25 Strategies for Weak Zonules Weak zonules complicate every step of the cataract procedure and challenge surgeons to anticipate, recognize, and manage intraoperative zonulopathy.1–9 If the capsular bag is successfully preserved, the surgeon must also consider and optimize long-term intraocular lens (IOL) fixation and centration in light of existing and potentially progressive zonular abnormality.10 The most common predisposing risk factors for zonular weakness include pseudoexfoliation, prior trauma, retinopathy of prematurity, advanced age and nuclear brunescence, and prior intraocular surgery (e.g., prior vitrectomy or trabeculectomy). Less common risk factors would be conditions such as Marfan’s syndrome, retinitis pigmentosa, and myotonic dystrophy. The presence of a traumatic mydriasis, iridodialysis, angle recession, or vitreous herniation is invariably associated with some degree of traumatic zonulopathy. Suspicion should also be high with a prior history of traumatic hyphema. Absent preoperative phacodonesis or visible zonular dialysis, however, the extent of zonular weakness is generally not known until surgery is initiated. Robert Osher’s group11 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. Pseudoexfoliation syndrome is characterized by progressive zonulopathy, and the whitish deposits are 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 in these eyes (Fig. 25.1a). Likewise, a brunescent nucleus with pseudoexfoliation is frequently accompanied by weak zonules. The most worrisome sign with pseudoexfoliation, however, is an unexpectedly shallow anterior chamber despite a normal axial length; this invariably indicates diffusely weak zonules.4,9 One should consider a retrobulbar or peribulbar anesthetic block in cases suspected of having a high risk of capsular rupture. Because of the progressive nature of the associated zonulopathy, it can be argued that cataract surgery in pseudoexfoliation eyes should be performed at the earlier end of the elective surgical window. The capsulorrhexis step provides the first opportunity for surgeons to directly assess zonular integrity. If firmly anchored by the zonules, the peripheral anterior capsule is normally immobile during this step. In contrast, with weak zonular fixation, the capsule will demonstrate “pseudoelasticity” by seemingly stretching, as the capsular flap is pulled.12 This is not true capsular elasticity but rather due to the failure of the zonules to immobilize the peripheral lens capsule. Another sign of severe or diffuse zonular weakness is difficulty incising the anterior capsule, as though the cystotome tip was dull (Fig. 25.1b). If the cystotome tip depresses rather than incises the central anterior capsule, a halo-shaped light reflex may be noted. These signs represent a lack of circumferential zonular traction that should normally create a taut anterior capsule. Finally, there may be significant movement of the entire lens as the cystotome first perforates and tears the anterior capsule. Weak zonules significantly increase the risk of a radial anterior capsular tear because of this property of pseudoelasticity. Because the zonules do not adequately immobilize the anterior capsule, the peripheral capsule moves along with the flap as it is being torn. Although a large diameter capsulorrhexis would be helpful for phaco in any challenging case, this also increases the risk of a peripheral extension if one is struggling to control the tear. Because use of capsular retractors or a capsular tension ring (CTR) requires a continuous curvilinear capsulotomy, the overriding priority 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. If capsular pseudoelasticity is noted, one might intentionally make the capsulotomy diameter slightly smaller to improve the odds of successfully achieving a continuous curvilinear capsulotomy. Brian Little et al’s13 capsule tear-out rescue technique is particularly helpful for controlling a tear that wants to veer radially because of weak zonules and pseudoelasticity. Upon successful completion of the capsulorrhexis, loose zonules still pose multiple problems for the phacoemulsification and cortical aspiration steps. Because of deficient capsular rotational stability and counterfixation, the nucleus is more difficult to rotate. One should always suspect significant circumferential zonular weakness if, despite proper hydrodissection technique, the nucleus does not spin easily. Finally, the epinucleus and cortex do not separate as easily from a capsular bag that is lax and 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, to do so, the rotating instrument (e.g., hydrodissection cannula or chopper) must partially push the nucleus against the capsular bag equator to achieve the necessary rotational force and counterfixation. In fact, of all of our surgical maneuvers, I believe that rotation of either the nucleus or a three-piece IOL imparts the most force against the capsular bag. This explains why these two steps are the most likely to extend a radial anterior capsular tear into the posterior capsule. With pseudoexfoliation, overly forceful efforts to rotate the nucleus may instead shear already weakened zonules in the process. This could potentially create a large zonular dialysis or dislocate the crystalline lens even prior to insertion of the phaco tip. Fig. 25.1 Poorly dilated pupil in eye with Pseudoexfoliation and dense nucleus (a). Following placement of iris retractors, anterior capsular striae indicate that it is difficult to puncture with the cystotome because of lax zonular tension (b). Double stranded capsule retractors (Microsurgical Technologies) are inserted around the capsulorhexis edge to support the capsular bag and equator during phaco (c). Vertical phaco chop is used to bisect the brunescent nucleus, while minimizing the zonular strain associated with sculpting (d). After cortical cleanup, a capsular tension ring is implanted while the capsule retractors are still supporting the capsular bag (e). One alternative is to use two 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 described below. By fixating the capsular bag to the eye wall, capsule retractors will facilitate nuclear rotation and prevent creation of a zonular dialysis in the process. Polymethylmethacrylate (PMMA) capsular tension rings (Morcher, Stuttgart, Germany; Ophtec, Boca Raton, FL) partially compensate for a weakened zonular apparatus in several ways.14–26 Using forceps or an injector (Geuder, Heidelberg, Germany; Ophtec), 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 those of nuclear sculpting or IOL insertion, toward areas of stronger zonular support. However, if the entire circumference of zonules is uniformly weak, this benefit is negated. A second advantage is that centrifugal equatorial 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 three-piece foldable IOL can provide some of the same benefits during cortical aspiration. In addition, the IOL optic can block a floppy posterior capsule from vaulting toward the irrigation and aspiration (I/A) tip in the subincisional area. The final benefit of a CTR is to counter the progressive contractile capsular forces. Postoperatively, centrifugal zonular tension normally limits capsulorrhexis diameter shrinkage as the capsular bag contracts. Therefore, severe capsulophimosis always indicates deficient zonular countertraction. Excessive or asymmetric capsular contracture can decenter the IOL and further weaken the remaining zonules. This is a likely factor in spontaneous late dislocation of the entire capsular bag and IOL in pseudoexfoliation cases.10,29 The CTRs have two important disadvantages to consider. Because of its larger diameter, significant compression is required to insert the ring into the capsular bag. This may stretch the capsulorrhexis and potentially shear the remaining 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. CTR insertion with an injector is preferable to reduce the forces exerted on the bag and zonules during insertion.27 A second drawback to CTRs is that they may impede cortical aspiration by pinning and trapping cortex within the capsular fornix. For this reason, surgeons should consider first 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, Pembroke, MA; Morcher) has a scalloped contour that facilitates cortical removal following placement.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. 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.31–34 Merriam and Zheng31 first described using self-retaining iris retractors through paracentesis openings to hook and fixate the capsulorrhexis. 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. Richard Mackool35 designed the Capsular Support System (Impex Surgical, Brooklyn, NY; FCI Ophthalmics) with capsular hooks that are sufficiently elongated to support the peripheral capsular fornix and not just the capsulorrhexis edge. In this way, the retractors function as artificial zonules to stabilize the entire capsular equator and bag during phaco and cortical cleanup. Unlike a CTR, capsule retractors provide support in the anterior-posterior direction and do not trap the cortex. This is because each retractor applies only point pressure to the capsular fornix without ensnaring the cortex. The disposable nylon capsular retractors from MicroSurgical Technologies (MST; Redmond, WA) are a more recent alternative to the Mackool retractor design (Fig. 25.1c). They feature a double-stranded design that creates a loop at the tip, which is less likely to puncture the equatorial capsule. One must take care, however, not to thread the CTR leading eyelet through this loop of the MST capsule retractor. Capsule retractors can be inserted through limbal stab incisions at any surgical stage including midway through the capsulorrhexis step. By anchoring the bag to the eye wall, the additional anteroposterior support and rotational stability facilitate hydrodissection and nuclear rotation. The self-retaining capsule retractors are also strong enough to center and immobilize a capsular bag that is partially subluxated due to a severe zonular dialysis. They also restrain the peripheral anterior and equatorial capsule from being aspirated and dehisced by the phaco or I/A tip. As a single strategy for severe zonular deficiency, capsule retractors are significantly more effective than CTRs at preventing posterior capsule rupture. Because CTRs can only redistribute instrument and mechanical forces to the remaining intact zonules, the greater the zonular defect or deficiency, the less effective a CTR can be at stabilizing the bag. However, a CTR can be used in conjunction with capsule retractors, particularly if there is a sizable zonular dialysis. If, after first inserting retractors, the unsupported equatorial regions of the capsular bag still tend to collapse inward toward the phaco tip, a CTR can be inserted to distend the equator of the bag to its proper anatomic configuration. Although the tip of the capsule retractor is dull, it is possible for the hooks to tear the capsulorrhexis margin during surgery. A key objective is to support the capsular bag without excessive tension and stretching of the anterior capsular rim. There is a tendency to overtighten the capsular retractors because the tension is initially adjusted with a soft eye. Inserting the phaco tip with irrigation suddenly displaces the nucleus and capsular bag posteriorly, which effectively tightens the retractors further. After inserting the phaco tip, it is therefore important to momentarily assess whether the capsule retractors have become so taut that they tent the capsulorrhexis edge. If so, they should be loosened slightly so that the capsular rim does not tear during phacoemulsification. This is particularly important if the capsulorrhexis diameter is on the small side. Fragile zonules are highly prone to further damage or breakage during nuclear emulsification, and poor capsular bag stability heightens the risk of capsular rupture. Forceful sculpting or rotation of the nucleus may shear zonules in the oppositely located quadrants. Care should be taken to avoid causing excessive nuclear movement with sculpting, chopping, or rotation. Phaco chop significantly reduces the stress placed on the zonules and capsule by replacing sculpting motions with the manual forces of one instrument pushing inward against another (Fig. 25.1d). Because of the centrally directed instrument forces, horizontal chopping is particularly effective at avoiding nuclear tilt or displacement, and this is my preference for weak zonule cases. The supracapsular flip technique, as popularized by David Brown,36 prolapses and flips the endonucleus out of the capsular bag prior to emulsification. If accomplished, this prevents the capsular bag from bearing any of the phaco instrumentation forces. The ease with which this flipping maneuver can be accomplished varies depending on the size of the endonucleus relative to the capsulorrhexis diameter. Using this technique with a nucleus that is too large or a capsulorrhexis that is too small risks further zonular dehiscence. Care must also be taken to avoid endothelial trauma during the nuclear flipping maneuver (see Phaco Flip Technique, below). With chopping, one should consider bringing larger sections of nucleus out of the capsular bag where they can be sub-chopped into smaller fragments within the supracapsular space. For example, with a medium density nucleus it may be possible to lift each hemi-nucleus out of the capsular bag following the initial bisecting horizontal or vertical chop. Throughout phaco and cortical cleanup, one should anticipate that deficient centrifugal zonular tension will result in greater posterior capsule laxity. The flaccid posterior capsule will trampoline or be drawn toward any aspirating tip as the nuclear fragments, epinucleus, and cortex are removed. Initially, the nuclear bulk will mask this situation, but one must be vigilant as increasingly more nucleus is removed to expose more of the posterior capsule. Compared with a standard 19-gauge phaco tip, a smaller-diameter, 20-gauge tip greatly reduces the risk of inadvertently aspirating the peripheral or posterior capsule. If one suspects or encounters zonular laxity, the aspiration settings can be lowered as progressively more of the nucleus is removed. To slow the pace, a lower than usual aspiration flow rate is advisable. A preprogrammed vacuum setting that usually avoids a postocclusion surge with routine cases may not be safe with a lax posterior capsule that is lacking normal centrifugal zonular tension. Therefore, one should consider decreasing the vacuum to lower than normal levels to prevent trampolining of the posterior capsule. Finally, repeatedly re-inflating the capsular bag with a dispersive ophthalmic viscosurgical device (OVD) can further restrain a flaccid posterior capsule from vaulting toward the aspirating instrument as the final fragments and epinucleus are aspirated. Guarding the phaco tip by placing the horizontal chopper tip beneath it is another strategy. These safety measures are especially important if there is no epinuclear shell remaining as the last nuclear fragment is emulsified. As adherent cortex is aspirated, the usual centrifugal capsular counterfixation afforded by stronger zonules is deficient. Lacing circumferential zonular tension, a lax posterior capsule tends to cling to any epinucleus and cortex that is being aspirated; redundant capsular folds can be easily ensnared by the aspirating instrument or snagged by a capsule polisher (Fig. 25.2). While removing cortex, inadvertently aspirating the more pliant anterior capsule may cause a zonular dialysis. Effective hydrodissection is crucial because the more easily lens material separates from a floppy capsule, the less likely it is for the capsular folds to be aspirated. As mentioned earlier, continually re-inflating the capsular bag with a dispersive OVD is an excellent strategy for removing cortex from a floppy bag as well. Placing both the anterior and posterior capsule on stretch prevents a pliant posterior capsule from trampolining toward the aspiration port. In this situation, cortical aspiration can be performed either with or without irrigation (dry technique). Dispersive agents are preferable to cohesive viscoelastics because they better resist aspiration. Finally, stripping the cortex tangentially rather than radially helps to distribute the tractional force across as large an area of zonules as possible. Bimanual I/A instrumentation provides several advantages in the presence of weak zonules (Fig. 25.3). The ability to alternate between two aspirating ports improves access to the sub-incisional cortex, which can be especially challenging to remove if the capsulorrhexis diameter is small and the posterior capsule is lax. A dual-incision system also means that the aspirating port never needs to turn toward the capsular fornix. It can be kept facing the cornea and away from the posterior capsule virtually at all times. Without a constraining infusion sleeve, the surgeon is better able to reach across to the opposite equatorial quadrants where the aspirating port can be safely buried within fluffs of cortex before vacuum builds. This prevents the tip from aspirating the pliant peripheral or posterior capsule. Finally, in the presence of a zonular dialysis, the ability to dissociate the I/A tips can minimize any misdirection of irrigating fluid through the zonular defect.
Preoperative Signs of Zonulopathy
Capsulorrhexis
Hydrodissection
Capsular Tension Rings
Capsule Retractors
Nuclear Emulsification
Cortical Cleanup
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