The reference point for monocular visual direction can, sometimes, be one of the eyes rather than the cyclopean eye

We found that the imaginary line passing through two stimuli that points to an eye appears to do so when seen monocularly, which is consistent with Porterfield's axiom but inconsistent with Wells's proposition regarding visual direction. We also found that the imaginary line appears to point to the bridge of the nose when the near stimulus is seen binocularly and the far one is seen monocularly, which is consistent with Wells's proposition but inconsistent with Porterfield's axiom. We argue that these findings themselves do not necessarily vitiate the axiom or the proposition and that one should explore the different experimental conditions and hypothesize about the processes that might be involved.