Pole receptor considers the potential for the human eye to perceive the Earth’s magnetic field. Research shows birds have this capability activated by molecules in the retina of the eye when excited by blue light. The molecules produce radical pair electrons sensitive to the magnetic field and as these molecules are found within the photoreceptor cells it is possible birds may visualise the magnetic field lines to aid navigation. A similar molecule is also found in the human eye. It is of course the brain that must receive a signal from the eye by which we see. Independently of the cryptochrome molecule, research monitoring alpha wave activity shows the human brain does appear to be sensitive to a magnetic field albeit unconsciously.
Photoetching with magnet and iron filings.