Additional Study Information: The main purpose of this study is to improve treatment of ocular side effects that result from depatuxizumab mafodotin (Depatux-M) use in patients with glioblastoma (GBM). Most people treated with Depatux-M will experience eye side effects. When these side effects are not tolerated, Depatux-M is usually interrupted until symptoms improve and then restarted at a lower dose. The use of preventative eye treatment and/or treating the side effect once it occurs may improve the tolerability of these eye side effects, decreasing the need for Depatux-M dose interruptions and dose reductions.