Ординатура / Офтальмология / Английские материалы / Bimanual Phaco Mastering the Phakonit MICS Technique_Agarwal_2004

Chapter

16

BIMANUAL MICROINCISION

REFRACTIVE LENS EXCHANGE

Richard S. Hoffman, MD; I. Howard Fine, MD; and Mark Packer, MD

INTRODUCTION

Advances in small incision surgery have enabled cataract surgery to evolve from a procedure concerned primarily with the safe removal of the cataractous lens to a procedure refined to yield the best possible postoperative refractive result. As the outcomes of cataract surgery have improved, the use of lens surgery as a refractive modality in patients without cataracts has increased in popularity.

The removal of the crystalline lens and replacement with a pseudophakic lens for the purposes of reducing or eliminating refractive errors has been labeled with many titles. These titles include clear lensectomy,1,2 clear lens phacoemulsification,3 clear lens replacement, clear lens extraction,4-12 clear lens exchange, presbyopic lens exchange, and refractive lens exchange. Since these procedures may be performed in older patients with significant nuclear sclerosis but normal spectacle corrected visual acuity, the term “clear lens” may not be appropriate to describe many older individuals undergoing lens exchange surgery. Similarly, a “clear lens exchange” in a young highly hyperopic patient may be performed for refractive purposes but not necessarily to address pre-existing presbyopia and thus “presbyopic lens exchange” would not be an appropriate term for this group of patients. The term refractive lens exchange (RLE) appears to best describe the technique of removing the crystalline lens and replacing it with a pseudophakic lens in any aged patient for the purpose of reducing or eliminating refractive errors and/or addressing presbyopia.

REFRACTIVE LENS EXCHANGE

VS CORNEAL REFRACTIVE SURGERY

Removal of the crystalline lens for refractive purposes offers many advantages over corneal refractive surgery. Patients with high degrees of myopia, hyperopia, and astigmatism are poor candidates for excimer laser surgery. In addition, presbyopia can only be addressed currently with monovision or reading glasses. RLE with multifocal or accommodating intraocular lenses (IOLs) in combination with corneal astigmatic pro-

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cedures could theoretically address all refractive errors including presbyopia while simultaneously eliminating the need for cataract surgery in the future.

Current attempts to enhance refractive results and improve functional vision with customized corneal ablations using the excimer laser expose another advantage of RLE. The overall spherical aberration of the human eye tends to increase with advancing age.13-16 This is not the result of significant changes in corneal spherical aberration but rather increasing lenticular spherical aberration.17-19 This implies that attempts to enhance visual function by addressing higher order optical aberrations with corneal refractive surgery will be sabotaged at a later date by lenticular changes. Addressing both lower order and higher order aberrations with lenticular surgery would theoretically create a more stable ideal optical system that could not be altered by lenticular changes since the crystalline lens would be removed and exchanged with a stable pseudophakic lens.

BIMANUAL MICROINCISION PHACOEMULSIFICATION

RLE with bimanual microincision lens extraction offers a potentially safer and more controlled method of crystalline lens removal than standard coaxial phacoemulsification. Bimanual microincision phacoemulsification entails the removal of the crystalline lens through two 1.2 mm incisions. Infusion is provided through a separate irrigating handpiece and phacoemulsification and aspiration are performed through a sleeveless phacoemulsification needle.

The notion of removing the crystalline lens through two microincisions is not a new concept and has been attempted with varying degrees of success and failure since the 1970s.20-24 With the development of new phacoemulsification technology and power modulations,25 we are now able to emulsify and fragment lens material without the generation of significant thermal energy. Thus removal of the cooling irrigation sleeve and separation of infusion and emulsification/aspiration through two separate incisions is now a viable alternative to traditional coaxial phacoemulsification. Machines such as the AMO WhiteStar (Santa Ana, Calif), STAAR Sonic Wave (Monrovia, Calif), Alcon NeoSoniX and Infiniti (Fort Worth, Tex), Bausch & Lomb Millennium with burst mode (San Dimas, Calif), and Dodick Nd:YAG Laser Photolysis system (ARC Laser, Salt Lake City, Utah) offer the potential of relatively “cold” lens removal capabilities and the capacity for bimanual lens surgery.26-30

Advantages

While it is true that coaxial phaco is an excellent procedure with low amounts of induced astigmatism,31 bimanual phaco offers the potential for truly astigmatic neutral incisions. In addition, these microincisions should behave like a paracentesis incision with less likelihood for leakage and theoretically, a lower incidence of endophthalmitis.

The major advantage we have seen from bimanual microincisions has been an improvement in control of most of the steps involved in endocapsular surgery. Since viscoelastics do not leave the eye easily through these small incisions, the anterior chamber is more stable during capsulorrhexis construction and there is much less likelihood for an errant rhexis to develop. Hydrodelineation and hydrodissection can be performed more efficiently by virtue of a higher level of pressure building in the anterior chamber prior to eventual prolapse of viscoelastic through the microincisions.

Figure 16-1. A left-handed, 1.2-mm clear corneal microincision placed 45 degrees from the temporal limbus utilizing a Mastel Paratrap diamond knife.

In addition, separation of irrigation from aspiration allows for improved followability by avoiding competing currents at the tip of the phaco needle. In some instances, the irrigation flow from the second handpiece can be used as an adjunctive surgical device—flushing nuclear pieces from the angle or loosening epinuclear or cortical material from the capsular bag. In the same respect, it is important to avoid directing the fluid flow from the second irrigating handpiece at the tip of the phaco needle since this will dislodge nuclear fragments from the tip and actually worsen the followability.

Perhaps the greatest advantage of the bimanual technique lies in its ability to remove subincisional cortex without difficulty. By switching infusion and aspiration handpieces between the two microincisions, 360 degrees of the capsular fornices are easily reached and cortical clean-up can be performed quickly and safely.

BIMANUAL REFRACTIVE LENS EXCHANGE TECHNIQUE

With advances in multifocal, accommodative, and microincision lens technology, RLE should become a more popular procedure in the future. The independent advantages of bimanual microincision phacoemulsification make it a procedure of choice for RLE. Our current technique for RLE utilizing bimanual microincision phacoemulsification is simple and straightforward.

The procedure is performed under topical anesthesia after appropriate informed consent, preoperative measurements for IOL determination, and preoperative dilation and antibiotics. A Mastel Paratrap diamond keratome (Mastel Precision, Rapid City, SD) is utilized to create two 1.2-mm clear corneal incisions 30 to 45 degrees from the temporal limbus (60 to 90 degrees from each other) (Figure 16-1). Half of a cc of nonpreserved lidocaine 1% is instilled into the anterior chamber followed by complete expansion of the anterior chamber with Viscoat (Alcon, Fort Worth, Tex). A capsulorrhexis forceps, specially designed to fit and function through a 1.0-mm incision is then inserted through the right-handed incision and used to begin and complete a 5.0- to 6.0-mm rhexis (Figure 16-2).

Cortical cleaving hydrodissection32 with decompression is then performed in two separate distal quadrants followed by a third round of hydrodissection to prolapse the entire lens or at least one-half of the lens out of the capsular bag. The microincision

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Figure 16-2. Capsulorrhexis formation utilizing a ASICO microincision capsulorrhexis forceps.

Figure 16-3. The soft lens is carouselled in the iris plane and consumed utilizing high vacuum levels. Forward movement of the lens is prevented with the irrigating handpiece.

irrigating handpiece is placed in the left-hand incision and the sleeveless phaco needle is inserted through the right-hand incision. Lens extraction is then performed in most cases without phaco power, utilizing high levels of vacuum while carouselling the relatively soft lens in the plane of the iris until it is consumed (Figure 16-3). Small amounts of ultrasound energy can be utilized when needed. Care should be taken to avoid directing the infusion flow towards the phaco needle tip so as to prevent dislodging nuclear material from the tip. While maintaining infusion with the irrigating handpiece, the phaco needle is removed and the aspiration handpiece is inserted to remove residual cortex and polish the posterior capsule. If subincisional cortex is difficult to extract, the irrigation/aspiration (I/A) handpieces can be alternated between the two incisions in order to gain easier access to the subincisional capsular fornix (Figure 16-4).

Once all cortex has been removed, the aspiration handpiece is removed and viscoelastic is injected into the capsular bag and anterior chamber while withdrawing the irrigating handpiece. Following this, the viscoelastic cannula is removed from the eye and a new 2.5-mm clear corneal incision is placed between the two microincisions for

Figure 16-4. Subincisional cortex is easily removed using the Duet System (MST) bimanual irrigation and aspiration handpieces. (Note the Effective Phaco Time EPT=0 and Average Percent Phaco Power AVG=0 following lens removal).

IOL insertion. Eventually, access to microincision lenses in the United States. will afford the ability to eliminate the 2.5-mm incision and perform the entire procedure through two microincisions.

Following IOL insertion, stromal hydration of the 2.5-mm incision is performed to assist in self-sealing of the incision. Bimanual (I/A) is performed to remove all viscoelastic. Following removal of the viscoelastic, the aspiration handpiece is removed while maintaining irrigation of the anterior chamber, and stromal hydration of the empty incision is performed to assist in closure of the microincision. The irrigation handpiece is then removed, followed by stromal hydration of that incision. In this manner, the eye is fully formed and pressurized throughout the procedure avoiding hypotony and shallowing of the anterior chamber.

BIMANUAL FLUIDICS

The greatest criticism of bimanual phaco lies in the fluidics and the current limitations in intraocular lens technology that could be utilized through these microincisions. By nature of the size of these incisions, less fluid flows into the eye than occurs with coaxial techniques. Most current irrigating choppers integrate a 20-gauge lumen that limits fluid inflow. This can result in significant chamber instability when high vacuum levels are utilized and occlusion from nuclear material at the phaco tip is cleared. Thus, infusion needs to be maximized by placing the infusion bottle on a separate IV pole that is set as high as possible. Also, vacuum levels usually need to be lowered below 350.0 mmHg to avoid significant surge flow. Although chopping instruments are generally not necessary for routine RLE, the 20-gauge irrigating choppers and 20-gauge irrigators from Microsurgical Technology (MST, Redmond, Wash) appear to have improved infusion flow compared to other irrigating choppers secondary to their thinwalled construction (Figure 16-5).

Another device that has been helpful for improving fluidics during bimanual surgery has been the Cruise Control (STAAR Surgical, Monrovia, Calif). The Cruise Control has a cylindrical mesh within it designed to capture all lens material and will never become completely occluded by virtue of its large surface area. Fluid will always be

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Figure 16-5. Relative infusion rates of various 20-gauge bimanual irrigating choppers (courtesy of MST).

able to pass through some portion of the mesh but is restricted on the downstream side of the device by a small I/A sized exit port. This port restricts flow at high flow rates such as those that occur following consumption of nuclear material at the tip with high vacuum in the aspiration line. The device has been shown to prevent intraocular pressure from dropping below atmospheric pressure, preventing chamber instability and forward movement of the iris and posterior lens capsule. It should allow for safer bimanual surgery by allowing surgeons to utilize higher vacuum levels while maintaining better chamber stability.

Utilization of bimanual microincision RLE as we have described offers an enormous advantage of maintaining a more stable intraocular environment during lens removal. This may be especially important in high myopes who are at a greater risk for retinal detachment following lens extraction.33-35 By maintaining a formed and pressurized anterior chamber throughout the procedure, there should be less tendency for anterior movement of the vitreous body with a theoretical lower incidence of posterior vitreous detachment occurring from intraoperative manipulations. Vitreous detachments occurring in the postoperative period would obviously not be avoided, however, future lens technology that completely fills the capsular bag may help eliminate posterior vitreous detachments occurring in the postoperative period.

LENS TECHNOLOGY

Microincision Lenses

New lens technologies are currently being developed that will allow surgeons to perform RLEs by means of a bimanual technique through two microincisions. Medennium (Irvine, California) is developing its Smart Lens—a thermodynamic accommodating IOL. It is a hydrophobic acrylic rod that can be inserted through a 2.0 mm incision and expands to the dimensions of the natural crystalline lens (9.5 mm x 3.5 mm) (Figure 16-6). A 1.0-mm version of this lens is also being developed. ThinOptX fresnel lenses (Abingdon, Virginia) will soon be under investigation in the U.S. and will also be able to be implanted through 1.5 mm incisions. In addition, Acri.Tec GmbH (Berlin, Germany) has released the Acri.Smart acrylic IOL that is available outside of the United States. and can be injected through a cartridge injector system through a 1.4-mm incision. Finally, injectable polymer lenses are being researched by both Pharmacia/Pfizer (New York, NY) and Calhoun Vision (Pasadena, Calif).36,37

Figure 16-6. Expansion of the Medennium Smart Lens from rod to full size lens after being immersed in a warm saline solution (Courtesy of Medennium).

Multifocal IOLs

Perhaps the greatest catalyst for the resurgence of RLE has been the development of multifocal lens technology. High hyperopes, presbyopes, and patients with borderline cataracts who have presented for refractive surgery have been ideal candidates for this IOL technology.

Historically, multifocal IOLs have been developed and investigated for decades. Newer multifocal IOLs are currently under investigation within the United States. The 3M diffractive multifocal IOL (3M Corporation, St. Paul, Minn), has been acquired, redesigned, and formatted for the 3-piece foldable Acrysof acrylic IOL (Alcon). Alcon is currently completing the US (Food and Drug Administration) FDA clinical trials of their multifocal IOL and will eventually be releasing the lens on their single-piece acrylic platform under the name ReStor (Figure 16-7). Pharmacia/Pfizer has also designed a diffractive multifocal IOL, the CeeOn 811E that has been combined with the wavefront adjusted optics of the Technis Z9000 with the expectation of improved quality of vision38 in addition to multifocal optics (Figure 16-8).

The only multifocal IOL approved for general use in the United States is currently the Array (AMO). The Array is a zonal progressive intraocular lens with five concentric zones on the anterior surface (Figure 16-9). Zones 1, 3, and 5 are distance dominant zones while zones 2 and 4 are near dominant. The lens has an aspheric design and each zone repeats the entire refractive sequence corresponding to distance, intermediate, and near foci. This results in vision over a range of distances.39

A small recent study reviewed the clinical results of bilaterally implanted Array multifocal lens implants in RLE patients.40 A total of 68 eyes were evaluated, comprising 32 bilateral and four unilateral Array implantations. One hundred percent of patients undergoing bilateral RLE achieved binocular visual acuity of 20/40 and J5 or better, measured one to three months postoperatively. Over 90% achieved uncorrected binocular visual acuity of 20/30 and J4 or better, and nearly 60% achieved uncorrected binocular visual acuity of 20/25 and J3 or better. This study included patients with

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Figure 16-7. The Alcon ReStor multifocal

IOL (Courtesy of Alcon Laboratories).

Figure 16-8. The Tecnis ZM001 multifocal IOL (courtesy of Pfizer).

preoperative spherical equivalents between 7.0 D of myopia and 7.0 D of hyperopia with the majority of patients having preoperative spherical equivalents between plano and +2.50. Excellent lens power determinations and refractive results were achieved.

Another recent study by Dick et al evaluated the safety, efficacy, predictability, stability, complications, and patient satisfaction after bilateral RLE with the Array IOL.41 In their study, all patients achieved uncorrected binocular visual acuity of 20/30 and J4 or better. High patient satisfaction and an absence of intraoperative or postoperative complications in this group of 25 patients confirmed the excellent results that can be achieved with this procedure.

Figure 16-9. The AMO Array Multifocal IOL (courtesy of Advanced Medical Optics).

Accommodative IOLs

The potential for utilizing a monofocal IOL with accommodative ability may allow for RLEs without the potential photic phenomena that have been observed with some multifocal IOLs.42-44 The two accommodative IOLs that have received the most investigation to date are the Model AT-45 CrystaLens (Figure 16-10) (Eyeonics, Aliso Viejo, Calif) and the 1 CU (Humanoptics, Mannheim, Germany). Both lenses have demonstrated accommodative ability45,46 although the degree of accommodative amplitude has been reported as low and variable.47,48

As clinical investigators for the US FDA clinical trials of the AT-45 CrystaLens, we have had experience with the clinical results of the majority of accommodative IOLs implanted within the U.S. In our practice, 96 AT-45 IOLs were implanted with 24 patients implanted bilaterally. All patients had uncorrected distance vision of 20/30 or better and uncorrected near vision of J3 or better. Eighty-three percent of patients were 20/25 or better at distance and J2 or better at near. And 71% were 20/20 or better at distance and J1 or better at near. These results confirm the potential clinical benefits of accommodative IOL technology for both cataract patients and refractive patients and place accommodative IOLs in a competitive position with multifocal IOL technology.

Newer accommodative models incorporating dual optics for increased accommodative amplitudes are being designed and evaluated. The Sarfarazi elliptical accommodating IOL contains two 5.0 mm optics connected with three flexible haptics and is designed to fill the capsular bag with both optics moving away from each other during accommodative effort. Similarly, the Visiogen Synchrony has a dual optic configuration with a positive powered anterior lens and a negative powered posterior lens designed to separate with an increase in overall functional power during accommodation (Figure 16-11). These dual optic accommodating IOLs may produce greater accommodative amplitudes than single-piece designs, however clinical comparisons are to date lacking.49

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Figure 16-10. The eyeonics CrystaLens accommodating IOL (courtesy of Eyeonics).

Figure 16-11. Side-view of the Visiogen

Synchrony dual optic accommodating

IOL (courtesy of Visiogen).

Future Lens Technology

There are lens technologies under development that may also contribute to increased utilization of RLE in the future. One of the most exciting technologies is the light adjustable lens (LAL) (Calhoun Vision). The LAL is designed to allow for postoperative refinements of lens power in situ. The current design of the LAL is a foldable three-piece IOL with a cross-linked silicone polymer matrix and a homogeneously embedded photosensitive macromer. The application of near-ultraviolet light to a portion of the lens optic results in polymerization of the photosensitive macromers and precise changes in lens power through a mechanism of macromer migration into polymerized regions and subsequent changes in lens thickness (Figures 16-12 and 16-13B).