The Balanced Two-String Technique for Sulcus Intraocular Lens Implantation in the Absence of Capsular Support

Purpose. To describe and explore an alternative approach for sulcus intraocular lens (IOL) implantation in the absence of capsular support. Methods. The commonly available one-piece poly(methyl methacrylate) (PMMA) lens is stabilized in the sulcus by two intraocular horizontal strings of 10/0 polypropylene suture passed through the lens dialing holes in opposite directions to achieve a mechanical balance. The horizontal strings of 10/0 polypropylene work as a rail track for the IOL optics, allowing some side to side lens adjustment even following wound closure. The stability of the IOL was tested in vitro. Six aphakic patients underwent in-sulcus IOL secondary implantation using the balanced two-string technique. Patients were followed up for a minimum of six months. Best spectacle corrected vision was assessed. Lens centration and lens tilt were measured by anterior segment optical coherence tomography (AS-OCT). Results. All patients had successful lens insertion. Best spectacle corrected visual acuity (BSCVA) improved in all patients. Lens decentration ranged between 0.21 mm and 0.9 mm (average 0.53 mm). Lens tilt ranged between 1.2° and 2.8° (average 2.17°). Conclusion. The mechanically balanced two-string technique is an alternative option for sulcus IOL implantation in absence of capsular support, allowing lens centration adjustment with no additional risks.


Introduction
In the absence of capsular support intraocular lens (IOL) implantation behind the iris plane is still possible with various scleral fixation techniques [1,2]. Globe collapse, lens decentration, lens tilt, and sutures related complications are known encountered difficulties with sclera fixated IOL (SF-IOL) [3][4][5]. Although more points of fixation allow greater stability with less risk of decentration and tilt [6], there are greater risk of complications from multiple sutures passing through the sclera and the uvea [7]. The IOL is usually fixated to the sclera via their haptics. Stability of haptic fixation was questionable and required special lens designs, haptic modifications, or adopting a technique that avoids the use of sutures for haptic fixation [6][7][8][9][10][11].
In this study, the widely available one-piece PMMA lens was stabilized in the sulcus by two 10/0 polypropylene horizontal strings. These strings were passed in a mechanically balanced way through the lens dialing holes. The technique addresses lens decentration, tilt, and sutures related complications.

Methods
The efficacy of the two mechanically balanced strings in stabilizing an IOL was experimented on a cardboard disc with two opposite peripheral holes mimicking the dialing holes of a PMMA IOL (Figure 1). A similar experiment was repeated in vitro with a PMMA lens suspended by two mechanically balanced strings of a 10/0 polypropylene suture through its dialing holes. (Figure 2). Temporal and nasal conjunctival periotomies are fashioned from 2 to 4 o' clock and from 10 to 8 o' clock. Two parallel 1/3 partial-thickness scleral  Figure 1: In vitro experiment on a cardboard disc showing disc resistance to tilt even with disc rotation. grooves 5-6 mm long are made 2 mm from the limbus (at 3 and 9 o' clock). Two rectangular scleral pockets are dissected from each scleral groove towards the cornea by a crescent knife till they reach the limbus at 3 and 9 o' clock. A 7 mm superior corneal incision is fashioned and sutured to become water tight. The straight needles of a double-armed 10-0 polypropylene suture (Alcon STJ-6) are introduced into the eye by piercing the scleral bed at the upper and the lower extremities of the rectangular scleral pocket 2 mm from the limbus. The needles are directed in the iris plane to appear

Results (Table 1)
All patients had IOL implants as a secondary procedure. Age ranged between 22 y and 73 y (mean 51 y). Two patients had aphakia because of cataract surgery with loss of capsular support. One patient had preoperative subluxated cataractous lens and had primary intracapsular cataract extraction. One patient had lens removal with a cutter and irrigation aspiration due to zonular dehiscence. One patient had a sunset subluxated IOL implanted in the bag due to zonular dehiscence. One patient had traumatic cataract with lack of capsular support.
Preoperative BSCVA ranged between 20/80 and 6/60 mainly due to irregular astigmatism caused by sutures following the primary surgery or lens displacement. Two patients had limited intraoperative bleeding during the passage of sutures. Postoperative follow up ranged between 6 and 36 months. Postoperative BSCVA ranged between 20/20 and 20/80 measured at least four months following the removal of corneal sutures. Corneal sutures were removed after 2-3 months. All patients gained BSCVA. Lens decentration ranged between 0.21 mm and 0.9 mm (average 0.53 mm). Lens tilt ranged between 1.2 ∘ and 2.8 ∘ (average 2.17 ∘ ). There were no other complications or a need for another intervention.

Discussion
Variable approaches for scleral fixation are described in literature with common documented difficulties: lens tilt, decentration, and sutures related complications [2,4,8,12]. In most scleral fixation techniques lens haptics are fitted directly to the sclera. That is why once the haptics are fixated, lens readjustment can be quite difficult. In this work, the IOL is suspended in the ciliary sulcus through its optics by two horizontally placed strings passing through the lens dialing holes. The two mechanically balanced strings prevent lens tilting as proved by the in vitro experiment. Vertical and horizontal centration of the IOL is dependent in one plane on accurate symmetrical location of the suture entry sites, but it can be adjusted along the parallel sutures in the orthogonal plane, which is a potential advantage. The scleral entry and exit sites can be precisely determined because the direction of scleral penetration is always from the outside to the inside. The two polypropylene strings are in fact a single loop and require only one knot that can be sutured and secured adequately enough to the bed of the scleral pocket under proper tension. The polypropylene suture is placed isolated from the subconjunctival space within the scleral pocket to avoid producing a track for infection. In comparison to the standard use of scleral flaps for other SF-IOL techniques, a scleral pocket would not require suturing. Scleral collapse during IOL suturing is managed by frequently reforming the intraocular pressure, which is helped by the temporary corneal stitches. Using the commonly available one-piece PMMA lens is an advantage. No lens modification is required. There is also no need to keep special lens design in stock which can be difficult to keep in most ophthalmic theaters.
The main difficulties with this technique are that it requires an attentive skillful surgeon, who should pay utmost care for choosing the proper site and direction of needle insertion, guard against sutures entangling, and adjust string tension on a reformed globe. Too tight loop may lead to cheese wiring and too lax loop would cause lens sagging. This technique also requires a 7 mm wound for PMMA lens insertion and consequently wound sutures, which can induce astigmatism.
Visual results are comparable to other reported SF-IOL techniques [1][2][3][4][5][6][7][8][9][10][11][12]. The degree of lens tilt and decentration were comparable to in-the-bag IOL lens implantation [13]. AS-OCT was used in this study to measure IOL tilt and decentration. IOL periphery is usually obscured by the iris in AS-OCT images. The IOL surface curvature angles were determined by geometrically blotting IOL periphery along the well determined central IOL surface curvatures. The IOL surface curvatures angles may not match precisely the actual lens edges but would have a symmetrical relation to them on both sides of the AS-OCT images. Deduction of the right and the left segments from each other would provide a precise measurement for IOL decentration. The ICA-line was determined on the vertical and horizontal meridians and was correlated to a reference scleral spur line or limbus line. This measurement technique provides precise IOL planerepresenting line suitable for different lens edge designs.
Suture break was reported in literature to occur long time after the surgery. The use of a more durable suture material like polytetrafluroethylen (Gore-Tex) or a thicker (9-0 instead of 10-0) polypropylene suture material would be a safer option and was suggested by some authors [12,14].
This work sheds light on an alternative technique to implant one-piece PMMA IOL in the absence of capsular support that may be of value in certain surgical circumstances.