Preoperative subconjunctival injection of mitomycin C as an adjunctive treatment 24 hours before excision of primary pterygium.

Sir,

We read the article by Ghoneim et al.1 with keen interest and have the following comments:

Recurrence of pterygium is the most enigmatic complication of pterygium surgery. The bare sclera technique is associated with a recurrence rate of 37% to 91%. Subconjunctival mitomycin C (SC-MMC) before excision of pterygium is a new adjunctive therapy with very low recurrence rates.12 Literature on this technique is rare. We thank the authors1 for presenting this interesting modification of SC-MMC prior to pterygium excision.

The authors1 did not discuss the detailed mechanism of prevention of reccurence due to their modification. Moreover, they1 did not perform the histopathology or ultrastructural study of excised specimens of pterygia which could have demonstrated the effect of MMC on fibrovascular tissues in stroma of the the pterygia, 24hrs after injection. Readers would be very eager to know the effect of 24hrs exposure of MMC on pterygium tissue compared to a control group.

Donnenfeld et al, waited one month after the injection of MMC before performing bare sclera pterygium surgery on the basis of their previous experience with SC-MMC for pemphigoid, where the inflammation decreased at one month.2 Histopathology of recurrent pterygia pretreated with SC-MMC injection one month before pterygium excision also showed evidence of an inhibitory effect of MMC on vascular endothelium and stromal fibroblasts.2 Transmission electron microscopy of excised specimens of pterygium one month after SC injection of 0.1 mL of 0.15 mg/mL MMC demonstrated inhibition of fibrovascular activity in the pterygial stroma, leading to degeneration of the extracellular matrix and nerve axons.3 The ultrastructural changes verified the effectiveness of SC-MMC injection one month before pterygium excision in decreasing the risk of pterygium recurrence.3

The authors mention that excision of pterygium was performed 24hrs after SC-MMC to reduce the exposure time of tissues to MMC to avoid complications related to MMC.1 However, we believe that 24hrs after SC-MMC does not appear to be a short exposure time to MMC. Vass et al.4 studied the effect of varying the application time of MMC on the scleral concentration of MMC and found that 64% of the MMC was delivered to the sclera within the first minute. In fact, a five minute intraoperative treatment with MMC resulted in prolonged inhibition of treated SC and scleral tissue fibroblasts for at least 30 days in rabbits.5 One study concluded that extra- and intra- ocular concentrations of MMC were highest after SC injection.6 MMC is distributed in extraocular and intraocular tissues resulting in a rapid decrease in MMC concentration from the conjunctiva and sclera at the injection site after a single SC injection of the drug.7 Thus, we believe that in Ghoneim et al.'s modification1 the residual MMC at and surrounding the surgical site after excision of pterygium may be adequate to inhibit the fibrovascular activity to reduce the recurrence of pterygium. This modification1 enjoys all the advantages of SC-MMC and does away with the drawback of waiting for I month for the second stage.