Zonular Dehiscence With Lens Subluxation or Dislocation
Common causes of zonular incompetence include pseudoexfoliation syndrome (Fig 12-8), ocular trauma, prior vitrectomy, prior trabeculectomy, and high myopia. Marfan syndrome, Ehlers-Danlos syndrome, homocystinuria, hyperlysinemia, and Weill-Marchesani syndrome are less-common sources of inadequate zonular support. Iridodonesis, detected at the slit lamp, is often an initial finding that signals zonular weakness or absence. If the entire lens becomes dislocated into the posterior segment, surgical removal of the lens may not be necessary, unless uveitis develops. In some eyes, the remaining zonular fibers tether the lens within the anterior vitreous such that when the patient sits upright at the slit lamp, the lens seems accessible for extraction. However, when that patient is supine during surgery, the lens tilts backward, out of the surgeon’s reach. Thus, when iridodonesis or phacodonesis is detected preoperatively, it is helpful to confirm lens position with the patient supine during the preoperative examination.
Figure 12-8 Subluxed lens. This lens with pseudoexfoliation is displaced inferiorly because zonular fibers at the superior edge of the lens are stretched, damaged, or broken. Arrows indicate the superior edge of the inferiorly displaced lens. Cataract surgery on a displaced lens requires meticulous preoperative planning to minimize surgical complications.
(Courtesy of Lisa Rosenberg, MD.)
Zonular status may be determined by direct visualization of the lens equator through a widely dilated pupil or by use of a goniolens to visualize zonular fibers behind the dilated pupil. If zonular disruption is extensive preoperatively, the surgeon may consider removal of the cataract using one of the following:
extracapsular cataract extraction (ECCE)
intracapsular cataract extraction (ICCE)
phacoemulsification with capsular hooks followed by suturing a capsular segment to stabilize the capsule during and after surgery (see the Appendix)
Zonular incompetence becomes apparent intraoperatively with phacodonesis, decentration of the capsular bag, and sometimes vitreous prolapse into the AC. If phacodonesis prevents the use of a CCC or if zonular disruption is extensive, the surgeon may convert from phacoemulsification to ECCE or ICCE. Otherwise, phacoemulsification can proceed safely with application of the same measures recommended in the Advanced Cataract section, earlier in this chapter. Reducing the flow rate diminishes turbulence and fluctuation in AC depth, lowering the risk of vitreous prolapse through the area of zonular absence. A larger capsulorrhexis enables easier separation of lens components within the capsular bag. Thorough hydrodissection and hydrodelineation of the nucleus facilitate smooth rotation during phacoemulsification. Viscodissection helps separate cortical attachments that may impede rotation. Excessive mechanical maneuvers in the nucleus, cortical aspiration, and inadvertent aspiration of the anterior capsule edge contribute to further zonular compromise. Viscodissection of cortical remnants and IOL insertion prior to complete cortical removal are maneuvers that help maintain capsular integrity. Tangential, rather than radial, removal of cortex from the bag minimizes zonular stress. Pars plana lensectomy may be preferred to lens extraction in cases of severe zonular loss and in the absence of contraindicating ocular comorbidities.
If capsular support is insufficient for safe phacoemulsification, capsular hooks, a CTR, or CTR segments can be used (Videos 12-4, 12-5). Capsular hooks (Fig 12-9) support the anterior capsule edge in the area of weakened zonular fibers. They are placed through paracentesis incisions, and adjustment of tension on each hook centers the capsule for phacoemulsification. CTRs provide support by exerting centrifugal force against the capsule equator in areas of absent or weakened zonular fibers.
Insertion of capsular tension ring. Courtesy of David F. Chang, MD.
Capsule hooks and capsular tension ring. Courtesy of David F. Chang, MD.
Radial tension may further extend the capsular defect. Therefore, placement of either capsular hooks or a CTR may be cautiously considered if the anterior capsule is torn radially or if the capsulorrhexis is interrupted. The ring can be used in patients with posterior capsule defects as long as the anterior rhexis remains continuous; its use is controversial in the presence of a noncontinuous rhexis. With a CTR in position, the surgeon can proceed to nuclear and cortical removal more safely and can place the chosen IOL in the capsular bag (ie, an “in-the-bag” IOL). Insufficient zonular support can also be managed with a modified CTR or CTR segment sutured to the scleral wall. If there is severe instability, the help of a vitreoretinal surgeon may be enlisted to employ a pars plana approach.
Figure 12-9 Hooks are placed around the anterior capsule edge to stabilize the capsular bag during phacoemulsification in this eye with a subluxed lens. Trypan blue is used to aid visualization of the capsular edge.
(Courtesy of Lisa Rosenberg, MD.)
If zonular support is insufficient to use a 1-piece IOL in the capsular bag, the surgeon can choose from the following options:
a 3-piece IOL with the haptics placed in the location of zonular weakness
a 3-piece IOL placed in the ciliary sulcus (with or without optic capture)
a transscleral-fixated or iris-fixated posterior chamber IOL (PCIOL)
It is preferable to avoid the use of premium IOLs, such as multifocal and toric lenses, in eyes with capsular decentration or significant potential for decentration.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.