Design: This Phase I, non-randomized, prospective, uncontrolled, dose-escalation, single-center study will involve a one-time instillation or series of instillations of interferon gamma-1b on the cornea and measure the potential response with optical coherence tomography (OCT) . Treatment success is defined as a 25% decrease in excess central macular thickening at any timepoint post-instillation as compared to baseline. The first two participants will receive one instillation (each instillation contains 10 microg in 0.05 mL solution), the next two participants will receive two instillations and the final participant will receive three instillations. OCT will be obtained at -60 minutes, -30 minutes and just before the instillation(s). Repeat OCTs will be taken at +30 minutes, +60 minutes and +120 minutes and again at the end of the day. All participants will return for a one-week safety visit.