On November 11, 1965, research on DMSO in the United States came to an abrupt halt. A conference between the Food and Drug Administration and the pharmaceutical companies who were involved in the research was called because lens changes had been observed in a number of mammalian species. No changes ha been observed in man or any primates. The FDA and the pharmaceutical companies agreed, because there had been no pretreatment examinations of eyes and a large number of patients were under therapy, to discontinue the clinical studies: Somehow, at this time, DMSO gained a reputation of extreme toxicity, comparable to that of thalidomide and some other drugs that had previously run into major toxicology problems. Many of us in the pharmaceutical industry felt that this reputation was undeserved.

A refractive index change in the lens (not an opacity) had been observed after ? months at a dose of approximately 5 g/kg in dogs, rabbits, and pigs. No microscopic or chemical differences could be found between the lenses of the treated animals am the controls. In the affected animals, there appeared two distinct zones of different refraction. This could easily by observed with an ophthalmoscope and with the slit lamp. It appeared to be a dose-related effect, and it diminished as the dose was reduced. It is noteworthy that the effect was produced at 50 to l00 times the usual human therapeutic dose.

In November, 1965 there had been no cases of confirmed eye damage or significant complaints in the studies of any of the pharmaceutical firms. Pre-treatment examinations of eyes had not been performed. We all felt that to re-examine all the patients who had been under treatment at this stage would be fruitless exercise, because of the age of many of the patients and their preexisting eye problems. We elected, therefore, to check