An ultrasonic method for preoperative differentiation of the nonmagnetic from the magnetic intraocular foreign body has been described. This method is useful when the intraocular object cannot be seen ophthalmoscopically.
PENNER R, PASSMORE JW. Magnetic vs Nonmagnetic Intraocular Foreign BodiesAn Ultrasonic Determination. Arch Ophthalmol. 1966;76(5):676-677. doi:10.1001/archopht.1966.03850010678009