Intravitreal injection or topical eye-drop application of a μ-calpain C2L domain peptide protects against photoreceptor cell death in Royal College of Surgeons' rats, a model of retinitis pigmentosa

► We identified the specific peptide inhibitor of mitochondrial μ-calpain. ► We intravitreally injected the peptide into an animal model of retinitis pigmentosa. ► The peptide prevented retinal photoreceptor apoptosis and preserved retinal function. ► Eye drops containing the peptide also inhibited photoreceptor apoptosis. ► The peptide offers a new modality for treating retinitis pigmentosa.