I read with great interest article by Khakshoor and associates in the recent issue of The Journal. The authors evaluated and compared the recurrence rates and complications between 2 therapeutic methods for primary pterygium: subconjunctival injection of mitomycin C (MMC) 1 month before bare scleral excision and conjunctival rotational flap with intraoperative MMC use. They injected 0.1 mL 0.02% MMC solution sublesionally via a 30-gauge insulin syringe and along the limbus at the site of pterygium overgrowth over the cornea. One month after MMC injection, the patients underwent bare sclera excision of the pterygium. They examined the patients at all visits with special focus on probable complications such as dellen formation, persistent corneal epithelial defect, recurrence, and scleral necrosis. The authors concluded that subconjunctival MMC seems to be an effective treatment for this condition.
I acknowledge that the technique used and results of the study are very impressive. However, the study focused on the ocular surface toxicity of this potent antimetabolite, and I would like to attract draw readers’ attention to another aspect of subconjunctival MMC application. I am concerned regarding subconjunctival injection of MMC into a closed and restricted space under pterygium tissue. In this method, it is not possible to use copious irrigation of exposed tissues under conjunctiva. This procedure can cause accumulation of MMC in the subconjunctival space. Thus, the solution including MMC can contact or seep into episclera and sclera. Then, MMC can penetrate into deep intraocular tissues. Also, I had previously shared my concerns on this very important point.
The toxic effects of subconjunctival MMC on ciliary body of rats recently were reported. In this study, 0.2 mL 0.4 mg/mL MMC was injected subconjunctivally 2 mm posterior to the corneal limbus. One month after the injection, flattening of epithelial cells, marked irregular cell surface, enlargement of intervilli spaces, pyknotic nuclei, and electron dense cytoplasm were observed in electron microscopy of the ciliary body epithelium. Besides its known effect on the conjunctiva, the authors concluded that subconjunctival antimetabolite MMC can penetrate the sclera and can exert toxic effects on the epithelium of the ciliary body, even in low doses. In addition, the authors cited several references with regard to pathologic or toxic changes in the ciliary body as a consequence of subconjunctival administration of MMC. Similarly, Mietz and associates reported that even a low concentration and volume of subconjunctival MMC can have adverse effects on the ciliary body. Overall, subconjunctival MMC can decrease production of aqueous humor by the epithelium of the ciliary body.
Although the 1-year follow-up reported by the authors is reassuring, the intraocular pressure level was not measured at follow-up visits after MMC injection, and I think this is a limitation of the study. Because of the possible toxic intraocular affects of subconjunctival MMC, reports concerning safety with larger numbers of patients and longer follow-up is desired.