In an ophthalmic laser surgical system, a real-time optical coherence tomography (OCT) measurement method acquires OCT data during laser treatment. The treatment laser beam and OCT sample beam are generated simultaneously, and the optical delivery system scans them simultaneously in the eye tissue, where the focus of the treatment laser beam and the focus of the OCT beam coincide with each other in space. While both beams simultaneously scanned in the eye tissue, the OCT device detects returned OCT light from the sample during a data acquisition period, and generates an OCT A-scan based on the detected OCT light. Based on the A-scan, a controller determines a structure of the eye in a depth direction relative to the focus of the OCT beam, and controls the operations ophthalmic laser surgical system accordingly. One exemplary application is the formation of an arcuate corneal incision in cataract surgery.