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PHACO STRATEGIES WITH ZONULOPATHY
David F. Chang, MD
Weak zonules complicate every step of the cataract procedure and challenge surgeons to diagnose and manage intraoperative zonulopathy (Figure 1-1).1–10 Even if the capsular bag is successfully preserved, the surgeon must then consider and optimize long-term intraocular lens (IOL) fixation and centration in the setting of concurrent and potentially progressive zonular abnormality.11 The most common predisposing risk factors for zonular weakness include pseudoexfoliation, advanced age, prior trauma, retinopathy of prematurity, and prior intraocular surgery (eg, prior vitrectomy or trabeculectomy). Less common risk factors would be conditions such as Marfan syndrome, retinitis pigmentosa, and myotonic dystrophy.
Preoperative Signs of Zonulopathy
The presence of a traumatic mydriasis, angle recession, iridodialysis, and vitreous herniation is invariably associated with traumatic zonulopathy or zonular dialysis. Suspicion should be high with any history of blunt force trauma, particularly if there was a traumatic hyphema. In the absence of preoperative phacodonesis or visible zonular dialysis, however, the extent of zonular weakness is usually not known until the initiation of surgery. Robert Osher has described subtle signs of zonular weakness that include a wider iridolenticular gap (space between the iris and the anterior lens surface), a decentered nucleus, focal iridodonesis, and visibility of the peripheral lens equator upon lateral gaze.12 Iridodonesis is best detected at the slit lamp prior to pupil dilation.
Pseudoexfoliation is associated with progressive zonulopathy and is characterized by whitish deposits found not only on the zonules but also on the posterior iris surface and pupillary margin. Therefore, smaller pupils are often associated with more advanced zonulopathy. Likewise, a brunescent nucleus is frequently accompanied by diffuse zonular weakness. An ominous preoperative sign with pseudoexfoliation is an unexpectedly shallow anterior chamber despite a normal axial length; this invariably indicates extremely weak zonules.4,9 One should consider a retro- or peribulbar anesthetic block in cases at higher risk of capsular or zonular tears. Because of the progressive nature of the associated zonulopathy, it can be argued that pseudoexfoliation is an indication to perform cataract surgery earlier rather than later.
Capsulorrhexis
In higher-risk cases, I consider the capsulorrhexis to be a zonular stress test, because the first indication of how weak the zonules are becomes evident during this step. There are a variety of clues that indicate focal or diffuse zonulopathy.
The earliest sign of severe or diffuse zonular weakness is difficulty incising the anterior capsule with the cystotome (see Figures 1-1B and 1-2). If the anterior capsule is not taut, the cystotome tip will tend to first dimple, wrinkle, and indent it, rather than immediately puncture it, and a halo-shaped light reflex around the cystotome tip may be noted (see Figure 1-2). The appearance mimics that of using a dull cystotome. In eyes with diffuse zonulopathy, this sign represents the absence of circumferential traction that should normally create a taut anterior capsule. Asymmetric zonular weakness may instead result in prominent capsular folds due to focal loss of centrifugal traction as the capsular flap is pulled. Finally, there may be significant movement of the entire lens as the cystotome first perforates and tears the anterior capsule, or as the capsule forceps applies traction to the flap.
Figure 1-1. Case 1. (A) Eye with pseudoexfoliation. (B) Diffuse zonular weakness creates a lax anterior capsule that dimples rather than being incised by the cystotome. (C) Horizontal chop minimizes lateral and vertical displacement of the nucleus. (D) A lax posterior capsule is much more easily snagged by I/A instrumentation.
Figure 1-2. Pseudoexfoliation. Due to insufficient circumferential zonular tension, the anterior capsule is not taut and the cystotome needle tends to indent rather than incise the capsule, creating radiating capsular folds.
As the capsular flap is advanced, the peripheral anterior capsule is normally immobilized by centrifugal zonular tension. This countertraction facilitates precise control over the ensuing direction of the tear. Without normal zonular countertraction, the lax and pliant peripheral anterior capsule moves and stretches as the flap is pulled—what I have called pseudoelasticity (Figure 1-3). In other words, the zonular weakness and laxity make the capsule appear unusually elastic. The tear is difficult to control and will tend to veer radially. In addition to regrasping the flap more frequently with a pair of forceps, Brian Little’s capsular tear-out rescue maneuver must be continually employed to increase the capsular countertraction enough to control the flap (Figure 1-4).13
If pseudoelasticity is severe, the surgeon can use iris hooks or specially designed capsule retractors to help anchor the bag during the capsulorrhexis step. After completing several clock hours of the capsulorrhexis, one or more capsule retractors can be used to stabilize the bag and provide helpful countertraction against the tugging flap. It is easy to exert too much tension on the capsule edge with the retractors, which will abruptly extend the tear peripherally. One should never insert a capsular tension ring (CTR) before completing the capsulorrhexis because the expansive force of the ring will extend the tear. If the pupil is of borderline size, enlarge its diameter with iris retractors. Optimal visualization of the peripheral capsular region is of far greater importance here than with a routine case.
Opinions differ regarding the target diameter of the capsulorrhexis in eyes with loose zonules. A larger-diameter capsulorrhexis will facilitate nuclear and cortical removal, but it is much harder to control and complete in eyes with capsular pseudoelasticity. With weakened zonules the more peripherally the tear advances, the more it wants to veer radially, and the more difficult it is to rescue the flap. By comparison, a smaller-diameter capsulorrhexis is much easier to control and increases the opportunity to recognize and rescue a peripherally escaping tear. Because use of capsule retractors or a CTR requires a continuous curvilinear capsulorrhexis, the overriding importance of achieving an intact capsulorrhexis dictates that one should err on the side of a smaller diameter that can be secondarily enlarged after the IOL has been implanted. Therefore, if pseudoelasticity is observed, one should intentionally make the capsulotomy diameter slightly smaller to improve the odds of success (see Figure 1-3).
Figure 1-3. (A, B) Pseudoelasticity. This patient with pseudoexfoliation has weak zonules, allowing the peripheral capsule in this area to behave as though it were elastic. It moves excessively with manipulation of the capsule flap.
Figure 1-4. Little tear-out rescue maneuver. (A) The capsulorrhexis tear is escaping peripherally due to focal zonular laxity. The flap is pulled backward and placed on tension to improve directional control as the tear is (B-D) advanced and (E, F) completed.
Although a smaller capsulorrhexis may hinder subsequent surgical steps, it is far preferable to a torn anterior capsule, particularly when other risk factors are present. The surgeon should mentally visualize the capsulorrhexis diameter during nuclear emulsification, to avoid tearing it with the chopper shaft or phaco tip. Bimanual instrumentation is superior for cortical clean-up in a floppy capsular bag and greatly improves subincisional access through a small capsulorrhexis. Finally, the surgeon should consider secondarily enlarging a small capsulorrhexis after the IOL and CTR are safely implanted as will be described.
Figure 1-5. The Henderson CTR has scalloped contours, which makes it less likely to pin cortex to the capsular fornix.
Hydrodissection
Despite successful completion of the capsulorrhexis, loose zonules still pose multiple problems for the phacoemulsification and cortical aspiration steps. It can be very difficult to turn the nucleus because of deficient capsular rotational stability and counterfixation. One should always suspect significant circumferential zonulopathy if, despite proper hydrodissection technique, the nucleus does not rotate easily. Finally, the epinucleus and cortex do not separate as easily from a capsular bag that is loosely anchored.
Normally, we are able to rotate a hydrodissected nucleus with a single instrument because of the counterfixation provided by the capsular bag. However, the rotating instrument (eg, hydrodissection cannula or chopper) must partially push the nucleus against the capsular bag to impart the necessary rotational force. In fact, of all of our surgical maneuvers, I believe that rotation of either the nucleus or a 3-piece IOL imparts the most force against the capsular bag. This explains why these 2 steps are the most likely to extend a radial anterior capsule tear into the posterior capsule. With pseudoexfoliation, overly forceful efforts to rotate the nucleus may shear already weakened zonules. This may potentially create a large zonular dialysis or dislocate the crystalline lens even prior to insertion of the phaco tip.
One alternative is to use 2 instruments to bimanually rotate the nucleus. In this situation, the second instrument tip, rather than the capsular bag, becomes the counterfixating fulcrum around which to rotate the nucleus. However, when severe zonular laxity is diagnosed during the capsulotomy step and the nucleus cannot be easily rotated following hydrodissection, the safest strategy is to insert capsule retractors as will be described. By fixating the capsular bag to the corneoscleral limbus, capsule retractors will facilitate nuclear rotation and prevent creation of a zonular dialysis in the process.
Capsular Tension Rings
Polymethylmethacrylate (PMMA) CTRs (Morcher GmbH, Ophtec BV) partially compensate for a weakened zonular apparatus in several ways.14–26 Using forceps or an injector (Geuder AG, Ophtec BV), the ring can be inserted at any stage following completion of the capsulorrhexis.27,28 If there is a focal zonular dehiscence or weakness, the ring redistributes mechanical forces, such as that of nuclear sculpting or IOL insertion, to areas of stronger zonular support. However, if the entire circumference of zonules is uniformly weak, this benefit is lost.
A second advantage is that centrifugal pressure applied by the ring makes the flaccid capsular bag tauter. This reduces redundant capsule folds, forward trampolining of the posterior capsule, and inward collapsing of the capsular fornices toward the aspirating instrument tip. In the absence of a CTR, the stiff PMMA haptics of a 3-piece foldable IOL can provide some of the same benefits during cortical aspiration. In addition, the IOL optic can block a lax and floppy posterior capsule from vaulting toward the irrigation/aspiration (I/A) tip in the subincisional area.
The final benefit of a CTR is to counter progressive contractile capsular forces. Postoperatively, centrifugal zonular tension normally resists capsulorrhexis shrinkage as the capsular bag contracts. Therefore, severe capsulophimosis is always a result of deficient zonular countertraction. Excessive or asymmetric capsular contracture can decenter the IOL and further weaken the remaining zonules. This is likely a contributing factor in spontaneous late dislocation of the entire capsular bag in pseudoexfoliation cases.10,29
CTRs have 2 important disadvantages. Significant compression is required to implant the ring into the capsular bag because of its larger size. This may stretch the capsulorrhexis and potentially shear zonules by distorting or decentering the bag. Because of this compressive force, CTRs should never be inserted in the presence of an anterior or posterior capsule tear. In addition, insertion with an injector is preferable in order to reduce the forces exerted on the zonules during insertion (see Figure 1-8H).27 A second drawback to CTRs is that they may impede cortical aspiration by pinning and trapping cortex in the capsular fornix. For this reason, surgeons should consider using capsule retractors instead of a CTR to stabilize the bag during phaco. Ideally, CTR insertion can then be delayed until after the cortex has been removed.27 The Henderson modified CTR (FCI Ophthalmics, Morcher GmbH) has a scalloped contour that facilitates cortical removal following placement (Figure 1-5).30 If one area of cortex is difficult to remove because the Henderson CTR impinges on it, the ring can be rotated slightly until one of the gaps overlies the cortex.
Capsule Retractors
In addition to enlarging a small pupil, flexible iris retractors can be used to support the capsular bag in the presence of extremely loose zonules (Figure 1-6).31–34 Merriam and Zheng first published the use of self-retaining iris retractors through paracentesis openings to hook and fixate the capsulorrhexis.31 However, because the hooked ends are very short and flexible, iris retractors may tend to slip off of the anterior capsular edge during phaco and will not support the equator of the capsular bag.
Figure 1-6. Case 2. (A) Small pupil in a tamsulosin patient with pseudoexfoliation and a brunescent lens. (B) Four Prolene (Ethicon) iris retractors are placed prior to the capsulotomy and trypan blue dye staining. (C) Because diffuse and significant zonular weakness is noted during the capsulorrhexis step, the iris retractors are advanced around the edge of the capsulotomy to support the bag during lens removal. (D) Following nuclear removal, the retractors can remain in place during the cortical clean-up because they do not trap the cortex (unlike a CTR). (E) The retractors are removed after a Staar AQ2010V 3-piece foldable IOL has been placed in the ciliary sulcus. Some stromal iris trauma has occurred following iris prolapse to the left-hand side-port incision during phaco.
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