentially lead to anterior chamber collapse. As is commonly known, in biaxial phacoemulsification, there is no sleeve surrounding the phaco tip. This sleeve serves three purposes: (1) it helps deliver irrigation fluid into the eye; (2) it keeps the phaco tip cool; and (3) protects the cornea from direct contact with the phaco tip.[4]
Part of the solution to reducing the risk of biaxial phacoemulsification has been to reduce the amount of ultrasonic energy that is delivered into the eye. The main phacoemulsification equipment manufacturers, including Advanced Medical Optics (AMO, Santa Ana, CA), Alcon Laboratories (Ft. Worth, TX) and Bausch & Lomb (Rochester, NY), all began to introduce software changes to their systems that would enable biaxial surgeons to better control ultrasound energy during the procedure. The AMO offering, Sovereign with WhiteStar technology, enabled ‘ultrapulse’ modulation, making it possible to adjust the duty cycle and pulse duration.[39] Studies by Donnenfeld, Soscia and Olson, et al, and Packard reported the results of using a 21-gauge irrigating chopper and a 21-gauge bare phaco needle and using WhiteStar micro-pulse power modulation with the Sovereign phacoemulsification machine. Soscia, et al, also reported in a study of cadaver eyes that thermal injury did not occur during the procedure, even with 100% power and aspiration completely occluded.[7,][40] Packard noted that the Sovereign system did not produce wound burns and provided adequate surgical efficiency through sub-2mm incisions.[41]
Braga-Mele studied biaxial microincision surgery using the Bausch & Lomb Millennium Microsurgical System with burst mode and moderate incisional outflow, which allowed frequency, energy and pulse width control, promoting cooling and preventing wound burn and contracture. The linear footpedal interval control and constant percent power enabled minimal ultrasonic energy and, subsequently, heat release.[42]
Alcon, with its Infiniti Vision System, introduced sonic oscillatory motion with longitudinal ultrasonic vibration, as well as modifiable pulse and burst modes, which were designed for minimal occlusion and reduced energy use.[4] The Infiniti system also features Aqualase using saline pulses rather than ultrasound to further reduce thermal corneal damage risk.[43]
To avoid fluid instability and subsequent anterior chamber collapse, fluid infusion is required to be greater than the vitreous pressure and the atmospheric pressure, but its measurement is dependent on specific variables. Choppers and cannulae have been developed especially for this procedure to ensure that a safe amount of fluid reaches the eye regardless of forced or passive infusion. Agarwal attempted to solve the problem of fluidic instability by developing a three-port Phakonit technique that utilizes a separate anterior chamber maintainer. Agarwal and Agarwal also introduced the concept of pressurized infusion by injecting air into the infusion bottle, allowing the use of 20- and 21-gauge irrigating choppers during phacoemulsification. Agarwal also resolved the issue of fluid spraying over the cornea during phakonit by ensuring that the hub of the infusion sleeve was only present at the base of the needle.[17,][44]
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Instrumentation
The advent of biaxial phacoemulsification has resulted in the development of numerous instruments designed to improve the efficiency of this procedure. These endeavors have primarily focused on sleeveless phaco needles and irrigating choppers, but also include microkeratomes for the incisions and microincision capsulorrhexis forceps for the creation of the capsulorrhexis. Typically, 19- or 20-gauge instrumentation is used in biaxial phacoemulsification:
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Keratomes. Diamond, sapphire or metal keratomes can be used to create the 1.2–1.4mm clear-corneal trapezoidal incisions for the irrigation chopper and the phaco needle. |
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Needle or microforceps for capsulorrhexis. The instrument used for creation of the capsulorrhexis really is a matter of personal preference. If using a needle, a 24- or 27-gauge bent needle works best.[21] If forceps are the preferred method, a number of instrument companies have created microincision 23-gauge capsulorrhexis forceps for the task.[45] |
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Phaco needle. The optimum needle for biaxial phacoemulsification is a 21- or 20-gauge needle (Figure 19-3) with a 0–30° beveled tip.[46] |
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Irrigating choppers. There are two types of irrigating choppers: side irrigating and forward irrigating. Once again, numerous instrument manufacturers have developed irrigating choppers for biaxial phacoemulsification. The authors' preference is to use a 19-gauge chopper with two irrigation ports to the side (Figure 19-4) or one at the end of the tip (G-32059, Geuder, Heidelberg, Germany).[21] |
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Bimanual irrigation and aspiration. As with the phaco needle and irrigating chopper, for cortical clean-up the recommended gauge size for these tips is 20-gauge. Most instrument companies now also offer disposable I–A tips that can be easily switched around to facilitate the removal of subincisional cortex.[4] |
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Figure 19-3 A phaco needle with a cut sleeve for biaxial phacoemulsification. |
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Figure 19-4 A 19-gauge chopper (1.1 mm) with two irrigation ports to the side (2 x 0.75 mm) for biaxial phacoemulsification. This chopper is also available in an oval diameter with a terminal opening. |
Phaco machines, pumps and software
With the increased use of biaxial phacoemulsification, most equipment manufacturers have worked with cataract surgeons to develop modifications and improvements to their systems that enable surgeons to better control ultrasound power. The overall goal is to use minimal ultrasound power to emulsify the cataract, avoiding or reducing corneal tissue trauma – this technique has come to be known as “cold phaco:”
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Advanced Medical Optics (AMO): AMO's offering for biaxial phacoemulsification, its WhiteStar Technology, utilizes what the company calls “ultrapulse” modulation of the ultrasound energy. This software is used on either the Sovereign and Sovereign Compact systems. WhiteStar has been clinically proven to result in clearer corneas on the first postoperative day.[47] The patented microburst technology is designed to increase cutting power vs. continuous ultrasound in many situations, and there is no need to switch handpieces or modes during lens removal to adjust for lens density. It also reduces the energy directed into the eye to minimize thermal damage and improve outcomes. WhiteStar Biaxial microphacoemulsification can be used for removal of all lens types through incisions as small as 1.4mm using little or no ultrasound. The software allows the surgeon to adjust both the duty cycle and pulse duration.[48] A 10-patient study to evaluate WhiteStar in biaxial phacoemulsification by Donnenfeld et al. showed that there was a decreased thermal effect with the software, with corneal wound temperatures well below those that can cause corneal shrinkage.[7] An in-vitro study by Soscia et al. using human cadaver eyes showed similar results when using settings well beyond the norm of those found in cataract surgery.[41] |
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Alcon: Alcon's offering for biaxial phacoemulsification with its Infiniti Vision System includes adjustable pulse and burst modes, as well as the ability to customize fluidic parameters based on the surgeon's preferred surgical technique and patient pathology. The Infiniti's Custom Fluidics Software monitors and adjusts fluidic parameters, providing increased fluidic versatility and control. It also allows customized lens removal while minimizing fluidic flow and turbulence. The system's custom power modulations offer precise energy delivery with an improved thermal safety profile and reduced repulsion of the cataract. A new feature of the Alcon system is the OZil Torsional Handpiece that uses an ultrasonic, oscillating, side-to-side movement to break up the lens. It is designed to help improve followability and reduce cavitation.[48]Another feature on the Infiniti system is the AquaLase Liquefaction Device. Aqualase utilizes 4 μL pulses of heated balanced salt solution to liquefy the cataract and appears to be most successful in mild-to-moderate nuclear sclerosis.[48] It is intended to reduce the risk of thermal damage to the cornea, however, there have been no published studies to confirm this. |
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Bausch & Lomb: The Millennium Microsurgical System gives biaxial surgeons a number of options for controlling phacoemulsification power during surgery, including, conventional pulse mode, fixed-burst mode and multiple-burst mode with its Custom Control Software (CCS). In addition, the Millennium system operates at a lower ultrasound frequency (28.5 kHz), which is thought to reduce friction and cause less tissue damage. However, the Millennium has a longer stroke length, which means the same amount of heat is likely produced during emulsification.[48] The Millennium System also offers cataract surgeons a choice of pumps systems – either a peristaltic pump (Advanced Flow System [AFS]) or a venturi pump. The AFS pump is designed to provide improved intraoperative stability, efficiency and control, while the direct-response venturi vacuum system provides simultaneous, dual-linear foot pedal control of flow, aspiration and ultrasound power.
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Geuder: The Megatron S3 VIP, for cataract and vitreoretinal surgery, features a Venturi Inclusive Peristaltic (VIP) dual pump system, CFM Phaco Matrix with numerous ultrasound settings including Geuder's new Cool Flash Mode for biaxial phacoemulsification technique and SOS – minimized ultrasound energy through Safe Occlusion System. The Realtime Vac Sensor (RVS) in combination with innovative software is intended to provide superior anterior chamber stability. |
Air pump and internal infusion
One of the greater challenges in biaxial phacoemulsification is proper fluidics and maintenance of a stable anterior chamber. Because the instruments used are smaller in gauge, the amount of fluid into the eye is reduced. There are a number of options available for addressing this issue, including using large-bore irrigating choppers, raising the infusion bottle, reducing the rate of vacuum/aspiration or forcing infusion with an external mechanism such as an air pump. A number of equipment manufacturers have also introduced innovations that help answer the fluid issue:
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Air pump. An air pump is attached to the infusion bottle and is used to inject air into the bottle in order to increase the flow rate. As described by Agarwal in his book, the benefits to this approach are increased infusion through the irrigating chopper, as well as helping to maintain a stable anterior chamber.[49] With the availability of new instruments and phacoemulsification systems for biaxial phacoemulsification the use of an air pump is not necessary. |
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Thin-walled tubing. Along with raising the height of the infusion bottle, thin-walled tubing will help to increase inflow and keep the chamber stable.[46] |
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Intellesis Sensor Accuracy. This offering by AMO is said to monitor the pressure variations at the phaco tip, providing vacuum control over the tubing, and reducing the potential for surge and a loss of chamber stability.[50] |
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Innovative Stable Chamber System. Offered by Bausch & Lomb on its Millennium Microsurgical System, this system is also said to reduce post-occlusion surge and improve chamber stability. It is available as part of the Millennium Micro Incision Vacuum Pack.[51] |
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Cruise Control. Staar Surgical offers low compliance (thin-walled) tubing and post-occlusion surge control (Cruise Control) for its phacoemulsification system. |
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Surgical technique for biaxial phacoemulsification
Our preferred technique for biaxial phacoemulsification begins with a 1.3mm trapezoidal corneal incision with a tunnel that is 1.3mm in length. This is made at 11 o'clock and is parallel to the limbus. Prior to creation of the biaxial incisions, the pupil is dilated with tropicamide 0.5% and phenylephrine 0.5%, followed by 1 drop of diclofenac. Anesthesia was accomplished with an injection of bupivicaine 0.5% with lidocaine 2% into the eyelid and tetracaine 1% onto the conjunctiva.
To create the trapezoidal incision (Figure 19-5), we use a trapezoidal steel microkeratome that is designed specifically for biaxial cataract surgery (Nanoedge, Geuder, Heidelberg, Germany). The second incision for the irrigating chopper is made at 2 o'clock and is 1mm in width. After filling the anterior chamber with ophthalmic viscosurgical device (OVD), we perform a capsulorrhexis with a 24-gauge bent needle and then do hydrodissection and hydrodelineation. According to Hoffman, free rotation of the entire epinucleus helps to make lens removal easier during biaxial phacoemulsification. As a result, he recommends performing hydrodissection, then rotation of the lens before performing hydrodelineation. Hoffman also recommends applying external pressure on the posterior lip of the microincision during this step in order to avoid excessive pressure in the anterior chamber.[45]
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Figure 19-5 Creation of the trapezoidal clear corneal incision using a trapezoidal steel microkeratome designed specifically for biaxial cataract surgery. |
After completion of hydrodissection and hydrodelineation, the next step is to insert a 20-gauge phacoemulsification needle through the 11 o'clock incision and a 19-gauge irrigating chopper, with two irrigation ports, through the 2 o'clock incision. Our preferred method for cataract removal is to use a stop-and-chop technique using the Sovereign machine with WhiteStar Software (v. 6). The normal settings are:
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Maximum phacoemulsification power: 55% |
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Bottle height: 57cm |
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Aspiration rate: 29cm3/min |
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Maximum vacuum: 50mmHg. |
For the emulsification and aspiration of the nucleus, the following settings are typically used:
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Maximum phacoemulsification power: 40% |
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Bottle height: 76cm |
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Aspiration rate: 30cm3/min |
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Maximum vacuum: 300mm Hg. |
The phacoemulsification energy was done in pulses with a duty cycle of 33%, which means that phacoemulsification energy was on for 33% of every 1 s.[21] The WhiteStar Software enables the surgeon to make two critical changes to the manner in which ultrasound energy is used. First, the surgeon can shorten the duration of the phacoemulsification pulse to as little as 6 ms. Second, the surgeon can change the duty cycle to prolong and vary the amount of time the ultrasound cycles off. Chang reports that there are three benefits to these features: (1) a lower duty cycle means less ultrasound energy into the capsular bag; (2) in combination with the interrupted ultrasound, more frequently delivery means the build-up of less heat; and (3), the two features means less repelling forces at the tip of the phaco needle.[49]
There is another aspect about the effect this software has on ultrasound power. Baudouin describes this pulsing as a “microburst” effect that helps to sustain transient cavitation – the effect that occurs at the beginning of ultrasound power and leads to the breakdown of tissue.[52] By using microbursts to sustain transient cavitation, the use of ultrasound is expected to be more efficient, requiring less heat and energy introduced into the eye. The vast majority of biaxial surgeons agree that a chopping technique works best for this procedure, except in cases with extremely soft nuclei or in refractive lens exchange when biaxial I–A is typically all that is necessary.[5–17],[45]
The maintenance of a stable anterior chamber during biaxial phacoemulsification is down to using appropriately sized incisions, proper bottle height, as well as an ophthalmic viscosurgical device (OVD) to help keep the eye pressurized.[51] Although much has been made about unstable anterior chambers during biaxial phacoemulsification, the reality is that the chamber should actually be more stable, because there should be very little outflow from the eye.[18]
In a study conducted at the authors' university comparing the biaxial technique with coaxial phacoemulsification, the effective phacoemulsification time (EPT) was <3s in the majority of the biaxial cases (66%). This compared to an EPT of 32% in the coaxial eyes.[21] This study found that a shorter EPT was associated with more rapid visual recovery in the biaxial eyes.
To perform biaxial I–A, the bottle height is raised, and irrigation and aspiration tips are inserted through the nasal and temporal incisions to remove the residual cortex and polish the posterior capsule. We then inject additional OVD into the eye and enlarge the incision. The amount of enlargement is currently determined by the IOL to be implanted (Figure 19-6). In almost all cases of biaxial surgery, it is necessary to enlarge the incision in order to insert IOL. A few surgeons opt to create a third incision in order to insert the IOL, placed between the nasal and temporal incisions.[48] In case of a trapezoidal corneal incision this additional incision is not necessary. Precise measurement of the small incision (starting with 1mm size) can be performed using a titanium microincision caliper (Figure 19-7, Duckworth & Kent, 9–646).
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Figure 19-6 Enlargement of the incision for subsequent intraocular lens implantation. |
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Figure 19-7 The titanium microincision caliper accurately measures very small incisions as used in biaxial phacoemulsification. |
After IOL implantation and removal of the OVD, both incisions were checked to ensure that they were watertight and left sutureless.
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Biaxial advantages
As was shown in our study, the results between biaxial phacoemulsification and coaxial phacoemulsification are relatively similar – both patient groups had no complications and very good clinical results. So, why bother with biaxial cataract surgery? There are a number of very sound reasons for using this approach. Consider that in this particular study, the biaxial group showed an earlier improvement in best-corrected visual acuity (BCVA) compared to the coaxial group.[21] Similar results have been reported by Agarwal and Olson.[7,][10]
There are additional advantages outlined by Paul and Braga-Mele:[4]
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Smaller incisions should lead, theoretically, to a more stable anterior chamber due to a closed operating environment with less leakage of balanced salt solution and OVD. |
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These microincisions should heal more quickly and further reduce postoperative astigmatism. They should also be associated with a lessened risk of postoperative endophthalmitis. |
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By separating the irrigation from the phaco needle, removal of the nucleus fragments should be simplified because irrigation from the needle no longer pushes the pieces away. |
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As the microincision sizes are similar, the I–A handpiece ports can be interchanged to better manage subincisional cortex or nuclear fragments. |
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The micro-instrumentation used in biaxial phacoemulsification makes visualization of the operating field much better, which improves the safety of the procedure. |
More importantly, are these advantages:
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Reduced phacoemulsification energy. As evidenced by our prospective randomized study, as well as those by Alio, Donnenfeld, Chang and others, there is a statistically significant reduction in the amount of phacoemulsification energy that is used in biaxial phacoemulsification when compared to coaxial phacoemulsification surgery.[7,][18,][49]As Chang notes there does not really exist an apples to apples method of comparing the effective phacoemulsification times, because all equipment manufacturers have different ways of measuring EPT. However, there is little doubt that less ultrasound energy is better for the eye and the corneal incision.[49] In Alio's study, he found that total surgical time was less in biaxial surgery than in the coaxial cases and that by decreasing the surgical time it reduced the ultrasound energy introduced into the eye, making it the superior procedure.[18]
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Improved control and chamber stability. As a result of the separation of ultrasound power and irrigation, in biaxial phacoemulsification, surgeons actually have a much greater degree of control over what is happening within the capsular bag. With traditional phacoemulsification, the irrigation from the phaco needle has a tendency to push the lens fragments away from the tip. This necessitates the need to “chase” after fragments and guide them back to the phaco tip. In biaxial phacoemulsification, the irrigating chopper can be used to direct fragments to the tip making it quicker to emulsify and remove the nucleus. There is also less “acoustical streaming” from the phaco tip to push lens fragments away, according to Baudouin, due to the reduction and modulation of ultrasound energy.[52]
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Enhanced safety and efficacy. The authors' clinical study, as well as those conducted by Alio, Donnenfeld and others, point to the improved safety and efficacy of biaxial phacoemulsification when compared to coaxial and other standard techniques.[7,][18,][53–55] There is a trend toward quicker visual recovery in these eyes, as well as reduced induced astigmatism. Studies have also shown that there is no difference in corneal endothelial cell loss or endothelial morphology when biaxial phacoemulsification is used.[19,][56] |
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Challenges of biaxial phacoemulsification
Realistically, there are some challenges to successfully performing biaxial phacoemulsification. Chief among these is the learning curve, particularly for cataract surgeons who have not adopted a chopping technique for cataract removal. The smaller incisions used in biaxial phacoemulsification can also limit movement of the instruments that is necessary in order to avoid tissue trauma. Fluid leakage can be a problem if there is not a perfect fit between instruments and incisions, leading to chamber instability.[48] This is illustrated by a case report of leakage from an irrigation port incision.[57]
There is also the lack of an IOL that can go through an un-enlarged microincision. In almost all cases, it is necessary to enlarge the incision in order to implant the IOL. A number of biaxial critics, therefore, see this need for enlargement as defeating the purpose of creating the tiny incisions initially.[4] Next, is the concern that the bare phaco needle will overheat and cause corneal tissue damage and wound burns. Granted this is a risk, but as studies by Agarwal, Donnenfeld, Olsen and Braga-Mele have demonstrated by using new software that enables to minimize and control ultrasound energy, the risk of wound burn during biaxial phacoemulsification is actually extremely low.[7,][10,][43,][51,][58]
Finally, biaxial cataract procedures can take more overall surgical time, particularly in eyes with a greater than +4 cataract. This is due to the downsizing of the instruments, as well as the tighter fit around the phaco needle and irrigating chopper. When starting out with biaxial phacoemulsification, it is important to choose your first cases with care in order to learn to understand and manage these challenges.
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Current clinical findings
Results on biaxial cataract surgery published over the past 18 months certainly confirm the positive view we have of this procedure. In a study of the thermal effect of microburst and hyperpulse settings during sleeveless biaxial phacoemulsification with advanced power modulations, Braga-Mele concluded that this technique reduced wound temperatures during the phacoemulsification procedure, enhancing safety and efficiency. With power varying from 20% to 80% in 10% increments, pulse modes were set with and without aspiration-line occlusion, and wound temperatures were measured three times per second. The results verified that wound temperature did not exceed 39°C using 80% power during 3 min of occlusion, and 29°C with fixed microbursts of 4 ms on, 4 ms off.[5]
As discussed earlier in this chapter, the clinical outcomes of biaxial microincision were compared to those of coaxial small-incision clear cornea cataract surgery in the authors' prospective series. In this study, phacoemulsification using pulsed ultrasound energy with variable duty cycles was used, followed by mini-incision IOL implantation. The outcomes of BCVA, astigmatism, laser flare photometry value, effective phacoemulsification time (EPT), and endothelial cell count were assessed, revealing that BCVA improved more rapidly and EPT was shorter in the biaxial group. The median BCVA was 20/20 in the biaxial group and 20/25 in the coaxial group, and 68% of coaxial procedures had an EPT of over 3 s compared to only 34% of biaxial procedures.[21]
Another study of biaxial microincision phacoemulsification through two 1.4mm incisions for posterior polar cataract extraction found that adequate anterior chamber stability was provided by the low-infusion and low-vacuum system, and lens fragments were removed without hydrodissection or nucleus rotation. The study concluded that the biaxial technique enhanced safety by reducing risks of complication.[59]
In an assessment of the feasibility of biaxial microincisional phacoemulsification in hard cataracts of N3+ using the AMO Sovereign with WhiteStar technology, the ultrasound power was set at 30–25% according to nuclei hardness, with a duty cycle of 33%. The results showed no cases of thermal burn, and the amount of infusion solution used was less than that used in conventional coaxial phacoemulsification, placing this technique at an advantage over coaxial phacoemulsification.[12]
Prakash et al. assessed the efficiency of biaxial microincision phacoemulsification followed by the implantation of an injectable ThinOptX IOL in the capsular bag. The results verified that ThinOptX IOLs could be safely inserted through 1.7mm incisions used for biaxial phacoemulsification, with adequate distance and near visual acuity. Although the results suggested there was no notable change in keratometric astigmatism, the posterior capsular opacification rate was substantially higher with the ThinOptX IOL.[60]
Khng et al. looked at the changes in intraocular pressure (IOP) during standard coaxial and biaxial microincision phacoemulsification using a pressure transducer positioned in the vitreous cavity, which recorded IPO at 100 readings per second. The results revealed that biaxial microincision phacoemulsification was safer. The findings showed that IOP was lower for at least one of the biaxial phacoemulsification eyes than for the standard coaxial phacoemulsification eye in four of the eight stages of the procedure: hydrodissection and delineation, nuclear disassembly, irrigation–aspiration and anterior chamber reformation.[20]
Fine et al. also recently published a technique for refractive lens exchange using biaxial microincision phacoemulsification. Their study involved removal of the crystalline lens through two 1.2mm incisions, with capsulorrhexis formation, cortical cleaving hydrodissection, lens extraction in the iris plane and residual cortex removal all performed through the microincisions. The study found that this technique offered more surgical control during the procedure, in addition to the safety of a constant pressurization of the eye during the removal of the lens far from the posterior capsule.[61] Fine noted that this technique was safe and the least invasive, as the irrigating cannula was held above the lens to eliminate the risk of corneal damage. Hydrolineation was also avoided due to the use of a sleeveless phacoemulsification needle with the bevel turned towards the lens equator, which was carouselled in the plane of the capsulorrhexis without ultrasound energy and with high vacuum. Visual acuity results showed that 43% of the patients achieved both 20/25 and J2 or better.[62]
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Risk management
Certainly, there is a greater risk of complications when a surgeon first begins biaxial phacoemulsification. What follows is a listing of some of the most common problems and how to manage them effectively, where appropriate:
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Wound construction. There may be differences in removal techniques in biaxial phacoemulsification surgery, but all biaxial surgeons agree on one point: the need for a well-constructed incision. A poorly constructed incision will lead to wound leakage, chamber instability, corneal trauma and astigmatism.[49] |
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Phaco tip occlusion. This can occur when a highly viscous OVD is used. This type of OVD can also be difficult to remove at the end of biaxial cases, leading to IOP spikes and occlusion of the anterior chamber. In routine cases, it is best to use a regular medium viscous OVD such as Healon (AMO, Santa Ana, CA).[21] |
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Irrigation flow rate. Particularly when high vacuum is in use or following occlusion, the irrigation rate from the smaller gauge choppers used in biaxial surgery may not be able to maintain a stable anterior chamber. The surgeon must take these factors into account and adjust the infusion rate, aspiration rate and vacuum accordingly.[21] When exiting the eye the phaco tip has to be taken out first followed by the irrigating chopper to prevent anterior chamber collapse (Figure 19-8). |
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Figure 19-8 Anterior chamber collapse due to removal of the irrigating chopper prior to the removal of the phaco tip. |
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Complicated and special cases
As a result of the microincisions required for biaxial cataract surgery, as well as the almost completely closed environment, the procedure actually lends itself very well to some of the more complicated cataract cases (Figure 19-9).
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Figure 19-9 The biaxial approach facilitates phacoemulsification in an eye with a hard nucleus, reduced pupil size and loose zonules (pseudoexfoliation syndrome): e.g., non-sleeved (improved approach into the nucleus) phacoemulsification to the intended zonular direction (interchangeable). |
Among them are advanced and hypermature cataracts with a tense capsule. Under a grant from the Research to Prevent Blindness, Olson looked at which complicated cases would benefit from the biaxial approach. In hypermature cataracts with a tense capsule, a biaxial approach enables the cataract surgeon to perform an incision, inject a highly OVD material and create a capsulorrhexis without the risk of the capsulorrhexis going out of control, or for visualization to become obscured due to the milky cortex.[63] The same approach can also work in cases where iris prolapse is a concern due to a flat anterior chamber. In eyes with zonular dialysis, the biaxial approach allows the surgeon to place the two incisions away from the area of risk and, thus, operate with reduced risk.
Another complication that can benefit from biaxial cataract surgery is in the management of floppy iris syndrome. Douglas Koch combines a highly viscous OVD with a biaxial phacoemulsification technique in these cases using a modified stop-and-chop technique to keep the iris under control.[64]
A final potential use for biaxial cataract surgery is in pediatric and young cataract cases. Although there are no published reports establishing the use of biaxial surgery in these young eyes, the need for a completely closed environment would seem to lend itself to the procedure.[65]
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Future trends
Based on studies published in the past 2 years, as well as on anecdotal reports, there is an upsurge in the number of surgeons who now make biaxial cataract surgery a part of their surgical armamentarium. This situation has been helped by equipment manufacturers developing software that helps facilitate sleeveless, microincision cataract surgery, as well as by surgeons and instrument manufacturers working together to develop tools that can effectively work through these minute incisions.
The next piece of the puzzle is an IOL that can be delivered easily and safely through an un-enlarged microincision. At the present time, there are a number of IOLs that can be inserted through incisions of between 1.7 and 2.2mm. In the authors' series, an aspheric acrylic mini-incision IOL (Figure 19-10, Acri.Smart 36A, Acritec, Hennigsdorf, Germany) was injected through a 1.7mm incision (Figure 19-11). This company also manufactures the Acry.Lyc acrylic IOL that is capable of being inserted through a 1.5mm incision when the injector is placed just inside the incision. ThinOptX (Abingdon, VA) developed a hydrophilic acrylic IOL that is rolled and placed into a special injector for insertion into the capsular bag. Published reports indicate that this lens was injected through a 1.5mm incision.[4,][16] Insufficient capsular bag performance and high posterior capsule opacification rates with this IOL were reported.[64] Finally, Bausch & Lomb (Rochester, NY) recently introduced an aspheric (aberration-free), hydrophilic acrylic one-piece IOL called MI60 (26% water content) with 10° average angulation that can be injected through a 1.8mm incision using the wound-assisted technique. The 4-point fixation design is proven to offer good stability with its parent design, Akreos Adapt (Figure 19-12). Moreover, three overall diameters are available to better fit capsular bag sizes. The 360° barrier and square edge design in the Akreos MI60 incorporates the 360° posterior ridge as its Akreos predecessors in resisting posterior capsular opacification. Its 10° angulation is a further improvement, reinforcing the lens contact with the posterior capsule.
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Figure 19-10 Scanning electron microscopy overview of the aspheric acrylic Acri.Smart 36A intraocular lens for mini-incisional implantation. |
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Figure 19-11 Implantation of an aspheric acrylic microincision intraocular lens (IOL) (Acri.Smart 36A) after uncomplicated biaxial phacoemulsification using a second instrument (iris manipulator) to ensure one-step direct IOL implantation into the capsular bag. |
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Figure 19-12 Aspheric (aberration-free), hydrophilic acrylic one-piece MI 60 intraocular lens (Bausch & Lomb) provides a 4-point fixation design for good stability and a 360° square edge barrier for posterior capsular opacification prevention. |
When phacoemulsification came into the mainstream, the IOLs being implanted were between 5.5 and 6mm and required enlargement of the incision. The need for incisional enlargement is not a new phenomenon. However, the argument in favor of biaxial phacoemulsification will certainly become an easier one when there are IOLs widely available that can go through a <1.5mm incision.
The authors have become convinced that biaxial cataract surgery is the way forward. With the equipment, software and instrumentation now available, the surgery is safe, efficient and minimally invasive. Patients have better visual recovery in the immediate postoperative period with very low complication rates. The arguments used for many years against the biaxial approach really no longer stand. In fact, this technique may actually show a benefit in complicated cases and in hard cataracts. It is entirely possible that longer-term follow-up will show that there are fewer cases of cystoid macular edema and retinal detachment in these eyes due to the almost completely closed environment in which the cataract surgery is performed.
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