Purpose To evaluate the long-term effects of intraoperative application of mitomycin C on the scleral thickness and the conjunctival epithelium at the surg ical site of pterygium excision.Design Prospective observational case series.Participants Twenty-four patients who underwent excision of primary pterygiumwith intraoperative mitomycin C in our department during the year 1996.Methods Patients were evaluated by slit-lamp biomicroscopy,impression cytology,and high-frequency ultrasonograph y.Impression cytology was performed by applying a small nit rocellulose filter paper for a few seconds at the excision area and for a few seconds at the opposite perilimbal area,and subjecting the speci-mens to the periodic acid-Schiff-Gi ll modified Papanico-laou staining protocol.The morphology of the conjunctival epithelium and goblet cell density(GCD)-were record-ed.High-frequency ultrasound was p erformed at the same sites,and the scleral thickness was measured at a distance of 1mm from the limbus.Main outcome measures Goblet cell density,conjunetival epithelialmorphology,and the scleral thickness at the operated an d nonoperated sites. Results All patients had successful pterygium removal with no corneal recurrence after a mean fo llow-up of 77.2±3.9months(range,72-84).Impression cytology revealed normal nongoblet conjunctival epithelial cells at the excision area,with a 4-fold decrease in the GCD at the excision area when compared with the contrala teral nonoperated site(296±120cells /mm 2 and 1183±310cells /mm 2 ,re-spectively;P=0.0036).No differences were noted be-tween the scleral thicknesses at the operated site(750±70μm)and the opposite site(740±80μm)(P=0.84).Conclusions A single application of mitomyein C after pterygium excision is not associate d with reduction in sel-eral thickness more than 6years postoperatively.The eonjunetival epithelium retains its normal phenotype,with a marked reduction of the GCD. Purpose To evaluate the long-term effects of intraoperative application of mitomycin C on the scleral thickness and the conjunctival epithelium at the surg ical site of pterygium excision. Design Prospective observational case series. Participants Twenty-four patients who underwent excision of primary pterygium with intraoperative mitomycin C in our department during the year 1996. Methods Patients were evaluated by slit-lamp biomicroscopy, impression cytology, and high-frequency ultrasonograph y.Impression cytology was performed by applying a small nitrocellulose filter paper for a few seconds at the excision area and for a few seconds at the opposite perilimbal area, and subjecting the speci-mens to the periodic acid-Schiff-Gi ll modified Papanico-laure staining protocol. The morphology of the conjunctival epithelium and goblet cell density (GCD) -were record-ed . High-frequency ultrasound was p erformed at the same sites, and the scleral thickness was measured at a distance of 1mm from the limbu s.Main outcome measures Goblet cell density, conjunetival epithelialmorphology, and the scleral thickness at the operated an d nonoperated sites. Results All patients had successful pterygium removal with no corneal recurrence after a mean fo llow-up of 77.2 ± 3.9months (range, 72-84). Impression cytology revealed normal nongoblet conjunctival epithelial cells at the excision area, with a 4-fold decrease in the GCD at the excision area when compared with the contrala teral nonoperated site (296 ± 120 cells / mm 2 and 1183 ± 310 cells / mm 2, re-spectively; P = 0.0036) .No differences were noted be-tween the scleral thicknesses at the operated site (750 ± 70 μm) and the opposite site (740 ± 80 μm) application of mitomyein C after pterygium excision is not associate d with reduction in sel-eral thickness more than 6years postoperatively. The eonjunetival epithelium retains its normal phenotype, with a marked reduction of the GCD.