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Innovations | Feb 2010

MICS With the Stellaris

Microincision technology reduces the risks associated with surge and high aspiration settings.

The Stellaris (Bausch + Lomb, Rochester, New York) represents a major advance in cataract surgery. This phaco machine was developed according to the principle that microincision cataract surgery (MICS) involves not simply a reduction in the size of the ports but a true reimagining of fluidics to find a balance among aspiration, irrigation, and ultrasound delivery with the smaller incisions. This revisitation has resulted in an improvement in all phases of phacoemulsification.

FEATURES Less volume. The Stellaris was designed to provide faster responses to the surgeon's commands. To reduce the hysteresis in the system, the volume of air and fluid had to be reduced, and expansion and contraction of the tubing had to be minimized. The vacuum pump of the Stellaris is smaller than that of the Millennium (Bausch + Lomb), thus offering a quicker response. The quest for volume reduction led to the use of 1.1-mm diameter tubing to limit the expansion and contraction of gases dissolved in the irrigation fluid during surgery. These gases can impair fluidics and promote surge.

Surge-limiting features. The Stellaris' aspiration pipe is stiffer than the Millennium's, which limits expansion and contraction following vacuum variations. As a result, the surgeon appreciates the absence of delay in the transfer of commands from the footpedal to the eye and the absence of extra aspiration on occlusion break. In fact, the Stellaris produces an incredibly low level of postocclusion surge. The machine has optimized several surge-limiting factors: (1) the vacuum pump maintains the system under the same pressure regardless of the presence of flow, and on disocclusion the rigid tubing does not expand; (2) the volume of fluid is small; (3) the double venting system (fluid and air) is quick; (4) the smaller ports limit the increase of aspiration as vacuum increases; (5) and the hysteresis of the pump is low. Surge control has two main consequences for the surgeon—a higher vacuum can be applied (personal use is up to 600 mm Hg), and a lower irrigation can be adopted. Both are important elements when dealing with small ports. With this level of surge control, the technology is now ready for the small phaco sleeve designed for a 1.8-mm incision. Additionally, the reduced irrigation flow required by the Stellaris allows us to lower the bottle as low as 60 to 80 cm, limiting intraocular pressure and patient discomfort during surgery.

Stability. With small ports—and especially with small tubing—clogging can be a problem. Lens particles passing through the phaco needle can hydrate or turn 90° within the small aspiration line, eventually blocking it. To overcome this problem, the Stellaris retains all particles larger than 0.5 mm within a filter positioned close to the phaco handpiece. As a result, particles are not usually visible within the aspiration line upon inspection. The absence of particles allows the adoption of ports of any small size and ensures the stability of the fluidics throughout the procedure, for which we coined the term microfluidics of phacoemulsification.

C-MICS needle. The Stellaris handpiece has been redesigned to reduce hysteresis and improve stroke efficacy. The 28-KHz ultrasound frequency, which limits heat production, has been maintained. The coaxial MICS (C-MICS) phaco needle is single-use, ensuring reliable cutting. It has been designed with a 0.51-mm inner diameter and an external flared tip to fit and seal to the transparent small sleeve. This sleeve should be bound to the needle edge, allowing irrigation through only the two lateral holes. When properly assembled, the phaco needle and sleeve can easily enter a 1.8-mm incision, providing enough irrigation even with high vacuum.

Other innovations. Although the Bluetooth (Bellvue, Washington) footpedal and built-in vacuum production are greatly appreciated by our operating room nurses, they are probably the least important features for surgeons themselves. When we are concentrating on the eye, we forget about the wired and the wireless. Rather, we are thinking only about how to turn our surgery into a perfect symphony. Other innovations, such as the user-friendly screen and the luer-lock connections, are directly related to safer surgery.

We always use the dual-linear footpedal control system. With this modality, the surgeon controls both vacuum level and ultrasound power with the footpedal. We choose to control vacuum by pedal depression and ultrasound power by pedal rotation to the right. We can activate any ultrasound level at any vacuum level. This is especially useful with soft cataracts to prevent capsular rupture. As the vacuum level controls the flow level with vacuum pumps, levels of vacuum, flow, and ultrasound power can easily be switched from low to high.

We prefer low-pressure irrigation and avoid pressurized irrigation in particular. Our bottle height is now 60 to 70 cm for the C-MICS needle and 80 to 90 cm for needles with inner diameters of 0.6 mm or more. It is not necessary to increase bottle height with the Stellaris, as this will induce high pressure in the anterior chamber and increase patient discomfort. Additionally, it promotes vitreous hydration and disruption because of the passage of fluid through the zonules, sometimes complicating surgery and always increasing the risk of vitreous floater formation.

Vacuum is set at 550 mm Hg for MICS and 400 mm Hg for standard surgery (Table 1). The vacuum rise is set at the second slowest setting; however, with experience, higher speeds can be adopted to offer the surgeon the ability to attract lens fragments prior to engaging them with high vacuum for emulsification. Followability is maximized by aspiration control through vacuum control. Holdability is obtained by combining high vacuum with slow ultrasound power increase and then decreasing both with the dualfootpedal control system.

Default ultrasound delivery is the micropulse mode (4 msec on/8 msec off; 80 pulses per second; 35% duty cycle), with linear control of power up to 10% of maximum. The micropulse mode acts on cataracts like high-speed cutting acts on vitreous, gently biting and removing fragments step by step, allowing most cataracts to be removed using less than 1 second of total ultrasound time. With hard cataracts, we use 10% fixed ultrasound power in the burst mode, starting with 160 msec on/320 msec off and increasing frequency until continuous ultrasound is delivered. A third modality we use for rock-hard cataracts employs a fixed burst (60 msec on/40 msec off), with linear ultrasound power up to 10%. On rare occasions, we employ an ultrasound power higher than 10%.

We always prefer C-MICS. As all surgeries are performed under topical anesthesia, we avoid grasping the eye with forceps and employ a cotton swab to stabilize the eye when creating the incisions. The 1.8-mm incision is created with a trapezoidal shape, which is of great help when inserting the phaco tip. This is done with the irrigation off to avoid bulging of the sleeve. Capsulorrhexis is easier in MICS than in standard phaco because the coaxial forceps are smaller than the Corydon forceps (Figure 1), and the incisions do not leak ophthalmic viscosurgical device substance. However, for this last reason hydrodissection can be more complicated.

We use a phaco-chop technique, with the needle bevel maintained opposite to the chopper to avoid suction loss during nucleus division (Figure 2). The following steps are repeated: a fragment is approached with low vacuum, the fragment is grasped, the vacuum is increased, ultrasound is turned on, and both vacuum and ultrasound are slowly released as emulsification progresses (Figure 3). Even with 10% power, the needle cuts perfectly, and sometimes no ultrasound is required with soft cataracts. Throughout the procedure, the chamber remains stable, even if the bottle height is lowered to 50 cm to decrease patient pain (this happened once during a live surgery session).

We use the single-use coaxial handpiece provided for irrigation and aspiration. This handpiece is curved to reach every part of the capsular bag, thin enough to fit through the 1.8-mm incision, and has a transparent sleeve to increase visibility (Figure 4). The Stellaris' luer-lock connection adds safety and helps avoid complications. The procedure is concluded with the implantation of the Akreos MICS IOL (Bausch + Lomb).

Regardless of the machine or the technique one is using, MICS lowers the risks associated with excessive aspiration. It decreases surge with peristaltic pumps and allows a lower flow rate with vacuum pumps. By allowing use of smaller instruments, MICS improves visualization and does not change the optics of the cornea.

Roberto Bellucci, MD, is Director of the Ophthalmic Unit Hospital at the University of Verona, Italy. He states that he is a paid consultant to Bausch + Lomb. Dr. Bellucci may be reached at tel: +39 045 812 3035; e-mail: roberto.bellucci@azosp. vr.it; robbell@tin.it.

Simonetta Morselli, MD, is Chief of the Ophthalmic Unit, San Bassiano Hospital, Bassano del Grappa, Italy. Dr. Morselli is a member of the CRST Europe Editorial Board. She states that she is a paid consultant to Bausch + Lomb. She can be reached at e-mail: simonetta.morselli@gmail.com.