Many behavioural phenomena have been replicated using web-based experiments, but evaluation of the agreement between objective measures of web- and lab-based performance is required if scientists and clinicians are to reap the benefits of web-based testing. In this study, we investigated the reliability of a task which assesses early visual cortical function by evaluating the well-known ‘oblique effect’ (we are better at seeing horizontal and vertical edges than tilted ones) and the levels of agreement between remote, web-based measures and lab-based measures. Sixty-nine young participants (mean age, 21.8 years) performed temporal and spatial versions of a web-based, two-alternative forced choice (2AFC) orientation-identification task. In each case, orientation-identification thresholds (the minimum orientation difference at which a standard orientation could be reliably distinguished from a rotated comparison) were measured for cardinal (horizontal and vertical) and oblique orientations. Reliability was assessed in a subsample of 18 participants who performed the same tasks under laboratory conditions. Robust oblique effects were found, such that thresholds were substantially lower for cardinal orientations compared to obliques, for both web- and lab-based measures of the temporal and spatial 2AFC tasks. Crucially, web- and lab-based orientation-identification thresholds showed high levels of agreement, demonstrating the suitability of web-based testing for assessments of early visual cortical function. Future studies should assess the reliability of similar web-based tasks in clinical populations to evaluate their adoption into clinical settings, either to screen for visual anomalies or to assess changes in performance associated with progression of disease severity.