Toxicities and Potential Complications of MMC
Although MMC has shown promising results in treating ocular disease, there are a variety of potential complications to consider. In pterygium surgery, complications reported include: corneal edema, corneal perforation, scleral stromal necrosis with possible infectious scleritis, secondary glaucoma, corectopia, iritis, cataract, and endophthalmitis.76,77,78,79,80,81 Safianik et al.79 documented two cases of scleral melt and one case of limbal perforation with iris incarceration after using 0.02% MMC for 3 minutes for pterygium surgery. These patients ultimately required a tectonic graft in the case of the limbal perforation, and conjunctival grafts for the scleral melts. Rubinfeld et al.78 documented the possible complication of developing secondary iritis after pterygium surgery with postoperative 0.04% MMC drops 4 times a day. In another case in this series, a patient developed a scleral melt that led to a peaked pupil toward the side of the lesion.78 Importantly, MMC has been associated with scleral necrosis decades after exposure, and therefore continued and regular follow-up of these patients is necessary.
MMC use in ocular surface surgeries has also been associated with endothelial cell loss. Bahar et al.77 reported that employing intraoperative 0.02% MMC for 2 minutes in pterygium surgery resulted in an endothelial cell loss of 6% at 1 month after surgery, while no significant endothelial cell loss occurred in the control group. Avisar et al.76 reported that employing 0.02% MMC for 5 minutes during pterygium surgery can lead to endothelial cell loss of 21.05%±3.2% at 3 months after surgery. In the case of epithelial downgrowth, Yu et al.70 reported a 13.3% decrease in endothelial cell density following the use of 0.0002 mg/mL MMC for 5 minutes. MMC usage in PRK has also been linked to endothelial cell loss. Some studies have reported that employing 0.02% MMC for 10-50 seconds correlated to a statistically significant decrease in endothelial cells compared to PRK alone.82,83 However, the vast majority of studies regarding this potential toxicity report no statistically significant change in endothelial cell density when employing MMC with PRK.54,84,85,86,87,88,89 Even studies with a larger number of subjects and longer follow-up periods did not find any correlation, suggesting a favorable safety profile with minimal, if any, risk of endothelial cell loss when employing MMC with PRK.84,85
Endophthalmitis after pterygium surgery with MMC is very rare. Peponis et al.81 published a case report of a patient who developed endophthalmitis following the use of 0.02% MMC for 1 minute. In this case, the subject had a scleral melt 21 days after surgery with fungal endophthalmitis (Fusarium species). The patient was treated with antibiotics and antifungals, vitrectomy, scleral patch, tectonic graft, and finally enucleation.81 Yi et al.90 presented another case in which the subject developed endophthalmitis with Serratia marcescens which was treated with vitrectomy and antibiotics. This treatment led to the resolution of the infection, but the patient developed significant vision loss. The authors suggested that the impaired scleral barrier after surgery with MMC and the patient’s immunosuppressed state may have played a role in the infectious process.90
MMC use in the other aforementioned applications has a less severe complication profile. MMC employed for OSSN has a risk of allergic reaction, epithelial surface toxicity, punctal stenosis, and limbal stem cell deficiency. These are managed with topical steroids, artificial tears, and punctal plugs.91 Conjunctival hyperemia and lacrimation are well documented, in addition to delayed epithelial healing.92,93 MMC use for PAM and melanoma may lead to keratoconjunctivitis, corneal abrasion, pannus, and corneal haze.44 To minimize the risk of complications as a result of MMC, it may be beneficial to limit exposure times and use lower concentrations.10,19,20