The Foldable Capsular Vitreous Body (FCVB) is a vitreous replacement device developed in 2008 at the Zhongshan Ophthalmic Center, Sun Yat-sen University, China 1).
FCVB consists of the following three components 1):
The capsule has pores with a diameter of 300 nm, which also function as a platform for a drug sustained-release system (DDS) 1). The device is inserted into the eye in a folded state and expanded by injecting BSS (balanced salt solution) or silicone oil. Currently, clinical exploration is underway in China and several European countries 1).
The main indication is severe monocular eye disease with no prospect of visual recovery, with the primary goal of preserving the eyeball 1).
Currently, it is in the clinical exploration stage in China and parts of Europe, and is not approved in Japan 1). Receiving treatment in Japan is currently not possible.
The indication for FCVB is limited to severe cases that are difficult to manage with existing vitreous substitutes 1).
Other candidates may include perforating/penetrating trauma, silicone oil-dependent eyes, severe proliferative vitreoretinopathy (PVR), and high myopia.
Silicone oil (SO) has been used for many years as a vitreous substitute for refractory retinal detachment. However, SO has the following serious complications1).
FCVB has the following advantages compared to SO.
Omnidirectional support
360-degree arc pressure: The solid strength of the capsule provides arc pressure from all directions to support the retina.
Difference from SO: SO provides only superior support via surface tension. FCVB can handle retinal detachment in all directions, regardless of orientation 1).
Emulsification prevention
Capsule membrane barrier: SO is sealed inside the capsule, physically preventing emulsification, anterior chamber invasion, and tissue migration 1).
Long-term stability: SO-filled FCVB has higher hydrolytic stability than BSS-filled FCVB, making it advantageous for long-term placement 1).
Postoperative management
No positioning restrictions: Due to 360-degree support, there is no need to maintain a specific posture after surgery 1).
Intraocular pressure adjustment: The valve mechanism allows adjustment of intraocular pressure by injecting or draining the contents.
Note that the refractive change with BSS-filled FCVB is about -0.338 D, which is smaller than the approximately +8.71 D (model eye measurement) with SO filling.
FCVB supports the retina from all directions with 360-degree arc-shaped pressure, so there is no need to maintain a specific posture like with SO1). However, postoperative rest should follow the surgeon’s instructions.
The main structural parameters of FCVB are shown below.
| Structural Element | Specification |
|---|---|
| Capsule Thickness | 30 μm |
| Material | Modified liquid silicone rubber |
| Pore Size | 300 nm |
| Axial Length Compatibility | 16–28 mm (custom) |
Surgery is performed according to the following steps1).
FCVB removal is possible through a 2 mm sclerotomy and can be performed with relatively low invasiveness when necessary1).
An overview of clinical studies to date is provided below.
| Study (Year) | Subjects | Main Results |
|---|---|---|
| Lin 2011 | 11 cases of severe RD | 3-month follow-up: assessed as flexible, effective, and safe1) |
| Lin 2012 | SO-filled FCVB | 1-year follow-up: good. SO filling is more inert than BSS filling1) |
| Lin 2016 | SO-filled FCVB | 3-year follow-up: effective. No SO emulsification or migration1) |
| Zhang 2019 | 20 cases, 1-year follow-up | All eyes well supported. Retinal reattachment in 6/20 eyes. No BCVA improvement1) |
In the 20-case 1-year follow-up study by Zhang et al. (2019), good ocular support with FCVB was achieved in all cases. Anatomical retinal reattachment was confirmed in 6/20 eyes (30%). Mean intraocular pressure stabilized from 12.90±7.06 mmHg preoperatively to 15.15±3.36 mmHg postoperatively. Complications included corneal disease in 1 eye and intraocular inflammation in 1 eye, but no SO emulsification was observed in any case. No improvement in BCVA was obtained1).
Case 1 (31-year-old male, hockey puck injury): After FCVB implantation, BCVA maintained light perception, and intraocular pressure stabilized at 10–15 mmHg. Corneal opacity and anterior chamber exudative membrane appeared at 9 months postoperatively, but the eye was successfully preserved1).
Case 2 (34-year-old male, iron plate trauma 10 years ago): BCVA remained unchanged with no light perception before and after surgery, but intraocular pressure improved and stabilized at 12 mmHg. One month after surgery, intraocular hemorrhage decreased, and the FCVB remained clear. Eye preservation was successful1).
The following complications related to FCVB have been reported1):
The main purpose of FCVB is to preserve the eyeball, not to restore vision. In existing reports including a 20-case follow-up study by Zhang et al. (2019), no improvement in BCVA has been observed 1). It is important to confirm with the attending physician before surgery regarding the possibility of vision recovery.
Silicone Oil
Support principle: Supports the retina by contacting it through surface tension.
Direction dependency: Since SO is lighter than water, buoyancy acts upward. Effective support is obtained only in the upper part, and postural restrictions are necessary for inferior lesions 1).
Emulsification risk: Emulsification occurs over time due to mechanical forces and eye movements, leading to anterior chamber infiltration, trabecular meshwork obstruction, and glaucoma 1).
FCVB
Support principle: Supports the retina with 360-degree uniform arc-shaped pressure due to the solid strength of the capsule.
Direction independence: It can handle RD in all directions, and no postoperative postural restrictions are required 1).
Emulsification prevention: The capsule membrane encloses the SO, functioning as a cellular barrier that prevents emulsification, anterior chamber invasion, and tissue migration 1).
The refractive change with BSS-filled FCVB is as small as approximately -0.338 D, which is significantly different from the hyperopic shift of about +9.30 D with silicone oil tamponade. This refractive neutrality is one of the important advantages of FCVB.
Silicone oil-filled FCVB is reported to have higher hydrolytic stability compared to BSS-filled FCVB, and can suppress long-term degradation of the capsule membrane 1). From the perspective of managing phthisis bulbi (ciliary body dysfunction due to repeated surgery and chronic inflammation leading to ocular atrophy), long-term stability is also an important factor.
Research on drug sustained-release systems using the 300 nm diameter pores in the FCVB capsule is actively being conducted 1).
The main research results are shown below.
| Drug | Reporter (Year) | Target |
|---|---|---|
| Dexamethasone sodium phosphate | Liu (2010) | Inflammation suppression |
| Levofloxacin | Jiang (2012) / Wang (2013) | Intraocular infection / severe endophthalmitis model |
| siRNA-PKCα | Chen (2011) | Downregulation of PKCα in retinal pigment epithelial cells |
| 5-Fluorouracil | Zheng (2012) | PVR suppression |
These studies are at the animal experiment and cell experiment level, and clinical application in humans has not been established1). By using FCVB as a sustained-release drug reservoir, it is expected to realize a new treatment concept that simultaneously performs vitreous replacement and postoperative drug therapy.
Research combining FCVB with hydrogel materials is also progressing1).
Currently, most studies are single-center, small-sample, and retrospective; large-scale prospective multicenter comparative studies are needed to establish the efficacy and safety of FCVB 1). Regulatory approval reviews in Japan and other countries will also be important future tasks.
Animal experiments on sustained drug release using the 300 nm pores in the FCVB capsule have been reported 1). Sustained release experiments with dexamethasone, levofloxacin, siRNA, 5-fluorouracil, etc., have been conducted, but all are at the animal or cell experiment stage, and clinical application in humans has not been established.
