Bimanual MICS: Advantages Extend Beyond Incision Size
The technique can facilitate successful completion of difficult cases.
BY WILLIAM W. CULBERTSON, M.D.

In bimanual microincision cataract surgery (MICS), the infusion source is separated from the phaco needle, allowing lens removal through an incision smaller than 2 mm. The name MICS emphasizes the smaller-than-routine size of the incision; however, the advantages of this technique extend beyond that.

First, by separating the infusion source from the phaco tip, attraction of nuclear material to the phaco needle is not resisted by infusion fluid coming out of the infusion sleeve surrounding the phaco needle (as it is in traditional coaxial phaco). Instead, infusion fluid is brought into the anterior chamber through a separate port usually through an infusion chopper. The irrigation flow through this instrument can be directed so as to stream or push the nuclear material towards the phaco needle, not away from it. Lower aspiration flow rates and vacuum settings are therefore possible, leading to enhanced stability of the anterior chamber.

In bimanual microincision cataract surgery, the infusion source is separated from the phaco needle.

Other Benefits

Other benefits provided by bimanual MICS are:

Greater maneuverability of the phaco needle. The phaco needle alone is smaller in diameter than with the irrigation sleeve. This allows greater maneuverability of the phaco needle into narrower areas, such as the bottom of the groove in a hard nucleus or beneath the iris to attach a nuclear fragment.

In addition, the enhanced mobility of the phaco needle creates more delicate and precise control of the four classic phaco techniques. In divide and conquer, the initial grooving is not inhibited by the bulk of the coaxial infusion sleeve. In subcapsular horizontal chopping maneuvers, the anterior capsule is lifted up by the flow of the irrigation fluid when the infusion chopper is passed beneath the edge of the anterior capsule to chop the nucleus. Likewise in carouseling the nucleus, flow does not oppose the vacuum-assisted aspiration of the phacoemulsified edge of the lens.

	The sleeveless phaco needle allows for greater maneuverability into narrow areas, such as the bottom of the groove in a hard nucleus or beneath the iris.

Two incisions available for instrument placement. Another advantage of bimanual microincision cataract surgery is that in both phacoemulsification of the lens nucleus and aspiration of lens cortex, the infusion chopper/aspiration needle and the phacoemulsification needle/aspiration needle may be passed through either incision port. This permits access to difficult-to-reach spaces, such as under the incision or iris where nuclear or cortical material may be sequestered.

Help in difficult cases. Bimanual MICS actually facilitates difficult types of cataract surgery. For example:

► In eyes with shallow chambers and narrow angles, the decreased diameter of the bare phaco tip without an infusion sleeve allows for more working room inside the restricted confines of the shallow chamber.

► The absence of the infusion sleeve can be employed to restrict leakage around the phaco needle and thus increase the depth of the anterior chamber. The potential for iris prolapse though the incision is limited as well.

► In eyes with small pupils, the smaller diameter of the sleeveless phaco tip provides more maneuvering room in the pupil. The infusion stream from the infusion chopper may be used to balloon up the iris or anterior capsule or irrigate a nuclear fragment out of the capsular bag into the papillary space.

► In the presence of pseudoexfoliation, rotation of the lens nucleus is generally undesirable because it may create added stress on weak zonules. The bimanual MICS approach allows placement of the phaco needle through two different equal length incisions up to 90 degrees apart. The surgeon thus has the option to attach and phacoemulsify nuclear material in any position in the capsular bag without having to first rotate it to the tip of the phaco needle. In this fashion less stress is exerted on the zonules.

The greater mobility of the sleeveless phaco needle enhances control in all four of the classic phaco techniques, including carouseling, which is shown here. Flow does not oppose the vacuum-assisted aspiration of the phacoemulsified edge of the lens.

► In hard or mature lenses, the sleeveless phaco needle can burrow down deep into the nucleus to create a very deep groove, which facilitates cracking of the nucleus. In chopping techniques the bare phaco needle can be passed deep into the nucleus to attach it by vacuum and facilitate horizontal or vertical chopping with the infusion chopper.

► For soft lenses such as are routinely encountered in refractive lens exchange, the carousel technique is facilitated by MICS. The rotation of the lens into the phaco tip is not resisted by opposing flow through the infusion sleeve.

Leveraging Technology and Handling Limitations

Bimanual MICS has been gradually refined over the past 3 years through improvements in infusion choppers, incision blades and phaco power settings and duty cycles. The two critical requirements for safely performing bimanual MICS are a cool phaco tip and adequate infusion.

With hyperpulse technology, such as is available in the AMO Sovereign phaco machine with WhiteStar software, short bursts (4 to 8 ms) of phaco power can be programmed to be followed by longer rest periods (8 to 14 ms) to keep the phaco needle cool without sacrificing phaco power. Heat generation is also minimized by low phaco power settings, such as from 40% to 60%, as well as allowing minimal leakage of cooling infusion fluid around the bare phaco needle in the incision.

In bimanual microincision cataract surgery, the infusion chopper/aspiration needle and the phacoemulsification needle/aspiration needle can be passed through either incision port, permitting access to difficult-to-reach spaces.

Adequate infusion can be ensured by using large-diameter, thin-walled, end-opening infusion choppers, which provide greater than 50 ml per minute of flow when the infusion bottle is elevated to at least 35 in. above the eye. Alternatively, infusion flow may be supplemented by a separate infusion port created through the limbus (three-port technique). This may be needed when smaller diameter side-opening infusion choppers are employed.

One disadvantage of bimanual MICS is that the second instrument infusion chopper is bulkier than traditional noninfusion side port manipulators and choppers. In addition, capsulorhexis cannot be performed through the small incision with standard capsulorhexis forceps. Instead either a cystotome or special capsulorhexis forceps may be used. Finally, at present, the incision must be enlarged to allow insertion of the IOLs available in the United States.

However, as smaller-incision IOLs become available, incision enlargement will not be necessary, and the enhanced stability and neutral refractive effect of a small incision will be maintained. Through minor adjustments in technique, proper instrumentation and advanced software, bimanual MICS has become an enhancement of our standard coaxial phacoemulsification technique.

Dr. Culbertson is professor of Ophthalmology and director of Refractive Surgery at Bascom Palmer Eye Institute, Univeristy of Miami.