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Gas-forced infusion useful in MICS
Two surgeons describe their methods for using an air pump to facilitate 700-µm cataract surgery.
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Minimizing postoperative astigmatism can be achieved by managing cataract incision size. One of the foremost advances in modern-day cataract surgery has been the decrease in the incision size for phacoemulsification. Small-incision cataract surgery has continued to gain in popularity over time, and this has resulted in a trend toward smaller surgical wounds. The smaller the wound, the less amount of iatrogenic astigmatism, until a small enough wound is attained that virtually eliminates induced astigmatism — so-called astigmatism-neutral surgery. Sutureless cataract surgery eliminates suture-induced corneal distortion.
Further, smaller incisions can seal better, and such a wound can potentially contribute to a lesser chance of postoperative intraocular infection. However, as the entry incisions into the anterior chamber are made smaller, this usually impacts the surgical instrument architecture and alters the fluid dynamics within the anterior chamber during phacoemulsification. When fluid from a container is removed using small-diameter tubing, often an increase in the overall suction force occurs, which results in an increased time to fully drain the contents.
In this surgical maneuvers column, Drs. Kumar and Agarwal describe the use of an air pump for gas-forced infusion to facilitate 700-µm cataract surgery, also known as microphakonit. However, it is important to note that in the U.S., devices used for human surgery need to be U.S. Food and Drug Administration-approved.
Thomas “TJ” John, MD
OSN Surgical Maneuvers Editor
The key problem during bimanual microincision cataract surgery (MICS), or phakonit, has been the intraoperative destabilization of the anterior chamber. This problem has been solved to a certain extent by using an 18-gauge irrigating chopper. However, after the introduction of the anti-chamber collapser by Sunita Agarwal, MD, the issue of chamber collapse has been reduced.
The anti-chamber collapser, or gas-forced infusion, injects air into the infusion bottle, maintaining the chamber. It pushes more fluid into the eye through the irrigating chopper and also prevents surge. Thus, by using a 20-gauge or 21-gauge irrigating chopper, the problem of anterior chamber destabilization during cataract surgery is solved.
In microphakonit, because of gas-forced-infusion, it is possible to remove cataracts with a 0.7-mm irrigating chopper (22-gauge) and a 0.7-mm phacoemulsification needle (both MicroSurgical Technology). Gas-forced infusion is achieved with the aid of a simple fish-aquarium air pump. This system can be used in all coaxial phacoemulsification cases, including coaxial MICS, to prevent complications like posterior capsular ruptures and corneal damage.
Fluid mechanics
A gas-forced infusion system is connected through a nitrocellulose membrane air filter (Millipore) to the infusion fluid bottle. The air filter prevents contaminants in the air of the OR from entering the eye. The air pump produces a positive pressure head above the fluid in the bottle, significantly increasing the amount of fluid entering the eye and balancing the excess outflow occurring on break of the occlusion. The pressure generated by 1 cm of fluid height in the infusion line is 0.73 mm Hg. The gas-forced infusion additionally increases the pressure of fluid reaching the eye over this level.
Advantages
Some of the advantages of using gas-forced infusion include:
- The posterior capsule is pushed back and there is always a deep anterior chamber. The phenomenon of surge is neutralized. This prevents posterior capsular rupture.
- Intraoperative manipulation of hard cataract is made easy because of the deep anterior chamber.
- Corneal complications due to shallow anterior chamber, such as striate keratopathy or endothelial cell loss, are reduced.
- The surgical time is reduced, as the phacoemulsification becomes faster in eyes with no surge.
- One can easily perform the MICS/phakonit technique, as a large amount of fluid passes into the eye. Thus, the cataract can be removed through a smaller opening.
- Fluctuations in IOP are reduced.
- It becomes comfortable for the surgeon to operate with the patient under topical or no anesthesia.
Systems with built-in pumps
Bausch + Lomb installed the gas-forced infusion feature in its phaco system, the Stellaris, in 2009. The advantage is that the external gas-forced infusion system is available inside the system as internal-gas forced infusion. Additionally, there is a monitor in the panel of the machine, and one can easily lower or raise the pressure of the air pump.
Technique
A side-port incision is made and an ophthalmic viscosurgical device is injected through this port. The main and the side-port incisions are made with microphakonit knife. A 5-to 6-mm capsulorrhexis is performed with a bent 26-gauge needle to form a cystitome. A 25-gauge capsulorrhexis forceps (MicroSurgical Technology) may also be used (Figure 1). In the nondominant hand, a globe stabilization rod can be used to control the eye movement.
Cortical cleaving hydrodissection is performed, and the fluid wave passing under the nucleus and rotation of the nucleus is checked. One can do hydrodissection from both incisions so that even the subincisional areas are easily hydrodissected. It is of note, however, that because there is little escape of fluid, one should be careful during hydrodissection. If too much fluid is passed into the eye, complications such as a posterior capsular rent may occur; therefore, it is necessary to decompress the anterior chamber during this maneuver by applying slight posterior pressure on the scleral lip.
The 22-gauge irrigating chopper (MicroSurgical Technology) is connected to the infusion line of the phaco machine and introduced with the foot pedal on position 1. The phaco probe is connected to the aspiration line, and the 0.7-mm phaco tip is introduced through the clear corneal incision without an infusion sleeve.
Figure 1. Capsulorrhexis is performed with a capsulorrhexis forceps. However, a 26-gauge needle bent to form a cystitome can also be used. See the rod in the nondominant hand stabilizing the eye.
Images: Agarwal A, Kumar DA
Figure 2. (A) Microphakonit performed with 700-µm phaco needle and 700-µm irrigating chopper (MicroSurgical Technology). (B) Bimanual irrigation aspiration done with 700-µm bimanual irrigating and aspirating set (MicroSurgical Technology).
Figure 3. In small, nondilating pupils, use iris hooks (A, B) intraoperatively for dilating the pupil.
Figure 4. High-resolution, cross-sectional image of wound in the anterior segment OCT on day 1. (A) Microphakonit without extension. (B) Microphakonit with 2.8-mm extension.
Figure 5. Postoperative picture after 700-µm cataract surgery, in which an IOL was not implanted. Note the two sub-1-mm incisions.
Using the phaco tip and moderate ultrasound power, the center of the nucleus is directly embedded starting from the superior edge of the capsulorrhexis, with the phaco probe directed obliquely downward toward the vitreous. The settings at this stage are: phaco power, 50%; aspiration flow rate, 20 cc/min; and vacuum, 100 mm Hg to 200 mm Hg. This setting is usually for grades 1 and 2 nuclear sclerosis cataracts. However, for denser cataracts, phaco power can be increased.
Using the karate chop technique (Figure 2a) the nucleus is chopped and removed. Cortical wash-up is then accomplished using the bimanual irrigation and aspiration technique (Figure 2b). During this whole procedure, gas-forced infusion is used. In small pupils, one can use iris hooks comfortably and still do 700-µm cataract surgery (Figure 3).
Microphakonit wounds showed faster wound healing (Figure 4). This procedure also showed less postoperative shallow anterior chamber or wound leak (Figure 5). One of the advantages with the microphakonit wound has been the tight closure at the incision site in the immediate postoperative period.
The air pump is a device that helps prevent intraoperative surge. This, in turn, prevents posterior capsular rupture, helps deepen the anterior chamber and makes MICS/coaxial phacoemulsification safe even in patients with hard cataracts.