March 2009

 

CATARACT/ IOL

 

Understanding and learning the PAL technique


by Maxine Lipner Senior EyeWorld Contributing Editor

 

 

Best method for rescuing a descending nucleus after capsular rupture

With the PAL technique practitioners are able to rescue the nucleus before it descends posteriorially, bringing it forward into the anterior chamber when possible Source: David F. Chang, M.D.

In the stressful situation of posterior capsular rupture, the Viscoat PAL (posterior assisted levitation) technique can help surgeons to save the day. When the posterior capsule ruptures while the nucleus is still present, the surgeon’s immediate priority becomes extracting the nucleus before it descends posteriorly, according to David F. Chang, M.D., clinical professor, University of California, San Francisco. However, this often presents even very experienced surgeons with significant challenges. “The pupil and the capsulorrhexis may be small, which may have been contributing factors to the antecedent capsular rupture, and the nucleus may have been divided into multiple smaller fragments,” Dr. Chang said. “In addition, vitreous prolapse may block access to the lens material and will become ensnared by the aspiration instruments.”

Keeping the nucleus from sinking is difficult. “Recognizing the danger of chasing the nucleus with the phaco tip, most surgeons understand the need to bring it forward into the anterior chamber if possible,” Dr. Chang said. “However, this becomes very difficult if the nucleus or the nuclear fragments have partially descended.” Dr. Chang explained. “Particularly if the pupil or capsulorhexis diameters are small, the steep angle of approach required by directing a cannula through the phaco incision may make it very difficult to get an ophthalmic viscosurgical device [OVD] behind the lens,” he said.

Posterior assisted levitation techniques

The posterior assisted levitation technique, or “PAL,” solves this problem by using a pars plan sclerotomy for instrument access. “Charles Kelman, M.D., popularized this [PAL technique] using a cyclodialysis spatula through the pars plana as a mechanical lever to lift a partially descended nucleus up into the anterior chamber,” Dr. Chang said. “Richard Packard, M.D. [London], advocated using a dispersive OVD, such as Viscoat [chondroitin sulfate 4%/ sodium hyaluronate 3%, Alcon, Fort Worth, Texas] to levitate the nucleus from a pars plana approach,” Dr. Chang said. This technique allows the surgeon to approach the nucleus from below. As a result, it can be pushed anteriorly rather than pulling it forward with aspiration, Dr. Chang explained. If the surgeon succeeds in levitating the residual nucleus, cautiously continuing phacoemulsification is an option if there is no vitreous prolapse and if a trimmed sheet glide can be positioned behind the nucleus. “As popularized by Marc Michelson, [M.D., Birmingham, Ala.] this artificial posterior capsule can simultaneously prevent the pieces from falling posteriorly and shield the aspirating tip from ensnaring vitreous,” Dr. Chang said. “The alternative is to enlarge the incision in order to manually extract the nucleus with a lens loop—a safer option with a large or dense nucleus or if vitreous prolapse has already occurred.”

In 2003, Dr. Chang together with Dr. Packard published a combined series of eight cases managed with the Viscoat PAL technique in the October 2003 issue of the Journal of Cataract and Refractive Surgery. They were able to retrieve the partially descending nucleus in all eight consecutive cases and were able to implant a posterior chamber IOL in seven eyes following either phaco (50%) or manual ECCE (50%) removal of the nucleus. They reported no posterior segment complications during the minimum 18-month follow-up period.

Mastering the method

Dr. Chang believes that a combination of the Kelman and Packard principles works the best. “The first priority is to stabilize and support the nucleus that is threatening to sink.” He finds that the pars plana provides the ideal angle of approach to quickly inject a dispersive OVD such as Viscoat or Healon D (sodium hyaluronate 3%, Advanced Medical Optics, Santa Ana, Calif.) behind the nucleus to support it and prevent further descent. “If necessary, subsequent injections of OVD can hydraulically maneuver the pieces into a central position from which they can be mechanically lifted with the OVD cannula tip,” Dr. Chang said. “Additional OVD aliquots can be injected whenever the need to reposition the pieces arises.”

Dr. Chang recommends using a dispersive OVD rather than a cohesive one in this situation. “It tends to stay where it is injected, rendering it most effective as an OVD safety net,” he said. “Secondly, it better resists being aspirated or burped out, which is a desirable property in these situations.” Finally, he notes that because much of the posteriorly injected OVD will not be surgically removed, the smaller molecular weight dispersive OVD is less likely to cause a severe IOP rise. In performing the PAL technique, Dr. Chang uses a disposable MVR blade to make the pars plana sclerotomy 3.5 mm behind the limbus in the oblique quadrant which best aligns with the surgeon’s dominant hand. “The peritomy, the cautery, and the sclerotomy can be performed with the patient still under topical anesthesia alone if necessary,” he said. “If there is a more urgent time frame, placing a disposable 25-gauge needle on the OVD syringe and directly injecting through the conjunctiva and the pars plana can save valuable time.”

During the procedure it is important to keep the cannula tip in view as much as possible . “This maneuver is not appropriate once the nucleus has descended to the posterior half of the vitreous cavity,” Dr. Chang said. He cautions that it is also important to avoid excessive OVD injection because this can raise the intravitreal pressure to dangerous levels and cause tissue expulsion through an incision.

Overall, Dr. Chang acknowledges that many cataract surgeons will not be comfortable performing these techniques. “Many anterior surgeons will understand, embrace and feel comfortable applying these principles in appropriate cases,” he said. “However it is important that individual cataract surgeons not overstep the boundaries of their experience and skill set. Removing retained lens material from the posterior segment can always be done in a second and appropriately timed procedure by a vitreoretinal surgeon with an excellent prognosis.”

Editors’ note: Dr. Chang’s consultant fees from Advanced Medical Optics (Santa Ana, Calif.) and Alcon (Fort Worth, Texas) are donated to the Himalayan Cataract Project.

Contact information

Chang: 650-948-9123, dceye@earthlink.net

Understanding and learning the PAL technique Understanding and learning the PAL technique
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