NO-TILT, FOUR-POINT TRANSSCLERAL FIXATION OF PMMA POSTERIOR CHAMBER IOLS

Michael E. Snyder, MD and Gregory S. H. Ogawa, MD

It is telling that the need has now arisen for this comprehensive text on intraocular lens (IOL) fixation techniques when there is inadequate capsular support for conventional lens placement. The breadth and depth of this book demonstrates the wide range of approaches for addressing this situation, and highlights the fact that no one approach has emerged as the gold standard. In fact, in that regard, our world is strikingly similar to that described in 2003 by an American Academy of Ophthalmology report indicating that the 3 main categories of alternate IOL fixation were all reasonable options.¹

For cases in which the capsular bag can be salvaged, our strong preference is to preserve the bag, even if a combination of elegant surgical techniques and zonular augmentation devices is needed to achieve this desired outcome. However, in many cases, there is inadequate or no capsular material remaining. In these situations, we need to affix an IOL within the eye in other ways. Although no one technique is perfect for every case, this chapter describes 2 technique variations sharing the same core principles and foundations for expanded polytetrafluoroethylene (ePTFE; Gore-Tex; WL Gore & Associates) scleral fixation of single-piece polymethylmethacrylate (PMMA) posterior chamber IOLs (PCIOLs). We outline the principles for these procedures, the detailed surgical steps, and the relative strengths of these techniques.

Our technique for 4-point transscleral IOL fixation requires the following:

• A single-piece PMMA IOL with a 7-mm optic and eyelets on the apex of the haptics that allow for suture separation to match transscleral incisions placed behind the iris
  
• Sound scleral tunnel incision architecture
  
• Globe pressurization to optimize anatomic configuration and minimize chance of hemorrhage
  
• Effective use of vitrectomy for retinal safety
  
• Management of the knots to avoid conjunctival erosion
  
• Use of peripheral iridectomy (PI) to help avoid optic capture

Core Principles

PREPARATION

Dilation drops are beneficial preoperatively for a better view during the surgery, but a very widely dilated pupil is not necessary. We recommend the avoidance of placing epinephrine or phenylephrine in the infusion bottle so that the pupil may be constricted later in the case with an intraocular miotic agent should that be needed. If the procedure is performed with a temporal approach, then we have a small triangle of instrument wipe sponge available to place over the lateral canthal skin and lashes that can be notoriously difficult to cover with the surgical drapes. Placement of 4-0 silk bridle sutures under the superior and inferior rectus muscle insertions with a tapered needle can be useful in cases where a superior main incision is created or to elevate eyes that are more enophthalmic than average. If iris retractors were used prior to placing this new IOL (such as during removal of a dislocated IOL), the surgeon may want to loosen or remove the retractors in the areas where the scleral incision and sutures will be placed to minimize the chance of incising the iris during sclerotomy creation and/or capturing iris material with the IOL support sutures.

We prefer to maximize optic size for several reasons. First, the anterior segments in this population of eyes are frequently imperfect, and the pupils are not always small and not always round. A larger optic can reduce the likelihood of edge exposure due to pupil irregularities or less than perfect IOL centration. Also, a larger optic reduces the risk of IOL capture of the pupil margin, which can occur even with perfectly positioned IOLs because these eyes are definitionally unicameral. Blinking, brief eye rubbing, or squeezing can transiently increase the anterior chamber pressure, creating posterior aqueous flow that can push the iris against the IOL optic and even behind the optic margin.2 A larger optic makes this less likely.

Overall diameter of the IOL and haptic surface finishing are other considerations. We, like others, have found that small-diameter, rounded haptic material is better tolerated when in contact with the uvea than square-edged haptic configurations. IOL haptics that can compress or extend with very little stress on the sclera to which it is affixed are adaptable to eyes both small and large. Although some foldable acrylic IOLs with loops are available in the United States, their overall diameter is small, and their haptic contours are squared.

Optic material is also important. Silicone IOLs provide good optical quality, but the subset of patients needing alternate IOL fixation is more likely to require subsequent vitreoretinal interventions than most other eyes. The silicone material can create an impediment for the vitreoretinal surgeon when condensation forms on the hydrophobic IOL’s posterior surface as gas or air is used intraoperatively. Additionally, if silicone oil is required as part of a vitreoretinal procedure, the oil adheres to the silicone optic, creating significant optical obscuration both intra- and postoperatively. We prefer acrylic or PMMA implants for these potentially complex eyes.

Lastly, these techniques are best suited to IOLs that have an eyelet on the haptic. This eyelet can provide an aperture for suture passage, a mechanism to secure a suture to the implant, a fixture to prevent suture slippage, and a spacer to separate the 2 arms of a suture—a critical element in the creation of 4-point fixation. This type of fixation is what allows the surgeon to gain true control over IOL tilt. To our knowledge, such haptic modifications are currently commercially available only on PMMA IOLs in the United States (CZ70BD; Alcon Laboratories, Inc). When calculating the desired dioptric power for this IOL, we find that targeting as if this lens were being placed in the sulcus gives good results, with a slight bias toward a minimally myopic outcome.

SCLERAL TUNNEL INCISION WITH INTERNAL CORNEAL VALVE

Because our optimal available IOL choice has a 7-mm, nonfoldable optic, the main incision needs to be large enough to accommodate that IOL. To achieve acceptable astigmatism control with this wide of an incision, one needs to create a scleral tunnel incision. We start with a 7-mm wide scleral groove—either straight or in a frown configuration—then proceed with a lamellar dissection into clear cornea. This part of the incision is ideally performed before other incisions have been created so that the globe’s anatomy remains normalized for more precise groove and tunnel creation. Once a flowing infusion cannula is in place, then one can proceed to enter the anterior chamber at the scleral tunnel main incision, ensuring enough of a posterior corneal lip to allow that tissue to function as a valve and provide a good fluid seal.

GLOBE PRESSURIZATION

Maintaining a well-pressurized globe during these procedures is important for several reasons. It decreases the risk of intraocular bleeding associated with incisions through the sclera and ciliary body, likely decreases the risk of suprachoroidal hemorrhage, and helps keep the anatomy in a more normalized configuration for increased accuracy of incision and suture placement. Achieving adequate intraocular pressure during the procedure is dependent on both providing inflow and curbing fluid egress. The corneal valve on the inside of the main incision plays a major role in minimizing outflow, but this can be augmented as needed with temporary suture supplementation. Keeping other incisions as small and self-sealing as possible additionally curtails outflow. Because these eyes are unicameral, the infusion is the safest and most reasonable way to provide inflow. Filling a unicameral eye with ophthalmic viscosurgical device (OVD) may keep an eye formed but not pressurized, and since removal of that much OVD is virtually impossible, there is a significant risk of difficult to manage postoperative intraocular pressure elevation. Our standard is to use a high-flow, 23-gauge, limbal self-retaining infusion cannula (eg, 8-616; Duckworth & Kent Ltd), but if a vitreoretinal surgeon is part of the case and has already placed a pars plana infusion cannula, then we may use that. The caveat regarding pars plana infusion is that it creates a posterior to anterior pressure gradient that can increase the chance of iris prolapse compared with anterior chamber infusion that maintains more of an anterior to posterior pressure gradient. A gravity flow machine or cassette may be better for these cases because it does not create the aggressive fluid flow sometimes produced with an active pump system. Adjusting the bottle height may be necessary at different portions of the procedure, depending on the fluid egress from the wound during different steps and on the aspiration flow rate settings used, with the goal of maintaining a pressurized globe without excess flow.

VITREOUS REMOVAL

Avoidance of vitreous traction during surgery is an important step for minimizing the potential for retinal tears and detachments. In most situations, prior to doing other work in the eye, we use a 23- or 25-gauge vitrectomy probe to remove vitreous from the anterior chamber, the area behind the iris, and often from at least the anterior one-third of the vitreous cavity. Special attention is given to vitreous removal in the retro-iridal regions where we plan to create sclerotomy incisions. If there has not been a need to open the main incision with the keratome prior to this point, then we often leave the main incision closed during vitrectomy for fluidic integrity. Depending on the situation, we will insert the vitrector either through a limbal paracentesis or a pars plana approach (trocar/cannula system) when the eye’s anatomy permits.

For securing the IOL with suture, we prefer ePTFE in the smallest size currently available, which is a 6-0 equivalent based on US Pharmacopeia suture size specifications (CV-8; Gore-Tex). This suture has exceptional longevity (much better than polypropylene) and very good strength. It is now widely used for this ophthalmic indication, including publication in the peer-reviewed literature.3–5 As of June 2017, the manufacturer’s product instructions still bears the decades-old notation of being unstudied and contraindicated for eye surgery,⁶ but the manufacturer does not have any data indicating the suture is unsafe for eye surgery (personal communication, Carrie Ortiz, product specialist at WL Gore & Associates, January 7, 2015). Because needles on this suture are not designed for the ophthalmic microsurgical environment, we cut the needle off one end and use 25-gauge curved coaxial forceps for passing the suture through the small scleral incisions.³

SUTURE MANAGEMENT

Keeping track of the sutures and their paths is critical with these procedures. The ePTFE sutures need to be in the proper position, orientation, and alignment to achieve the excellent IOL position and stability these procedures deliver. Both arms of the suture should come over the top of the haptics so the sutures are in alignment with the scleral incisions through which the sutures will pass; this avoids IOL tilt. Each of these procedures uses the eyelet at the apex of the haptic to provide spacing between the suture arms for the 4-point fixation, so the surgeon will want to pay attention to these configurations (described later) for proper execution of the procedures. Equally important is maintaining the left-right orientation of the sutures as they are externalized through the scleral incisions. More specifically, when the IOL is oriented roughly the way it will be once it is in its final position, a suture arm that tracks off the left side of a haptic should go through the left-most incision of the paired scleral incisions. The same is true for a suture tracking off the right side of a haptic and the right-most incision of the pair. Fortunately, these sutures are white and relatively large for microsurgical sutures, so it is not difficult to visualize them through the microscope.

SCLEROTOMY INCISIONS FOR SUTURES

We create 2 openings in the scleral wall at each fixation site at the level of the ciliary sulcus. We prefer to make our openings parallel to the plane of the iris so that the suture tract is father away from the limbus externally, which theoretically minimizes the potential of late suture exposure. Also, the chance of a spontaneous seal is greater because the incision is oblique to the sclera. Since there is notable variation in how far back from the limbus the external entry site is between different globes, we find the surgeon’s use of human stereopsis to be the best way to assess proper sclerotomy placement (taking into consideration the optics of the peripheral cornea). A sharp blade should be used when making these incisions to minimize the potential for pushing the ciliary body centrally from the sclera. Incisions should be at least 0.8 mm in width (24-gauge size) to allow smooth passage of the 25-gauge forceps. An incision size of 0.9 to 1.0 mm for one of the paired incisions facilitates burial of the knot through the sclera.

Some surgeons prefer to use an external landmark of 1 mm behind the scleral spur, as visualized through the posterior blue edge of the limbus. This is a reasonable landmark for an incision that is perpendicular to the globe surface, but since we advocate an incision parallel to the iris, one would need to take that into consideration if using this as a landmark for incision placement. If one elects to make incisions perpendicular to the sclera, then additional attention should be paid to seal at these incision sites to minimize the potential for transient fluid flow and early postoperative hypotony.

For these procedures, a second pair of scleral incisions is created 180 degrees away from the first set, the same distance posterior to the iris. Determination of the point 180 degrees away can be done in a number of ways, including visual inspection (as in Variation 1 technique), using an axis marker, or visually splitting the cornea with the aid of a cyclodialysis spatula (as in Variation 2 technique). If the surgeon succeeds at placing all 4 incisions the same distance back from the limbus and all sutures are positioned correctly, then the resulting IOL position will be parallel to the iris, without tilt. Avoiding tilt is critical for good visual results. A tilted IOL creates marginal oblique astigmatism that comes from pantoscopic tilt. With a positive-powered lens, pantoscopic tilt induces plus-powered astigmatism, plus-powered sphere,⁷ and coma-like aberration that cannot be corrected with spectacles.

PERIPHERAL IRIDECTOMY

As discussed in the IOL section, these unicameral eyes can have marked fluid movement in an anterior to posterior direction. If the iris is intact, it can be pushed back against the IOL, causing repeated impacts with the IOL, or even capture of one side of the optic as the iris forms a valve-like seal on the IOL at the pupil. Creation of an alternate path for fluid flow readily decreases these iris movements and can prevent IOL capture. Given the large size of the IOL optic, a peripheral location for the alternate route produces the best yield; hence, a PI works for this purpose. Since the fluid flows from corneal compression are rapid, the PIs need to be of moderate size to allow adequate fluid flow. This is very different than the very small PIs needed to prevent pupillary block, where the fluid flow is at the rate of aqueous production. To minimize the potential for optical side effects of a single larger PI, we often create 2 smaller PIs just under 1 mm in size to prevent pupillary block. Routine creation of PIs in scleral-sutured IOL cases can essentially eliminate iris capture of the optic.⁸

SUTURE KNOTS AND SUTURE COVERAGE

ePTFE is a highly fluorinated, slippery material. Because of its slick nature, the manufacturer’s instructions recommend at least 7 equally tensioned throws when tying knots in this suture material. That recommendation was based on nonophthalmic work; nevertheless, we use and recommend 5 to 7 throws for the knots in this material when securing transscleral-sutured IOLs (2 wraps for the first throw, and then 1 wrap for each successive throw). A common annotation for describing a 7-throw version of the knot configuration we advocate is 2-1-1-1-1-1-1. With ample throws like this, it becomes unimportant if the last throw becomes loose or untied while burying the knot. Also, this type of knot stays rather narrow—it never gets wider than the initial 2-wrap throw—so it goes through scleral incisions more easily. Because of the length of the knot, it is advantageous to actually push the knot through the sclerotomy and swing its tail inside the sclera in addition to rotating the suture itself. Microforceps or even conventional tying forceps work well for pushing the knot through the sclera. The surgeon should be completely sure that the knot is fully buried inside the sclera because the diameter of this suture and the size of the knot could otherwise create the potential for knot erosion through the conjunctiva. We have not experienced this suture material, lying flat on the sclera, eroding through conjunctiva, except on very rare occasions where a patient has extremely inflamed and thin conjunctiva from other ocular/systemic disease.

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