Phacoemulsification of the High-Risk Lens

Long-standing, mature cataracts frequently present many challenges simultaneously. One or two complicating factors are sufficient to increase the difficulty of cataract surgery, and four or more risk factors may be present in cases of advanced cataract. The overripe lens is commonly associated with a small pupil, a super-dense nucleus, a shallow anterior chamber, and shaky zonules.

Surgeons need to plan ahead for the difficulties they are likely to encounter in high-risk cases. A small mistake or unplanned move early in the case can snowball into a serious, multifaceted complication. This article elucidates the techniques and technology available to confront the probable challenges of mature cataracts and to prevent escalating complications. I find that the three keys for success in hypermature lenses are (1) constructing a capsulorhexis that is as large as possible, (2) deepening the chamber by means of a 25-gauge vitrectomy, when indicated, and (3) using a vertical chopping technique (also known as quick chop) for nuclear disassembly.

LARGE CAPSULORHEXIS
Although the sizing of the capsulorhexis varies from surgeon to surgeon (and in many instances from case to case), bigger is definitely better with a hypermature lens. A large (greater than 6mm), continuous, central capsulorhexis has a number of advantages. First, locating the capsulorhexis' edge toward the periphery greatly reduces the likelihood of inadvertent capsular damage by the phaco tip due to poor visibility. Second, a large capsulorhexis allows quadrant or segment removal to proceed without capsular trapping or increased zonular stretching. Finally, and most importantly, in case of trouble, a large capsulorhexis will allow the dense nucleus to prolapse out of the capsular bag for capsule-free phacoemulsification.

In order to construct a large capsulorhexis, one must overcome difficulties such as a small pupil, a shallow chamber, iris prolapse, and poor capsular visibility. Unless one plans to perform a blind capsulorhexis under the iris, prudent pupillary expansion is necessary. Enlarging the pupil can be done in a number of ways: with an all-in-one pupil dilator such as the Beehler (Moria, Antony, France); a pupil-expansion ring; manual pupillary stretching; or iris hooks (older techniques such as multiple macrosphincterotomies or sector iridectomies are less practical, because they result in the permanent loss of pupillary anatomy and function). A shallow chamber and close endothelial proximity to the iris make the insertion of the relatively large Beehler or the placement of a pupil expansion ring risky. Manual pupillary stretching is therefore the procedure of choice. Iris hooks can also work well and may be relied upon as a backup at any point in the case.

Another trick for creating a large capsulorhexis is to start with a smaller, more controllable capsulorhexis. When coming around to finish the capsulorhexis, overlap the starting point and continue the tear around again at a wider diameter. With intralenticular pressure resolved, removing the circumferential ribbon of capsule on the second pass will be much easier and allow the creation of a large capsulorhexis, even in a challenging case.

PUPILLARY STRETCHING
The location and construction of the incision should facilitate pupillary management. For a temporal clear corneal approach, the two paracenteses should be placed 45º to either side of the main incision in order to allow the instruments plenty of leverage to stretch in all meridians. This placement also enables the surgeon to easily switch to iris hooks later in the case, if necessary, by creating two more paracenteses 90º apart.

Stretching is best accomplished with two smooth Kuglen hooks. At least one of the hooks, if not both, should have an angled handle to allow easy access beneath the brow (Figure 1). Stretching works by breaking the fibrotic pupillary margin/sphincter complex—in essence, a microsphincterotomy. To achieve the maximal effect, the surgeon should use the Kuglen hooks to stretch two opposite pupillary edges all the way to the angle and hold them there for a few seconds. Typically, stretching in the four cardinal directions is sufficient. Viscoelastic injection can then clear the iris pigment and keep the pupil enlarged. Healon5 (Advanced Medical Optics, Inc., Santa Ana, CA) or Viscoat (Alcon Laboratories, Inc., Fort Worth, TX) are quite retentive and tend to be efficacious for this step. Using too much viscoelastic can lead to iris prolapse, however.

IRIS PROLAPSE
Iris prolapse from the incision is not uncommon in complex cases. The complication results from a number of anatomic variables, including a shallow chamber, a floppy iris, a posteriorly placed entry incision, and diverse pressure dynamics. Prolapse can cause pain (in topical anesthesia cases), lead to iris depigmentation and atrophy, complicate instrument entry through the wound, and alter the pupil's size and shape, thereby affecting visibility. If the iris prolapses early in the case, it is likely to have “memory” and prolapse repeatedly throughout the surgery. Preventing and managing iris prolapse is critical to good visibility and a complication-free procedure.

The iris will prolapse initially either during the capsulorhexis or, more commonly, during hydrodissection. Prolapse occurs when the closed system of the anterior chamber is disrupted, such as during instrument insertion. Similarly, once the surgeon has passed the phaco sleeve through the incision, thus re-establishing the closed system, the iris will remain controlled.

Preventing iris prolapse depends on careful wound construction and management of the IOP dynamics. The paracentesis should be narrow and parallel to the iris surface. The clear corneal wound should begin as temporally as possible, with an intrastromal tunnel that is approximately 2mm in length. A shorter tunnel will predispose the eye to iris prolapse, whereas a longer tunnel will cause the oar-locking of instruments and visually significant corneal striae.

Understanding the pressure dynamics of iris prolapse is critical to managing the complication without frustration. In conjunction with the aforementioned anatomic variables, prolapse can only occur when the pressure inside the anterior chamber is greater than the atmospheric pressure outside. In such an instance, when an instrument breaches the self-sealing wound, fluid (aqueous or viscoelastic) exits the eye and sweeps out the iris in a susceptible case. The surgeon must maintain the equilibrium in pressure between the anterior chamber and outside. One suggestion is to avoid overfilling the anterior chamber with viscoelastic initially. Also, during hydrodissection, the surgeon should angle the cannula diagonally across the wound (and above the subincisional iris) while simultaneously pressing down on the posterior lip. When fluid is injected, displaced viscoelastic and fluid exit the eye instantaneously, before pressure has built up.

Once prolapse has occurred, it is tempting to place more viscoelastic in the chamber and push the iris back inside. Paradoxically, doing so actually increases the anterior chamber pressure and can lead to aggravated prolapse. Depressurizing the anterior chamber by depressing the paracentesis can equalize the pressure and cause the iris to pull itself into the eye. Although this technique works for most cases of iris prolapse due to increased anterior chamber pressure, it will not work in the rare instance of increased posterior pressure. The vitrectomy technique outlined later in this article can help in such a case.

If persistent iris prolapse hinders capsulorhexis creation despite the techniques just described, it may be necessary to close the incision and perform the capsulorhexis via the paracentesis. Once the closed system is re-established, viscoelastic may be used to deepen and dilate the already stretched pupil. The surgeon may create the capsulorhexis in a controlled fashion with either a cystotome or, preferably, a microcapsulorhexis forceps.

CAPSULAR VISIBILITY
Visualization is critical to achieving a large capsulorhexis. Even if the cataract is not white, dense lenses typically obscure the red reflex. Capsular staining with either indocyanine green or trypan blue (where available and approved) should be used. The dye should be injected after pupillary enlargement (under air, viscoelastic, or both), although the dye may be placed at any time, even in the middle of the capsulorhexis procedure, if necessary. If visualization remains poor due to coexisting corneal clouding or opacity, a coaxial vitrectomy light pipe can be helpful. The surgeon should turn off the microscope light and place the light pipe perpendicular or oblique to the limbus.

SHALLOW-CHAMBER MANAGEMENT
In most cases, placing viscoelastic in the eye provides adequate chamber depth, but this step may not be sufficient in eyes with extremely thick lenses. In the presence of severe anterior chamber shallowing (my threshold is less than two corneal thicknesses centrally), one should resort to a limited pars plana vitrectomy (PPV). This step can dramatically improve the chamber depth and IOP dynamics. For the anterior segment surgeon, the most effective manner in which to perform the PPV is with the 25-gauge, sutureless, transconjunctival vitrectomy system (TSV25) on the Millennium microsurgical system (Bausch & Lomb, Rochester, NY). The TSV25 system allows for safe and efficient vitrectomy, especially for the purpose of chamber deepening. No conjunctival dissection, cautery, or scleral suturing is necessary. That only one port is required further simplifies the process.

The location of the sclerotomy depends on exposure. For a temporal approach, a supra- or infranasal spot allows the easiest access. The TSV25 system uses an entry-site alignment cannula over a 25-gauge trocar. The surgeon inserts the trocar/cannula unit transconjunctivally, 4mm from the limbus, at the beginning of the case, when the eye is firmest. The trocar is then removed, but the cannula is left in place for easy instrument insertion and removal (Figure 2). After placing a 25-gauge, high-speed vitrectomy cutter through the cannula into the vitreous cavity, the surgeon performs a minimal core vitrectomy with settings of 1,500 cuts/min and vacuum of 500mmHg (Figure 3). After chamber deepening, the vitrector may be removed and the cannula sealed with the plug provided. Phacoemulsification may then proceed (Figure 4). Further vitrectomy may be performed at any time, if necessary. After completing phacoemulsification and IOL insertion, the surgeon employs a forceps to remove the cannula and the plug as a unit and uses a Weck cell sponge to slide conjunctiva over the sclerotomy site. The 25-gauge sclerotomy is self-sealing and requires no sutures.

The TSV25 system is efficient, elegant, and also highly efficacious. With this technology, performing a limited PPV is simple, takes only a few additional minutes, and can transform a difficult case into a manageable one.

Preferred Technique
Of all the elements addressed so far, a large capsulorhexis is the most important by far when preparing to disassemble a superdense nucleus on loose zonules. Even with suboptimal pupillary dilation, vertical chopping or quick chop is the procedure of choice for nuclear disassembly. Quick chopping has numerous advantages over disassembly techniques such as divide and conquer. In vertical chopping, the phaco tip and chopper remain within the central 2 to 3mm of the eye during the entire case, a positioning that allows safe phacoemulsification even if pupillary constriction occurs. The phaco tip stays at a safe depth throughout quick chop (unlike the grooving technique) and never approaches the posterior capsule. Chopping is also friendlier to the zonules. Because the forces used in chopping are equal and opposite, they balance each other out and minimize zonular stress.

Vertical chopping of a hypermature nucleus differs slightly from chopping a cataract of regular density. Hydrodelineation is not possible in most cases. Because the multiple layers of a dense nucleus typically become one, the usual epinuclear cushion is lacking. Also, the density of the nucleus may require numerous chops instead of the typical three. Chopping the nucleus into smaller pieces will facilitate its removal.

A leathery posterior plate is present in certain dense red or brown cataracts that prevents the complete separation of the chopped segments. In such cases, it is best to phacoemulsify and debulk the anterior aspect of the segments and to leave the tenuous posterior plate intact. A viscoelastic cannula may then be placed behind the plate to elevate it from the posterior capsule for final emulsification.

Sources of Trouble
During phacoemulsification, further problems such as zonular dehiscence or capsular compromise may occur. After identifying such a complication, one should cease phacoemulsification and reform the chamber with Viscoat via the sideport incision before removing the phaco tip in order to prevent chamber fluctuation. At this point, it is important to tamponade any prolapsing vitreous with Healon5 or Viscoat. Further intracapsular manipulation of the nucleus is very risky, and the case must be converted to a supracapsular or capsule-free procedure. A large capsulorhexis is of real benefit in these instances, because it permits the use of this escape maneuver.

One method for elevating the lens out of the bag through the capsulorhexis opening is to inject viscoelastic behind the lens to prolapse the nucleus completely above the anterior capsule. If a large portion of the lens remains, the surgeon may need to elevate it with a spatulated nucleus manipulator by sweeping under the anterior capsular rim and behind the lens. Once the lens is free from the confines of the capsule, placing Viscoat in front of and behind it will provide capsular and endothelial protection. The surgeon should emulsify the lens in one piece in a carousel fashion while supporting it underneath with the second instrument. Intentionally prolapsing the nucleus out of the compromised capsular bag resembles the conversion to an extracapsular, large-incision procedure, except that the latter involves a large, uncontrollable incision. Although converting to an extracapsular procedure can be safely accomplished, I believe maintaining a closed system is critical in complicated situations with capsular compromise and vitreous prolapse. Using the aforementioned technique can help re-establish control of an errant case and achieve excellent results.

CONCLUSION
Phacoemulsification has become the procedure of choice for even the most hypermature cataracts. With a meticulous, stepwise approach that combines advanced technical skills and the newest technologies, surgeons can transform a feared, complex cataract surgery with multiple risk factors into an anticipated challenge. n

Tal Raviv, MD, FACS, is Assistant Professor of Ophthalmology, New York Medical College, Valhalla, New York; is an attending cornea and refractive surgeon at the New York Eye and Ear Infirmary; and is in private practice in New York City. He states that he holds no financial interest in the products or companies mentioned herein. Dr. Raviv may be reached at (212) 448-1005; tal.raviv@nylasereye.com.