Canabrava et al. recently introduced the concept of using 5-0 polypropylene haptics taken from a 3-piece intraocular lens (IOL) to perform fixation of the capsular bag in a patient with traumatic zonular dialysis.1 In the next step, Canabrava et al. further modified the technique using a 5-0 polypropylene suture instead of an IOL haptic together with a 26-gauge needle.2 Finally, Canabrava et al. developed the four flanged IOL for scleral IOL fixation in aphakic patients applying a 6-0 polypropylene suture and a 29-gauge needle.3 Mahler et al. presented a modified technique for the same IOL type, the Akreos AO60 (Bausch & Lomb, Inc.), engaging a 6-0 polypropylene suture and a 30 gauge needle.4 Moreover, Mahler et al. showed a scleral fixation technique for subluxated 1-piece IOLs using a 6-0 polypropylene suture and a 30-gauge needle.5 At the same time, Assia et al. demonstrated techniques for scleral IOL fixation applying a 6-0 polypropylene suture and a 27-gauge needle.6,7
Flange size is critical for all those techniques: A too small flange may slip through the scleral tunnel and a too large flange may remain outside the scleral tunnel and later erode through the conjunctiva resulting in a risk for endophthalmitis. We describe a technique that can be used with polypropylene sutures to get an optimal flange size fitting each scleral tunnel size.
We tested 5-0 polypropylene and 6-0 polypropylene (both Ethicon, Johnson & Johnson Vision) sutures in a dry laboratory setup to achieve the optimal flange size. An optimal flange size is the size of a flange that is just above the size of the outer diameter of the scleral tunnel created by the needle used for inserting the suture. An optimal flange size meets two criteria: First, the flange is big enough not to slip through the tunnel. Second, it is small enough to be buried in the scleral tunnel to prevent eroding through the conjunctiva. Polypropylene sutures were heated using a cauter (Accu-Temp Cautery, Beaver-Visitec International) holding the forceps close to the end of the intended heating length. In addition, polypropylene sutures were heated without the use of a forceps. Moreover, to test material properties, polypropylene sutures were squeezed with the forceps at the end and then heated.
For the analysis of flange shape and size, the polypropylene sutures were observed in reflection mode by circular differential interference contrast using an optical upright microscope (Axio Scope.A1, Carl Zeiss Meditec AG) equipped with a x5 EC Epiplan Neofluar HD differential interference contrast objective. A compact CCD monochrome camera (Lumenera Corp.) recorded 1392 × 1040 pixel images with a resolution of 1.3 μm/pixel.
Heating of 5-0 polypropylene with and without forceps grip showed no difference in size and shape of the flange (Figure 1). Similarly, heating of 6-0 polypropylene with and without forceps grip showed no difference in size and shape of the flange (Figure 2). However, the forceps grip using minimal force produced microtrauma, that is flattening, of all sutures (Figures 1 and 2). Heating of 5-0 polypropylene sutures resulted in flanges of bigger size than heating of 6-0 polypropylene sutures. Heating length and flange size were directly proportional (Figure 3). Applying maximal force with the forceps created a flat end of the polypropylene sutures but did not influence the size of the flange after heating (Figure 4).
Unlike flanging of poly(methyl methacrylate) (PMMA) haptics, flanging of polypropylene sutures behaves in a similar fashion to that of polyvinylidene fluoride haptics, independent of whether gripped with forceps.8 Suboptimal flanging may cause complications such as endophthalmitis as previously reported.9,10 Therefore, we calculated the linear least square line for flange size and heating length of 5-0 polypropylene and 6-0 polypropylene sutures (Figure 3). Afterward, we estimated the optimal heating length for each technique considering the outer diameter of the recommended needle (Table 1).
Table 1. -
Optimal heating length for each technique
||Polypropylene (U.S.P. size)
||Needle thickness (gauge)
||Optimal heating length (mm)
|Assia primary IOL fixation
|Assia subluxated IOL fixation
|Mahler modified Canabrava
Iglicki et al. showed for flanged haptics that using a 30-gauge needle is more predictable and resulted in less complications compared with a 27-gauge technique.11 The risk profile may be similar for flanged polypropylene sutures favoring a technique with 6-0 polypropylene sutures and a 30-gauge needle.
We were not able to produce conic flanges like in PMMA and in polyvinylidene fluoride haptics.8 A continuous increase in diameter like in a conic flange might be more advantageous than an abrupt increase like the flange in polypropylene sutures (Figures 1, 2, and 4) providing better hold in the scleral tunnel and less leakage to the subconjunctival space. Further research is needed to evaluate which shape of the flange is most advantageous.
2Assia et al. and Canabrava et al. used polypropylene sutures from Ethicon.2,3,6,7 It is unclear which brand of polypropylene sutures Mahler et al. applied because it is not mentioned in his articles.4,5 We tested polypropylene sutures from Ethicon. Results might be different in other polypropylene brands. However, we do not expect much difference in other polypropylene brands because the material should be similar.
This was a dry laboratory study. Therefore, it is lacking the ability to fully account for scleral properties and other variables. To calculate the variance of the outer diameter of 30-gauge and 27-gauge needles, we measured the outer diameter of 10 randomly chosen 30-gauge needles (Messo-relle, Biotekne SRL) and 10 randomly chosen 27-gauge needles (Sterican, Braun GmbH) from the manufacturer's box with an electronical digital micrometer and optical microscope. The variance was 0.43 μm for 30-gauge needles and 3.61 μm for 27-gauge needles. These results show that the variance of outer needle diameter can be neglected for those manufacturers. We did not measure the outer diameter of other manufacturers' needles. However, we would like to emphasize the importance of creating a long scleral tunnel as described by Canabrava et al. to avoid endophthalmitis and late internalized flanges.12,13
In summary, we recommend using the heating length as depicted in Table 1 to achieve the optimal flange size for each specific polypropylene suture technique. In general, the optimal flange size for a 27-gauge needle tunnel requires 1 mm heating of a 5-0 polypropylene suture. The optimal flange size for a 30-gauge needle tunnel requires 1 mm heating of a 6-0 polypropylene suture. Alternatively, 2 mm heating of a 6-0 polypropylene suture creates an optimal flange for a 27-gauge needle tunnel.
WHAT WAS KNOWN
- Flanged polypropylene techniques for intrascleral fixation of IOLs are increasingly popular.
- Achieving an optimal flange size of a polypropylene suture is crucial for the procedure.
- Flanges that are too small might slip through the scleral tunnel. Flanges of too large may remain outside the scleral tunnel and erode through the conjunctiva increasing the risk for endophthalmitis.
WHAT THIS PAPER ADDS
- Even small forces of forceps grip of the polypropylene suture result in microtrauma causing flattening of the suture.
- Flattened suture endings unfold during heating to standard shaped and sized flanges.
- Forceps grip does not influence the shape or size of the flange.
- How to achieve the optimal flange size is presented.
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13. Canabrava S, Pinheiro L, Chaves V, Barrientos R. Late internalized double-flanged polypropylene with canabrava technique in patient with Marfan syndrome. Eur J Ophthalmol 2022;6:11206721221092216. Epub ahead of print