CATARACT SURGERY: Managing Weak Zonules
Profiles of several devices and strategies
that can help.
BY CHRISTOPHER KENT, SENIOR ASSOCIATE EDITOR
One of the hot topics in ophthalmology recently has been the use of capsular tension rings (CTRs), which provide internal support for the capsular bag after -- and sometimes during -- phacoemulsification when the zonule is weak. Availability of these devices has spurred extensive discussion of the current alternatives (some of which are only available outside the United States), as well as surgical techniques for managing a weak zonule that may or may not involve using a CTR.
We asked several surgeons to share their experience performing surgery under these conditions. Here, they offer advice for inserting a CTR, suturing a CTR or IOL into position, removing a CTR, using an anterior chamber lens instead of a posterior chamber lens, and using "slow motion phaco" to perform surgery without making the zonular problem worse.
We've also provided detailed information about several of the most promising devices for supporting the bag during and after surgery, (see "Alternatives for Supporting the Bag," starting on page 74), and a discussion of how the resistance-free cutting made possible by the Plasma Blade (aka Fugo Blade) can make it possible to remove a cataract while putting little or no stress on the zonule (see page 157).
Inserting a CTR
Howard Gimbel, M.D., founder of the Gimbel Eye Center in Calgary, Alberta, Canada, offers the following strategies to help ensure successful implantation of a CTR:
► When inserting the ring, watch the behavior of the anterior capsulorhexis; it should ovalize a little as the ring gradually moves into place. If you don't see this happen, it could indicate that the ring has punctured the equator or is outside of the capsular bag.
► If a zonule is too weak to withstand standard ring insertion, try pulling the ring into a small circle with a suture to get it inside the capsulorhexis and then let it expand into position.
► If the zonule is only weak in one particular area (for example, as the result of trauma), make sure that the end of the CTR that enters first goes into the bag in this area. This puts the initial pressure of insertion on the strong part of the zonule that lies opposite the weak area.
► Place the first end of the CTR as close to the initial incision as possible; then bend the ring a bit with gentle pressure against the equator to have the ring more tangential to the equator when starting to slide it along the equator to advance its entry.
Suturing Capsule Support in Position
Several modified versions of the CTR provide a fixation loop to allow suturing. Robert J. Cionni, M.D., a pioneer in the development of these rings, suggests the following strategy for situations in which it's not clear whether a CTR will need to be sutured in place:
"If you believe a patient is borderline in terms of possibly needing to have the tension ring sutured in position, you can use a modified tension ring that includes a fixation hook, preloaded with a 9.0 prolene or 8.0 gortex double-armed suture (looped through the eyelet, not tied). If fixation turns out to be unnecessary, simply cut and remove the suture, then tuck the fixation loop inside the capsule. Because it sits only 0.25 mm above the plane of the ring, it will stay out of the way under the capsulorhexis rim where it won't allow iris touch or capture."
It's also possible to suture the IOL in place rather than using a CTR. Luther L. Fry, M.D., who practices in Garden City, Kan., suggests trying these strategies in that situation:
"As an alternative to using CTRs in cases of extremely weak zonules, the posterior chamber lens can be sutured to the sclera or the iris. When suturing to the sclera, I prefer the Jim Lewis technique, in which the needles are placed across the anterior chamber and docked in a #27 needle to go out the other side.
"For iris suturing, I prefer capturing the lens anterior to the pupil, with haptics behind, and then passing the sutures through the iris and under the lens haptic, a technique popularized by Garry Condon, M.D.
"The Siepser sliding knot technique is helpful when tying these sutures inside the eye," he adds.
Removing a Standard CTR
Dr. Gimbel notes that some surgeons are nervous about removing a CTR because it's out of sight inside the bag. "If a problem such as a torn capsulorhexis rim occurs after a CTR has been inserted," he says, "reach in with a Sinskey hook and grab any part of the ring and pull it into view so you can hook the eyelet with another Sinskey hook or grasp it with a forceps.
"You may risk tearing the capsule further, but you're already dealing with a torn capsule; it's unlikely that a Sinskey hook will cause more damage."
The Anterior Chamber Lens Option
Richard Mackool, M.D., director of The Mackool Eye Institute and Laser Center in Astoria, N.Y., and senior attending surgeon at the New York Eye and Ear Infirmary, notes that being able to put an IOL in the bag with the endocapsular ring doesn't mean you always should.
"When you know that a weak zonule could lead to eventual dislocation of the capsular bag and its IOL," he says, "consider placing an endocapsular ring in the bag to establish a (hopefully) permanent position for the capsule -- but implant an anterior chamber lens instead of placing the IOL in the bag or sulcus. The capsule will separate the anterior and posterior segments, reducing the likelihood of macular edema and vitreoretinal complications; meanwhile, the anterior chamber lens will remain perfectly fixated."
Dr. Fry agrees about the usefulness of implanting an anterior chamber lens. "Despite the advantages of a capsular tension ring, I think placing an anterior chamber lens is much easier and less time-consuming than managing all of the intraocular gymnastics required to place the ring. Anterior chamber lenses work just as well as posterior chamber in these cases, and they have a long track record of providing good results.
"The bad reputation of anterior chamber lenses, in my opinion," he adds, "is the result of poorly manufactured rough edge lenses in the 1970s, as well as closed-loop anterior chamber lenses, all of which caused problems."
Using Slow Motion Phaco
Robert Osher, M.D., professor in the Department of Ophthalmology at the University of Cincinnati College of Medicine, and medical director emeritus at the Cincinnati Eye Institute in Ohio, offers the following advice for minimizing further stress on the zonule during surgery:
"One of the most important strategies when managing a cataract with a weak zonule is to stabilize the anterior segment during the emulsification procedure. This is best accomplished by controlling the vacuum, aspiration, power and infusion carefully, which I call 'slow motion phaco.'
"By keeping the vacuum and aspiration rate lower than normal, you take less fluid out of the eye, which allows you to turn down the infusion rate. Too much infusion can literally fire-hose the nucleus backward. With lower infusion, turbulence is minimized and the intraocular environment becomes very stable; it's easier to control the nucleus that you're working with, and the lower vacuum prevents inadvertent contact with the iris and capsule. Also, less turbulence results in exceptionally clear corneas on the day following surgery.
"Here's how I perform slow motion phaco:
"Before starting phacoemulsification (using the Alcon Infiniti) I inject Healon5 into the anterior chamber for the capsulorhexis. This is followed by hydrodissection to loosen the nucleus and cortex; then I refill the chamber with Healon5, which remains throughout the phaco. If vitreous is present, I use Viscoat for vitreous tamponade and Healon5 for the capsulorhexis.
"During phaco I use a 1.1-mm tip and shift between three modalities. I set the aspiration rate at 25cc/minute, where it remains throughout the procedure; the bottle is set at 45 cm.
"The power and vacuum vary in each modality.
"For the first modality I set the vacuum at 250 mm Hg because I have an undiluted fresh cast of Healon5 in the anterior chamber. When I start the phaco in the nucleus, I put the tip right on top of the cortex, bevel down, and sculpt three passes. Because the vacuum is at 250 mm Hg, no viscoelastic obstruction can occur; this vacuum is sufficient to pull any visco through the tip. At the same time, because I'm working adjacent to the cortex, bevel down, the Healon5 cast is left undisturbed.
"Once I've completed three passes, my scrub tech shifts the Infiniti into the second modality, with the vacuum reduced to 40 mm Hg. There's no problem with viscoelastic at this point because I'm working in the groove, below the Healon5. The low vacuum setting keeps things from moving; everything is very controlled as the groove is deepened.
"Next we shift into modality three. The vacuum is set at 170 mm Hg, and I use NeoSoniX. (This feature of the Infiniti adds tip oscillation to the ultrasound.) I set the ultrasound at 50 pulses per second, with a duty cycle of 55% on, 45% off, which prevents the tip from heating up. Linear power is surgeon controlled.
"Next, I chop each hemisphere of the nucleus into quadrants and remove. Chopping is safest because it exerts no stress on the weak zonule.
"Slow motion phaco requires a great deal of precision," he concludes, "but if you do it right, you won't get into trouble." Dr. Osher adds that using this "slow motion" strategy doesn't require much extra time. "These cases take me an extra minute or two at most."
|
Alternatives for Supporting the Bag |
||||||||||||
A capsular tension ring (CTR) is a flexible, open ring that can be placed inside the capsular bag at the fornix during cataract surgery. It pushes out gently, keeping the bag expanded and relatively stable. Insertion follows capsulorhexis, either before or after phacoemulsification. Having a CTR in the bag serves several purposes: It allows the stronger zonular fibers to stabilize the entire capsule; it maintains space inside the capsule and helps keep the bag from being attracted to the aspiration port; it provides counter-traction during phaco; it stabilizes the vitreous base; it removes large posterior striae that can undermine quality of vision post-op; it helps achieve and maintain IOL centration; it minimizes post-op capsular contraction; and it appears to speed visual recovery after surgery. Also, the ring may help prevent capsular opacification by inhibiting epithelial cell migration. On the down side, a standard CTR can trap cortex if it's implanted before phaco, making removal significantly more difficult, which can stress the zonule further. Also, surgeons have occasionally reported torn capsules and unintentional straining of zonules during insertion. Despite these potential disadvantages, surgeons estimate that anywhere from 1% to 10% of cataract cases would benefit from implantation of a CTR, and a recent survey found that 91% of cataract surgeons plan to use CTRs. With a variety of alternatives already available outside the United States (see the following pages), these devices should become a surgical mainstay. The basic capsular tension ring. Several models are available outside the United States. One, the Morcher Capsular Tension Ring, was approved by the FDA in October 2003, and is currently available from FCI Ophthalmics. A second ring, called "StabilEyes," was created by Ophtec and is set to be marketed by Advanced Medical Optics (AMO) upon FDA approval, which is expected in the near future. The two rings are similar, but feature some subtle design differences. (See images, right). Both capsular tension rings can be inserted using either forceps or an injector. They have eyelets at both ends that can be used to position them in the bag with a Sinskey hook, or to "dial" them out should they need to be removed. The Morcher rings are available in three diameter sizes (measured at full expansion): 12.3 mm (for axial lengths less than 24 mm); 13 mm (for axial lengths between 24 and 28 mm); and 14.5 mm (for axial lengths greater than 28 mm). Ophtec markets the StabilEyes rings overseas as Ophtec Capsular Tension Rings. These are available in two sizes:
The Cionni Modified Capsular Tension Ring. When patients have significant zonular dialysis (180° or more) or marked decentration of the bag, a standard ring may not prevent the IOL from decentering or tilting. The Cionni Modified Capsular Tension Ring (MCTR) addresses this problem by providing a fixation hook that can be used to immobilize the ring exactly where you want it. The fixation appendage is a horseshoe-shaped hook with an eyelet at the end. It loops from the ring inward toward the center of the capsule, far enough to clear the edge of the capsulorhexis, and then circles back toward the outside edge. The fixation hook eyelet is about 0.25 mm above the plane of the tension ring. As a result, the eyelet is positioned on the anterior surface of the capsulorhexis in the area of the ciliary sulcus, so it can be sutured to the scleral wall. (See diagrams, above.) Like a standard ring, this modified ring should only be implanted if you're dealing with an intact capsulorhexis and posterior capsule. The MCTR is manufactured by Morcher GmbH. (You can reach them at [508] 771-6777.) It's not currently approved for use in the United States.
Dr. Iqbal Ahmed's Capsular Tension Segment. One problem with the use of a capsular tension ring is that insertion -- especially before phacoemulsification -- can create significant torque and stress that may further weaken zonules. The Ahmed Capsular Tension Segment (CTS) solves this problem. It's a partial ring with a fixation hook (similar to that on the Cionni Modified Capsular Tension Ring) for temporary or permanent fixation. It can be placed following anterior capsulotomy and fixated using an iris retractor. For permanent fixation, it can be sutured in place. Advantages of the CTS include:
The CTS is not yet FDA approved, but can be obtained by writing to the FDA's office of compliance. (Send a letter to Harold Pellerite, c/o FDA Compliance, 2094 Gaither Rd., HFZ-300, Rockville, MD 20850.) Explain what the CTS is and the indication for its use. Once the CTS receives FDA approval, it will be available from Morcher GmbH.
The Mackool Capsule Support System. A capsular tension ring may not hold the bag in place during phaco if the zonule is especially weak. Surgeons sometimes use iris retractors on the rim of the capsulorhexis to try to manage this problem, but iris retractors aren't designed for this purpose; their hooks have a short return, and if the retractor comes in at an angle, the hook is not in the plane of the rim you're trying to grab. In contrast, the capsule support system designed by Richard Mackool, M.D., has a hook return of 2.5 mm, and the hook is angled to be in the plane of the anterior capsule. (See images, left.) As a result, it's easy to get a firm and reliable grip on the rim. An endocapsular ring can be inserted before the Cataract Support System is removed. The Mackool system:
The system is available from Duckworth & Kent in reusable titanium, and from Impex as a disposable model. Dr. Mackool points out that the reusable titanium model can't be removed through the small incision used to insert it; it has to be removed through the phaco incision. This isn't the case with the more malleable disposable version. (Dr. Mackool has a financial interest in the titanium version.)
|
||||||||||||
|
Minimizing Zonular Stress with the Plasma Blade |
Using a plasma blade (also known as the Fugo Blade, developed by Richard Fugo, M.D.) to open the capsule appears to place significantly less stress on weak zonules -- both during the procedure and postoperatively. The plasma blade is a lightweight, portable, handheld instrument. The tip is a fine filament (about the same width as a human hair) that generates a cloud of high-energy plasma around itself. The cloud is shaped and controlled by a focused electromagnetic field. The plasma cloud ablates tissue, in much the same manner as a laser, making an incision 20 to 40 times sharper than an incision made with a diamond blade. The plasma cloud dissolves the molecular bonds of the material it comes in contact with, producing virtually resistance-free cutting, even though sclera. Remarkably, the plasma blade is powered by two AA-sized rechargeable batteries.The instrument can be used for about an hour on a single charge. This technology can reduce zonular stress in three ways:
The plasma blade is currently in clinical trials for FDA approval as a tool for performing Transciliary Filtration to treat glaucoma. (For more on this procedure, see the November 2002 issue of Ophthalmology Management.)
|
![]({"src":"/media/q2tbf1rz/image-not-available.png","focalPoint":null,"crops":[{"alias":"thumbnail","width":1110,"height":700,"coordinates":null}]})