We validated an optical method for measuring the display lag of modern head-mounted displays (HMDs). The method used a high-speed digital camera to track landmarks rendered on a display panel of the Oculus Rift CV1 and S models. We used an Nvidia GeForce RTX 2080 graphics adapter and found that the minimum estimated baseline latency of both the Oculus CV1 and S was extremely short (∼2 ms). Variability in lag was low, even when the lag was systematically inflated. Cybersickness was induced with the small baseline lag and increased as this lag was inflated. These findings indicate the Oculus Rift CV1 and S are capable of extremely low baseline display lag latencies for angular head rotation, which appears to account for their low levels of reported cybersickness.