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Intra-Tenon’s injection of MMC during trabeculectomy improves dose control, management
The technique appears to provide results that are at least equivalent to those of standard MMC sponge method.
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One of the abstracts presented at the recent meeting of the American Glaucoma Society generated a lot of buzz among the glaucoma surgeons present: the technique of intra-Tenon’s injection of mitomycin C at the time of trabeculectomy. The retrospective study presented by Michele C. Lim, MD, from UC Davis, showed improved IOP control and fewer glaucoma medications sustained to 3 years after surgery, with no difference in adverse events.
At the UPMC Eye Center, we have employed this technique for the past several years for trabeculectomy as well as during implantation of the Ex-Press glaucoma filtration device (Alcon Laboratories). Indeed, although not routinely practiced, intra-Tenon’s injection of MMC is also not a completely novel idea. I will describe briefly the application of this technique in my own practice.
Injection application
I prefer to inject before the full surgical prep to allow several minutes for the MMC to diffuse and bind within the tissue before opening my fornix-based peritomy. Our compounded MMC arrives from the hospital pharmacy at a concentration of 0.2 mg/mL (a concentration commonly used with the standard sponge technique) and is further diluted using 2% lidocaine with epinephrine in the operating room. I then dilute the MMC to the desired concentration, typically 0.05 mg/mL for older patients with thinner conjunctiva at higher risk for postoperative hypotony vs. 0.1 mg/mL for younger patients.
After topical tetracaine and several drops of 5% Betadine on the ocular surface, I then inject 0.1 mL to 0.2 mL of the diluted MMC into the superior intra-Tenon’s space using a 30-gauge needle on a tuberculin syringe. The needle is inserted as posterior from the superior limbus as possible, typically 8 mm to 10 mm from the future trabeculectomy site, and advanced so that the tip is overlying the surgical sclera. This is usually accomplished by initially advancing parallel to and then toward the limbus. Care is taken during the injection not to hydrodissect the conjunctiva all the way to the limbus. Usually, the patient can provide adequate exposure by infraducting his or her eye by holding a wire lid speculum in place, although a bridle suture is occasionally required.
Ian Conner
While holding one Weck-Cel (Beaver-Visitec International) flush against the perilimbal conjunctiva to prevent anterior migration of the MMC, I use a second Weck-Cel to gently massage the bleb of diluted MMC nasally, temporally and superiorly. The goal of this step is to diffusely spread the MMC along the entire area of the scleral flap and desired postoperative bleb, but to avoid, if possible, the perilimbal conjunctiva to minimize the risk of wound leak.
After the bleb has been adequately dispersed, I irrigate the entire ocular surface with a small bottle of balanced salt solution in case of any leakage from the needle track and finally proceed with standard prep and drape. The rest of the case proceeds without any other special considerations. I do not typically re-irrigate the sub-Tenon’s space after opening the peritomy, although it would be reasonable to do so in a particularly high-risk patient.
Advantages
This entire procedure usually requires 2 to 3 minutes. It can be performed with any type of anesthesia, because the MMC is diluted with lidocaine and provides additional scleral anesthetic as it is injected. Depending on the concentration used and the volume injected, the total dose of MMC can then be calculated and recorded — 5 µg to 10 µg for older patients at higher risk of hypotony, or 10 µg to 20 µg for more typical younger patients.
The advantages of this technique are manifold, but chief among them are precise control of the MMC dose and management of MMC in the operating room. This technique limits MMC exposure to only the intended treatment tissue, which in turn is exposed to a much lower concentration than is typical in the traditional sponge technique (using 0.2 mg/mL to 0.4 mg/mL directly applied to sclera and Tenon’s tissue).
Anecdotally, we have observed a lower incidence of tense or ischemic blebs after beginning to use this technique. There may be a time savings as well, although this is likely insignificant for all but the fastest surgeons.
In conclusion, this technique appears to provide at least equivalent, and possibly superior, results compared with the standard MMC sponge method. Adverse events appear to also be equivalent, although long-term management of blebs treated with MMC has demonstrated that many of the most-feared complications, including hypotony, bleb leak, blebitis and endophthalmitis, can present years after the initial surgery.
Most attractively, intraoperative administration, dosing and MMC disposal are simplified for the surgeon and OR staff.
Please feel free to contact me with your comments or questions. I sincerely hope that this description helps you in your own practice.