A well-centered posterior chamber IOL is the anatomic goal of every cataract surgery. Good centration is best assured by in-the-bag placement of both haptics and a capsulorrhexis sized slightly smaller than the optic diameter so that its edge is "all on" the optic surface. This avoids the potential decentering force of asymmetric capsule fibrosis that develops wherever the anterior and posterior capsules come into contact. In addition, an "all on" rhexis helps to prevent posterior capsule opacification by increasing the pressure of the optic against the posterior capsule. If the lens must be placed in the sulcus because of posterior capsule rupture, capsulorrhexis capture of the optic may provide the best centration.
Failure to achieve these goals is more likely in complicated cases. For the purpose of this discussion, "high risk" refers to eyes with anatomic features that increase the chance of either a torn capsulorrhexis or posterior capsule. To avoid complications in these eyes, it is important to understand the mechanisms by which capsule problems occur. Factors that predispose an eye to capsulorrhexis complications or posterior capsule complications will be discussed separately.
In addition to trapping the IOL haptics in the bag, the capsulorrhexis renders the capsular bag more resistant to tearing.1 With forces such as cracking, a capsulorrhexis stretches like an elastic waistband without tearing. A single radial tear is precarious, however, because all of the stress placed upon the capsule is transmitted to that single weak point. Enough force will cause an anterior radial tear to extend around the equator into the posterior capsule.
There are four general conditions that increase the risk of developing a radial tear in the capsulorrhexis: poor visibility, eye movement, chamber shallowing, and increased capsular elasticity. These conditions may arise either because of the ocular anatomy or because of poor surgical technique.
(1) Poor visibility. A good red reflex is necessary for optimal visualization of the capsule. This is important in order to guide the flap and to monitor the direction of the tear as it develops. Delayed recognition of a peripherally escaping tear may preclude any chance to redirect it in time.
Ocular causes of a poor red reflex include tear film debris, decreased corneal clarity, small pupils, anterior cortical opacity (spokes), nuclear opacity (brunescence), and vitreous opacities such as asteroid hyalosis or hemorrhage. At the extreme, the red reflex is absent in mature white cataracts. Errors in surgical technique may also compromise visibility. Excessive drying or anesthetic can cloud the corneal epithelium. Poor run off of irrigation fluid may submerge the cornea. The capsulotomy needle can stir up the anterior epinucleus by penetrating too deeply. Finally, faulty instrument maneuvers may create cornea striae or displace the globe out of optimal microscope alignment.
(2) Eye movement. Lack of akinesia is characteristic of topical anesthesia or may be the unintentional consequence of a poor regional block. In this situation, performing the capsulorrhexis requires good fixation and cooperation on the patient’s part. Sudden, unanticipated head or eye movement may result in a peripheral radial tear.
Patients must be properly selected for topical anesthesia, and appropriate levels of sedation and communication enhance cooperation. Fixation is improved by avoiding excessive microscope light intensity, which can induce squeezing. During the capsulotomy, the cornea should be moistened in a way so as to avoid startling the patient or surgeon.
(3) Anterior chamber (AC) shallowing.The natural anterior convexity of the lens tends to steer any tear toward the periphery. The shallower the chamber, the more convex the anterior capsule becomes, and the more the tear tends to run centrifugally "downhill." The direction of the tear is best controlled if the anterior capsule surface is flat.
The most common cause of anterior capsule convexity is intraoperative anterior chamber shallowing due to egress of fluid or viscoelastic through the wound. Excessive instrument pressure on the posterior incision lip will burp out fluid through a momentary wound gape. Interrupting the capsulotomy to refill the anterior chamber with viscoelastic is important in this situation. A shallow anterior chamber may also be the natural result of a small globe or an intumescent lens.
(4) Capsular elasticity.The more elastic a material is, the more difficult it is to control how it tears. For example, latex is more difficult to tear than paper. When an elastic material tears, it first stretches before abruptly splitting. Because of the rebound energy, the resulting tear is overly rapid and tends to advance away from, rather than toward, the grasping instrument. Because pediatric anterior capsules are very elastic, these capsulorhexes are among the most difficult to achieve. The adult posterior capsule has less tensile strength and is more elastic than the anterior capsule. Accomplishing a posterior capsulorrhexis is more challenging because of this.
Two conditions give rise to what could be called "pseudoelasticity" of the anterior capsule. The first is poor surgical technique, whereby the capsular flap is allowed to become too long. The farther the capsule forceps is from the tearing point, the more pliant the flap becomes and the more difficult it is to direct the tear. If this starts to happen, the flap must be regrasped closer to the leading edge of the tear.
"Pseudoelasticity" also results from zonular laxity. Lacking sufficient circumferential tension, a capsule that is not taut will exhibit elastic properties. Such zonular weakness may first become apparent during initiation of the capsulorrhexis. If the anterior capsule is very lax, the capsulotomy needle tip will tend to dimple it rather than immediately puncture it. Next, as the capsular flap is pulled, the entire lens capsule may decenter from lack of zonular fixation. As with an elastic material, the capsular flap seems to stretch before suddenly tearing toward the periphery. Weak zonules are more common in eyes with exfoliation, advanced age, or a history of retinopathy of prematurity, Marfans, blunt trauma, or prior surgery (e.g., vitrectomy or trabeculectomy).
Strategies for the Difficult capsulorrhexis
Visualization and control of the tear must be optimized in the high-risk case. These same objectives apply to redirecting and rescuing a peripherally escaping tear. Although many of these principles are part of the basic capsulorrhexis technique, they are far more critical when dealing with a difficult case.
(1) Maintain a deep anterior chamber. Frequent replacement of viscoelastic may be necessary depending on how much escapes through the wound. While attempting to rescue a peripherally escaping tear, pushing the nucleus posteriorly with a second instrument, as described by Dr. Christopher Conner using the Conner Wand (Rhein), can make the anterior capsule more concave.
Cohesive viscoelastics perform better in flattening the anterior capsule surface than dispersive viscoelastics. However, dispersives better resist being burped out through the incision. By using both types together, Steve Arshinoff’s soft shell technique seeks to combine the advantages of each. Healon V (Pharmacia) is a maximally cohesive viscoelastic that combines both of these desirable features in a single agent. It represents the best choice when confronted with narrow angles and a shallow anterior chamber. Rarely, an eye may have a nearly flat anterior chamber that cannot be deepened with viscoelastic. This not only makes the capsulorrhexis difficult, but also may not allow enough room to mechanically stretch or enlarge the pupil. This also increases the proximity of the phaco tip to the endothelium during nuclear emulsification.
In such cases, a mechanical pars plana vitreous tap may be necessary to achieve a sufficiently deep anterior chamber. A pars plana sclerotomy with a disposable MVR blade is made 3.5 mm behind the limbus. To avoid vitreous traction, an automated vitrectomy cutter without infusion is inserted until the tip is visualized through the pupil. After a small amount of vitreous is removed, viscoelastic is immediately injected through a limbal side port incision to deepen the anterior chamber.
(2) Maximize visibility. With challenging cases, greater attention than usual must be paid to sharp focus, a clear tear film, and an ocular position that optimizes the red reflex. The microscope zoom should be increased if necessary.
Many techniques have been proposed for improving anterior capsule visualization in a mature white cataract. Although oblique illumination with a fiberoptic light pipe is effective, the most reliable method is the use of a dye to stain the anterior capsule. Indocyanine green (ICG) dye, as reported by Horiguchi,2 and trypan blue dye, as reported by Melles,3 are both superior to fluorescein, which, because it is a much smaller molecule, diffuses into the lens and vitreous.
ICG (Akorn) is widely used for fundus angiography, but is not approved by the Food and Drug Administration (FDA) for capsule staining. It comes as a lyophilized compound that must be mixed with 0.5 cc of diluent and 4.5 cc of BSS Plus (Alcon) immediately prior to use. Trypan blue dye (Vision Blue, DORC) is not FDA approved, but is widely used in Europe for capsule staining. It is supplied as a premixed sterile solution. Besides the white cataract, capsular staining is helpful in other situations where the red reflex is poor, such as with a dark brunescent nucleus or in the presence of corneal edema.
An identical technique is used with either dye. The anterior chamber is filled with air to avoid excessive dilution of the dye. Several drops of dye from a TB syringe are placed through a 30-gauge cannula directly onto the anterior capsule surface, which is stained immediately. The air is then exchanged for viscoelastic, and the capsulotomy is performed in the usual manner. No special illumination is needed. The egress of white cortical "milk" may still impair visibility somewhat. In addition, if there is liquefied cortex, the resulting intralenticular fluid pressure may also encourage peripheral extension of the capsular tear.
Even with a capsulorrhexis, removal of the nucleus is challenging without a red reflex because the capsule edge cannot be visualized during sculpting or chopping. Dye staining of the anterior capsule is helpful in this context as well. Trypan blue dye tends to provide a more persistent staining of the capsule, which frequently lasts throughout the remainder of the procedure.
(3) In higher risk eyes, the curvilinear capsular tear should be performed at a slower rate than with routine cases. To enhance control, especially in the presence of pseudoelasticity, frequently regrasp the tear to minimize the distance from the forceps to the tearing point.
(4) Enlarge small pupils. When done prior to the capsulorrhexis, this improves the red reflex and provides enough working space for an adequately sized capsulotomy.
(5) Because a smaller diameter capsulorrhexis is easier to control than a larger one, the former should be attempted if difficulty with visualization or control is encountered. The more peripheral the developing tear is located, the more it wants to veer centrifugally outward. This may be due to the increased convexity of the peripheral anterior capsule. In addition, a smaller capsulorrhexis increases the margin for error by allowing more opportunity to recognize and rescue a peripherally escaping tear.
Posterior Capsule Risk Factors
Conditions that increase the risk of posterior capsule rupture during phacoemulsification include ergonomic obstacles, limited intraocular working space, poor visualization, increased nuclear size and density, weakened zonules, a radial tear in the capsulorrhexis, and an inability to rotate the nucleus or epinucleus.
(1) Ergonomic problems make it difficult for the phaco tip to safely access the nucleus and may be either extraocular or intraocular in origin. Extraocular problems might include severe esotropia, a deep-set eye, a Bell's phenomenon, patient eye movement, and an inability to position the head properly because of respiratory or musculoskeletal problems.
Intraocular conditions that decrease the surgical working space include a small pupil, a small capsulorrhexis, and a shallow anterior chamber. Compared to the norm, these situations place the phaco tip closer to the iris, the capsulorrhexis, the cornea, or the posterior capsule. Excessive anterior chamber depth may result from axial myopia or a prior vitrectomy. This forces the phaco needle to approach the lens from a very steep vertical angle, which compromises both visualization and access.
Sudden imbalances between fluid inflow and outflow can result from post-occlusion surge, inadequate bottle height, and incisions that are too tight or too large. As more and more nucleus is removed, fluctuation in chamber depth becomes manifest as trampolining of the posterior capsule. The amplitude of this fluctuation is exaggerated in young patients and in myopes with thin sclera because of decreased scleral rigidity.
(2) Poor visualization increases the risk of cutting either the capsulorrhexis or the posterior capsule with the phaco tip. Small pupils diminish visualization in two ways. First, the iris conceals the peripheral lens. Secondly, the intensity of the red reflex is significantly reduced with each millimeter less of pupil diameter. A poor or absent red reflex makes it harder to judge the depth at which the phaco tip is cutting. Because one clue of proximity to the posterior capsule is an increasingly brighter red reflex, sculpting a deep groove is more precarious with a small pupil or a mature white lens.
(3) Increased nuclear size and density elevates the risk of posterior capsule rupture. Like a pillow, a soft nucleus absorbs pressure from instrument forces. In contrast, a bulky, firm lens more resembles a stiff board in transmitting these forces directly to the posterior capsule and zonules. Maneuvers such as sculpting, rotation, and cracking all generate some lateral displacement of the nucleus, which applies stress to the capsule and the zonules.
The epinucleus helps to cushion the posterior capsule against these forces. However, as the endonucleus becomes larger, the epinucleus becomes proportionately thinner and may even be absent. Fragments generated by disassembly of a brunescent nucleus may have edges sharp enough to puncture the capsule if sufficient pressure is applied.
Finally, the deeper profile of a large endonucleus makes it difficult to completely bisect the nucleus with chopping or divide and conquer techniques. Dividing the leathery posterior plate requires one to sculpt much closer to the posterior capsule with little or no epinucleus behind to shield it. Cracking it apart requires a further separation of the instrument tips that, in turn, imparts more force to the capsular bag.
(4) Loose zonules pose several different problems.4,5 First, the epinucleus and cortex do not separate as easily from a capsule that is poorly anchored. As a result, it may be difficult to rotate the nucleus, and the lax, adherent posterior capsule may later follow epinucleus and cortex centrally toward the aspirating instrument.
Weakened zonules will dehisce more easily. Forceful sculpting or rotation of the nucleus may shear zonules in the subincisional or lateral quadrants. Aspirating the anterior capsule or adherent lens material may dehisce the zonules in that location. Stripping the cortex tangentially rather than radially helps to distribute this force upon as large an area of zonules as possible. Finally, deficient centrifugal zonular tension permits excessive trampolining of the flaccid posterior capsule during epinuclear and cortical cleanup. Redundant folds of a lax posterior capsule may be accidentally aspirated during I&A or snagged by a capsule polisher.
(5) A radial tear in the capsulorrhexis can easily extend around the fornix into the posterior capsule with the application of sufficient force against the capsular bag. Such force may result from nuclear sculpting, cracking, or rotation. If the phaco tip or the second instrument creates a radial tear, recognition may be delayed because of poor visibility during the initial stages of nuclear emulsification.
(6) An inability to rotate the nucleus and epinucleus complicates any phaco technique by forcing the phaco tip to be aimed in a direction other than toward the contraincisional quadrant. Particularly with epinucleus, this increases the risk of aspirating the posterior capsule. Causes include ineffective hydrodissection, a very soft nucleus, and significant zonular laxity. As with a pillow, a soft nucleus absorbs the rotational force and is less likely to revolve as a unit. With loose zonules, the capsular bag may be so poorly fixated that it wants to rotate together with the nucleus.
Strategies for Eyes at Increased Risk of PC Rupture
(1) Achieving capsulorrhexis and hydrodissection is especially important when operating on a high-risk eye. A capsulorrhexis renders the capsular bag more resistant to tearing. However, if the capsulorrhexis is too small, there is a greater chance that it may be incised by the phaco tip or torn by the shaft of a peripherally positioned chopper. Therefore, a wider diameter capsulorrhexis is desirable for a large, brunescent endonucleus.
To maximize safety, hydrodissection should accomplish three objectives. The first goal is to be able to rotate the endonucleus with a minimum of stress applied to the zonules. The second is to be able to rotate the epinucleus. This allows the phaco tip to always aspirate the epinucleus in the contraincisional and safest quadrant. Finally, cortical cleaving hydrodissection, as described by Fine,6 loosens the adhesion of the cortex to the capsule. The more easily the cortex separates from the capsule, the less likely a floppy capsule will be pulled toward the aspirating instrument tip.
(2) Surgical enlargement of the pupil should be undertaken when necessary. Besides improving surgical safety, a secondary goal is to preserve a reactive pupil of a functional size. The surgical pupil size required will depend upon the individual surgeon’s skill level and the presence of other risk factors such as exfoliation or a brunescent nucleus.
Following lysis of any posterior synechiae, viscoelastic alone may expand the pupil enough for the capsulorrhexis. Representing the most cohesive viscoelastic, Healon V is ideal for this purpose. If the iris stroma is rigid, bimanual stretching with two Lester hooks will enlarge the pupil through the creation of tiny sphincter tears.7 This is usually the case with chronic miosis due to pilocarpine. The Beehler pupil dilator achieves this with a single instrument.
If the iris is floppy, the pupillary margin may simply stretch without tearing or enlarging. In this case, multiple partial thickness sphincterotomies can be performed with a Vannas or Rapazzo scissors prior to bimanual stretching. Care must be taken to avoid transecting the entire sphincter muscle. If this is still insufficient, self-retaining 5-0 nylon flexible iris retractors (Grieshaber)8-10 may be inserted through limbal stab incisions in four quadrants to mechanically retract the iris Alternatively, an iris pupil expander ring such as the Morcher Pupil Dilator (Morcher), the Graether Pupil Expander11 (Eagle Vision), or the "Perfect Pupil" ring (Becton Dickinson) can be used to hold the pupil open. These maneuvers should precede the capsulotomy in order to avoid hooking or tearing the capsulorrhexis margin.
(3) Insertion of a Witschel endocapsular tension ring12,13 (Morcher) is of tremendous help in the presence of zonular laxity. This can be done at any point in the procedure following completion of the requisite capsulorrhexis. Ring insertion can be accomplished using either forceps or a specially designed injector (Geuder).
The PMMA tension ring partially compensates for the weakened zonular apparatus in several ways. It evenly redistributes capsular forces across all of the zonules, rather than toward a single area. The centrifugal pressure applied against the capsular fornix prevents the peripheral capsule from following the epinucleus and cortex toward the aspirating instrument tip. This pressure also keeps the posterior capsule taut, which reduces trampolining and the development of folds that can be accidentally aspirated. Postoperatively, the permanently implanted ring will resist the development of capsulophimosis to which eyes with weak zonules are predisposed.
(4) In addition to enlarging a small pupil, flexible microhook iris retractors can also be used to stabilize the capsular bag in the presence of extremely loose zonules. Self-retaining retractors are inserted through paracentesis openings in each of four quadrants to hook and fixate the capsulorrhexis. Both Mackool and Lee14 have reported this technique of an artificial capsular support system. Mackool has developed specially shaped titanium hooks (Duckworth & Kent) for this purpose.
(5) In the presence of excessive trampolining of the posterior capsule, use of a non-coaxial, separate infusion source should be considered. A self-retaining anterior chamber maintainer can be used through a limbal paracentesis either during phaco or irrigation and aspiration I&A, as described by Blumenthal and others. Alternatively, a bimanual system of separate irrigation and aspiration handpieces, each introduced through snug clear corneal ports, can be helpful for epinuclear and cortical removal in these situations.
In the presence of loose zonules, cortical cleanup is further facilitated by the increased capsular tension provided either by an endocapsular tension ring or the haptics of the IOL. The IOL optic can block a floppy posterior capsule from reaching the I&A tip. Using a syringe and cannula, "dry" aspiration of cortex can be accomplished using a dispersive viscoelastic to both expand the capsular fornix and restrain the lax capsule from vaulting toward the aspiration port.
Phaco Techniques for High Risk Eyes
In the presence of posterior capsule risk factors, phaco technique is a critical variable. Particular emphasis should be directed toward achieving stable chamber fluidics through the elimination of any post-occlusion surge. To slow the procedure down, a lower aspiration flow rate than usual may be warranted.
It is important to employ a technique that minimizes zonular and capsular stress. The firmer and larger the nucleus, the greater the degree to which sculpting forces are transmitted to the capsular bag. To reduce movement of the nucleus during sculpting, one should sculpt at a slower rate, have lesser amounts of nucleus with each pass, and use enough phaco power for the tip to cut, rather than push, the nucleus.
Several techniques exist that avoid intracapsular sculpting altogether and may be preferable for higher risk cases. The supracapsular flip technique, as popularized by Dr. David Brown, displaces and flips the endonucleus out of the capsular bag prior to emulsification. If accomplished, this prevents the phaco instrumentation forces from being borne by the capsular bag. Care must be taken to avoid endothelial trauma. The ease with which this flipping maneuver can be achieved varies depending upon the size of the endonucleus relative to the capsulorrhexis diameter. A nucleus that is too large or a capsulorrhexis that is too small would limit the suitability of this technique.
One of the best techniques for complicated cases is phaco chop. Although "stop and chop" involves chopping,15 the term "nonstop" phaco chop16 as originally described by Nagahara in 1993 in which pure chopping techniques eliminate sculpting. A Nagahara-style chopper is placed peripherally beneath the anterior capsule, where it hooks the lens equator. As it moves toward the centrally impaled phaco tip, it first compresses and then fractures the nucleus along a natural lamellar cleavage plane. This maneuver is repeated until nuclear fragmentation is complete.
By replacing sculpting and cracking forces with the centripetally directed manual forces of one instrument pushing against another, phaco chop reduces stress on the zonules and capsule. In sculpting, the nucleus is fixated by the capsular bag. In chopping, it is immobilized instead by the phaco tip. This significant difference in zonular stress is readily appreciated when chopping and sculpting are compared from the Miyake-Apple viewpoint in cadaver eyes.
Finally, with the elimination of sculpting, ultrasound energy is reduced17,18 and reserved for the phaco-assisted aspiration of the individual nuclear fragments. Once these pieces have been elevated out of the capsular bag, they are emulsified at a safe distance from the posterior capsule — an advantage that phaco chop shares with other "supracapsular" techniques.
If hydrodissection fails, phaco chop can create the initial fragments of nucleus without the need for sculpting or rotation. The chopper initially bisects the nucleus by moving centrally toward a stationary phaco tip. Compared to the latter, there is much more versatility in terms of where the chopper can be placed. By repositioning the chopper several clock hours to one side, the next chop will create the first pie-shaped piece, which can then be aspirated or tumbled out.
Variations of "nonstop" phaco chop include Dr. Takayuki Akahoshi’s "prechop" technique, and phaco "quick chop" whose originators include Drs. Hideharu Fukasaku, Abhay Vasavada,19,20 and Vladimir Pfeifer. Although these variations all employ different strategies, they share the common advantages of reducing phaco power, phaco time, and mechanical stress on the capsule and zonules. They are, therefore, particularly helpful in the presence of loose zonules, a torn capsulorrhexis, and large brunescent nuclei.
Summary — Combination Strategies
Outlining an approach for the following high-risk categories of eyes will summarize the multiple strategies that, in combination, can reduce the frequency of anterior and posterior capsule complications.
Small Pupils
Surgically enlarging the pupil will improve the red reflex and expand the horizontal working space. This facilitates the
capsulorrhexis and phacoemulsification steps. With phaco chop, the phaco tip always remains in the central 2-mm zone of the
pupil, where it is least likely to aspirate the iris or anterior capsule. Because it is a kinesthetic technique that, unlike sculpting,
does not require visualization of the depth of the phaco tip, there is less dependence upon a bright red reflex. Supracapsular
flipping techniques can bring the nucleus into the pupillary plane so that the emulsification takes place just anterior to the pupil.
Iris retractors or a pupil expander ring may be needed for a floppy, elastic iris.
Narrow Angles/Shallow AC
The most cohesive viscoelastics may be required to deepen the AC for the capsulorrhexis. Healon V is the optimal choice,
or alternatively the soft-shell technique of Arshinoff can be used. Phaco chop, by reducing phaco power and time, may be a safer
technique because of the closer proximity of the endothelium. A mechanical pars plana vitreous tap can convert a flat chamber to
one of normal depth. This creates enough clearance to enlarge the pupil, complete a capsulorrhexis, and phaco the nucleus at a
safer distance from the endothelium.
Mature Cataracts (White or Brown)
ICG or trypan blue dye provides excellent visualization of the anterior capsule both during the capsulotomy and during
phaco. In the presence of high intralenticular fluid pressure, the capsulorrhexis should be made smaller. If the nucleus is large
and brunescent, phaco chop can reduce stress on the zonules and decrease overall phaco time. Although the red reflex is poor
or absent, phaco chop is a more kinesthetic maneuver and, unlike sculpting, does not require visualization of the depth of the phaco
tip. If a can-opener capsulotomy is necessary, outward-cracking motions should be minimized, in favor of inwardly directed chopping
maneuvers.
Loose Zonules
To improve control of a "pseudoelastic" capsule, a small-diameter capsulotomy coupled with frequent
regrasping of the flap may be necessary. An endocapsular tension ring more evenly distributes instrument forces across all of the
zonules. It can also reduce the tendency for a lax posterior capsule to trampoline forward. Flexible iris retractors can immobilize
an otherwise unstable capsule. Phaco chop minimizes stress placed upon the capsule by using centripetally directed opposing
instrument forces to segment the endonucleus.