Cataract surgery is one of the most frequently performed ophthalmic surgeries. Over 9.5 million procedures are performed annually worldwide. The standard technique is phacoemulsification with intraocular lens (IOL) implantation in the capsular bag.
However, residual lens epithelial cells (LECs) can proliferate and migrate on the posterior capsule postoperatively, leading to posterior capsular opacification (PCO). The prevalence of PCO is reported to be 0.3–28.4%, but with modern surgical techniques and IOL designs, it is typically below 5% 2). Treatment involves Nd:YAG laser posterior capsulotomy, which carries risks of acute intraocular pressure elevation, retinal tears, retinal detachment, macular edema, and IOL damage 1).
The Bag-In-the-Lens (BIL) fixation technique was developed to fundamentally address the issue of PCO. It was first reported in adults by Tassignon et al. in Belgium in 2002, and its application in pediatric cataracts was reported in 2007 3,4). The procedure involves creating an anterior capsulorhexis and a posterior continuous curvilinear capsulorhexis (PCCC) of the same diameter, then engaging the capsular edges 360 degrees into the groove of a dedicated IOL. In contrast to the conventional “lens-in-the-bag” (in-the-bag implantation), the concept is “bag-in-the-lens.”
The standard BIL IOL is the Morcher 89A (FCI, Germany). It is a 5 mm diameter biconvex acrylic hydrophilic lens with an interhaptic groove between two haptics perpendicular to the optic. The total diameter is 7.5 mm. It is available in spherical monofocal and toric (astigmatism-correcting) versions.
| Model | Total diameter | Indication |
|---|---|---|
| 89A (optic diameter 5.0mm) | 7.5 mm | Adult (standard) |
| 89D (optic diameter 4.5mm) | 6.5 mm | Pediatric (axial length <18mm) |
| 89F (optic 5.0mm) | 8.5 mm | Simultaneous vitrectomy |
In the conventional method, the intraocular lens is placed inside the capsular bag (lens-in-the-bag). In BIL, conversely, the incised edges of the anterior and posterior capsules are fitted into the groove of the intraocular lens (bag-in-the-lens). This allows the two capsules to fuse circumferentially, forming a barrier against proliferation of lens epithelial cells.
The BIL fixation method is applicable to all cataract cases, but it is particularly useful in the following patient groups.
After cataract surgery, residual lens epithelial cells (LECs) remaining in the capsular bag proliferate and undergo metaplasia on the posterior capsule 1). The incidence of PCO increases over time after surgery 1). The rate of Nd:YAG laser posterior capsulotomy varies widely, from less than 5% to 54% 1).
Multiple factors are involved in the development of PCO 1). Capsular contraction syndrome is a related complication, thought to be caused by metaplasia and fibrosis of residual LECs after anterior capsulotomy 2). Known risk factors include small anterior capsulotomy size, zonular weakness, pseudoexfoliation syndrome, retinitis pigmentosa, diabetes, chronic intraocular inflammation, and high myopia 2).
The prevalence of PCO varies widely by report, ranging from 0.3% to 28.4% 2). With modern surgical techniques and intraocular lens designs, it is typically less than 5% 2). When BIL fixation is performed properly, no PCO development has been observed even after 7 years of follow-up in adults.
The main steps of the surgery are as follows:
Tips for Anterior Capsulotomy
Ring caliper: Align with the center of the Purkinje reflex. Ensure the caliper is firmly pressed against the anterior capsule.
Incision size: Stay inside the caliper and aim for a slightly smaller size. Smaller is safer than oversized.
Callisto: A 5.2 mm projected digital guide can also be used.
Tips for Posterior Capsulotomy
Ophthalmic viscosurgical device (OVD): Inject onto the anterior capsule, not into the capsular bag, to appose the anterior and posterior capsules.
Posterior continuous curvilinear capsulorhexis (PCCC): Perform a posterior capsulotomy of the same size using the anterior capsulotomy as a guide.
Anterior vitrectomy: Perform only if vitreous prolapses into the anterior chamber. Usually not required.
When using a Malyugin ring, its full diameter (6.25 mm) is smaller than that of the IOL (7.5 mm), so it must be removed before IOL insertion. For severe miosis, iris hooks are easier to use.
For extensive zonular deficiency (exfoliation syndrome or traumatic cataract), the BIL technique can be applied by using a bean-shaped segment in addition to a capsular tension ring (CTR).
When using tamponade agents (gas or oil), there is a risk of iris capture. Use Morcher 89F (with a larger anterior support). If using 89A, avoid mydriasis until the tamponade agent is more than 50% absorbed (1 week for SF6, 2 weeks for C2F6, 3–4 weeks for C3F8).
In children, the capsule is more elastic and miosis is more likely, increasing difficulty. The main differences are as follows.
Since the first report in pediatric cases in 2007, multiple studies have confirmed its safety and feasibility. The incidence of visual axis opacification is 5–9%, significantly lower than conventional methods, and most cases are due to lens placement errors. However, it is performed under general anesthesia and requires an experienced surgeon.
In the BIL fixation method, the incised edges of the anterior and posterior capsules overlap and fuse 360 degrees within the intraocular lens groove. Residual LECs are confined to the peripheral capsular space, physically blocking their migration to the optical zone. Histological examination of postmortem eyes has confirmed that proliferative material is limited to the intercapsular space and the visual axis is preserved.
The BIL technique has a lower incidence of postoperative inflammation than conventional methods. The following mechanisms are considered.
Regarding secondary glaucoma after pediatric cataract surgery, the incidence rate with the BIL technique is low (1.3–8%). In contrast, the conventional method is reported to have a rate of 12–17%. The following factors are thought to contribute to the low risk.
In a 7-year follow-up by Tassignon et al. (547 patients, 807 eyes), 481 eyes without comorbidities showed improvement in mean decimal corrected visual acuity from 0.276 logMAR preoperatively to 0.012 logMAR postoperatively. No PCO occurred in any adult eye during the follow-up period. Postoperative iris capture by the intraocular lens haptic occurred in 19 eyes (2.4%), and postoperative retinal detachment occurred in 10 eyes (1.24%).
In a study of 54 eyes of diabetic patients, PCO was prevented in 100% of cases (mean follow-up 1 year). Progression of diabetic retinopathy was observed in 3 eyes, but there was no statistically significant difference in severity classification. Prevention of PCO facilitates fundus examination and contributes to diabetes monitoring.
In a 5-year follow-up study, a clear visual axis was maintained in 91.2% of cases. The incidence of VAO was 4.6–8.6%, which is significantly lower than conventional methods (PCO rate 10.8–100%). All VAO cases were due to lens placement errors.
A French study examined 36 patients (60 eyes), including 10 with Down syndrome, 5 with cerebral palsy, and 6 with autism. The BIL group showed a lower reoperation rate compared to the non-BIL group (8% vs. 14%).
A multifocal BIL intraocular lens is scheduled to be marketed. This may simultaneously achieve both distance and near vision and prevent posterior capsule opacification.
