American Academy of Ophthalmology Web Site: www.aao.org
By Laura J. Rongé
Here are the best ways to use these tools and manage these patients.
Weak zonules. They worry every cataract surgeon, but new tools and techniques will help you optimize your approach to these tough cases.
Late last year, the first capsular tension ring received FDA approval. Many variations on these rings, including partial rings and rings with eyelets for suturing, are being used, though they are not yet FDA approved. Capsular retractors, which are iris hooks modified to work on the lens capsule, are another option.
“With these new aids and improved phaco technology, the prognosis for cataract patients with weak zonules is markedly improved. No question,” said Louis D. Nichamin, MD.
Predicting Weak Zonules
For example, “Eyes with pseudoexfoliation syndrome, almost across the board, have some degree of weakened zonules and loose or abnormal capsular integrity,” Dr. Nichamin said.
Trauma, genetic syndromes such as Marfan and advanced age are other well-known risk factors, said David F. Chang, MD. One should also suspect weak zonules in eyes with retinopathy of prematurity and those with 4+ brunescent nuclei, he said.
High myopes, with axial myopia greater than 26 millimeters, can have weak zonules, said Mark Packer, MD.
Previous eye surgery also raises a red flag. For instance, radial keratotomy or glaucoma surgery may lead to shallow or flat anterior chambers, through perforation or excessive filtration, and thereby place stress on the zonular apparatus, Dr. Packer explained.
Vitrectomy can weaken zonules, too. Because the vitrectomized eye is filled with aqueous posteriorly, the lens tends to move posteriorly when the surgeon enters with infusion, thereby stretching and weakening zonules, Dr. Nichamin said. In addition, the vitreoretinal surgeon may inadvertently hit the posterior capsule or dehisce zonules.
“I had a complicated case this week, with a vitrectomy performed several years previously. On entering the eye, it was obvious that there were several clock hours of weak zonules,” Dr. Nichamin said.
At the slit lamp. Look for the presence of phacodonesis. “With eye movement, one can sometimes see a little shimmering movement of the crystalline lens,” Dr. Nichamin said.
Also, look for an abnormal position of the lens. Occasionally, the lens takes a posterior position, he said, with a visible little gap between the anterior lens surface and the back of the iris.
Dr. Nichamin finds that it is even more common to see a more anterior position of the crystalline lens, as though it is bulging through the pupil. “This is always worrisome to me. In a number of my cases, I saw that sign preoperatively and confirmed weak zonules intraoperatively.”
During surgery. Often, phacodonesis and other telltale signs of weak zonules are absent at the slit lamp. Even pseudoexfoliation can be missed preoperatively, Dr. Nichamin said. A small bound-down pupil, for example, may obscure the pseudoexfoliative material on the anterior surface of the lens. Intraoperatively, after the pupil has been stretched or opened in some surgical fashion, pseudoexfoliation becomes obvious, he said.
“You usually don’t know how weak the zonules are until you are in surgery,” Dr. Chang said.
The first clues, he noted, come during the capsulorhexis. “You may have more trouble incising the capsule with the cystotome, and the peripheral capsular rim tends to move along with the flap as it tears,” he said. He has called this “pseudoelasticity.” Lacking circumferential zonular tension, the anterior capsule behaves as though it were elastic.1
Dr. Nichamin agreed. “Sense the status of the zonules during the rhexis formation. As the anterior capsule is punctured and torn, one can feel just how secure the crystalline lens is in the capsular bag. That is often an important indicator for potential trouble.”
Working with Weak Zonules
The larger capsulorhexis allows the surgeon to bring the cataract up out of the capsular bag and complete surgery within the anterior chamber, if needed, without further risk of zonular dialysis and compromise to the bag, he explained.
A larger rhexis also decreases the risk postoperatively of capsular phimosis, or constriction of the rhexis, which is much more prevalent in cases of exfoliation and weak zonules. “Because there is no counter-traction from the zonules to keep the rhexis open, the bag really constricts down,” Dr. Nichamin explained.
Because they can still see well, these patients are not aware of the anterior constriction until they get really advanced anterior capsular fibrosis. “They don’t come in until the zonules are really stretched, the bag is off-center, and the implant may be unstable in this very fibrosed bag,” Dr. Nichamin said.
The compromise is that posterior capsular opacification is more likely when the rhexis is larger than the diameter of the implant optic. “That is a small price to pay, however, compared to significant phimosis,” he said, noting that if these patients develop central PCO, routine treatment with a YAG laser is not much more difficult.
Dr. Chang takes a different tack. Because the anterior capsule exhibits pseudoelasticity with zonular laxity, the capsulorhexis tear tends to veer radially. “Unlike many others, I err on making the capsulorhexis on the small side to ensure that I complete it,” he said. This enables him to use capsule retractors or a capsular tension ring during the surgery.
“I can then secondarily enlarge the capsulorhexis by re-tearing it after the IOL is safely in place,” Dr. Chang said.
Phaco chop. Once the capsulorhexis is complete, phacoemulsification of the lens also requires extra care in patients with weak zonules. Moderate weakness creates the following problems:
If the zonules are very weak, the bag may be avulsed by the phaco maneuvers, or it may collapse into the phaco tip along with the nucleus, Dr. Chang said.
Dr. Chang prefers horizontal phaco chop, while Dr. Nichamin uses vertical quick chop, but both agreed that chopping minimizes zonular stress, compared with sculpting. In either case, Dr. Nichamin suggests the following steps to minimize nuclear movement and zonular stress.
Rings and Retractors
Capsular tension rings. In October 2003, the FDA approved the first capsular tension ring (Morcher; distributed by FCI Ophthalmics Inc). A second capsular tension ring, StabilEyes (Ophtec; distributed by AMO), was approved in April.
A simple ring of PMMA with an eyelet at either end, the capsular tension ring (CTR) may be inserted into the capsular bag to enhance stability and centration, Dr. Packer reported.
The CTR is helpful any time the surgeon questions the integrity of the zonular apparatus, Dr. Packer said, as long as one can ensure the preoperative integrity of the capsule itself. The CTR substantially reduces intraoperative risk by redistributing applied force to the entire circumference of the capsule and by stretching the posterior capsule, he said.
Three Morcher rings (types 14, 14A and 14C) have been approved, with different diameters to accommodate various sizes of capsular bags, including those in highly myopic eyes. The StabilEyes ring is available in 12- and 13-mm diameter sizes.
Questions of timing. Some surgeons insert a CTR as early as possible, but Dr. Nichamin tends to wait. “It is harder to get the ring in when you have substantial lens material still in the bag, and one can inadvertently impart additional stress to the bag and weaken zonules during the insertion process,” he explained. In addition, the ring can interfere with the surgeon’s ability to engage and remove peripheral lens material, specifically cortex.
“I wait until I have to put it in, and that is an ‘artsy’ call based on one’s experience and comfort level,” he said.
Dr. Packer, on the other hand, prefers to insert the ring sooner rather than later. After completing the capsulorhexis and gentle hydrosdissection, he inserts the ring with an injector available from Geuder. A small hook on a plunger attaches to the eyelet at one end of the ring; the ring is then drawn up into the shaft of a cannula and is ready for injection.
After capsulorhexis and hydrodissection, Dr. Packer places a small amount of viscoelastic under the rim of the capsulorhexis to facilitate entry of the ring into the capsular bag. With small-incision surgery (2.5 mm), he passes the injector through the incision and directs the ring under the capsulorhexis toward any region of particular zonular weakness. With microincision surgery (1.2 mm or less), he still injects the ring through the incision, but he keeps the injection cannula outside the incisions and guides the ring into position with a hook through the fellow incision. Again, he directs the ring initially toward the area of zonular weakness or dialysis, to avoid putting stress on this region.
Dr. Packer likes to have the CTR in the bag during phaco, because the ring allows the bag to center and thereby provides greater exposure of the capsulorhexis and access to the cataract. In cases of pseudoexfoliation, the ring reduces unwanted movement of the lens capsule during phaco, reducing the risk of a capsular tear, Dr. Packer explained.
Inserting the ring this early does increase the difficulty of cortical cleanup, as Dr. Nichamin noted. The ring holds the cortex against the equatorial capsule and creates a counterforce to aspiration, Dr. Packer agreed. In most cases, however, he overcomes this by stripping the cortex tangentially rather than radially and using a 0.2-mm aspiration port to maintain occlusion.
“The increased stability of the bag with the ring in place permits the use of fairly aggressive infusion-aspiration without compromise to the capsule. Bimanual I-A works particularly well here, because it eliminates the uniquely challenging process of removing subincisional cortex,” Dr. Packer said.
Capsule retractors. Because CTRs redistribute capsule forces across the remaining intact regions of zonules, they are optimally used if there is a small, focal loss of zonules, such as with some traumatic cataracts, Dr. Chang said. “With increasing clock hours of zonular deficiency, this strategy becomes less effective.”
If there is diffuse zonular weakness, or when there is a large zonular dialysis, he relies on capsule retractors for operative support.
Mackool capsule retractors, called the “Cataract Support System,” represent a modified version of a standard iris retractor, with an elongated hook that is shaped so as to slide around the rhexis edge and support the peripheral capsular fornix with a blunt tip. They come in a reusable titanium design (Duckworth and Kent Ltd.) or a single-use design (Impex).
“If, during formation of the rhexis, the bag is so weak that one doesn’t have any counter-traction, I would stabilize the bag with capsular hooks,” Dr. Nichamin said.
Capsule retractors can center the bag and provide anterior-posterior support. They also prevent the bag from torquing as the nucleus is rotated. Finally, because they apply point pressure to the capsular fornices, they don’t trap the cortex as capsular tension rings do, Dr. Chang said.
Ring segments. Ike K. Ahmed, MD, assistant professor of ophthalmology at the University of Toronto and clinical assistant professor of ophthalmology at the University of Utah, Salt Lake City, designed the capsular tension segment (Morcher). This partial ring, which is not yet FDA approved, comes with or without a ringlet that enables temporary or permanent fixation.
The surgeon can place an iris hook in the ringlet to secure the segment during surgery. “On completion of the case, you remove the iris hook and leave the ring in place as it is,” Dr. Nichamin said. One could also use the ringlet to suture the segment to the sclera.
Compared with the CTR, the capsular tension segment is easier and less traumatic to insert, Dr. Nichamin said. You can target the sector of the eye that has weakened zonules, and you can use two segments if needed, he said.
Although he uses silicone IOLs in his routine cases, Dr. Nichamin avoids them in cases of zonular weakness, because they are associated with greater anterior capsule fibrosis. “I use a stiff acrylic lens to prevent this problem.”
Dr. Chang agreed: “To resist capsular contracture and capsular phimosis, I would choose a three-piece hydrophobic acrylic IOL with stiff broad haptics. The single-piece AcrySof, with its floppier haptics, was found to have a greater incidence of capsular contracture than the three-piece AcrySof in one retrospective study,” he said.1
The availability of CTRs is incredibly important for a propitious outcome in cases of zonular weakness, Dr. Nichamin said. Nonetheless, there is some question about the long-term prognosis.
The endocapsular ring allows surgeons to stabilize the bag during and after surgery, but what happens 10 years later, with further zonular dialysis? “Perhaps the whole bag could dislocate posteriorly,” Dr. Nichamin speculated.
“There is some debate over whether we will see an epidemic of this,” he said, “because we are now successfully implanting within the bag in eyes that formerly might have gone with AC IOLs or suture PC IOLs.”
Should surgeons take the additional step of suturing capsular rings in place, using the Cionni modified CTR? In cases of profound capsular weakness, Dr. Nichamin says yes, suture. “Otherwise, the capsule will most likely fall back.”
On the other hand, he does not suture-fixate all cases with moderately weak zonules. He explained that suturing the ring into the eye adds complexity and concerns about long-term erosion or infection from the sutures, and increases intraocular manipulation.
“If we see a lot of IOLs that dislocate in the future, we may need to use these rings and adjunctive devices in a different fashion, fixate them in a permanent way,” he said. “In cases of mild zonular weakness, I think we just have to wait and see.”
David F. Chang, MD Clinical professor of ophthalmology at the University of California, San Francisco. Financial interests: Is a consultant for AMO and has received educational travel support from Alcon, but has no financial interest in any product or instrument.
Louis D. Nichamin, MD Medical director at Laurel Eye Clinic, Brookville, Pa. Financial interests: None.
Mark Packer, MD Clinical assistant professor of ophthalmology at Oregon Health & Science University, Eugene. Financial interests: Has received travel and research funds from AMO and Alcon.