Figure 3. Three assumptions about glucocorticoid medication use, senile cataract and iridocyclitis in this Mendelian randomization study. (i) The instrument variables (IVs) are strongly associated with iridocyclitis and glucocorticoid medication use; (ii) the genetic IVs are independent of confounders; (iii) the genetic IVs affect senile cataract only through their effect on iridocyclitis and glucocorticoid medication use, and not through an alternative causal pathway.