Cataract surgery has evolved since the development of ultrasonic emulsification in 1967. The introduction of foldable IOLs in the early 1990s greatly impacted the reduction of incision sizes. The ongoing process to improve surgical outcomes and minimize complications is complemented by a further reduction in incision size.
Bimanual Phaco Controversies
Until recently, microincisional cataract surgery was only performed by bimanual phacoemulsification. Two bare metal tips passed through two 1.5-mm incisions, separating irrigation and aspiration pathways. This controversial bimanual technique has been debated, and its adoption rate has been slower than anticipated in its early stages. Advocates of this technique have emphasized the advantages in great detail:
• Less astigmatism induction occurs;
• The technique boasts improved fluid dynamics, with the separated irrigation flow acting as an extra tool in the anterior chamber; and
• The wound experiences less temperature rise due to the lower friction coefficient between the bare metal tip and the corneal tissue.
Skeptical surgeons, however, question:
• The associated longer learning curve;
• The more complex manipulation for nucleus disassembly in the anterior chamber;
• The extended procedure time; and
• Significant wound distortion caused by manipulation of the rigid metal tip and cannula inside the tight corneal incisions.
Increased mechanical stress of corneal incisions is a major concern with regard to the higher risk of wound leakage and endophthalmitis. The recent and alarming rise of endophthalmitis has been associated with the construction of clear-corneal incisions.1-3 In my opinion, wound architecture and integrity contribute to the quality and safety of cataract surgery outcomes.
From Coaxial To Microcoaxial
Since the breakthrough of ultrasound in cataract surgery, the initial wound size has already been reduced from 3.2 mm to the current 2.8-mm or 2.6-mm incisions with the use of micro sleeves. The smaller sleeve size — and therefore potential lower irrigation flow — were compensated by thinner sleeve designs as well as innovations in ultrasound modulation, innovative phaco tip designs and improved tubing/cassettes with superior fluid dynamics characteristics. The trend toward smaller incisions coincided with the development of newer IOL designs and injector systems.
Wound-Assisted Injection Techniques
Some surgeons also introduced alternative techniques to inject the IOL. During the wound-assisted injection technique, the corneal tunnel is used as an extension of the cartridge tip;4 only the cartridge tip end is pressed against the wound (Figure 1). This technique allows for smaller incisions. The IOL volume, and not the cartridge tip, is the determining factor for the final wound size. Single-piece IOL designs (eg, Acrysof single-piece IOL [Alcon Laboratories, Fort Worth, Texas], Idea 2.2 [Xcelens, Geneva, Switzerland], IOLtech MICS [IOLTech, La Rochelle, France], C-flex 570C [Rayner, East Sussex, UK]) allow the IOL to be compressed to a significant degree. Therefore, injections through very small incisions (2.0 mm to 2.2 mm) appear feasible using the wound-assisted principle (Figure 2).
Sleeve Development
The idea to develop a reduced-diameter infusion sleeve was a logical step in the evolution of cataract surgery. Several companies are making smaller sleeves. Alcon will release the Intrepid Ultra sleeve. Xcelens sells the Objective 2.2 with the Idea IOL. This is a 2-mm sleeve and IOL injection system.
Advantages Of Microcoaxial Phaco
The greatest advantage of microcoaxial phaco is that the soft-sleeved phaco tip does not significantly stretch the incision. Well-constructed two- or three-step (near) clear-corneal incisions are 100% watertight, even without stromal hydration (Figure 3).5,6 This is in contrast with the distortion of wounds by rigid cannulas in bimanual phaco. Even 0.9-mm incisions with bimanual I/A rigid cannulas need to be stromally hydrated to stop wound leakage.
Microcoaxial phaco has a further distinct advantage over bimanual phaco in that it does not involve a learning curve; it is basically identical to the surgeon's own technique, with the exception of a smaller incision. With a 2.0-mm to 2.2-mm incision, capsulorhexis formation is still possible with conventional forceps.
Drawbacks Of Microcoaxial Phaco
Smaller sleeves in microcoaxial phaco, as well as the limited-diameter irrigating choppers in bimanual phaco, reduce irrigation flow compared with conventional-sized sleeves by as much as 35%. This difference in size has a negative impact on fluid dynamics, and an adjustment of aspiration flow is required. The reduction of fluid dynamics should directly correlate to the reduction of irrigation flow. I suggest measuring free-flow irrigation with a normal-size sleeve and compare it with the flow of the new smaller sleeves. Sophisticated ultrasound modulation and special fluid dynamics settings of the most modern phaco machines can partly compensate for the reduction of irrigation flow.
Torsional Ultrasound: A Revolution?
In 2005, at the 23rd Congress of the European Society of Cataract and Refractive Surgeons meeting in Lisbon, a new and exciting concept of ultrasound technology was demonstrated during the live surgery session; I was the surgeon who performed the first microcoaxial torsional phacoemulsification case in public. Emulsification of a hard rubbery cataract was performed through a 2.2-mm incision by the recently globally introduced torsional ultrasound handpiece (Ozil; Alcon) and Intrepid Ultra sleeve.
The torsional ultrasound has several distinct advantages compared with the conventional longitudinal ultrasound:
• It virtually eliminates repulsion;
• There is a phenomenal cutting effect on even the hardest lenses;
• Lower aspiration flow settings have little effect on the technology's efficiency;
• The nucleus evacuation is strikingly fast;
• Enhanced safety, with lower vacuum settings, is still tremendously effective; and
• There is a lower heat disturbance at the wound site (only 35% to 40% compared with conventional ultrasound).
From my experience, torsional ultrasound technology has vastly improved cutting during sculpting and greatly enhanced quadrant removal, even when dealing with the most difficult cases. The low heat emissions from the Ozil ultrasound greatly reduce (or virtually eliminate) the incidence of wound burn. Even the hardest lenses can be emulsified by torsional ultrasound without the fear of creating a wound burn.
Anterior chamber stability may be enormously improved by using lower vacuum levels. Rapid emulsification is achieved at lower vacuum levels due to the lack of intrinsic repulsion (in contrast to traditional longitudinal ultrasound). This decreases the surge flow volume on occlusion break and therefore increases the safety margin in a significant way. At modest and therefore safe aspiration flow and vacuum settings, a microcoaxial phaco procedure with torsional ultrasound is as fast or faster than normal coaxial phaco with traditional ultrasound. The transition to microcoaxial phaco will be easy and comfortable for cataract surgeons when using this revolutionary ultrasound modality.
Microincisional Foldable Iols
Foldable IOLs for sub–2.0-mm incisions (eg, Acrismart [Acritec, Hennigsdorf, Germany] and Ultra Choice 1.0 [Thinoptix, Abingdon, Va]), have been on the market for several years but have not yet gained wide acceptance. In 2005, the 6.0-mm Acrysof (Alcon) single-piece IOLs, which have a long track record and excellent results for optical stability and very low posterior capsule opacification rates, were safely and easily injected through 1.9-mm to 2.2-mm incisions using wound-assisted injection techniques after microcoaxial phaco with the Alcon Infiniti Vision System machine.
The unique material of these hydrophobic acrylic lenses is widely accepted, and properties of the foldable IOLs make them suitable for highly compressed injection through
2.0-mm to 2.2-mm wounds in microcoaxial phaco. The aspheric Acrysof IQ has a 9% central thickness reduction compared with the nonaspheric lens. This makes the Acrysof IQ particularly well suited for microincisional surgery.
Xcelens has launched the 2.2-mm Idea 613XC hydrophilic acrylic (patent pending FR0403615), with a familiar 6.0-mm optic single-piece, closed-loop, double square edge IOL design. Other companies will certainly follow this trend. Some already have smaller than 6.0-mm optic IOLs that can be injected through microincision. The ophthalmic industry will further innovate IOL designs for even smaller incisions.
The Perfect Marriage
The combination of torsional ultrasound and microcoaxial phaco complement each other perfectly, with the limitations of the first being compensated by the latter device. This could have a dramatic influence on the adoption of microcoaxial phaco in cataract surgery.
I believe that more surgeons will realize the benefits of microincisional surgical techniques and embrace them within their surgical practice. The latest developments in instrumentation and IOL technology will drive us to an even higher quality of surgery without compromising safety. I think that a new standard in cataract surgery is set by microcoaxial torsional phaco.
Khiun F. Tjia, MD is an anterior segment surgery specialist at the Isala Clinics, in Zwolle, Netherlands. He is a research consultant for Alcon Laboratories, but he states that he holds no financial interest in any of its products. Dr. Tjia is a member of the CRSToday Europe Editorial Board and cosection editor of the Cataract Complications column. He may be reached at K.Tjia@Isala.nl or +31 38 424 2980.
Innovations | Mar 2006
Microcoaxial Phacoemulsification: A New Standard in Cataract Surgery?
The combination of microcoaxial phaco and torsional ultrasound technology has the capability to revolutionize cataract surgery.
Khiun F. Tjia, MD
