The following search phrases were used: (topical insulin OR ophthalmic insulin OR insulin eye drop* OR insulin drop*) AND (cornea OR corneal OR ocular surface) AND (keratopathy OR keratitis OR diabetic keratopathy OR neurotrophic keratopathy OR infectious keratitis OR dry eye OR dry eye disease OR dry eye syndrome OR epithelial defects OR persistent epithelial defect* OR dystrophy OR corneal dystrophy). Here, INS is linked to dry eye syndrome.