The scleral fixation technique is an essential method for all intraocular surgeons. Scleral fixation is usually performed for complicated cataract operations, aphakia, intraocular lens (IOL) decentration, or severe ocular trauma. Since Malbran et al.1 first reported using an IOL transscleral fixation technique in an aphakic patient, the technique has been modified to reduce complications and improve outcomes.2–4
Previous reports using hydrophilic foldable IOLs show outcomes comparable to those using poly(methyl methacrylate) (PMMA) IOLs.5 However, foldable IOLs may present difficulties in IOL centration6 or develop glistenings and undergo opacification.7–12 In 2012, a hydrophobic foldable IOL with ring-shaped connecting bridges (Figure 1, A) between the haptic and the optic (enVista MX60, Bausch & Lomb) became available. Its design allows the surgeon to use the ring-shaped connecting bridges for new fixation suture sites. We introduce a new scleral fixation technique with a ring-shaped connecting-bridge IOL and compare the early clinical efficacy and safety with those of a PMMA IOL after a mathematical evaluation of the suture site.
Before IOL transscleral fixation, an anterior vitrectomy is performed. Triangle-shaped scleral flaps are made at the 8 o’clock and 2 o’clock positions in a right eye or at the 4 o’clock and 10 o’clock positions in a left eye (Video 1, available at: http://jcrsjournal.org). A double-armed 10-0 polypropylene suturing needle is inserted into the globe through the 8 o’clock sclera and anchored by a 24-gauge needle that is passed through the 2 o’clock sclera using the routine ab externo technique (insertion site 2.0 mm ventral to the limbus anterior margin). The mid-portion of the thread is pulled out through a main wound at the 11 o’clock position and then cut. Using another double-armed 10-0 polypropylene needle, the ring-shaped connecting-bridge IOL is sutured at both inner ring-shaped connecting bridges (inner shorter rim, Figure 1, D). This suture site is selected to conform to the mathematical calculations of the center-of-mass concept described below (Figure 2). A thread at the leading ring-shaped connecting bridge is passed through the IOL cartridge and the injector and then tied with the cut thread originating from the 8 o’clock sclera. The ring-shaped connecting-bridge IOL is carefully injected with gentle pulling of the thread at the 8 o’clock position. The thread at the following ring-shaped connecting bridge should remain outside the globe until it is tied to the other fixation thread from the 2 o’clock site (Figure 3, A). The externalized sutures are tied at the corresponding sites. All ties between 2 cut threads are made using a European death knot (Figure 3, B). This is done by laying the 2 ends of the threads together, pointing in the same direction. The overhand knot is made in both threads at the same time. The knot is pulled tight, leaving long tails. The main corneal wounds are 2.8 mm and 6.0 mm, respectively, when using the ring-shaped connecting-bridge IOL and a PMMA IOL (CZ70BD, Alcon Laboratories, Inc.).
This technique was performed in 25 eyes of 25 patients. All patients were followed for at least 3 postoperative months. Transscleral fixation of PMMA IOLs were performed between January 2011 and December 2012; ring-shaped connecting-bridge IOL surgeries were performed after December 2012. In patients with complicated cataract surgery, including posterior capsule rupture or zonular weakness, conversion to extracapsular cataract extraction with anterior vitrectomy was performed before the transscleral fixation. In aphakic patients, anterior vitrectomy was performed before the fixation. In patients with subluxated lenses or IOLs, lensectomy or IOL removal was performed with concomitant anterior vitrectomy. In all cases, additional pars plana vitrectomy was performed, if necessary, at the surgeon’s discretion.
The total patient population and subgroup preoperative demographics are shown in Table 1 and the preoperative and postoperative values in Table 2.
Evaluation of the Optimum Suture Site
The ring-shaped connecting-bridge IOL has 2 connecting bridges, 1 on each side between the haptic and the optic, and there are 3 possible suture sites for fixation (Figure 1; Video 2, available at: http://jcrsjournal.org). The first is at the haptic that is 2.0 mm proximal from the haptic tip (site 1, Figure 1, B). The second and third suture sites are located, respectively, on the inner (position 2, Figure 1, C) and outer (position 3, Figure 1, D) sides of the ring-shaped connecting bridges. Position 1 is similar to the traditional suture site; it is closest to the scleral fixation site anatomically. However, a lot of pressure is transmitted to the optic, haptic, and ring-shaped connecting bridges so the IOL can easily be tilted even under moderate strain. Although using position 2 produces good results under low-level strain, the IOL is rotated by relatively large pressures because the thread-pulling vector is slightly outside the midline of the center of mass, causing counterclockwise rotation. Using position 3, which is along the midline of the center of mass, results in a stable IOL even under large strain levels.
The center of mass is the unique site at which the weighted relative position of the distributed mass sums equals zero. To identify the center of mass, the half portion of the ring-shaped connecting-bridge IOL is divided into 2 regions; ie, a half optic and a haptic (Figure 2, A to C). Using ImageJ software (National Institutes of Health), the relative weight of each piece was calculated with a random multiple (a half optic = 4.402; a haptic = 1.199). The centroid of the haptic (a curved line) can be calculated by the equation below:
where r is the radius, Symbol is the angle of the curved line, and y is the distance from the center of curvature (Figure 2, B [black asterisk]).
The centroid of the half optic (a half circle) can be calculated by
where r is the radius and y is the distance from the center of curvature) (Figure 2, C [white asterisk]).
The center of mass in each half of the ring-shaped connecting-bridge IOL can be computed using measures of weight and distance and presuming that the IOL has an even thickness. The center of mass (Xc) for any number of bodies of mass (eg, m1, m2) having distances ×1, ×2 is found by the formula
As a result, the center of mass in each half piece of the IOL is proximally a quarter of the distance from the center of mass of the half optic on the straight line connecting the center of mass in a haptic and in a half optic (Xc ≒ 2.58, Figure 2, D [white ring]). These calculations showed that position 3 was the nearest of the 3 potential suture sites to the center of mass of a half IOL, so it was used as the suture site in the surgeries evaluated in this study.
We can summarize modern secondary IOL implantation methods by 4 critical factors: The IOLs used must be foldable so the surgeon does not have to widen the wound for implantation, the technique can be easily performed, the technique results in good IOL centration, and IOLs should be made of a suitable material that resists opacification and clinically important glistenings.7–12 The ring-shaped connecting-bridge IOL fulfills these requirements.
The mean refractory difference after scleral fixation with the ring-shaped connecting-bridge IOL was approximately −0.68 D; however, the refractory difference after scleral fixation with the PMMA IOL was smaller (−0.01 D). We believe the myopic shift associated with using a ring-shaped connecting-bridge IOL is primarily due to the fixation site at the sclera (ie, 2.0 mm ventral to the limbus anterior margin). Although the fixation distances of the 2 groups are similar, the anterior pulling vector is slightly more prominent with the ring-shaped connecting-bridge IOL (Figure 3, C). The PMMA IOL is also harder and more resistant to the pulling vector, and the hydrophobic acrylic ring-shaped connecting-bridge IOL may be less resistant to the same amount of force. On the contrary, Park and Lee6 suggest that long and rigid PMMA haptics might compress the ciliary tissue, the IOL might tilt, and eventually the distal portion of the haptics might be posteriorly displaced. However, the outcome of scleral fixation using PMMA IOLs in our patients was excellent and the diopter goal and preoperative SE was minimal.
Throughout the entire procedure, we used only 1 type of knotting technique, the European death knot, to attach the threads together. The European death knot is well known for canyoneering and is very secure when the 2 threads are of the same material. This knot was tight enough to pass through a scleral tunnel as well as the pathway from the sulcus to the scleral flap site. In all the cases, we thought that other knot types, such as the Fisherman’s knot or double figure-8 knot, were unnecessary and that the European death knot was a sufficient and especially simple knot for our purpose.
The greatest advantage of the hydrophobic ring-shaped connecting-bridge IOL for scleral fixation is that it eliminates issues of IOL positioning, such as postoperative IOL rotation and decentration. Suturing at the haptic midpoint is vulnerable to rotating forces for 2 reasons: (1) Of the 3 possible suture sites, the haptic suture site is positioned farthest from its center of mass. This makes the IOL susceptible to tilting by any kind of external force; eg, gravity or tension from the thread (Video 2, available at: http://jcrsjournal.org). This is similar to having less control of a baseball bat when it is held long versus the increased stability gained by holding it short. (2) We cannot be absolutely sure of the relative positions of the 2 corresponding haptics. Discordance between the 2 positions might cause IOL tilting or decentration due to IOL deformity.13 The conventional method (suturing at the haptic) is usually promising but could produce a gap between the haptic and the sulcus area, leading to IOL tilting in a rare case of ciliary body atrophy.
Using hydrophobic ring-shaped connecting-bridge IOLs for scleral fixation is very safe, and outcomes are comparable to the outcomes using PMMA IOLs. However, one should consider the possibility of myopic shift, and it is necessary to adjust the preoperative diopter goal.
What Was Known
- Modern scleral fixation requires 4 critical elements: a foldable IOL, easy technique, good IOL position, and suitable IOL material.
- Most previously used foldable IOLs were made of hydrophilic material, which can be vulnerable to IOL opacification or to IOL tilting in terms of material and shape.
What This Paper Adds
- The hydrophobic foldable IOL with ring-shaped connecting bridges allowed surgeons to fixate the IOL more firmly without IOL tilting and to be free of IOL opacification issues. The suture site at the IOL (inner rim of the ring-shaped connecting bridges) was determined using a theory of physics. This method meets the 4 critical conditions of a modern scleral fixation technique.
- Surgeons should be aware of a possible myopic shift.
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Video 1 This is the case of a patient who has an aphakic eye. Cataract surgery was performed in the left eye 30 years earlier, and the eye was left aphakic. The preoperative visual acuity was 0.1. On postoperative day 1, the corrected distance visual acuity was 0.5 without correction; the spherical equivalent was zero. Two scleral flaps were used to fixate the intraocular lens (IOL) sutures at 4 o’clock and 10 o’clock in the limbal area. A 10-0 polypropylene suture was made at each side of the medial rim of the connecting bridge. The needle of the leading side was passed through the cartridge and the injector, while the following haptic has only the sutured thread without a needle. The thread from the following side of the IOL should remain outside the globe until tied with the other fixation thread from 4 o’clock. The 2 threads are then tied and pulled from the 4 o’clock site.
Video 2 Comparison of suture sites. There are 3 possible suture sites for fixation: at the haptic, at the lateral side of the ring-shaped connecting bridge, and at the medial side of the ring-shaped connecting bridge. The first site is at the traditional suture site. It is closest to the scleral fixation site. However, a lot of pressure is exerted on the optic, haptic, and the bridge; therefore, it is easy to tilt the IOL, even with moderate strain. The second site at the lateral side of the ring showed a good result when there was a certain amount of strain. However, it rotated under relatively strong pressure because the pulling vector is slightly outside the midline from the center of mass, causing a counterclockwise rotation. At the third site, which is along the midline corresponding to the center of mass, the IOL was stable even under a large strain.