ADVANCED POSTERIOR CAPSULOTOMY TECHNIQUES
Lisa Brothers Arbisser, MD
Repositioning subluxated intraocular lenses (IOLs) is safest and most stable when capsule fixation can be employed. When the anterior capsulotomy is not continuous, is larger than the optic, or cannot be centralized to allow anterior capture from the sulcus, we should turn to the posterior capsule for fixation. This may necessitate creating a posterior capsulotomy primarily or converting a noncontinuous posterior capsule tear into a continuous rhexis. Only then can we depend upon the strength and integrity of the capsule opening to resist the splitting and tearing forces required for lens insertion and stabilization as well as the postoperative forces of progressive fibrosis and the minor traumas of everyday life. Whenever possible, hyaloid-sparing techniques minimize the potential for sequelae of retinal pathology and trabecular meshwork compromise.
This author is an advocate for a future where routine planned, primary hyaloid-sparing posterior optic capture into Berger’s space becomes a reality. The “clear” 20/20 capsule causes underrecognized stray light visual distortion. Secondary cataract causing the patient to undergo a second period of visual degradation is the main complication of modern phacoemulsification. The only current cure, Nd:YAG laser, virtually always destroys the anterior hyaloid, whose preservation has myriad potential and proven advantages. Even if not yet adopted as routine, facility with handling the thin and elastic posterior capsule must be part of the armamentarium of the comprehensive anterior segment surgeon. It is vital for converting unintended posterior capsule tears to continuous ones in complicated cataract surgery, for avoiding another anesthetic risk for patients who cannot sit at the laser, and for immediate rehabilitation for unpolishable plaques and posterior polar cases. This chapter will focus on current and future techniques that can be adapted to the conditions of secondary IOL implantation or exchange and management of the subluxated IOL. Using proper technique, creation of a hyaloid-sparing posterior capsulorrhexis is very reliable with a short learning curve. When the hyaloid has been previously violated, 1-port pars plana vitrectomy with sutureless trocar system placement should be part of the surgical planning by anterior segment surgeons. This approach to anterior vitrectomy does not enlarge the existing rent in the posterior capsule, often permitting a continuous rhexis capable of optic capture, which is the Holy Grail for long-term, minimally invasive subluxated lens repair.
Anatomy
The anterior capsule is 12 to 14 μm thick. The posterior capsule has a thickness of 4 to 6 μm and is more elastic. During embryology, the basement membrane that covers the ciliary processes and the pars plana is a continuation of the basement membrane of the visual portion of the retina. It has the same origin and the same structural make-up as the hyaloid membrane. The anterior hyaloid membrane appears to line the entire ciliary body and the ciliary processes and, at the same time, to participate in the development of the zonule of Zinn. Before reaching the tips of the heads of the ciliary process, the anterior hyaloid membrane veers toward the lens, in this manner forming the anterior wall of the zonular fibers.
The designation anterior hyaloid membrane identifies the cellophane-like covering over the anterior aspect of the crust of the vitreous. It is a structure that adheres at Wieger’s ligament, from which it extends like a transparent parachute toward the ora serrata and joins the ciliary processes to the pre-equatorial portion of the lens, thus forming the posterior boundary of the posterior chamber.
The anterior hyaloid membrane has no anatomic or histologic relationship to the so-called posterior hyaloid membrane. It should be considered an independent and distinct entity and not misconstrued as an anterior condensation of vitreous. This membrane is like a transparent parachute composed of 2 scalloped, concentric circles. The free or open end inserts circumferentially into the spike of the ora serrata and extends anteriorly toward the posterior capsule where it inserts to become the hyaloid capsular ligament of Wieger. The central post-lenticular hyaloid membrane is its thinnest part, occasionally seen to herniate through the pupil into the anterior chamber in the days of intracapsular cataract extraction.
The area delimited by the posterior capsule anteriorly, the anterior hyaloid posteriorly, and Wieger’s ligament circumferentially is known as Berger’s space. Although the literature indicates this real or potential space is at least 6 to 8 mm in diameter, how much it may vary from one individual to the next remains controversial. Berger’s space is often only potential with the hyaloid in contact with the posterior capsule of the lens, biomicroscopically blending as a single layer but retaining the capability of separating or detaching under many conditions. The anterior hyaloid, also extending anteriorly to ciliary processes, is the true barrier between the anterior and posterior segments with the posterior capsule playing a redundant role.1
Surgical Goals
Detailed understanding of the retrolenticular anatomic space has been largely ignored because intracapsular cataract surgery regularly interrupted it. Today, this author believes we have underappreciated the significance of the anterior hyaloid’s role in maintaining ocular homeostasis. When violated, its influence on morbidity of both the anterior and posterior segments is multifactorial. Therefore, the first goal in surgical planning for subluxated or secondary IOLs, when at all possible, is to avoid an unnecessary breach of the hyaloid membrane and subsequent vitrectomy. Every surgeon has a protocol for choosing a surgical technique for a given situation. For this author, when the bag-lens complex is subluxated without vitreous prolapse, a minimally invasive lasso technique is optimal. Transconjunctival scleral fixation with a flange technique is superior in a vitrectomized eye or when a total or extensive vitrectomy is required by the preoperative state of the eye without the possibility of bag support. When zonules are viable or supportable and there is the potential for capsule support of an IOL, using the capsule for fixation avoids invasion of uveal tissue, which is both blood vessel rich and immune reactive. Several options—anterior capture from the sulcus, creation of posterior capsulotomy for posterior optic capture, also known as posterior optic buttonhole, or suturing to mature fibrotic capsule—are superior for stability and a rapid, permanent return to a quiet eye status.
Posterior Optic Buttonhole in the Presence of Prolapsed Vitreous or a Preexisting Posterior Capsule Tear
When the vitreous is already disturbed, avoiding intra- and postoperative vitreous traction, which can lead to retinal tears and poor outcomes, is of paramount concern. Principles of anterior vitrectomy are thoroughly covered in another chapter of this book. This author favors a biaxial approach with irrigation provided through an anterior paracentesis. If the eye cannot be securely sealed, the bare vitrector needle is placed through a sutured pars plana sclerotomy under a fornix-based flap. When vitrectomy is part of the preoperative plan, allowing placement prior to any other incision, a sutureless transconjunctival pars plana trocar system placed in a limbus-parallel scleral tunnel fashion is preferable. With either approach, the vitrector is held under the rent in the posterior capsule to coax prolapsed vitreous home to the posterior segment. This is the only method that will reliably avoid enlargement of the preexisting posterior capsule tear.2 Dispersive ophthalmic viscosurgical device (OVD) is then placed over the tear followed by cohesive OVD to pack in the dispersive (compartmentalization by reverse soft-shell technique of Arshinoff).3 This maneuver prevents further egress of vitreous and flattens the anterior and posterior capsules together in one plane, thus allowing conversion to a posterior continuous curvilinear capsulorrhexis (PCCC). It is nearly impossible and dangerous to create a continuous rhexis while vitreous is prolapsed through the tear—vitrectomy should precede such attempts.
Assuming the preexisting posterior capsule rent does not extend too far peripherally for capture once the vitrectomy is completed, conversion to a continuous tear ensues. An edge of the tear is grasped with a pair of Utrata forceps through the main incision (when exchanging or adding a lens) or with coaxial forceps through a paracentesis (when repositioning an in situ lens) to begin the posterior rhexis. Occasionally, there will be no tag to grasp along the unintended tear, in which case a Vannas or intraocular scissors can be used to make a tangential cut, providing an edge to begin the rhexis. If the capsule is very fibrotic, preventing a tear at any point, a cut across a line of fibrosis to continue the curvilinear progression will likely hold for capture and will not necessarily foil the plan.
Posterior Capsulorrhexis Technique
There are several methods to gauge the preferred size of the intended opening for optic capture into Berger’s space. The nonfibrotic virgin posterior capsule is extremely elastic and forgiving of smaller sizing. A fibrotic capsule upon reoperation will need to be treated with more caution and precision. Because ultimately the IOL will be centered by the haptics located either in the bag or sulcus with only the optic below the elastic posterior capsule in Berger’s space, centration of the posterior capsulotomy is not absolutely critical. However, in a nonvirgin fibrotic situation, one’s best attempt at centration is called for.
To ensure appropriate sizing, employ a caliper hovered over the cornea to determine landmarks for a 4.0- to 4.5-mm PCCC opening. Although some surgeons use a marker to score the corneal epithelium, this author prefers not to for rapid and comfortable visual rehabilitation. Some technologies allow a reticle to be visualized in the microscope ocular for reference. If the anterior rhexis is intact and measures 5 mm, it can be used as a guide or cookie cutter for the posterior rhexis, although it is then tempting simply to perform anterior optic capture from the sulcus, not concerning oneself with a posterior rhexis at all. The use of forceps with etched millimeter markings (ASICO) to assess size as you proceed is most helpful.
When a PCCC is planned for subluxated IOL centration by capture into Berger’s space, cohesive OVD is placed in the sulcus to collapse the anterior and posterior capsule leaflets together into a single plane, facilitating shearing forces with vector control. If there is an IOL already in place, use the OVD first to elevate it out of the way off to the side in an OVD sandwich (to protect endothelium) within the anterior chamber. Establish a high magnification view with optimized red reflex and well-moistened corneal surface for visibility.
Employ a 30-gauge bevel-up needle on a syringe containing a small amount of balanced salt solution (BSS; to exclude air) as a handle. Putting the sharp needle on the OVD syringe seems efficient but is inadvisable because the sharp tip may rupture the hyaloid while instilling the OVD as the next step. Introduce the needle through the corneal incision or paracentesis at a flat angle approach to the posterior capsule. One does not use a cystotome, as the downward direction of the sharp tip might open the hyaloid membrane along with the capsule if there is no real space between them. Similarly, a forceps pinch to initiate the rhexis is inadvisable. Starting in the center of the pupil, the goal is to engage the diaphanous posterior capsule with the needle tip, lifting it upward slightly, away from the hyaloid below, causing a wrinkle to form (Figure 21-1). Open the posterior capsule with a simultaneous slight sideways and forward movement. The opening will likely assume an ovoid appearance.
Classically, cohesive OVD is now employed with the standard OVD cannula at or just below the posterior capsule opening to push the anterior hyaloid face posteriorly away from the posterior capsule thereby inflating Berger’s space. One can watch the viscous fluid fill into itself and begin to assume a round, bubble-like shape as it reaches the limits of Wieger’s ligament. There is a nuance to instilling just enough OVD at this stage to fill adequately, but not forcefully overfill, Berger’s space. One can alternately inject OVD on top of the posterior capsule as well as under it to keep it flat. It is exceedingly rare to see the incipient PCCC run outward as, by definition, before beginning, the chamber is entirely controlled and the posterior zonules do not exert the pull of the anterior zonules with the bulk of the lens fibers in situ. Losing chamber should be avoided, but an overly exuberant fill could potentially have this effect as well, so caution is indicated.
Figure 21-1. A 30-gauge needle initiating posterior capsule opening.
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