CAPSULAR TENSION RING IMPLANTATION AND RATIONALE

Lisa Brothers Arbisser, MD

Capsular tension rings (CTRs) are devices intended for implantation into the capsular bag of the crystalline lens for stabilization during cataract surgery in eyes with zonulopathy. Most commonly, zonular complex pathology is associated with pseudoexfoliation syndrome, trauma, or congenital conditions such as Marfan syndrome. Zonulopathy can also occur following previous ocular surgery, such as radial keratotomy, vitrectomy, or trabeculectomy—in essence, iatrogenic trauma. Hypermature cataracts and highly myopic eyes commonly display zonular fragility or hyperdistensibility. Post angle-closure attack eyes, homocystinuria, Weill-Marchesani syndrome, microspherophakia, retinitis pigmentosa, lens coloboma, scleroderma, porphyria, hyperlysinemia, as well as intraocular neoplasms may also be associated with zonulopathy. Given all these conditions resulting in either progressive or static zonular pathology, the CTR was first developed by Hara et al in 1991 and implanted in a human eye in 1993 by Witschel and Legler.^1,2 This device for high-risk surgical situations was not approved by the US Food and Drug Administration (FDA) until Fall 2003.

Standard Capsular Tension Ring Description and Purpose

The standard CTR is an open C-shaped ring made of polymethylmethacrylate (PMMA) with eyelets at both ends (Figure 2-1). Originally manufactured by Morcher GmbH, and later Ophtec BV and others, it is available in 3 sizes intended to mirror the size of the bag and pegged by the manufacturer to axial length.³ Many clinicians prefer to base size choice on white-to-white measurement, as this is thought to be more proportionate to bag size. Since FDA-approved rings do not lock and are compressible, it is doubtful whether size matters. In general, however, for average individuals, the Morcher Type 14 10.0-mm closed diameter is used; for highly myopic patients, Morcher Type 14A 12.0-mm; and for children, Morcher Type 1C, 9.0-mm. Some clinicians choose to place 2 rings in very large, lax bags.

The purpose of the CTR is to expand the bag, putting the posterior capsule on stretch by exerting centrifugal force and, most importantly, to redistribute forces between intact and weak or absent zonules. Its placement is contraindicated in the presence of a noncontinuous capsular tear or uncontrolled posterior capsule tear as the force of insertion is likely to extend the tear past the equatorial zonular network, causing a wraparound tear of the posterior capsule. Once the CTR is in place, a primary posterior capsulotomy can be safely initiated, however (Figure 2-2).

The goal for the original silicone CTR was to keep the bag expanded in highly myopic aphakic eyes.⁴ Emphasis shifted with the newer PMMA rings to zonulopathy management, however. Some surgeons believe all pseudoexfoliation patients deserve a ring, but it is a matter of opinion which, in fact, do. If the bag is decentered, there is no argument that a ring modified to enable scleral fixation must be employed. Most consider scleral fixation for eyes with more than 4 clock hours of zonulolysis, but one article showed good centration up to a year postoperatively with up to 150 degrees of zonular dialysis.⁵ The CTR has been touted to improve refractive predictability, though the literature varies on this point. Some surgeons use it regardless of zonulopathy, especially with “accommodative” implants.

Modified CTRs (M-CTR) facilitate scleral fixation without having to place a suture through fragile virgin capsule. The first was the Cionni M-CTR, which added an element to the ring to allow suturing through an eyelet in an anterior plane to the bag, leaving the ring within the bag equator (Figure 2-3).⁶ Next, the Ahmed segment was developed; this is essentially a truncated Cionni M-CTR with 120 degrees of arc. This has the advantage of being implanted without a dialing technique. The segment can be used with an inverted iris hook as a capsule suspension device during phacoemulsification and then either permanently sutured to the sclera through the eyelet or removed. The segment body remains in the bag only in the quadrant of use and therefore must be combined with a standard ring in most cases. Two segments can be used for added support, or one segment may be added to a Cionni M-CTR when needed for additional support. This is often easier and more economical than placing a double Cionni M-CTR, which is also available but both hard to implant and to keep in stock as it is so rarely required. The AssiAnchor (Hanita Lenses; CE but not approved) is similar in purpose but without the partial ring arc. Both segment and anchor provide a wide area of contact with the anterior capsule edge, reducing the risk of an anterior capsule tear while tension is applied, which is the greatest risk of standard capsule suspension hooks that use point pressure. Many surgeons, including this author, prefer to sclerally fixate all devices with off-label Gore-Tex (polytetrafluoroethylene; WL Gore & Associates) suture rather than on-label Prolene (polypropylene; Ethicon) suture because they believe the suture will last longer (Figure 2-4 and Videos 2-1 and 2-2). These devices and their implantation will be thoroughly covered in other chapters of this book.

CTRs with aniridia and coloboma shields are extremely useful for patients with iris defects but are no longer available even for compassionate use in the United States. Another modification of the CTR, the capsular bending ring, has an increased edge thickness to produce a sharp bend in the capsule in an attempt to prevent posterior capsule opacification. These rings have never been available in the United States.⁷

Different techniques exist to facilitate placement of a CTR. It can be threaded through a paracentesis with a 2-handed technique or introduced through the primary corneal incision with forceps stabilization in a fish-tail shape to minimize pressure on the lens equator and fragile zonules during insertion.8 A 1-handed inserter (Geuder AG) that fits through a microincision precludes contamination of the ring by the ocular surface and is therefore this author’s preference (Figure 2-5). The inserter’s plunger has a terminal hook with which to engage the trailing eyelet, thereby pulling the body of the CTR up into a hollow tube. Once in the anterior chamber, pushing the plunger allows the ring to be progressively dialed into the bag equator. When inserting the ring with the injector, it is better not to advance the ring along the inside of the capsule because the leading edge of the ring may pierce the capsule equator. Instead, the distal end of the ring should be placed as far around the circle of the bag as possible. Then, as the ring is injected, the injector itself is backed out so the ring stays relatively steady in place until the arc of injection is well established. Careful attention to proprioception allows the surgeon to feel any hang-up that threatens zonular or capsule integrity and to desist, withdrawing the CTR back into the inserter (Video 2-3). The bag fornix must be well expanded with an ophthalmic viscosurgical device (OVD) for safe insertion, and it may be worth refilling the bag to aid the smooth progress of the ring when there appears to be a hang-up. It is recommended always to inject toward intact zonules and away from defects. The CTR can be inserted in any direction without consequence by managing the leading eyelet. As the body of the CTR is extruded from the inserter, the eyelet is held in a more central position away from contact with the bag equator as it is extruded either with a Sinskey hook or a temporary 10-0 nylon suture threaded through the eyelet with the 2 ends held with forceps as a tether. This maneuver eliminates zonular torque or drag on the bag (Video 2-4). The suture also provides a visual marker showing the progress of the ring around the bag. The suture is removed whenever there is certainty the ring will not have to be retrieved for any reason.

Before releasing the trailing eyelet, care should be taken that the plunger is below the anterior capsule rim to be sure the end of the CTR does not pop into the sulcus upon release. A Sinskey hook through the paracentesis can aid in pushing the trailing eyelet off of the plunger hook and into the bag. When the trailing end finds its way into the sulcus, it can be hard to detect and a bit tricky to retrieve. A 2-handed technique works best, gently retracting the edge of the continuous curvilinear capsulorrhexis (CCC) with one instrument while retrieving the errant CTR with the other, working its way along the curve to the eyelet end and then bringing it centrally again to place it into the bag fornix.

Failure of the Capsular Tension Ring to Prevent Late Subluxation

The original intent to stabilize the bag and reduce intraoperative complications has been realized with the standard CTR, although there is a risk/benefit ratio to insertion of the device to be considered. The hope was also that the CTR would prevent phimosis and bag shrinkage, but this goal has proved unattainable. Capsular contraction syndrome associated with fibroblastic metaplasia of lens epithelial cells (LECs) is stimulated by contact with implant materials in the postoperative period. This transformation leads to refractive changes, implant decentration, and ultimately to bag-lens-CTR complex subluxation and dislocation with or without the presence of a CTR, particularly in progressive zonulopathy.9–11

The presence of a CTR definitely potentiates our ability to lasso the complex for scleral fixation at any clock hour for repair once subluxation has occurred, but it has not proved preventative. Although many techniques exist to exchange the lens or reposition and fixate the subluxated bag, these eyes are forever at a disadvantage. Combining advanced surgical sophistication (eg, reduced intraoperative complications) with the maintained goal of intraocular lens (IOL) in the bag will yield increasing numbers of subluxated bag-lens complexes with which the ophthalmic world must contend.

Alternative Surgical Techniques

The prevention of late subluxation remains an important field for advancement. The one feature that all bag-lens subluxations have in common is an intact capsulorrhexis. Prior to the development of CCC, there were considerably more IOL subluxations and dislocations, both early and late, but virtually no late bag-lens complex subluxations. It is also extremely rare to see spontaneous dislocation of the crystalline lens in pseudoexfoliation patients. Fibrotic transformation and metaplasia of LECs lead to capsule contraction syndrome, which causes centripetal forces that can overcome the weak centrifugal forces provided by the diseased zonular network. In this author’s opinion, though this is still unproven, we must either place the optic where it has minimal contact with LECs to excite the metaplasia and/or physically block the CCC to prevent phimosis. The technique to prevent bag-lens subluxation in eyes with significant progressive zonulopathy most observed by this author is to place the CTR in the bag as usual but then opt for a sulcus-implanted 3-piece IOL with optic capture through the anterior capsulotomy into the bag. Minor modifications of standard capture technique are needed. OVD should be removed from the bag before hermetically sealing it by capture to prevent capsule distention syndrome. After the CTR is in place, OVD defines the sulcus to ensure proper positioning of haptics before capture. Rather than the usual downward pressure 90 degrees away from the haptic-optic junction, in very weak zonule cases a 2-handed technique may be needed. The CCC edge is gently lifted as the optic is nudged into the bag (Video 2-5). Anterior optic capture stents the rhexis, preventing phimosis, and the lens is centered based on the CCC position, which remains stable. The haptics remain in the sulcus. The capture prevents iris chafing. The IOL power need not be adjusted from that of the bag.¹² Anterior optic capture results in a very stable complex without postoperative pseudophacodonesis from postoperative day 1, which is often seen in the usual technique of bag implantation with single- or 3-piece IOLs even with a CTR in significant zonulopathy (Figure 2-6). With the hindsight of 10 years, albeit a nonrandomized trial, this author has seen ongoing stability from the first postoperative day with this technique in significant zonulopathy pseudoexfoliation eyes.¹³

The technique of posterior optic capture or buttonhole where the haptics are in the bag but the optic is captured behind the bag into Berger’s space through an intentional posterior CCC has the advantage of very limited exposure of LECs to IOL materials. Touch occurs only at the haptic-optic junction, thereby reducing if not eliminating the stimulus for capsule contraction. It is necessary to place the CTR prior to initiating the posterior CCC, which is made easier by tightening the posterior capsule with the ring. This technique should be considered not only for cases of diffuse progressive zonulopathy but as a replacement for routine IOL in-the-bag surgery to eliminate visual axis opacification.¹⁴

This author’s own concept of hyaloid-sparing double capture, in which a 3-piece lens is sulcus implanted and then the optic captured through both anterior and posterior capsulotomies into Berger’s space, should also be considered. This technique combines the advantages of sequestering antigenic material like the bag-in-the-lens technology of Tassignon (not FDA approved), the positioning behind the bag with minimal LEC-IOL touch of posterior optic capture or buttonhole, and the stenting of the bag afforded by anterior optic capture (Video 2-6). It is hoped a new generation will take up the challenge to avoid a future where late subluxation is a common occurrence.

Timing of Insertion of the Capsular Tension Ring

The timing of insertion of the CTR is debated. It was once famously said, “as early as necessary and as late as possible,” which remains a matter of opinion and experience. When a CTR is placed early, there is a tendency to trap cortex. Even with the best technique of prior placement of dispersive OVD just under the anterior capsule edge to make space or with the Henderson M-CTR (FCI Ophthalmics, Morcher GmbH), which has 8 indentations intended to release trapped cortex, residual cortex is common. Additionally, a Miyake-Apple study showed clearly that early CTR placement caused significant tension, capsular torque, and displacement of up to 4.0 mm compared to insertion in an empty bag.¹⁵ This author believes that with the advent of reliable capsule suspension hooks, a CTR should only be placed once the capsular bag is cleaned of all lens material. When the nucleus cannot be freed to rotate without zonular stress by appropriate multidirectional hydrodissection or a 2-handed technique, rather than place the CTR, Chang modified MicroSurgical Technology capsular suspension hooks should be placed. The modified hooks do not have an open distal loop that can be accidentally threaded by the CTR. They not only support the bag, removing tension on zonules, but also extend to the equator, putting the otherwise floppy bag on stretch to keep it out of harm’s way during removal of the last nuclear fragments. The lens removal then proceeds without difficulty, allowing the CTR to be placed atraumatically in the clean bag.

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