EyeWorld Asia-Pacific September 2012 Issue

27 EWAP CAtArACt/IOL September 2012 Phaco with weak zonules: Part 1 by David F. Chang, MD Weak zonules complicate every step of the cataract procedure and challenge surgeons to diagnose and manage intraoperative zonulopathy. This two-part article will discuss surgical pearls for phaco in these cases. Capsulorhexis The capsulorhexis step provides the first opportunity to directly assess zonular integrity. The peripheral anterior capsule is normally immobile but will demonstrate “pseudoelasticity” by seemingly stretching as the capsular flap is pulled. 1 This is not true capsular elasticity but rather due to the failure of the zonules to immobilize the peripheral lens capsule. The lack of zonular circumferential traction due to diffuse zonular weakness will create difficulty incising the anterior capsule, as though the cystotome were dull. If the cystotome tip depresses rather than incises the central anterior capsule, a halo- shaped light reflex may be noted. Finally, there may be significant phacodonesis 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 pseudoelasticity. Because the zonules do not adequately immobilize the anterior capsule, the peripheral capsule moves along with the flap as it is being torn. While a large diameter capsulorhexis would be helpful for phaco, making a smaller opening reduces the risk of a peripheral extension if one is struggling to control the tear. Because capsular retractors or a capsular tension ring (CTR) require a continuous curvilinear capsulotomy, the overriding importance of achieving an intact capsulorhexis dictates erring on the side of a smaller diameter that can be secondarily enlarged after the IOL has been implanted. The capsule tear-out rescue technique of Brian Little, FRCS, is particularly helpful for controlling a tear that wants to run radially because of weak zonules and pseudoelasticity. 2 Hydrodissection When there is diffuse zonular laxity, the nucleus is more difficult to rotate because of deficient capsular rotational stability and counter fixation. One should therefore suspect significant circumferential zonular weakness if, despite proper hydrodissection technique, the nucleus does not rotate easily. 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 two instruments to bimanually rotate the nucleus. In this situation, the second instrument tip, rather than the capsular bag, becomes the counter fixating 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 (Figures 1-5). By fixating the capsular bag to the eye wall, capsule retractors will facilitate nuclear rotation and avoid creation of a zonular dialysis in the process. Capsular tension rings CTRs compensate for weakened zonules in several ways. With a focal zonular weakness or dehiscence, the ring redistributes mechanical forces (e.g., from 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. The final benefit of a CTR is to counter progressive contractile capsular forces post-op. Severe capsulophimosis is always a result of deficient zonular counter traction and is a likely factor in spontaneous late dislocation of the entire capsular bag in pseudoexfoliation. CTRs have two important disadvantages. Significant compression is required to implant the ring into the capsular bag because of its larger size. This may stretch the capsulorhexis and potentially shear zonules by ovalizing or decentering the bag. Because of this compressive rebound force, CTRs should never be inserted in the presence of an anterior or posterior capsule tear. Secondly, the ring may impede cortical aspiration by pinning and trapping cortex in the capsular fornix. Surgeons can delay CTR insertion by instead using capsule retractors to stabilize the bag during phaco. The capsule retractors should be left in place during CTR insertion to reduce zonular trauma (Figure 5). The Henderson modified CTR (FCI Ophthalmics, Marshfield Hills, Mass., USA) has a scalloped contour that facilitates cortical removal following placement. 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. 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 Mackool, MD, designed capsular hooks that are elongated enough to support the peripheral capsular fornix and not just the capsulorhexis edge. In this way, the retractors function as artificial zonules to stabilize the entire bag during phaco and cortical cleanup. Unlike capsular tension rings, capsule retractors provide much better support in the anteriorposterior direction and do not trap the cortex (Figure 4). The disposable nylon capsular retractors from MicroSurgical Technology (Redmond, Wash., USA) are a newer alternative to the Mackool Capsule Support System (Figure 1). Packaged three to a container, the former feature a double- barreled design that creates a loop at the tip, which is less likely to puncture the equatorial capsule. Capsule retractors can be inserted through limbal stab incisions at any stage including midway through the capsulorhexis step. By anchoring the bag to the eye wall, the additional antero- posterior support and rotational stability facilitate hydrodissection and nuclear rotation. The self- retaining capsule retractors are also strong enough to center and continued on page 29