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Slide 1 |
Evidence of zonular laxity can be obtained preoperatively, during surgery but before phacoemulsification, or during nucleus and/or cortex removal.
Preoperative Evidence of Zonular Laxity
Pseudoexfoliation or a history of ocular trauma increases the index of suspicion. A forward (convex) appearance of the anterior lens surface is highly indicative of weak/absent zonular support, which permits the lens to assume a more spherical shape. This may be seen in the absence of phacodonesis (the latter is an obvious and unmistakable sign of severe zonular deficiency). Many eyes with normal axial length but with a shallow chamber are found to have zonular weakness during subsequent surgery and reduced chamber depth in a highly myopic eye (e.g., axial length of 25 mm or more is virtually pathognomonic of zonular laxity). Anterior chamber shallowing in such an eye is nearly always caused by zonular weakness, which permits the lens to shift forward.
Intraoperative Evidence of Zonular Laxity
Movement of the entire lens-capsule complex during anterior capsulotomy is always a sign of severe zonular laxity; the lens may be so loose that completion of the capsulorrhexis by the usual means may be impossible because of lack of resistance and stability of the lens. However, the insertion of a retractor (iris or modified retractor as with the cataract support system described later) after the creation of an initial capsulotomy will provide a counterforce against which the capsulorrhexis can usually be performed.
The most obvious signs of zonular weakness include subluxation of the entire nucleus with visualization of the lens equator.
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More commonly seen is mild zonular laxity which results in the development of anterior capsule striae (Slide 1) adjacent to the capsular tear during capsulorrhexis. The location of these striae also indicates the weak region(s) of the zonule.
Zonular Laxity During Nucleus/Cortex Remova
During phacoemulsification, extreme deepening of the anterior chamber at the onset of infusion may be indicative of zonular laxity. However, this phenomenon is more commonly seen in highly myopic eyes that simply have poor ocular rigidity which permits the sclera to expand when intraocular pressure (IOP) is increased.
During sculpting of the nucleus, a tendency of the lens to move with the sculpted tip, that is, away from the surgical incision, is a clear sign of inadequate zonular strength. Ultrasonic power should be increased and stabilization of nuclear position by placement of a lens chopper or similar instrument over the equator opposite the phaco incision to stabilize the position of the nucleus should be considered.
During nucleus rotation, a tendency of the nucleus to return (i.e., rebound) toward its previous location when released by the rotating instrument is an ominous sign of zonular laxity. This indicates that the entire capsule had rotated somewhat with the nucleus, and subsequently returned to its normal anatomic location when the rotary force was discontinued.
One sign of zonular deficiency, visible as nucleus volume decreases, is inward collapse of the lens capsule with possible inadvertent aspiration by the phaco tip.
After nucleus removal and at any time during cortex removal, peripheral posterior capsule striae may straddle an area of zonular dehiscence. The length of the striae demarcate the area of dehiscence.
At any time during the terminal stages of phacoemulsification or cortex removal, a forward shift of the posterior capsule caused by infusion fluid accumulation behind the posterior capsule (infusion misdirection syndrome) may occur. This phenomenon is more common in eyes with pseudoexfoliation or other causes of zonular laxity.
Surgical Steps to Avoid Zonular Stress
It is generally advisable to perform phacoemulsification with a lower infusion pressure and, therefore, lower aspiration flow rate and vacuum levels in these eyes. Lowering the infusion bottle by approximately 30 cm and using proportionately reduced flow and vacuum levels are advised but may cause the emulsification process to proceed more slowly. A surgeons should maintain centration of the nucleus during rotation with bimanual rotation, using both the phaco tip and a second instrument such as a phaco chopper or spatula whenever possible.
Segmentation of the nucleus should be accomplished as gently as possible. Deep sculpting will enable the nucleus to be cracked with less effort; if a phaco chop technique is preferred, impaling the nucleus with the phaco tip permits it to be held in situ as it is chopped. However, if the zonule is extremely lax, it may be advisable to perform a capsulorrhexis that is large enough to permit elevation of all or part of the nucleus above the plane of the anterior capsule. Maintaining a dispersive viscoelastic anterior and posterior to the nucleus is highly recommended in such circumstances. Alternative measures are described in the following section Special Techniques/Instrumentation/Devices. After nucleus removal, tangential stripping of lens cortex from the capsular fornices may prevent further zonular dehiscence. In extreme circumstances, it may be necessary to position the distal end of a second instrument, such as a blunt spatula, against the capsular fornix to create countertraction as cortex is removed.
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During IOL insertion, undue pressure against the capsular fornix with the haptic of the IOL should be avoided. To accomplish this, the leading haptic can be placed into the capsular sac in the usual fashion. The trailing haptic can then be dialed into the capsular sac while using a capsule retractor/lens guide to simultaneously retract the anterior capsule and guide the trailing haptic (Slide 2). Single-piece acrylic lenses are also a desirable option; both haptics can be folded onto the optic, and this enables the IOL to be injected into the capsular sac without creation of zonular stress.
Special Techniques/Instrumentation/Devices
Stabilization of the lens-zonule complex during cataract removal can be helpful and can be accomplished using an endocapsular tension ring and retractors, which can be used to provide support to the lens capsule.
Endocapsular Tension Ring
An endocapsular tension ring device has been the subject of a completed U.S. Food and Drug Administration
investigation and I hope that it will be available soon in the United States. When inserted into the capsular sac,
an endocapsular ring provides a circumferential expansile force to the capsular equator. The capsule is, therefore,
much less likely to be attracted to the phaco tip and increased stability of the lens may be obtained. However, the
ring does not always stabilize lens position and often entraps lens cortex between itself and the lens capsule.
Removal of the trapped cortex can be difficult and, in fact, attempts to do so can cause further zonule dehiscence.
Nonetheless, expansion of the capsule sac is often desirable either during or after lens removal, and these devices
enhance implant centration and reduce postoperative pseudophacodonesis.
Endocapsular rings can also be sutured to the sclera (Cionni design). Such rings contain a small strut with a distal eyelet. Prior to inserting the ring, a double-armed 10-0 prolene suture can be passed through the eyelet. After ring insertion, both needles are passed through the appropriate region of the ciliary sulcus and tied to each other. I prefer to perform the latter maneuver by inserting a 27-gauge disposable needle through the sclera, 1 mm posterior to the limbus, at the desired meridian. This needle is advanced into the anterior chamber, anterior to the lens capsule. One of the two straight needles attached to a double-armed 10-0 prolene suture is then passed through the phaco incision (through which the endocapsular ring was inserted) and into the 27-gauge needle which is then withdrawn from the eye. This "needle pass" procedure is repeated, using the straight needle at the other end of the double-armed suture, through a site that is approximately 0.5 mm to 1 mm from the first needle pass. The straight needles are then amputated and the two ends of the prolene are tied to each other to establish permanent positioning of the endocapsular ring and surrounding capsule. This technique is similar to those used for suturing of posterior chamber lenses to the sclera, and other methods of accomplishing this can be successfully used.
Capsule Retraction Devices
Both iris retractors and specially designed lens capsule retractors have been used to stabilize both the capsule
and its contents during phacoemulsification. Multiple iris retractors, with which most surgeons are familiar, can be
inserted and used to engage the margin of the capsulorrhexis. However, the relatively short length of the hook and
the single plane design may cause them to easily slip off the capsule during manipulation of the nucleus. In addition,
the short iris retractors do not extend into the capsular fornix and, therefore, do not offer support to this region.
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Because of these disadvantages, I designed retractors (Slide 3) that were specifically shaped for the purpose of retracting the anterior capsule. Six retractors placed at 45° intervals provide reliable support to the capsule and the enclosed nucleus. The elongated return of the retractor extends into the capsular fornix and, therefore, functions to prevent attraction of the equatorial capsule to the phaco tip (Slide 4). After nucleus and cortex removal are complete, an endocapsular ring (standard or Cionni design) can be inserted prior to removal of the retractors and insertion of an IOL.
