BIODEGRADABLE COLLAGEN IMPLANT FOR TRABECULECTOMY

Guest author

SANA MAHREEN

Ajmal Khan Tibbiya College

Aligarh-India

INTRODUCTION

Trabeculectomy currently remains the “gold standard” for filtration surgery.

A disadvantage of this procedure is postoperative fibrosis and scarring, leading to bleb failure and rise of intra-ocular pressure (IOP).

Concern over postoperative scarring has led to the widespread intra- and post-operative use of antifibrotic agents, particularly 5-Fluorouracil(5-FU) and Mitomycin C (MMC). These agents, however, may bring an increased risk for chronic bleb leaks, hypotony, blebitis and even endophthalmitis.

One solution to this challenge may have its roots in the burgeoning field of “tissue bioengineering”.

BIODEGRADABLE COLLAGEN MATRIX IMPLANT

The biodegradable collagen matrix (BCM) implant is being marketed, depending on the country, as Ologen^TM (Aeon Astron Corporation) or iGen^TM (Life Spring Biotech Company), both based in Taipei, Taiwan.

It takes advantage of micro-technology and tissue bioengineering by having a molecular structure that permits the formation of a spongy filtration bleb without the use of antifibrotic agents.

The implant is a 3D porous scaffold made of 1% collagen/C-6-S copolymer with a pore size ranging from 20-200µ.

It measures 4x7 mm and has a cylindrical shape, allowing for easy insertion and manipulation during glaucoma surgery.

The implant encourages the formation of a spongy meshwork of fibroblasts and connective tissue in a controlled and organized pattern. It forces fibroblasts and myofibroblasts to only grow into the pores, during the early postoperative period and secrete connective tissue in the form of a loose matrix.

After the polymer scaffold biodegrades, it leaves a milieu of organized fibroblasts, myofibroblasts and extra-cellular matrix. This leads to a reduced scar formation.

The implant also maintains an elevated bleb while the healing process is underway.

In trabeculectomy, early inflammation can lead to adhesion of the conjunctiva and episcleral surface during the early postoperative phase.

SURGICAL TECHNIQUE

A conjunctival flap (limbus or fornix based) is created.

A partial thickness scleral flap is then formed.

A sharp blade is used to enter the anterior chamber at the base of the scleral flap.

A sclerostomy is created with a punch or en bloc excision, after which the scleral flap is closed with two-to-four 10-0 nylon sutures.

The BCM implant is then placed directly above the scleral flap and the conjunctiva closed as per surgeon’s preference.

RESEARCH

ANIMAL STUDIES:

Chen et al performed trabeculectomy with the BCM implant in one eye of 17 rabbits and standard trabeculectomy without anti-fibrotic agents in the fellow eye as control.

For the first 2 post-operative weeks IOP was similar in the two groups. Subsequently, the IOP decreased in the implant group as the matrix dissolved. Conversely, the IOP in the control group progressively elevated to post-operative levels.

Another study was performed in 30 rabbits undergoing trabeculectomy with the implant were compared with a control group of rabbits undergoing trabeculectomy without it.

In both groups, the conjunctiva was incompletely sutured to produce a wound leak. Although the conjunctival defect sealed equally well in both groups, IOP was significantly lower in the implant group after conjunctival healing was complete.

HUMAN STUDIES:

The BCM implant is now available in Europe and Asia.

Chen and Hsu reported the preliminary results of the experience in 12 patients. They found a 64% reduction in IOP four months after surgery. The average number of glaucoma medications also decreased from 2 to 0.3.

Ruokonen et al. reported their experience in 17 patients with open angle glaucoma. IOP improved from 30 to 14 mmHg within 3 months after surgery. The average number of glaucoma medications required decreased from 3.3 to 0.2. Eleven eyes developed bleb encapsulation with elevated IOP after 7 months. Of these some responded well to needling and 2 required further surgery to control IOP.

Another study reported the outcomes of 20 consecutive patients who underwent trabeculectomy with implant placement. After 3 months, mean IOP decreased from 33.8 to 13.3 mmHg. All patients tolerated the implant well and no systemic adverse-effects were noted.

Researchers in China studied the effects of trabeculectomy with the implant versus trabeculectomy without anti-fibrotics. The mean IOP was significantly lower in the implant group after 6 months of follow-up. The risk of bleb failure was 30% lower in the implant group.

The BCM implant is also being used in cases of combined cataract extraction and trabeculectomy. Grewel et al. studied 10 patients with POAG who were undergoing combined phacoemulsification with trabeculectomy and implant placement. At 3 months post-operatively, mean IOP had improved from 20 to 9 mmHg and the mean number of topical glaucoma medications needed reduced from 2.7 to 0.9.

CONCLUSION

The BCM implant invokes the concepts of tissue bioengineering to promote successful glaucoma filtration surgery. The implant is largely safe, easy to handle and effective in reducing IOP without any side-effects as seen with anti-fibrotic agents.

  ologen^® Collagen Matrix prevents subconjunctival, scleral and trabdoor scarring via three principal mechanisms:

1. The volume of ologen^® Collagen Matrix creates a functional bleb which maintains a physiological barrier in the subconjunctival space that prevents subconjunctival scar formation.
2. The porous structure of the collagen matrix induces random growth of the fibroblasts into the porous structure to prevent scar formation and to modulate the wound healing process.
3. ologen^® Collagen Matrix has a superior water-absorbing abilityand an excellent pliable strength. When ologen^® Collagen Matrix absorbs aqueous humor, it works like a reservoir and creates a tamponading effect on the scleral flap, which along with the use of a loose suture on the scleral flap maintains a dynamic controlled drainage of the aqueous humor outflow. These properties further prevent scar formation in the trabdoor and intra-scleral space and reduce the chances of hypotony which may be seen in trabeculectomy with the applications of anti-metabolites adjuncts before ologen^® Collagen Matrix can be applied.