Jason Jones, MD
Implanting an intraocular lens (IOL) in the absence of capsule support is complex surgery with many different options. Techniques described include anterior chamber IOL placement, iris-sutured 3-piece posterior chamber IOLs (PCIOLs), and scleral-fixated PCIOLs. Scleral fixation can be achieved either with scleral sutures or intrascleral haptic fixation.1–5 A more recently described technique is the double-needle flanged intrascleral haptic fixation technique for placing a 3-piece IOL in the posterior chamber of an eye without capsular support. Shin Yamane of Japan introduced this concept first in 20146 and then with refinement and simplification in 2016, while winning the American Society of Cataract and Refractive Surgery Film Festival Grand Prize.7 Yamane’s technique was also published in 2017.8 This IOL placement technique permits the use of a routine PCIOL without sutures, conjunctival dissection, or glue application and has rapidly gained interest and use around the world. The elegance of double-needle intrascleral haptic fixation is due to the economy of materials and time efficiency of the procedure; however, the apparent simplicity of this technique belies subtleties that can lead to difficulty and potential complications. This chapter will describe some of the complications and challenging issues for double-needle flanged intrascleral haptic fixation.
Preparing the Eye
A thorough anterior vitrectomy is imperative to avoid entanglement of the IOL in vitreous with subsequent inflammation, potential cystoid macular edema, or retinal tear or detachment. This may be best accomplished with a pars plana entry site for the vitrector in order to adequately remove vitreous posterior to the iris. A trocar is preferred for its advantage of scleral entry without surface dissection whereas a microvitreoretinal blade would require conjunctival opening and scleral suture closure. A limbal bimanual anterior vitrectomy may risk inadequate removal of the anterior vitreous. Staining of vitreous using diluted triamcinolone acetonide will ensure complete removal of vitreous anterior to the iris due to enhanced visualization.9 If a pars plana vitrectomy has been performed at a previous surgery, then careful inspection at the slit lamp and indirect ophthalmoscopy preoperatively may allow one to forgo vitrectomy while performing a secondary IOL implantation with the double-needle intrascleral haptic fixation technique.
Marking Entry Sites and Wounds
A decentered double-needle intrascleral haptic fixation IOL can result from incorrect or asymmetric passage of the needles through sclera leading to misplacement of haptics. Several aspects of symmetry need to be respected to achieve proper orientation. The entry sites need to be oriented 180 degrees apart while centering the imaginary connecting axis on the pupil. As described by Yamane, the needle entry should be angled at 20 degrees clockwise with respect to the tangent at the entry site, and the needle should also angle 5 degrees posterior to the plane of the iris. The needle entry site should be 2 mm posterior to the limbus to allow entry into the sulcus space. Each entry site should be 90 degrees from the meridian of the main wound to optimize access to each haptic for docking.8 Some surgeons have displaced their entry sites counterclockwise by 2 mm as they feel this permits easier access to the haptics and provides a visual target for creating adequate and perhaps more consistent scleral tunnel formation. The surgeon therefore marks off 2 mm posterior to the limbus and then 2 mm counterclockwise on the conjunctiva.10 Defining the limbus can be challenging in some eyes due to a more central insertion of the conjunctiva, and this needs to be recognized by the surgeon and accounted for appropriately. This asymmetric conjunctival insertion is more likely encountered where surgeons sit temporally as the superior scleral entry site is more often affected. Achieving these ideal needle angulations is complex and not easily accomplished. Intrusion of the lid speculum, infusion line (anterior chamber maintainer or pars plana cannula), lids, or nasal anatomy may challenge approximating these ideal needle orientations. Gentian violet or methylene blue dye can be used with calipers and a Mendez or similar ring to make offset marks that provide more reliable orientation. To enhance consistency in entry site placement, it is helpful to use infusion through an anterior chamber maintainer or pars plana sclerotomy to achieve better globe tension during the passage of needles. The surgeon should observe and compensate for any displacement of surface marks due to sliding of conjunctiva over the sclera resulting in misplacement of entry sites.
If the scleral entry sites are not 180 degrees apart or the trajectory of the scleral passage is significantly different between the 2 needle tracks (eg, one tunnel is shorter with a significantly different entry angle), then the IOL optic may be decentered. Additionally, IOL tilt may result if the needle track angle with respect to the iris plane is significantly different between the 2 scleral entry sites. Decentration of the IOL optic can also occur if thermal deformation of the haptic tips consumes asymmetric haptic length and therefore shortens one haptic more than the other. Conversely, using cautery to asymmetrically shorten one haptic can adjust and compensate for asymmetry of the scleral entry orientation. After both haptics have been externalized and cauterized, the surgeon can judge how well the optic centers. This provides an option to further shorten one haptic with cautery before pushing the haptic tips down into the scleral tracks until they are flush with the surface.
Haptic and IOL Issues
Slippage of the lead haptic from the lumen of the hypodermic needle is possible, especially considering the amount of manipulation of and the forces transmitted to the trailing haptic. Additionally, the lead haptic/needle complex is no longer visualized while the trailing haptic is docked because it is posterior to the iris and the surgeon’s attention is focused on the trailing haptic manipulation. When the lead haptic is threaded far enough into the needle lumen, the curve of the haptic is deformed into the straight needle shaft, creating tension that stabilizes and more securely docks the haptic into the needle.8 After docking, disengaging and then rotating the lead needle hub onto the conjunctival surface places it out of the way with less interaction with lids, speculum, and other structures or instruments. This will reduce unintentional external manipulation of this lead needle/haptic while the second needle is passed and docked with its haptic. An alternative is to first complete the lead haptic passage by pulling the needle out and cauterizing the haptic tip before proceeding to the trailing haptic docking. This single-needle technique does risk having a more acute angulation of the trailing haptic because the IOL will rotate counterclockwise. This could result in haptic damage and temporary torqueing of the optic with potential interaction with vitreous, iris, or ciliary body.
The haptics can become damaged during insertion into the eye or manipulation into the needle lumen. Most surgeons have found that haptics made from polyvinylidene fluoride (PVDF) are very robust and resist damage. Polymethylmethacrylate (PMMA) haptics are strong but more brittle and prone to kinking and breakage during intraoperative maneuvers required for the double-needle intrascleral haptic fixation technique. With enough care, PMMA can be used but subtle irregularities of haptic deformation can easily go unnoticed because the haptics are posterior to the iris and peripheral to full visualization. Other haptic material such as Prolene (Ethicon) is probably not suitable due its flexibility. In addition to deformation of the haptic material, the surgeon needs to consider the ability to dock the haptic into the needle lumen. When testing and rehearsing outside the operating room, one may feel confident that a particular IOL and needle combination will work only to discover intraoperatively that there is much less freedom of movement when working inside the eye. Researching the availability of a 3-piece PCIOL with PVDF haptics is advisable. These IOLs are not common and may be available in country- or region-specific distribution only. For most of the world, Carl Zeiss Meditec distributes the CT Lucia 602, which has PVDF haptics, a 6.0-mm hydrophobic acrylic optic, and an overall length of 13.0 mm. This lens was formerly known as the Aaren Scientific Aaris EC-3 PAL. There are some Japanese-manufactured 3-piece IOLs with acrylic optics and PVDF haptics that may be available in some markets outside of Japan (Santen X-70, 7.0-mm optic and 13.2-mm overall length; Kowa P6NA, 6.0-mm optic and 13.0 mm overall length). Most surgeons are calculating the lens power as though it were being implanted into the capsular bag. Targeting slight myopia does provide a more acceptable refractive outcome in case the result is more hyperopic than expected, which is more likely to occur with less experienced surgeons. With greater experience, appropriate adjustment of lens power selection can be done based on historical outcomes.
The needle used to accomplish haptic passage bears importance and deserves special attention as well. Most surgeons use a thin-walled 30-gauge hypodermic needle manufactured by TSK and distributed in the United States by Delasco. The thinner wall of the needle results in a larger lumen than with most other 30-gauge needles. This allows easier haptic docking while maintaining the smallest external needle diameter in order to create a very narrow scleral track. The small 30-gauge track is important for reducing potential leakage postoperatively and to provide more friction between the sclera and haptic. Additionally, the narrower needle track requires a smaller amount of haptic bulb formation to prevent the haptic from slipping back through the sclera into the eye, causing posterior IOL dislocation. A 27-gauge needle can be used for the double-needle technique of intrascleral haptic fixation, but the larger scleral track can allow slippage of the haptic back into the eye and will require a larger amount of haptic tip deformation to prevent this complication.
Properly preparing the needles prior to starting surgery is important as well. Bending the needle at approximately two-thirds to three-fourths of its length prevents the entire needle length from entering, while providing enough length to manipulate inside the eye. This configuration also permits the first needle hub to be rotated down onto the conjunctiva (either away from or toward the surgeon, depending on the anatomy), which improves access for the microforceps to dock the trailing haptic into the second needle. The needle should be bent bevel-up to make the bevel visible to the surgeon during docking. Most surgeons find it more comfortable to work with a needle attached to a syringe. Overtightening the needle hub to the syringe must be avoided to ensure that it can easily be removed from the syringe once the haptic is docked into the needle inside the eye. After docking the haptic, a hemostat can assist with removal of the syringe if necessary by stabilizing the hub while the syringe is disengaged. Priming the needles with saline is advisable because any pressure differential can cause air bubbles to percolate into the anterior chamber and obscure the surgeon’s view.
Thermal Deformation of the Haptic
A battery-powered hand-held cautery is used to thermally deform the externalized haptic tip. Typically, these come in 2 sterile, single-use versions: high and low temperature. Either can be used, but the surgeon should know which is on the table. The high-temperature version heats quickly and therefore melts the haptic material rapidly. The patient may have an uncomfortable sensation from the heat as well. The temperature rises more slowly with the low-temperature version, and the loop filament usually does not change appearance to indicate heating. The low-temperature cautery allows more control of thermal deformation (AA04 low-temp elongated fine tip; Bovie Medical Corp). With either version, it is imperative not to touch the haptic tip with the loop filament. Instead, first generate heat in the cautery filament and then approach the haptic tip while holding it above the conjunctival surface. Radiating heat surrounding the cautery filament causes noncontact thermal deformation that can be observed and controlled. The haptic tip will deform into a mushroom-like configuration. Continued heat application will shorten the haptic while the bulb enlarges slightly more. Intentionally shortening the haptic can be used to titrate to some degree the centration of the optic before the haptics are embedded back into the sclera.