Key Features
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Zonular integrity is evaluated at the slit lamp preoperatively by assessing for lens decentration, phacodonesis, and iridodonesis.
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Uveitis may complicate cataract surgery as a result of poor dilation, posterior synechiae, zonular laxity, and exaggerated postoperative inflammation.
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Preoperative endothelial cell density less than 1000/mm 2 , central corneal thickness greater than 640 µm, and corneal epithelial edema indicate increased risk for postoperative corneal decompensation in patients with Fuchs’ corneal dystrophy.
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Femtosecond laser-assisted cataract surgery may have distinct advantages for certain complex eyes because of ease in capsulorrhexis creation, assistance with nucleofractis, and reduced postoperative endothelial cell loss.
Associated Features
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A large capsulorrhexis (≥ 5.5 mm in diameter) facilitates removal of nuclear fragments and reduces postoperative anterior capsular phimosis in the setting of zonular laxity.
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Areas of weakened zonules may be stabilized intraoperatively and postoperatively by using capsular hooks, capsular tension rings, and capsular tension segments.
Introduction
Modern cataract surgery can normally be performed with minimal anesthesia, manipulation of ocular tissue, and postoperative morbidity. Although most surgeons perform routine surgery using the same basic techniques for all patients, in some circumstances, the surgical technique must be altered because of specific preoperative conditions in complex eyes.
Zonular Instability
When cataract surgery and intraocular lens (IOL) placement are planned for a patient with history of ocular trauma, intraocular surgery, pseudo-exfoliation syndrome, or systemic conditions associated with zonulopathy (e.g., Marfan’s syndrome), it is important for the surgeon to evaluate the status of the zonules. Zonular instability increases the risk of intraoperative complications and the likelihood of IOL subluxation postoperatively.
Zonular integrity may be evaluated at the slit lamp preoperatively by looking for the presence of lens decentration, phacodonesis, or focal iridodonesis. This may be facilitated by having the patient quickly shift the direction of gaze or by gently shaking the slit lamp table with a fist. When necessary, it often is possible to directly visualize the zonular ligament fibers by using a gonioprism. If a patient has a history of ocular trauma, the eye should also be examined for iridodialysis and vitreous in the anterior chamber, either of which makes zonular dehiscence likely.
During surgery, care must be taken to preserve as many of the remaining supporting zonules as possible. If discrete areas of zonular dehiscence are present, a cohesive ophthalmic viscosurgical device (OVD) may be used to force a dispersive OVD into the area of zonular loss and prevent vitreous prolapse into the anterior chamber. The anterior capsule may initially dimple under the cystotome tip in the presence of zonular laxity, rather than being immediately punctured. If difficulty is encountered when beginning the anterior capsular tear, two 27-gauge needles may be used in a crossing fashion to create countertraction and assist with initiation of the rhexis. After the capsulorrhexis is begun, pseudo-elasticity of the capsule may be experienced because of the reduction in counterresistance offered by the zonules to oppose the tearing forces applied by the surgeon. In cases of marked zonular loss, capsular hooks or retractors may be utilized to stabilize the bag and facilitate completion of the rhexis. If these are unavailable, nylon iris fixation hooks can be used in a similar manner, although the tips may tend to inadvertently tear the capsule. After starting the rhexis, the surgeon gently retracts the capsular edge with hooks in the direction of the area of dehiscence. After the rhexis is completed, the hooks may be left in place while hydrodissection and phacoemulsification (“phaco”) are performed. A large rhexis (at least 5.5 mm in diameter) is made to facilitate removal of nuclear fragments and prevent postoperative anterior capsular phimosis. Careful and complete hydrodissection is performed so that the nucleus rotates easily within the capsular bag with minimal zonular stress. Bimanual rotation may be utilized to further reduce zonular stress by simultaneously rotating the nucleus using two instruments located 180° apart.
A horizontal chop technique is preferable for nuclear disassembly in situations of zonular laxity because it causes minimal strain on the zonular fibers. If grooving is performed within the capsular bag, the main incision should be created in a position so that the phaco needle carves toward the area of dehiscence to prevent induction of forces that extend the area of zonular loss. If the surgeon feels that zonular support is inadequate for intracapsular manipulation, the nucleus may be prolapsed from the capsular bag, and phaco can be performed within the anterior chamber.
Once the nucleus and epinucleus have been removed, cortical cleanup must be performed delicately. Stripping the cortex in tangential fashion with forces perpendicular to the radial zonular fibers has been shown to exert reduced force on the zonule. With the nucleus removed, the capsular bag is floppier in nature, and the area of the dehiscence may be drawn toward the aspiration tip. In such cases, the surgeon may have more control when the irrigation and aspiration ports are separated to perform bimanual irrigation–aspiration. In this way, the irrigation tip can be used to hold back the capsular fornix of the area of dehiscence while the aspiration tip safely removes cortex.
After complete removal of the cataract, an appropriate IOL must be selected. Whenever possible, the IOL is placed within the capsular bag. Intracapsular IOL placement without a capsular tension segment or ring may be appropriate for patients who have small areas of zonular dehiscence. In such cases, a three-piece posterior-chamber intraocular lens (PCL) should be placed so that one of the haptics is oriented toward the area of dehiscence, thus extending the bag in that direction ( Fig. 5.14.1 ). If the haptics are rotated so that they are 90° away from the dehiscence, the optic is more likely to decenter in a direction away from the area of dehiscence.
Mild, diffuse, zonular laxity and zonular dehiscence up to 4 clock hours may be managed by placing a capsular tension ring within the capsular bag. Areas of dehiscence greater than 4 clock hours may be managed by using capsular tension segments to provide additional capsular support. Capsular tension segments and some tension rings, such as the Cionni ring, have eyelets to allow fixation to the scleral wall with a polypropylene or Gore-Tex suture. These devices are left in place postoperatively and have been shown to help expand and center the capsular bag, thus preventing the lens implant from migrating away from areas of zonular dehiscence.
If capsular support is felt to be inadequate for intracapsular lens placement, an alternative technique should be utilized ( Table 5.14.1 ). A sulcus-supported PCL can be placed so that the haptics are 90° away from the area of dehiscence ( Fig. 5.14.2 ). This orientation prevents the haptics from slipping posteriorly into the vitreous chamber. If a continuous curvilinear capsulorrhexis has been performed, it is advantageous to prolapse the optic posteriorly into the capsular bag while the haptics remain in the sulcus. This technique often results in more stable optic centration in the presence of zonular dehiscence.
| Procedure | Optic Position | Haptic Position | Haptic Fixation |
|---|---|---|---|
| Intracapsular posterior-chamber intraocular lens (PCL) implant | Capsular bag | Capsular bag | Capsular bag fornices |
| Intracapsular PCL with reverse optic capture * | Posterior chamber | Capsular bag | Capsular bag fornices |
| Sulcus-supported PCL | Posterior chamber | Ciliary sulcus | Ciliary sulcus |
| Sulcus-supported PCL with optic capture * | Capsular bag | Ciliary sulcus | Ciliary sulcus |
| Transscleral fixated PCL | Posterior chamber | Ciliary sulcus | Trans-scleral fixation |
| Iris-sutured PCL | Posterior chamber | Ciliary sulcus | Iris sutures |
| Anterior chamber lens | Anterior chamber | Anterior chamber | Anterior chamber angle |
| Aphakia | None | None | None |
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