An accurate measure of eye length can be obtained using concurrent OCT measurements. A position OCT device can be used to continually monitor the position of the front surface of the cornea, while a distance OCT device can determine the apparent distance between the front surface of the cornea and the front surface of the retina. Since the eye is likely to move during the period of time between measurements of the cornea and retina, the monitored position of the cornea can be used to correct the apparent length measurement by the amount of eye movement over that period of time, in order to obtain an accurate measure of eye length. In some embodiments a single OCT device can serve the dual role of monitoring eye position while making eye length measurements