Chapter 18

Phacoemulsification of the human lens requires the preservation of the posterior capsule for successful lens removal and subsequent intraocular lens (IOL) implantation. Rupture of the posterior capsule during phacoemulsification, however, is a potentially serious intraoperative complication and carries the risk of precipitating additional problems that require vitrectomy and present the possibility of loss of lens material into the vitreous cavity. In addition, postoperative complications including chronic inflammation, cystoid macular edema, IOL dislocation, and a retinal detachment may be engendered by an intraoperative tear in the posterior capsule. The incidence of posterior capsule rupture in extra-capsular cataract extraction and phacoemulsification has been reported to range from 0.05 to 10%.1–3 The outcome of the complicated operation, however, will be determined by the surgeon’s skills in recognizing when the posterior capsule ruptures and in managing it.

CAPSULAR ANATOMY

It is helpful to consider the key anatomic features of the lens capsule and to keep them in mind while performing phacoemulsification. The capsule is an elastic basement membrane made up of type IV collagen. It is laid down by the lens epithelial cells that reside just inside the capsule (see Chapter 5, Fig. 5–1). Interestingly, electron microscopic examination of the capsule fails to reveal elastic fibers despite the clinical elastic nature of this structure. The zonules insert on the anterior capsule approximately 3 mm from the anterior pole and on the posterior capsule approximately 4 mm from the posterior pole.⁴ The capsule has variable thickness. It is 2 to 4 μm thick at the posterior pole. It is thickest (17 to 23 μm) near the anterior and posterior equator where the zonular fibers attach.⁵ The anterior capsule can be as thick as 14 μm in adults and it continues to increase in thickness with age. The posterior capsule may be particularly fragile in patients with congenital posterior lenticonus and posterior polar cataract; age-related or corticosteroid-related posterior subcapsular cataracts (PSCs) involve migration and enlargement of the lens epithelial cells posteriorly where the capsule is thinnest.⁶

The surgeon must also consider factors such as age, disease (such as pseudoexfoliation or Marfan’s syndrome), or a history of ocular trauma, which may predispose to zonular weakness or dehiscence. Zonular dehiscence is also discussed in Chapter 17.

SIGNS OF CAPSULE RUPTURE(TABLE 18–1)

During phacoemulsification the hydrostatic pressure in the anterior chamber is elevated but stable. This is the result of the balance of hydrostatic pressure created by (1) the height of the infusion bottle (11 mm for every 15 cm of bottle height) opposed to (2) the evacuation of fluid as controlled by the machine-commanded vacuum and flow settings and (3) the controlled egress of fluid through the wound determined by wound size and configuration. Fluid flow is partitioned within the compartment created by the cornea and posterior capsule. When the posterior capsule unexpectedly ruptures, there is a sudden equalization of the hydrostatic pressure between the anterior chamber and the vitreous cavity. This will cause an abrupt and dramatic posterior displacement of the iris and dilation of the pupil as the posterior capsule opens. This is the first warning of capsular rupture that the surgeon may see. In addition the nucleus seems to “fall away” from the phaco tip. This is due to the loss of the support of the posterior capsule. Although subtle, these events should intensify the surgeon’s suspicion that the capsule may not be intact. This is especially important when the pupil is small, or the cataract is dense and the posterior capsule is not well visualized. These signs are not only the first to be observed when the capsule tears, but may be the only initial evidence of capsular rupture before more serious signs and events develop. Generally, if the surgeon is suspicious that the posterior capsule has ruptured, it probably has. The surgeon is therefore justified in modifying the surgical plan on the suspicion of a tear of the posterior capsule.

These signs of posterior capsule rupture occur not only during lens emulsification or irrigation and aspiration (I&A) of the cortex, but also during hydrodissection. Overzealous hydrodissection, especially in the presence of a small capsulorrhexis or an undisclosed noncontinuous capsulorrhexis, may result in a posterior capsular blowout. Once again, the anterior chamber will exhibit a sudden deepening as the posterior capsule opens, allowing pressure equalization between the anterior chamber and the vitreous cavity. If not recognized immediately, the next opportunity to realize that the capsule is torn will be when the phaco tip is introduced. Upon depressing the phaco foot pedal, without the support of the intact posterior capsule, the fluid infusion pressure may propel the entire contents of the capsular bag into the vitreous cavity.⁷

PREDISPOSING FACTORS FOR CAPSULAR RUPTURE⁸

Significant predisposing factors leading to the torn posterior capsule with subsequent management dilemmas are (1) the relationship of the surgeon’s hand position to the patient’s brow with ensuing visibility problems, (2) irrigation fluid pooling, and (3) torsion of the globe. The surgeon must attempt to minimize torsion of the globe during surgery as this impedes adequate visualization. If the brow is prominent (e.g., a deep-set eye), a temporal approach rather than a superior approach will minimize the inferior torsion of the globe. If there is pooling of fluid, turning the head temporally will allow fluid to drain. The use of a speculum, which allows easy access to the globe and will not get in the way during phacoemulsification, cannot be underestimated. Although, in general, one would like to operate in the axis of the plus cylinder, this cannot be done when the plus cylinder is at 90 degrees in the presence of a large brow and deep-set eye. The surgeon is wiser to forgo the issue of astigmatism and operate temporally, for access and exposure, rather than risk a capsular tear.

Poor microscope illumination or alignment is another cause of poor visualization. Once recognized, this should be simple to remedy. Other factors that impede visualization include dense arcus senilus, dense nasal or temporal pterygia, severe Fuchs’ corneal dystrophy with or without associated corneal edema, band keratopathy, old corneal scars, and interstitial keratitis. Faced with these challenges to visualization, the surgeon can do nothing more than slow down, pay more attention to detail and visualization, and be more careful about focusing through the corneal problem to allow visualization of the anterior segment.

Patients with long and short axial length eyes, with associated deep or shallow anterior chambers, represent predisposing factors for torn capsules. In high myopia, the anterior chamber is deeper with more trampolining of the posterior capsule due to the thinner, more resilient tissues. Eyes that have undergone previous vitrectomy behave in a similar manner. Lowering the infusion bottle, and machine vacuum and flow settings, lessens this tendency. In high hyperopia, the anterior chamber is crowded, making the posterior capsule closer to the area of phaco and increasing the risk of a torn capsule. In these situations the early use of pulsed phaco will assist in deepening the anterior chamber. Other causes of the shallow anterior chamber are considered below.

Pseudoexfoliation is known to cause weak zonules and poor dilation secondary to fibrosis of the pupillary sphincter. These problems lead to an increased incidence of torn posterior capsules or dehiscence of the zonules. These problems are discussed fully in Chapters 6 and 17. In addition markedly brunescent or black cataracts as well as mature or white cataracts make capsulorrhexis more difficult. These problems are discussed in Chapters 16 and 17.

Dense asteroid hyalosis may make it difficult it to visualize the posterior capsule during phaco. The surgeon must again exercise due caution, and if necessary viscoelastics, to stay away from the posterior capsule, thus avoiding inadvertent tears (Table 18–2).

Additional predisposing factors to complications could include (1) posterior polar cataracts (especially those that are calcified) due to an increased incidence of posterior capsular holes attributable to adherence of the cataract to the posterior capsule, as well as thinning of the posterior capsule in the region deep to the cataractous lens changes; (2) inexperienced surgeons (e.g., residents); (3) poor visualization, due to the microscope, as noted above; (4) demented, disoriented, or anxious patients with subsequent inadvertent patient movement; (5) equipment malfunction; and (6) preexisting trauma with unseen capsular rupture or zonular damage.

Small pupils are the final significant predisposing factor for tearing the posterior capsule during surgery. There are many regimens to provide adequate pharmacologic dilation in all patients. One recommended guideline is cyclopentolate (Cyclogel) 1%, neosynephrine (Mydfrin) 2.5%, and ketorolac tromethamine 0.5% (Acular) given every 5 minutes for four doses prior to surgery. In those patients who have not dilated adequately, an additional dose of neosynephrine 10% gel is applied. Neosynephrine 10% solution is avoided as there have been reports in the past of the development of recalcitrant cardiac arrhythmias in patients receiving this medication.

If the pupil does not dilate to a size deemed adequate for the surgeon to provide safe phaco, or even convert to extracapsular cataract extraction (ECCE), the surgeon is obligated to further dilate surgically. This can be accomplished by stretching with iris hooks, using the Beehler dilator made by Moria, performing multiple sphincterotomies with microscissors, using iris retractors, or using the Graether pupil expander⁸ (see Chapter 6).

WHEN DOES THE POSTERIORCAPSULE TEAR?

The highest incidence of posterior capsule rupture during phacoemulsification occurs (1) toward the end of emulsification when the last pieces of endonucleus are to be emulsified, (2) during posterior capsule polishing, and (3) during I&A. The tear in each of the above situations occurs when the posterior capsule is directly exposed to the phaco or I&A tip and thus can be more easily and inadvertently aspirated and torn. The next highest incidence of capsular tear is during early to mid-phaco when the phaco tip is inadvertently passed through the nucleus and tears the posterior capsule or capsular equator. The least common times to tear the capsule are during hydrodissection, capsule polishing, and IOL insertion.^2,7

In all cases, once the vitreous face is ruptured and vitreous is detected above the plane of the posterior capsule, in the anterior chamber, or at the wound, an anterior vitrectomy is mandatory. Most tears in the posterior capsule are small when they first occur. The surgeon should endeavor to keep them from enlarging or tearing anteriorally, destroying the integrity of the anterior capsular rim, which will enhance the potential for a posterior chamber IOL placement in the bag or sulcus.

DEVELOP A SURGICAL PLAN

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