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The time is now for MICS
Technique and technology align to permit ultrasmall cataract incisions.
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When it comes to cataract surgery, size is an important factor to consider.
Smaller incisions offer improved surgical control and quicker visual rehabilitation. As cataract surgeons demand ever-smaller incisions, 3-mm clear corneal incisions with standard silicone or acrylic lenses are no longer small enough. While wound size has decreased rapidly in recent years, 3 mm has been a barrier, as the efficiency of ultrasmall phacoemulsification tips was often considered too low for high-volume surgery.
Recent innovations in cataract removal technologies, however, have overcome this drawback. The introduction of “cold” phaco, laser phaco and sonic emulsification systems now allows the surgeon to efficiently remove cataracts through incisions smaller than 3 mm without fear of wound burn due to prolonged phaco times.
This leads to a question facing cataract surgery that is reminiscent of the early 1990s when foldable IOLs were first introduced: Is there a need for sub-3-mm incisions if the wound must be enlarged to allow insertion of the IOL?
Incision size
We have been evaluating various phacoemulsification systems and IOLs in search of a combination that allows us to break the 3-mm “barrier” for lens removal and IOL insertion.
We believe we have now found our answer using the Alcon Legacy phacoemulsification machine and an ultrathin IOL, the UltraChoice IOL from ThinOptX. Dr. Jorge Alio, of Alicante, Spain, was among the first to term this microincision cataract surgery (MICS). We are pleased that we are now able to do phaco and insert an IOL through an unenlarged 1.5 mm incision.
Small study performed
At the Instituto de Moléstias Oculares in São Paulo, Brazil, we evaluated MICS in a small, prospective, non-randomized study of cataract patients referred to us for surgery (10 eyes of eight patients). Preoperatively, all patients received routine ophthalmologic examinations, which included ultrasound biometry, interferometry, corneal topography, indirect ophthalmoscopy, specular microscopy and, when necessary, ocular ultrasonography. Lens power calculations were performed using the Holladay II formula. All patients signed an informed consent, and the same surgeon (VC) performed all surgeries. Patients were discharged immediately after surgery.
The technique step-by-step
Following is the surgical technique, step by step.
All patients received peribulbar anesthesia with sedation, followed by a lateral auxiliary corneal incision at 2 o’clock and oblique main incision at 11 o’clock using an Alcon 20-gauge sclerotome to make the 1.5 mm clear-corneal incision. Incision size was verified with calipers.
Cellugel viscoelastic (hydroxypropyl methylcellulose, Alcon) was instilled to re-form the anterior chamber, and 5-mm continuous circular capsulorrhexis was performed using a cystitome. Hydrodissection was performed using a cortical cleaving technique, and Viscoat (chondroitin sulfate, sodium hyaluronate, Alcon) was instilled to protect the corneal endothelium.
Nuclear fragmentation started with a stop-and-chop technique using a Crema (Kraft Instrumental Oftalmológico) irrigator-chopper through the lateral incision and a standard Alcon ABS microtip or 21-gauge, 30º (0.9-mm) flare tip, without sleeve, through the main incision.
Aspiration of residual cortex, when necessary, was performed with separate irrigation and aspiration, and additional Cellugel was instilled to re-form the capsular bag and anterior chamber.
A ThinOptX UltraChoice model PHC001 plate-haptic IOL was then rolled in its injector (Geuder, Germany) and advanced so that 1 mm to 2 mm of the rolled lens extruded from the tip of the injector. The external lip of the unenlarged corneal incision was then opened using atraumatic forceps, and only the extruded portion of the IOL was inserted through the incision.
Because the lens is so thin, it dehydrates rapidly, which makes the lens stiff at this point, allowing easy insertion of the lens through the incision. The entire lens can thus be advanced through the wound and its anterior aspect directed into the capsular bag without the injector ever entering the eye. Once in the eye, the lens hydrates immediately and completely unfolds within 10 to 15 seconds in the capsular bag in the posterior chamber, and the trailing haptic can easily be placed into the bag using only slight posterior pressure on the optic.
We were able to verify positioning completely within the capsular bag, and manual I&A was used to remove excess viscoelastic. After hydrating the corneal wound and ensuring watertight closure, an occlusive dressing was applied, and antibiotics (ciprofloxacin), anti-inflammatory drops (fluorometholone acetate 0.1%) and an ocular lubricant (chondroitin sulfate) were prescribed as a postoperative regimen.
Patients were examined at 1, 7, 30 and 180 days postop. At each exam (except at 1 day postoperative) near and distance best corrected visual acuity (BCVA) were examined, as well as biomicroscopy and potential ocular complications related to the IOL.
Results
Our patients, three women and five men, ranged in age from 59 to 64 years. Results so far have been outstanding. Preoperatively, eight of the 10 eyes (80%) had a BCVA worse than 20/40. At 30 days postoperative, nine (90%) of the eyes had 20/40 or better BCVA and 20/40 or better uncorrected visual acuity. The other eye, with a BCVA of 20/80, had age-related macular degeneration.
Interestingly, four (40%) of the eyes had near visual acuity of J 3, and the other six could read the J 5 line on the near card. All eyes were within ±0.75 of expected postoperative spherical equivalent refraction.
Although follow-up time has been short, we have seen no postoperative complications with these eyes to date (minimum follow-up is 4 weeks on all eyes, with a maximum of 12 weeks).
We did have some initial difficulties with the injection system, which led to one torn lens during handling. This lens was replaced with another and the case proceeded uneventfully.
UltraChoice IOL
The UltraChoice IOL is a single-piece, plate-haptic hydrophilic acrylic lens with an overall diameter of 11.2 mm and an optic diameter of 5.5 mm. The lens is lathe-cut from a HEMA material, into which a UV-blocker has been bonded. It has an a-constant of 118.9.
The optic has a meniscus shape, with concentric refractive rings on its anterior surface that function as independent, but cooperative, refractive units. This allows the lens to focus incident light onto a single point while maintaining an exquisite thinness. The lens thickness varies from 450 µm at the center of the optic to 50 µm at the haptic footplates, which enables the lens to be easily rolled and inserted through an incision smaller than could done with any other IOL — 1.5 mm).
Easy adjustment
Once in the eye, the lens unfolds completely within a few seconds and can then be easily positioned into the capsular bag. In our cases, we directed the leading haptic of the unfolded lens into the capsular fornix and then applied slight posterior pressure to the optic after the lens was unfolded to drop the trailing haptic into the bag. The lens must be correctly oriented so that the rings are on the anterior surface of the lens. This can easily be verified in-situ, as the leading haptic has a tear-drop fenestration oriented in a clockwise direction, while the fenestration on the trailing haptic is counterclockwise.
Injection technique
The Geuder injector we used is composed of two parts: a plastic, autoclaveable cartridge into which the rolled IOL is placed, and the metallic injector body. This is similar to other lens injectors in that it holds the folded lens within the cartridge as a piston-type injector pushes the lens into the eye. ThinOptX provides the lens in a 5-mL glass vial in balanced salt solution.
Lens loading and injection is fairly straightforward. The IOL is removed from the flask with Fine forceps. The surgeon verifies that the holes in the drops at haptic level indicate clockwise position. The IOL is held on its right longitudinal edge with holding forceps. The IOL is submerged with the folding forceps in warm saline solution for 20 seconds. The IOL is placed in the cartridge and rolled counterclockwise. When the lens is fully rolled, it is held with forceps in the center and introduced into the cartridge, previously moistened with saline. It is important to maintain the rolled configuration of the lens during this maneuver without rotating the lens to an upside-down position. The folding forceps are removed and the cartridge is placed in the injector. The injector is placed at the edge but not inside the incision, and the external corneal incision is opened using atraumatic forceps. The lens is injected while the leading haptic is directed into the capsular bag. Once the lens is inside the capsular bag, it will unroll in about 15 to 20 seconds, and the trailing haptic can then be pronated into the capsular bag. It is not advisable to rotate the lens inside the capsular bag. Viscoelastic is aspirated and the case is closed as usual.
Technology and safety
Other researchers have shown that small-incision surgery is less traumatic and produces less surgically-induced astigmatism than conventional cataract surgery. The boundaries for defining the smallest possible incision are not yet known, but we believe that surgery through a 1.5-mm incision represents either the final boundary or as close to it as we are likely to get in the near future.
Lens removal technology has actually been behind surgeons’ desires for smaller incisions, as there are currently no metal or diamond keratomes on the market that are designed for making 1.5-mm corneal incisions. We used 19- or 20-gauge Alcon sclerotomy knives for the cases described here. We hope that a 1.5-mm diamond keratome will be developed as this type of procedure gains acceptance.
Learning curve
Although we found no significant increase in our overall time required for surgery, there is a learning curve associated with the procedure. We found that the microincision makes capsulorrhexis, manipulation of the nucleus and cortical aspiration all more difficult.
The flare tip is difficult to introduce through the 1.5-mm incision; however, it allows greater and constant leakage that facilitates irrigation and cooling of the incision. A standard microtip seems to provide more stability.
During cortical aspiration, we suggest separate I&A handpieces, as they have an extremely thin external diameter, which helps maintain control of the anterior chamber. This presents a challenge to the right-handed surgeon, as it requires greater use of the left hand. However, as our results show, that did not result in any increase in operative complications.
Lens removal systems
The technology for addressing the nucleus has clearly undergone significant transformation, as the incidence of very hard nuclei is disappearing even in developing countries. Therefore, it is no longer necessary to have a tip that will always be delivering a high level of ultrasonic energy. We found it useful to employ modulation of fluidics with as little phaco power as possible for cataract removal.
There are several new lens removal systems compatible with MICS, including the Alcon Aqualase, STAAR Surgical Sonic Wave and the Sovereign with WhiteStar from AMO. Phaco-lasers, using Nd:YAG or Er:YAG laser sources, should also be included in this trend.
The primary appeal of these systems is their small-incision, low-energy approach to cataract removal, but their primary drawback is their inherent reduction in aspiration efficiency. However, that tradeoff may now be worthwhile, as surgeons once again are faced with the possibility of cataract extraction through incisions that must be enlarged after phaco just to allow introduction of the IOL. While these systems are probably not appropriate for very mature, dense cataracts, they appear to be appropriate for removal of routine cataracts and might be especially appropriate for MICS, where exquisite control of the eye is required.
Loading the inserter
The rolling and loading of the thin lens required some time to master. While the lens is easy to grasp and roll, insertion of the rolled lens into the cartridge was not always easy. However, the lenses do inject easily into the eye once loaded properly.
A considerable advantage of this lens is that its thinness and thermophilic properties enable it to stay rolled until it is placed into the anterior chamber. The UltraChoice gently unfolds within a few seconds, allowing quick verification of proper placement in the eye without concern for damage to the zonules or lens capsule. However, a new injector design is needed because the one we used, while effective, is tedious to load and insert the lens through 1.5-mm incisions.
In our cases, we found that we could use incision sizes as small as 1.5 mm, but insertion was much easier if we slightly enlarged the incision. This was more to accommodate the bulky injector than the lens itself, which we believe would easily fit through a 1.5-mm incision with a better injector. For these cases, we fashioned an internal valve of 1.9 mm with an external length of 3 mm.
Duckworth & Kent has recently introduced a new injector made specifically for the ThinOptX lens, which is said to be easy to load and allows the lens to be inserted through a 1.5-mm incision. However, we do not have experience with this as yet.
Conclusion
Our experience demonstrates that microincision cataract surgery using the ThinOptX IOL is now a reality. It offers the patient the obvious benefits of the smallest surgical wound possible, with no optical tradeoffs when it comes to IOL insertion and optical performance.
We plan to follow these lenses to document their long-term results, but we believe MICS represents a quantum leap forward in cataract extraction and lens implantation technology that will have an important place in ophthalmic surgery.
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For Your Information:
- Virgilio Centurion, MD, can be reached at IMO – Instituto de Moléstias Oculares; Av. Ibirapuera, 624 CEP: 04028-000; São Paulo, Brazil; e-mail: centurion@imo.com.br. Drs. Centurion, Caballero, and Lacava, have no direct financial interest in any product mentioned in this article, nor are they consultants for any companies mentioned.
- ThinOptX can be reached at 15856 Porterfield Highway, P.O. Box 784 Abingdon, VA, 24212-0784; (276) 623-2258; e-mail: thinoptx@naxs.net.