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Lens removal techniques different for refractive lens exchange
Capsule protection, soft lenses present challenges when performing the technique.
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We have been considering the elements of refractive lens exchange techniques and specific differences from cataract surgery. The basic components are the same, but it is a mistake to assume that the procedures are identical. We saw this in our consideration of presbyopia and astigmatism management. As we shall see today, it holds true for lens removal as well.
The overarching consideration with lens removal in refractive lens exchange (RLE) is to avoid capsular rupture at all costs. Of course, this is true of cataract removal as well. But there are important differences in how this is best accomplished. Understanding and negotiating these differences are vital to a smooth transition from cataract surgery to RLE.
Protective measures
The issue of protecting the cornea and the capsule has had a major impact on the evolution of phacoemulsification since before Charlie Kelman published his technique in 1967. Acutely aware of the potential vulnerability of the corneal endothelium and its inability to regenerate damaged cells, Dr. Kelman initially experimented with several variations of the “endocapsular” approach that, with the benefit of linear power control and other major advances, was to become more or less standard 20 years later.
In the beginning, however, Dr. Kelman recognized that limitations of the earliest phaco machine precluded working inside the confines of the capsular bag. The risk of capsular rupture with its attending complications, at a time before effective vitrectomy instrumentation, was too high. Dr. Kelman weighed the relative risks to both the capsule and the cornea, and given the technology available to him at the time, decided on the anterior chamber for phaco’s initial approach in 1967.
Kratz, Sinskey and others moved the phaco process to the posterior chamber, primarily at the iris plane and outside of the capsular bag, around 1977 as phaco entered its second iteration. This move was a direct attempt to better protect the cornea in this pre-viscoelastic era, while still maintaining a comfortable distance from the capsular bag.
In 1987, as phaco entered its third decade, it also began its third iteration — the endocapsular approach. The benefits of a smaller and stronger 5 to 6 mm capsulorrhexis were immediately apparent. Gone was the large 6 to 7 mm can opener anterior capsulotomy that facilitated access to the peripheral nucleus from where the “outside-in” iris plane approach began. Capsulorrhexis imposed significant restrictions on what had been easy access to the peripheral nucleus. Thus, by necessity of the smaller capsular opening, endocapsular phaco rapidly became an “inside-out” approach combined with some form of disassembly of the nucleus into component parts performed entirely within the confines of the capsular bag.
I include this brief historical review because it shows us that the trajectory of phaco’s evolutionary pathway has been determined by the answer to this central question: “Given the techniques and technology at hand, where best to locate the phaco process so as to provide protection to both the cornea and capsule?” The answer has been a compromise since increasing protection of one typically lessens it for the other. As we evaluate the various options for lens removal in RLE, we are going to see that this relative protection equation is still at work.
Capsule protection trumps corneal
It goes without saying that a capsular rupture is undesirable in cataract surgery, and every measure should be taken to eliminate it. This is even more true in RLE, where the possible associated complications could have a greater impact on the outcome of a purely refractive procedure.
Fortunately for RLE surgeons, the capsule-cornea equation can be shifted significantly in favor of capsular protection when the lens to be removed has little or no cataract. The typically soft lens, together with routine viscoelastic coating of the endothelium, allows us to once again relocate the phaco process safely away from the capsular bag to the iris plane or at times even the anterior chamber, without added risk to the endothelium. This shift from an endocapsular to a supracapsular approach is perhaps the single most important difference in refractive lens removal — the capsule must be maximally protected at all times. Removing the lens from the confines of the capsular bag before phaco is, to date, the only method I know of to ensure that the capsule will remain intact.
A variety of supracapsular cataract techniques have emerged in recent years. All begin with some form of hydrodissection to prolapse a portion of the lens through the intact capsulorrhexis. From that point, the various supracapsular techniques vary widely, and some are better suited to the soft refractive lens removal than others.
Phaco flip, first described by Dave Brown, is to my knowledge the original supracapsular technique. It is an extremely safe and efficient method for cataract removal, but the “flip” maneuver is often not possible when the lens is soft and does not have nuclear density to provide the resistance necessary to invert the lens. The instrument usually simply passes through the soft lens material to no effect. However, the flip is not required to relocate the lens out of the capsular bag.
Tilt and tumble, as described by Richard Lindstrom, does not incorporate a flip and is quite well suited to RLE, particularly if some form of disintegration, such as repeated hydrodelineation or a pre-chopping type instrument, is used to enhance followability.
Refractive lens removal principles
Here are some principles that can serve as effective general guidelines in refractive lens removal.
Soft lens removal presents a unique set of challenges different from, but sometimes no less difficult than, hard lenses. The intact soft lens has a considerable amount of inertia, tending to stay put and remain intact even when higher aspiration levels and emulsification are used. It readily gives way to aspiration forces often only after being manually disrupted and reshaped into smaller parts.
The traditional techniques for disassembly used in cataracts, such as quick chop or cracking, typically require some degree of lens resistance and firmness in the attempt to create smaller, completely separate pieces. Therefore, they are relatively ineffective in removing the soft lens we encounter in RLE.
Fortunately, the more malleable soft lens does not require such complete separation. Here, disruption of the lens’ uniformity rather than complete disassembly is usually sufficient to overcome soft lens inertia. This can often be achieved by simply deeply scoring the surface of the intact lens into segments with a Koch type lens hook followed by hydrodelineation as needed until spontaneous and continuous followability is achieved.
These soft lens challenges can often be exacerbated by the additional anatomic challenges that typically accompany large myopic or small hyperopic eyes. For example, the inertia of a soft lens can be made significantly more troublesome in a myopic eye with an unusually deep anterior chamber. On the other hand, iris prolapse, found with the shallow anterior chamber of hyperopia, may precipitate a cascade of frustrating difficulties that can interfere with lens removal as well.
Different approach
I do not want to leave the impression that lens removal is an inherently difficult part of RLE. Typically it is not. I simply want to remind you that refractive lens removal is different from cataract removal and that the approach for efficient refractive lens removal should not be taken for granted. Fortunately, these techniques and others that will be devised can be refined in the soft posterior subcapsular cataract cases that regularly arise before applying them to RLE.
Next month:
Making noninjection anesthesia work for RLE every time.