Seven years ago, one of us (Jorge L. Alió, MD, PhD) coined the term microincision cataract surgery (MICS) as a new operating method for cataract surgery performed through a 1.5-mm or smaller incision. This transition from conventional small-incision cataract surgery to MICS1 does not focus solely on achieving a smaller incision size but also on making a global transformation to a minimally invasive procedure.
The minimization of incision size is a consequence of natural evolution, and MICS will be the standard cataract practice in the near future. It offers confirmed advantages including separation of irrigation and aspiration, decreased effective phaco time, less surgically induced astigmatism and aberrations, faster postoperative recovery, and excellent visual acuity. Additionally, ophthalmic surgeons who perform standard phacoemulsification have a short learning curve when adopting MICS because the principles of manipulation inside the eye during MICS remain the same.
INDICATIONs, PROCEDURES FOR MICS SURGERY
We have found no limitations on what types of eyes— including hard and congenital cataracts, subluxated and posttraumatic lenses, and lenses with zonular laxity—are suitable for MICS. In such cases, small doses of ultrasound are recommended. We also recommend MICS for refractive cataract operations, such as multifocal and toric IOL implantation.2,3 Herein, we present our step-by-step surgical technique for MICS.
Incision. Compared with standard coaxial incisions, the amount of corneal swelling is less significant when a MICS incisions are used.4 Additionally, an incision size smaller than 1.5 mm typically does not induce astigmatism;5 this is the size we aim for in our MICS procedure. Maintaining a stable anterior chamber depth and avoiding counterstretching during IOL implantation is crucial for optimization of a small incision. Therefore, the proper tools and implantation technique are crucial. We prefer 19- to 21-gauge tools.
Two corneal incisions are made at a distance of 90° to 110° apart. The dominant is made in the positive meridian of astigmatism to reduce existing astigmatism. We have noted as much as a 30% reduction in refractive cylinder6 with this technique. Incisions should be watertight. If needed for further astigmatism reduction, limbal relaxing incisions may also be made.7,8
The shape of our wound is trapezoidal, which not only helps prevent induction of postoperative astigmatism but also allows easier manipulation of the tools inside the eye. The wound should be 1.2 mm wide near Descemet's membrane and 1.4 mm near the epithelium (Figure 1), enabling the tools to be inserted without distortion, deformation, or maceration. We use trapezoidal knives (Alió MICS Knife and MICS Diamond Knife; both manufactured by Katena, Inc., Denville, New Jersey) to achieve different incision lengths at the peak and the base. Trapezoidal incisions reduces the risk of liquid exchange between the anterior chamber and the conjunctival sac.9-11 If the incision is too small, equipment manipulation is harder; however, too large an incision may result in uncontrollable leakage.
Wound integrity for sub–2-mm incisions may be achieved by using tools specifically designed MICS tools, such as Alió's MICS flat instruments, which produce a self-sealing incision without stressing the surrounding tissue. The incision also induces no postoperative astigmatism in most cases.4
Anesthesia. After incision creation, we inject 1% lidocaine into the anterior chamber and dilate the pupil with a combination of tropicamide 10% and phenylephrine 10%.
Capsulorrhexis. During capsulorrhexis, we apply pressure to the capsule with the pointed hook of the 23-gauge Alió MICS Capsulorrhexis Forceps (Katena, Inc.). The cut is made with minimal movement, and the capsule is torn either clockwise or counterclockwise. The wide size of the forceps' shoulder enables free manipulation of the torn capsule. When using the Alió MICS Capsulorrhexis Forceps, there is no need for a second tool; the size of the surgical wound and the diameter of the forceps prevent OVD leakage and flattening of the anterior chamber. The lens and the capsule are also stabilized, and the probability of a bag tear occurring during capsulorrhexis decreases.
Hydrodissection and hydrodelineation. Dissecting the lens from the cortex is an important step, especially when using a prechopping technique. It must be done quickly and with little liquid to avoid complications. Successful hydrodissection can diminish the power of ultrasound and surgery time.12
During hydrodelineation, we elevate and separate the nucleus from the cortical mass by applying liquid under the ring of the anterior capsule. If rotation does not occur, hydrodissection must be repeated.13
Prechopping. We use prechopping because it reduces the amount of the energy delivered into the anterior chamber for fragmentation. Two Alió-Rosen MICS Prechoppers (Katena, Inc.) are inserted opposite each other under the anterior capsule rim. Prechoppers with a sharp internal edge facilitate the incision of the crystalline lens and reduce zonular stress. The hook of the chopper is placed parallel to the anterior capsule, and the chopper is then gently rotated along the axis of the tool until it is situated on the perimeter of the anterior capsule (Figure 2). This maneuver is completed symmetrically with both hands, and the choppers should end up opposite from one another. The choppers are then crossed, resulting in fracture of the crystalline lens. The cut should span from the perimeter to the center of the nucleus and produce two divided hemispheres. After the nucleus is rotated 90°, prechopping is repeated using the steps previously outlined. Four lens quadrants should remain in the capsule.
Phacoemulsification and lens removal. A sleeveless ultrasound phaco tip provides sufficient flow and cools the tip, minimizing the risk of thermal burn.14 Rapid on-off cycles (ie, microburst or hyperpulse) reduce the power delivered to the phaco tip without increasing the corneal temperature over the threshold for damage.15 During MICS, the total amount of ultrasound power is not high enough to cause damage to the cornea.16
For softer cataracts, we use 500 to 550 mm Hg vacuum, and we try to avoid or minimize the amount of ultrasound during irrigation and aspiration. If ultrasound is used, we prefer torsional. The fingernail-like shape of the Alió MICS Hydromanipulator Irrigating Fingernail (Katena, Inc.) is helpful during phacoemulsification of the first lens quadrant. A 1-mm irrigation hole on the lower side of the tool ensures an infusion rate of approximately 72 cc/min. The anterior chamber stability is outstanding, and liquid is directed toward the lens fragments at the back of the capsule, cleaning the back capsule of cortical cells and protecting the corneal endothelial cells from mechanical and thermal damage (Figure 3). The strength of the stream allows the capsule to be held at a safe distance from the phacoemulsification tip. It also enables convenient manipulation of tools and lens fragments.
To remove harder cataracts, we prefer the Alió MICS Irrigating Stinger (Katena, Inc.). The narrow, angled tip of this 19-gauge handpiece is useful for chopping or dividing segments of the nucleus. In these cases, we aspirate the lens fragments with high vacuum and, if needed, ultrasound energy.
Fluidics. The following elements are ideal for controlling fluidics during MICS: stable incision with no leakage, stable anterior chamber, and high vacuum. An infusion cannula with a smaller diameter may create an unstable anterior chamber if vacuum settings from 500 to 600 mm Hg are used because the chamber is not adequately filled with liquid. Therefore, irrigation cannulas must create an inflow higher than 50 cc/min. Gas-forced infusion is also required to provide a stable anterior chamber. We can achieve anterior chamber stability in two ways: (1) increasing fluidics and forcing infusion and (2) reducing outflow.
Irrigation and aspiration. Although MICS may be performed with different aspiration systems, we prefer a venturi pump because of its flexibility and fast reaction time. Because the aspiration and irrigation cannulas are different sizes, resistance of the flow is disproportional, guaranteeing stability of the anterior chamber. Compared with standard coaxial phacoemulsification, stability is indisputably higher with MICS.
It is extremely important to rinse the anterior chamber to remove any remaining lens fragments. As the depth of the anterior chamber increases, fragments are more likely to slip into the space behind the iris. Occasionally, fragments are still visible in the anterior chamber several hours after the operation.
End of surgery. Before MICS is complete, we inject 0.1 or 0.2 cc cefuroxime into the anterior chamber to prevent endophthalmitis. The wound is closed with corneal wound hydration, and two or three drops of povidone iodine are administered into the conjunctival sac. We wait 30 minutes and then verify the state of the incisions under the slit lamp. If leakage is visible, we repeat hydration.
IS MICS WORTHWHILE?
Some of the important achievements of MICS include a shorter total effective ultrasound power time17 and effective phacoemulsification time18 and smaller incision size. MICS is a less invasive and safer procedure compared with standard coaxial, resulting in less postoperative intraocular inflammation, fewer incision-related complications, and shorter surgical times.19
Our experience with MICS has proved its effectiveness in stabilizing the optical quality of the cornea after surgery.20 By making the wound smaller, we prevent surgically induced astigmatism and avoid corneal aberrations. Patients also experience faster visual recovery.
MICS will continue to evolve, allowing us to create even smaller incisions and use less ultrasound energy during phacoemulsification. The future belongs to micro-MICS, where cataract surgery will be accomplished through a sub–1-mm incision with smaller tools, subsonic oscillation, and lasers. Managing fluidics will also change as new infusion and aspirating pumps are developed. As MICS continues to progress, we will refine our surgical technique and keep up with the latest advances.
Jorge L. Alió, MD, PhD, is the Professor and Chairman of Ophthalmology, Miguel Hernandez University, Alicante, Spain, and the Medical Director of Vissum Corp., Spain. Professor Alió states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +965 15 00 25; fax: 965 15 15 01; e-mail: jlalio@vissum.com.
Bassam El Kady, MD, PhD, is on the Faculty of Medicine, Ain Shams University, Cairo, Egypt, and is a Clinical Research Fellow at Vissum-Instituto Oftalmologico de Alicante, Department of Research and Development, Alicante, Spain. Dr. Kady states that he has no financial interest in the products or companies mentioned.
Pawel Klonowski, MD, PhD, practices at the Vissum-Instituto Oftalmologico de Alicante, Department of Research and Development, Alicante, Spain. Dr. Klonowski states that he has no financial interest in the products or companies mentioned.
