Failure to extract a magnetic intraocular foreign body is often due to a misunderstanding of the pulling force of a magnet, which is not its field strength in gauss, but rather the product of the field times the field gradient. New equipment allows this pulling force to be plotted and the strength of different pole-tip shapes to be determined.
Bron NR. Practical Characteristics of Ophthalmic Magnets. Arch Ophthalmol. 1968;79(1):22-27. doi:10.1001/archopht.1968.03850040024008