Management of the Posterior Capsule in Pediatric Cataract Surgery

In young children who undergo pediatric cataract surgery, visual axis opacification (VAO) is rapid and virtually inevitable if the posterior capsule is left intact.^1-4 To prevent VAO, posterior capsulectomy and vitrectomy are recognized as essential surgical steps. The need for primary posterior capsulectomy and vitrectomy is especially acute in younger children because the onset of VAO is faster and the amblyogenic effect greater. As of 2006, primary posterior capsulectomy and anterior vitrectomy are considered by many to be “routine surgical steps,” or standards of care for the management of pediatric cataract, especially in younger children. To the contrary, however, several controversies regarding posterior capsulectomy and vitrectomy remain, and the quality of care ophthalmologists deliver to their pediatric cataract patients is in jeopardy. This article addresses some of the important questions and concerns regarding posterior capsulectomy and vitrectomy while managing childhood cataract, and it dispels some of the fallacies surrounding these surgeries.

When Should the Posterior Capsule Be Left Intact?

The answer depends on several factors including the age at cataract surgery, the condition of the posterior capsule, and the child’s presumed cooperation for YAG laser capsulotomy when later indicated. Generally speaking, the posterior capsule should be left intact when children present for cataract surgery at age 8 years or older. For patients between 5 and 8 years of age, the posterior capsule is left intact if the child will likely be able to sit for a YAG laser capsulotomy 12 to 24 months after surgery. Experience has shown that this postoperative time interval is when the risk for VAO is highest. A primary posterior capsulectomy is recommended at any age if YAG laser is unavailable, a posterior capsule anomaly (plaque, defect, etc.) is present, or the child is developmentally delayed or likely to be uncooperative for YAG laser capsulotomy.

Is an Anterior Vitrectomy Necessary Whenever a Posterior Capsulectomy Is Performed?

In general, for patients up to 5 years of age, anterior vitrectomy is an essential step; VAO is still likely to occur if an anterior vitrectomy is not performed. However, in children between the ages of 5 and 8, it is an optional step since the chances are better that a posterior capsulotomy (posterior capsulorhexis) alone will result in a long-term clear visual axis.

Opening the Lens Capsule: Posterior Capsulorhexis vs. Capsulectomy

The posterior capsule can be opened using a manual technique (capsulorhexis) or it can be cut with a vitrector or other cutting device (capsulectomy). Primary posterior continuous curvilinear capsulorhexis (CCC) makes it possible to achieve an opening with a strong margin that resists peripheral extension of tears. However, when an anterior vitrectomy has been planned, a posterior capsulectomy using a vitrector is more practical and quicker. When done well, the vitrector can provide a round and precisely sized posterior capsule opening that resists tearing.

Architecture of the Posterior Capsule Opening: Size, Centricity, and Shape

Treatment of the posterior capsule determines where and how safely the intraocular lens (IOL) can be fixed. It requires leaving behind enough peripheral posterior capsular support. Thus, the size of the posterior capsule opening should be large enough to help avoid VAO, but small enough that sufficient peripheral capsular support remains for capsular fixation of an IOL. Ideally, the surgeon achieves a central, circular opening in the posterior capsule about 1 to 1.5 mm smaller than the IOL optic.

Limbal Approach vs. Pars Plana/Plicata Approach

Anterior segment surgeons are often more accustomed to, and more comfortable with, a limbal (or anterior) approach when performing a posterior capsulectomy and anterior vitrectomy. Our current strategy, however, is to perform these procedures via the pars plana/plicata preferentially. With the aid of a highly viscous ophthalmic viscosurgical device (OVD), the IOL is inserted into the capsular bag while the posterior capsule is still intact. The OVD can be removed without fear of engaging vitreous, because removal precedes the posterior capsulectomy. While the irrigation cannula remains in the anterior chamber, a microvitreoretinal (MVR) blade is used to enter the pars plana/plicata 2 to 3 mm (depending on age) posterior to the limbus. The vitrector is then inserted through this opening and used to open the center of the posterior capsule. Using this bimanual technique, the size of the posterior capsule opening is easily controlled without displacing the IOL position within the capsular bag. In addition, the chance of an anterior wick of vitreous tracking to the corneal tunnel wound or the paracentesis is eliminated. With the aid of triamcinolone acetonide (Kenalog) for visualization, surgeons performing vitrectomy by the anterior approach will find residual vitreous in the anterior chamber more often than previously suspected. An undetected vitreous wick or strand to an anterior wound represents a much greater risk of retinal detachment over time than does a pars plana/plicata approach to the anterior vitreous and posterior capsule.

Intraocular lens dislocation has been mentioned as a risk of using the pars plana/plicata approach for posterior capsulectomy (Am J Ophthalmol. 1993; 115(6):722-728). However, this has not been the experience of several practitioners (J AAPOS. 2002;6(3):163-167). On the contrary, inserting an IOL into a small, soft, vitrectomized eye after an anterior-approach posterior capsulectomy represents a much greater risk of IOL dislocation into the posterior vitreous space.

When to Cut: Before or After IOL Implantation?

There is no universal agreement on whether the IOL should be implanted before or after the posterior capsulectomy and vitrectomy. Some surgeons advocate removing the posterior capsule and anterior vitreous before IOL implantation. Others prefer to have the IOL in place before removing the posterior capsule to allow for an adequate posterior capsulectomy and better anterior vitrectomy. The advantage of this latter approach is that the IOL can be safely fixed in the desired plane and the posterior capsule opening can be easily made up to 1-mm smaller than the optic size without displacing a well-centered IOL. The common practice is to perform the surgeries before IOL implantation if the limbal approach has been used. However, if the pars plana/plicata approach is used, the posterior capsulectomy and vitrectomy are generally performed after IOL implantation. Some surgeons prefer a retropseudophakic vitrectomy by limbal approach . In this technique, the IOL must be displaced from its central location and an instrument must be maneuvered under the anterior capsulotomy edge and around the IOL optic. The risks of an anterior vitreous wick remain present as with any anterior approach.

If the Pars Plana/Plicata Approach is Used, Where Should the Incision Be Placed?

The practiced and current approach is to enter 2-mm posterior to the limbus in patients less than 1 year old, 2.5-mm posterior to the limbus in patients 1 to 4 years old, and 3-mm posterior to the limbus in patients over 4 years old.

Are Special Aids or Techniques Needed for Visualization?

Dyes have been used less frequently for the posterior than for the anterior capsule. However, Kenalog injection into the anterior chamber provides the anterior segment surgeon a means for localizing and identifying vitreous gel (J Cataract Refract Surg. 2003;29(4):645-651). Clear visualization of the vitreous gel allows thorough removal of the prolapsed vitreous and alerts surgeons to residual strands of vitreous that might otherwise have gone unnoticed.

How Is the Endpoint of Vitrectomy Defined? And How Much Vitreous Should Be Removed?

Any frank surgeon will confess that the endpoint of vitrectomy is difficult to quantify. Sufficient vitreous should be removed centrally so that the lens epithelial cells cannot use the vitreous face as a scaffold for VAO. Any vitreous that tracks forward past the plane of the posterior capsulotomy needs to be removed. VAO after primary posterior capsulectomy and vitrectomy is often blamed on an inadequate posterior capsule opening or an inadequate vitrectomy. These assertions have not been verified scientifically. As mentioned, Kenalog can be injected into the anterior chamber to aid in visualization and thorough removal (J Cataract Refract Surg. 2003;29(4):645-651).

Peristaltic vs. Venturi machine

A Venturi vacuum pump system is recommended, as it cuts the capsule more easily than a peristaltic pump. Readers should follow the manufacturer’s instruction manual for using a specific machine and setting. Modern vitrectors have higher cut rates, and most now recommend that the vitreous be cut at a rate of at least 500 cuts/min. On the Accurus machine (Alcon Laboratories, Fort Worth, Texas), an irrigation rate of 30+ cc/min and a cutting rate of 500+ cuts/min have proven effective.

Summary

Posterior capsulectomy and vitrectomy are essential surgical steps in the management of pediatric cataract surgery. Various strategies for performing these surgeries have been suggested in the literature. Selection among the various technical alternatives is probably best left to the individual surgeon’s preference based on the particular case and circumstances, available facilities, and surgical experience. The authors recommend a pars plana/placata approach as the safest and most effective technique for removing a large central portion of posterior capsule while ensuring a well-centered IOL and a clear visual axis.

References

Author Disclosure

Dr. Wilson discloses that between 2005 and 2006, he received travel funds and honoraria from Alcon Laboratories for use toward educational presentations. Neither author has any proprietary interest in any of the procedures or products discussed in this article.