Timothy P. Page, MD
Most intraocular lenses (IOLs) are intended to be placed into the capsular bag at the time of cataract surgery, making the capsular bag essential for a stable lens position. Normally the capsular bag is held in position by the 360-degree support of the attached surrounding zonules at the lens equator. When there is inadequate zonular support due to a zonular dialysis, a number of complications may occur during surgery. They may include posterior capsule rupture, vitreous loss, and inability to place an IOL in the capsular bag or sulcus. Compromised zonules are often found in patients with pseudoexfoliation, ocular trauma, Marfan syndrome, mature cataracts, and a number of other conditions.1 Fortunately, in 2003, the Food and Drug Administration (FDA) approved the capsular tension ring (CTR) to assist in placing and centering an IOL in these eyes with compromised zonules. Since the initial introduction of the CTR, several modifications have evolved to allow endocapsular implantation of an IOL depending upon the surgeon’s assessment and extent of compromised zonules.2
While inserting a CTR into the capsular bag may be a relatively straightforward maneuver, there are significant complications that may occur during implantation. A large zonular dialysis will have unsupported areas at the equator allowing the capsular bag to twist and fold upon itself. This creates the potential for the advancing CTR eyelet to become entangled in the folds. If the CTR is entangled, any further advancement of the CTR by the surgeon will create stress on the intact zonules and will likely enlarge the existing dialysis or create a new iatrogenic zonular dialysis. Insertion of the CTR may also be made more difficult when presented with subluxated capsular bags, floppy capsular bags due to diffuse zonulopathy, or vitreous in the anterior chamber impeding the safe passage of the CTR into the capsular bag. In these complex cases, the seemingly simple maneuver of implanting a CTR can sometimes make matters worse. Over the years, several techniques to mitigate CTR complications associated with implantation have been described. Moreno-Montañes et al placed a safety suture in the leading eyelet prior to phacoemulsification to serve as a rescue and retrieval technique in the event of posterior capsule rupture. If the capsular bag were to rupture during surgery, the CTR could be removed with the suture through the leading eyelet.3 Others have described the fish-tail and fish-tail on a line techniques where the CTR is bent in half prior to insertion and then released to unfold within the capsular bag with the intent of avoiding a traumatic CTR insertion.4,5
The complications associated with CTR insertion may be divided into 2 categories. The first category includes those complications associated with the torque created by the advancing CTR when the leading eyelet encounters resistance. These forces may worsen an existing dialysis or create a new iatrogenic dialysis. The second category includes those complications associated with incorrect placement of the CTR outside of the capsular bag. This could either be into the angle, the ciliary sulcus, or into the vitreous (Table 3-1).
In this chapter the reader will learn to recognize the early signs of potential hazards associated with CTR insertion and how to mitigate them using the suture-guided CTR (SG-CTR) technique. The SG-CTR is designed to reduce the risk of extending an existing zonular dialysis or creating a new iatrogenic zonular dialysis. The SG-CTR has the added benefit of providing a visible tracer to identify the position of the leading eyelet of the CTR as it is being advanced. In addition, the SG-CTR provides a safety line in the event the CTR needs to be retrieved from being inadvertently placed into the ciliary sulcus or dislodged into the posterior segment.
|Advancing CTR Encounters Resistance From Entanglement or Obstruction||Incorrect Position of the CTR|
|Worsens existing zonular dialysis||Incorrectly placed into the sulcus|
|Creates new iatrogenic zonular dialysis||Dislodged into the vitreous|
Standard Capsular Tension Rings
Before we discuss the SG-CTR, it is important to understand the mechanism of how a CTR works. The same properties that give a CTR its stabilizing effect are also responsible for the complications that may arise. One key feature of a CTR is that it has 2 diameters—a larger diameter in the open extracapsular state and a smaller diameter in the compressed intracapsular. Most commercially available CTRs are available in 2 sizes. The open uncompressed 13.0-mm diameter of CTR compresses to 11.0 mm within the capsular bag. The smaller ring measuring 12.0 mm in the open uncompressed state compresses to 10.0 mm within the capsular bag6,7 (Figure 3-1). These dimensions are based on postmortem studies that have determined the empty capsular bag diameter to be between 10.0 and 10.8 mm.8–10 Vasavada and Singh found in vivo measurements of the capsular bag to reflect these postmortem studies with a range of 9.83 to 10.88 mm.11 Furthermore, Vass et al derived a regression formula to predict the capsular bag diameter for eyes with an axial length less than 25.0 mm: capsular bag diameter = 6.54 + 0.164 x axial length.12 However, many surgeons, including the author, advocate using a larger CTR for most eyes to maximize the effect of uniformly distributing intact zonular strength.
Compressing the larger diameter of the open CTR into the smaller diameter of the capsular bag creates outward tension across the capsular bag, which buttresses areas of weak zonules and recruits and redistributes the support of intact zonules. The CTR automatically expands as it enters the fornix of the capsular bag to its largest possible diameter based on its size and spring constant. It is worth mentioning that not all CTRs have the same spring constant.13 A CTR with a higher spring constant may be better at preventing capsular phimosis. This is important not only for conditions such as pseudoexfoliation but also with accommodating IOLs where capsular contraction can cause significant distortion and malfunction of the IOL.14,15 Implantation of a CTR at the time of accommodating IOL implantation protects against capsular contraction and subsequent vaulting with malfunction of accommodating IOLs.16
Contraindications and Complications
Standard CTR implantation is contraindicated in the presence of anterior radial and posterior capsule tears. Caution should also be exercised when implanting the CTR prior to completion of the continuous curvilinear capsulorrhexis (CCC) because it may cause the anterior capsule tear to extend posteriorly with dislodging of the CTR into the posterior segment.17–19
One of the most common complications that may occur with insertion of a CTR is extension of an existing zonular dialysis or creation of a new iatrogenic dialysis as the outward expansion of the CTR generates torque against the capsular bag.20 CTR insertion has been shown by Miyake-Apple analysis to produce zonular stress and elongation with capsular bag displacement ranging from 0.5 to 4.0 mm depending upon the timing of insertion of the CTR. The greatest displacement occurs after hydrodissection and the least displacement occurs following lens removal.21 When faced with these challenging cases in the operating room, the guiding principle on the timing of CTR implantation is to wait as long as is safely possible. For example, lens material still within the bag may obstruct the path of the advancing CTR eyelet and create resistance with torque on the capsular bag along the body of the CTR. This could worsen the existing dialysis or create a new iatrogenic dialysis. On the other hand, as lens material is removed in the area of a large dialysis, the risk of the unsupported capsular bag making contact with the phaco needle with subsequent posterior capsule rupture increases. Other devices such as capsule hooks or the Ahmed capsular tension segment are useful in this situation to prevent the capsular bag from being drawn to the phaco needle.
Capsular Tension Ring Insertion and Iatrogenic Zonular Dialysis
The fornix of the capsular bag loses its normal contour without the proper structural support of zonules. The unsupported capsular bag will often fold upon itself creating a dangerous situation for an advancing CTR (Figure 3-2). The folds in the capsule are prime areas for potential CTR entanglement and subsequent complications. If the leading eyelet is entangled within folds of capsule or if it becomes entrapped within fibrosis or cortical material, any further advancement of the CTR by the surgeon will create stress on the existing zonules approximately 180 degrees opposite the point of contact between the CTR and the capsular bag (Figure 3-3). If the surgeon fails to recognize that the entangled CTR has ceased to advance, any continued deployment with the injector or manual insertion risks extending the dialysis or creating a new iatrogenic dialysis.
Therefore, it is important to fully expand the capsular bag with an ophthalmic viscosurgical device (OVD). Complete OVD expansion of the capsular bag helps to prevent the bag from folding upon itself and prevents entanglement of the CTR in areas of unsupported capsule with folds. It is also helpful to use OVD to further separate any remaining nuclear material that might entrap the CTR in the capsular fornix.
|Position of CTR Leading Eyelet||Position of CTR Body Visible to Surgeon|
|As the CTR leaves the injector prior to making contact with the capsular bag||Right side of the injector lumen|
|As the CTR makes contact with the fornix of the capsular bag||CTR body will shift to the left side of the lumen of injector|
|As the advancing CTR meets obstruction||Bowing outward to the left side or away from the obstruction|
|As the CTR is firmly entangled and will not advance||An S-curve will appear in the body of the CTR—a critical sign to stop advancing the CTR|
A significant concern with standard CTR insertion is that it is a relatively blind procedure. The iris obscures any view of the leading eyelet as it is being advanced. This prevents the surgeon from detecting any blockade of the advancing CTR eyelet due to entrapment or entanglement. Since the only visible part of the CTR is the body of it as it leaves the injector (or forceps for manual insertion), the surgeon should be aware of the predictable signs that an advancing CTR has encountered potentially hazardous resistance. The surgeon must always be mindful of the position of the capsulorrhexis as the CTR is inserted. If CTR insertion is causing the capsulotomy edge to shift position, it means that the zonules are being stressed with displacement of the bag. However, shifting of the CCC is a relatively late sign and indicates that significant stress is being placed on the capsular bag. The surgeon should be on high alert for potential complications.
Cardinal Movements and Positions of Capsular Tension Ring Insertion
There are 4 key observations that the author identifies as cardinal positions of CTR insertion, which serve as early indicators of atraumatic or traumatic CTR insertion (Table 3-2). The first sign to observe is the movement of the CTR as it leaves the injector. The CTR eyelet will initially emerge on the right side (for clockwise insertion) of the injector opening (Figure 3-4). As the leading CTR eyelet disappears underneath the iris and into the fornix of the capsular bag, the surgeon should pay attention to the position of the capsulorrhexis and the position of the CTR shaft within the lumen of the injector. The surgeon will notice the second movement is a shift of the CTR to the center of the lumen as it makes contact with the capsular bag (Figure 3-5). This is the initial indication that the CTR is meeting the normal resistance of the capsular fornix and the shift toward center is expected with atraumatic insertion. The third sign occurs as the CTR is further deployed, and the body of the CTR will shift to the left side of the lumen (Figure 3-6). This may also be normal in atraumatic insertion; however, pay careful attention to the shaft of the CTR within the pupil as it leaves the injector to observe for any outward bowing toward the periphery of the capsular bag (Figure 3-7). If this occurs, remain vigilant and consider retracting the CTR and aborting insertion until more OVD can be added. This sign might indicate a potential traumatic insertion due to entanglement or entrapment of the leading eyelet. This outward bowing may be a precursor to the fourth and most critical sign, the S-curve (Figure 3-8). With the S-curve sign, the body of the CTR has bowed outward as seen in Figure 3-7, but due to the entrapment of the leading eyelet, the CTR has no place to go. The CTR will coil like a spring, causing a shift of the exiting CTR to the right side of the cannula, creating a distinct S-curve in the CTR. The danger here is that once the S-curve sign has occurred, there is potential energy stored within the body of the CTR similar to a spring held in compression by the already compromised zonules. The risk for complications is high with the potential for a large dialysis to occur before the surgeon has time to react and withdraw the CTR. (See Figures 3-9 through 3-14 and Video 3-1.) The S-curve sign is likely to be accompanied by displacement of the CCC indicating significant stress on the zonules. If the S-curve or CCC displacement occurs, it means that the leading eyelet advancement has been impeded by entanglement or entrapment, usually without the surgeon’s knowledge because the leading eyelet is obscured by the iris. This circumstance was recently observed with Miyake-Apple video analysis. The entrapment of the leading eyelet in capsular folds creates the S-curve sign, which is visible to the surgeon within the pupil. However, the Miyake-Apple illustrates the outward bowing of the CTR with displacement of the capsular bag and potential worsening of the dialysis. (See Figures 3-15A and B). If further deployment of the CTR is attempted with this impediment, a traumatic insertion is likely to occur by either extending the existing dialysis or creating a new dialysis. If the S-curve sign or displacement of the CCC is noticed, stop immediately and retract the CTR. Prior to the advent of the SG-CTR, the capsular bag would be refilled with OVD and another attempt would be made.