OCT images of OSSN. Clinical and OCT images of OSSN before (A and C) and after (B and D) 4 cycles of topical 5-FU 1% 4 times daily for 1 week, with 3 weeks off between each cycle. C, Note the thickened hyperreflective epithelium (asterisks) with abrupt transition (arrow) from normal to abnormal tissue, characteristic of OSSN. D, Resolution following 5-FU treatment; note the thin normal epithelium (arrowheads). Insets shows location of scan.