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A Replacement for Antimetabolites?
Ologen is a new product that modulates wound healing in glaucoma surgery.
For many years now, ophthalmologists have used antimetabolites such as mitomycin C (MMC) and 5-fluorouracil to modulate wound healing in glaucoma filtering surgery. These agents, however, can cause many complications, including hypotony, wound leaks, and endophthalmitis. A new collagen matrix implant for wound modulation may reduce these problems.
BACKGROUND
Surgeons in Asia and Europe have used collagen
matrix for several years. In the United States, Canada,
Central and South America, and South Africa, the
product is sold as Ologen Collagen Matrix Implant
(Optous, Roseville, CA), which was approved by the
FDA in August 2009. I have had the opportunity to use
the implant for the past several months in patients of
various ages and races, mostly with primary open-angle
glaucoma. This artificial porcine extracellular matrix is
made of atelocollagen cross-linked with glycosaminoglycan.
Ologen is a biodegradable scaffolding matrix
that induces a regenerative wound healing process
without the need for antifibrotic agents. The surgeon
places the device over the scleral flap during the filtering
procedure.
It is well known that episcleral fibrosis and subconjunctival scarring are the major causes of failure in glaucoma filtering surgery. Collagen matrix is designed to prevent such scarring. Specifically configured to facilitate the repair of connective and epithelial ocular tissue, the implant is designed to minimize the random growth of fibroblasts and instead promote their growth through the pores in the matrix. Ologen is biodegradable in 90 to 180 days.
The efficacy of collagen matrix has been demonstrated in animal models.1-3 Chen and colleagues performed standard trabeculectomy on 17 rabbits, with their left eye receiving the collagen matrix implant and their right eye serving as surgical controls. During the first few days, the postoperative reduction in IOP (15%) was equal in both groups. Pressure had decreased to 55% below baseline values at day 28 in the treated eyes but had returned to preoperative levels by day 21 in the control eyes. Histological examination showed a prominent bleb in the treated eyes compared with scarring and limited bleb formation in the control eyes.2
TECHNIQUE
Guarded filtering surgery is performed based on the
surgeon’s preferred technique. One can make either a
limbus- or a fornix-based conjunctival incision. The
main surgical change is in the closure of the scleral flap.
With trabeculectomy, many ophthalmologists prefer to
place several tight sutures to prevent early hypotony.
With Ologen in place, it is better to tie the sutures
loosely in order to encourage aqueous flow.
After tying the sutures, the surgeon places the collagen matrix over the scleral flap (Figure 1). No suture is required to secure the implant, and as soon as it touches the sclera, it absorbs aqueous and molds to the scleral tissue. Collagen matrix therefore need not be presoaked or prepared in any way.
Ologen currently comes in two sizes for glaucoma filtering surgery: 6 X 2 mm and 12 X 1 mm. The numbers 6 and 12 refer to the diameter of the round implant, and the numbers 2 and 1 refer to its thickness. I have used both sizes of the device with good success. I have been able to place the larger version through a 4-mm limbal incision with my fornix-based conjunctival wounds. The process does require some manipulation, however, and I have had to fold the implant slightly for insertion and then tease it flat (Figure 1). In my experience, the 6 X 2-mm device is much easier to place over the scleral flap with a small limbal incision because of the implant’s greater thickness and smaller diameter, but it can be more difficult than with the larger implant to visualize the sutures for laser suture lysis during the postoperative period. With a limbus-based conjunctival flap, I have found that no manipulation is required at all because of the large exposure afforded by the larger posterior wound in the fornix. Both sizes of the implant can be used with either type of conjunctival wound, and the surgeon’s comfort and experience over time will help dictate his or her preferred size.
After the collagen matrix’s placement, the surgeon closes the conjunctiva in his or her usual meticulous fashion to ensure that the wound is watertight.
POSTOPERATIVE COURSE AND
APPEARANCE OF THE BLEB
I am waiting until I have longer follow-up data before
requesting my institutional review board’s permission to
research my results in a systematic fashion. I can, however,
report that the blebs are not avascular in the eyes
in which I have implanted the collagen matrix, even 4 to
6 months postoperatively (Figures 2 and 3). Although
the period of observation is short, more than 100 patients
of mine who have received the collagen matrix prior to the writing of this article have maintained low
IOPs without medication, just like my patients who
have received intraoperative MMC.
During my first several cases, I was concerned that I would not be able to visualize the sutures through the collagen matrix, so I placed the collagen matrix on the posterior edge of the flap. Since then, I have found that I can see the sutures through the implant if I press firmly with a Blumenthal Suturelysis lens (Volk Optical, Inc., Mentor, OH). I now therefore place the collagen matrix directly over the flap, which probably allows for better wound modulation. Moreover, the collagen matrix helps to limit hypotony through a tamponading effect over the scleral flap. I have observed the presence of the collagen matrix under the conjunctiva even 5 months after surgery, but the implant does thin as it biodegrades (Figure 4).
ADVANTAGES
Currently, Ologen retails for $250 a unit, but with an
order of 10 or more devices, the company reduces the
price to $200 per unit. Although collagen matrix is
more expensive than MMC (by $100 or more), I believe
that the former offers several advantages.
First, not using antimetabolites saves a significant amount of time intraoperatively. In my experience, each case is at least 5 minutes shorter, and the nurses do not have to take time for the special handling and disposing of an antimetabolite. On a high-volume surgical day, the time saved with collagen matrix can allow me to perform more surgery (one or two cases) during my allotted time in the OR. If I do not have additional cases, the ASC saves money by being able to send the nursing staff home early. The cost of health care is a pressing issue and demands thoughtful analysis. For example, in a retrospective, consecutive, comparative case series, investigators found that using fibrin glue to secure the patch graft and to close the conjunctiva after glaucoma drainage device surgery saved 10 minutes compared with the use of sutures. They calculated a cost savings of over $389 for every case.4 Using their calculations, I estimate that reducing surgical time by 5 minutes by using collagen matrix at the same institution would save over $100 a case, when the cost of the collagen matrix and the need for no MMC are taken into account.
Second, unlike with antimetabolites, collagen matrix need not be special ordered, and there is no risk of a shortage, as recently occurred with MMC. Instead, collagen matrix can be ordered like any other implant, and its shelf life is 2 to 3 years.
Third, because the collagen matrix is not a teratogen like MMC, the former may be used for pregnant patients, and a pregnant member of the OR staff will not have to excuse herself during the procedure. The practice at my ASC has been not to schedule pregnant staff members with glaucoma surgeons, so I lost one of my most experienced scrub technicians for 9 months last year.
DISADVANTAGES
To date, even with the Blumenthal Suturelysis lens,
laser suture lysis has been difficult in a few cases. I was
unable to visualize any sutures in one eye with a Tenon’s
cyst, and I needed a 27-gauge needle to break what
sutures I could without no visibility of the flap. After the
needling and digital pressure, the IOP decreased nicely. I
have switched to using the 12 X 1-mm implant, which
seems to have reduced the problem. The thinner implant
can be more difficult to place than the 2 X 6-mm collagen
matrix, however, and careful dissection of the posterior
space under Tenon’s capsule is necessary.
I do not recall any other postoperative problems in my patients who received collagen matrix. I was concerned at first, however, that tying the sutures more loosely after trabeculectomy would lead to a higher incidence of hypotony. Thankfully, this has not been the case.
The cost of the collagen matrix may be an issue for some surgeons, regardless of the possible cost savings of a more efficient OR day.
CONCLUSION
Driven largely by surgeons’ desire to lower IOP more
safely and efficiently than by standard trabeculectomy
with MMC, an exciting period of innovation in glaucoma
surgery is underway. The use of collagen matrix in
glaucoma filtering surgery is the most recent such
development. I have found this device to be safe and
effective in the short term, and it may help to reduce
costs, improve efficiency, and increase surgical volume.
Clearly, a prospective, randomized trial comparing
MMC with collagen matrix is warranted. If time and further
study demonstrate that the device offers improved
safety (ie, fewer cases of bleb leaks and endophthalmitis)
compared with antimetabolites, it is possible that
glaucoma surgeons will come to rely on collagen matrix
for wound modulation after filtering surgery.
Steven R. Sarkisian, Jr, MD, is a clinical assistant professor at The Dean A. McGee Eye Institute of the University of Oklahoma in Oklahoma City. He is a consultant to Optous. Dr. Sarkisian may be reached at (405) 271-1093; steven-sarkisian@dmei.org.
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