Cancer-associated retinopathy is an autoimmune disease in which autoantibodies trigger retinal tissue destruction.1 Patients with cancer-associated retinopathy may develop visual acuity or visual field loss, photopsias, photophobia, and/or nyctalopia.1 Drug-induced toxic effects can also cause photoreceptor damage and corresponding visual symptoms.2 We describe a patient with nyctalopia during treatment of non–small cell lung cancer with AUY922, a heat shock protein 90 (HSP90) inhibitor.3