In the course of routine examinations of the fundi three patients were noted whose fundi presented an unusual appearance. All three patients had taken methylthionine chloride U. S. P. (methylene blue) over a long period, and their fundi appeared deep blue, as though seen through a blue filter. To our knowledge such a condition has not been recorded previously. We are therefore reporting these unusual cases, giving a foreword concerning methylthionine chloride.
Methylthionine chloride was isolated chemically for the first time in 1876 by Caro. It is a tetra-methylthionine chloride, the formula being C16H18N3SCl + 3H2O. It is dark bluish green with a metallic luster and is odorless and relatively stable. Alcohol and water dissolve the crystals readily. As early as 1880 this dye was used as an intestinal antiseptic to destroy lower forms of plant and animal life. Soon it was shown
GERBER A, LAMBERT RK. BLUE APPEARANCE OF THE FUNDUS CAUSED BY PROLONGED INGESTION OF METHYLTHIONINE CHLORIDE. Arch Ophthalmol. 1936;16(3):443–446. doi:10.1001/archopht.1936.00840210115008