A 52-year-old male patient presented with a painless rapidly growing grayish lesion in his left eye that he felt was interfering with his vision in dim light over the last month. Slit-lamp examination showed a grayish-white semitransparent slightly elevated lesion extending from 12 o'clock to 7 o'clock with a limbal leash of feeder vessels partially extending into the cornea (A). An optical biopsy using anterior segment optical coherence tomography (AS-OCT) (B) revealed an abrupt hyperreflective thickening of the corneal epithelium ranging from 123 to 190 microns. Based on the clinical and the tomographic data, a diagnosis of ocular surface squamous neoplasia (OSSN) was made and the patient was scheduled for 4 cycles of topical 5-FU 1%.