RGN-259 eye drops compared to placebo eye drops 5 times per day in both eyes for the treatment of Neurotrophic Keratopathy. Percentage of subjects achieving complete healing (defined as 0 mm lesion size) of the Persistent Epithelial Defect (PED) at Visit 5 (Day 29) determined by corneal fluorescein staining captured by corneal photography and analyzed by a central reading center