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Cataract Surgery | Apr 2010

FEATURE STORY: Cataract Surgery is Unsafe Without the Protection of OVDs

Viscoelastics replace the natural lining of hyaluronic acid present on endothelial cells.

Discussion has begun again among cataract surgeons about whether or not we need ophthalmic viscosurgical devices (OVDs) to perform cataract surgery using modern methods. OVDs were initially developed in the days of iris-supported, anterior chamber, and the earliest posterior chamber IOLs, with the first OVD available to most of the world in 1980. Early work with OVDs assigned them two principal functions: (1) to create and maintain surgical space, thereby facilitating intraocular surgery of all types, particularly IOL implantation, and (2) to protect delicate intraocular tissues, particularly the corneal endothelium, during surgery and especially during phacoemulsification.

OVDs rapidly became indispensible tools in cataract and other intraocular surgeries, and surgical techniques were developed that specifically depended upon the performance of OVDs. Arguments have ensued over what is the best OVD, with some championing lowerviscosity dispersive OVDs—represented principally by Viscoat (sodium chondroitin sulfate, sodium hyaluronate; Alcon Laboratories, Inc., Fort Worth, Texas)—because of its ability to be retained in the anterior chamber during the fluid turbulence and ultrasonic energy input of phacoemulsification, and others promoting viscous cohesive OVDs—represented principally by Healon (sodium hyaluronate; Abbott Medical Optics Inc., Santa Ana, California)—because of its ability to preserve and maintain space. These two OVDs remain their class champions because of their excellence and the financial ability of their manufacturers to support their arguments in the medical literature (Tables 1 and 2; Figure 1).

In the 1990s, the dispersive-cohesive viscoelastic soft shell technique (SST) emerged, taking advantage of the properties of both higher-viscosity cohesive and lowerviscosity lowerviscosity dispersive OVDs. This logical and ordered method achieves the benefits of both types of OVDs and minimizes the drawbacks of each in routine cataract surgery as well as in the management of complications (Figure 2).1-3 The SST was rapidly adopted across the world, with particular preference for use in eyes with dense cataracts, zonular deficiency, and other challenging situations.

OVDs EVOLVE
At approximately the same time that the SST was described, Healon GV (sodium hyaluronate 1.4%; Abbott Medical Optics Inc.) appeared, founding a new class of super viscous cohesive OVDs and thereby replacing Healon or Provisc (sodium hyaluronate; Alcon Laboratories, Inc.) as the best type of OVD to use with SST. Subsequently, other brands of each OVD class rapidly emerged in the marketplace.

The next step in the evolution of OVDs was the development of viscoadaptives. Healon5 (sodium hyaluronate 2.3%), the first to come to market, was launched at the European Society of Cataract and Refractive Surgeons (ESCRS) meeting in September 1998 and was approved for use in the United States in November 2000. Viscoadaptives are distinctive in that their rheologic behavior is dependent upon the fluid turbulence in their environment. When flow rates are less that 25 cc/min in the anterior chamber, they behave like extremely viscous cohesive molecules; however, when flow exceeds 25 cc/ min, they behave like fracturable solids (ie, pseudodispersive). The ultimate soft shell technique (USST) takes advantages of these properties of viscoadaptives and allows balanced saline solution to substitute for the dispersive OVD in the SST technique. Balanced saline solution can be contained in the eye because of the extremely high viscosity and cohesion of the viscoadaptive, which blockades the incision with a relatively impenetrable barrier (Figure 2).4

Subsequent to the development of the USST, combination combination techniques that merge ideas of SST and USST have appeared. Such methods can be useful in unusual cataract surgery situations. Examples include: (1) placing a thin layer of balanced saline solution between any cohesive OVD (as in USST) and the anterior lens capsule— whether the cohesive OVD is used alone or in a variant of SST—making capsulorrhexis easier, (2) using combined SST-USST for enhanced safety in eyes with Fuchs endothelial dystrophy, (3) and the intraoperative floppy iris syndrome (IFIS) OVD bridge technique in eyes with IFIS secondary to tamsulosin administration (Figure 3).5

The availability of a diverse range of OVDs by the beginning of the first decade of the millennium made it clear that the physics of phacoemulsification surgery is a combination of rheologic and phaco modulation parameters. Additionally, it was safe to say that some combination of OVDs could almost always create an ideal environment for the vast majority of intraocular surgical tasks encountered in cataract surgery.

The most recent development in OVDs is the advent of DisCoVisc (sodium chondroitin sulfate, sodium hyaluronate; Alcon Laboratories, Inc.), the first viscous dispersive OVD, which attempts to displace the need for SST by providing a single OVD with some of the properties of viscous cohesive and lower-viscosity dispersive OVDs. Indeed, DisCoVisc and similar OVDs can be used for a variety of routine cases, but they can never replace the ability to partition the anterior chamber and create different rheologic environments in specific areas of concern, as can be done with two or more different OVDs in the variety of combinations described briefly above.

HAS CATARACT SURGERY MATURED ENOUGH TO ABANDON OVDs?
With the history, evolution, and multiple uses of OVDs outlined above, we can begin to discuss the possibility of doing surgery without them. Knolle and Blumenthal have reported the use of an anterior chamber maintainer (ACM) to maintain anterior chamber depth and intraocular pressure during cataract surgery without the use of OVDs.6-8 It is true that sufficient balanced saline solution flow into the anterior chamber can compensate for fluid loss during extracapsular cataract extraction or phaco through a 6-mm incision. It remains true as well in modern smallincision phaco-emulsification with less incisional leakage. Therefore, it is fair to state that the space creation and maintenance function of OVDs can be replaced during phacoemulsification by an ACM or by controlled biaxial or microcoaxial surgery. Anterior chamber maintenance is still required during capsulorrhexis and IOL implantation, but irrigating cystotomes and incision-sealing cartridges for IOL injection into the capsular bag can take the place of OVDs during these portions of surgery. (The latter maneuver, however, is dangerous and associated with increased rates of capsular bag rupture.) However, what we have not managed to achieve yet is endothelial protection in the absence of OVD use, and continued high flow irrigation in the place of a stable OVD mass is itself associated with endothelial damage.

Cataracts vary in density, and consequently the total phaco energy dissipated and irrigation fluid volume varies from case to case; both parameters increasing (often dramatically) in proportion to nuclear density if the surgeon prefers flow rates in excess of 30 cc/min. It is a common observation that, on postoperative day 1, corneal clarity is noted to decrease proportional to nuclear density, phaco energy input, and irrigation fluid volume consumption during surgery. Some have suggested placing diluted OVD in the anterior chamber irrigating solution or designing phaco machines that require lower flow rates.

Even so, we must remember that OVDs replace the natural lining of hyaluronic acid present on endothelial cells. Surgery without an OVD increases endothelial trauma physically and from free radicals.9 Every once in a while somebody claims that cataract surgery can be done without OVDs. There is no doubt that it can, because modern machines can easily control anterior chamber depth and pressure, removing one of the historic roles of OVDs except during the IOL implantation step. But to perform phaco without an OVD is simply to imperil endothelial cells from damage due to fluid turbulence and free radical generation. It is perhaps pardonable to omit OVDs for quick refractive soft lens surgery in younger healthy eyes with healthy endothelial cells, but it is at best risky in more dense cataracts, especially in eyes with marginal endothelial populations. Such surgery would likely generate significantly greater numbers of patients with endothelial decompensation 10 years postoperatively than surgery with protective OVDs.

There are advocates for performing cataract surgery without OVDs; however, with the plethora of benefits attributable to them outlined above, I consider it ill advised to attempt this feat. My cataract surgery will be done with the best available OVDs.

Steve A. Arshinoff, MD, FRCSC, practices with York Finch Eye Associates, Toronto, Ontario, Canada, and is affiliated with Humber River Regional Hospital, Toronto, Ontario, Canada; University of Toronto, Toronto, Ontario, Canada; and McMaster University, Hamilton, Ontario, Canada. Dr. Arshinoff states that he is a paid consultant to Alcon Laboratories, Inc., and Carl Zeiss Meditec. He may be reached at tel: +1 416 745 6969; fax: +1 416 745 6724; e-mail: ifix2is@sympatico.ca.

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