On the other hand, the evidence of insulin and the IGF axis promoting corneal epithelial cell migration, proliferation, and nerve recovery largely via PI3K–Akt signaling [234] should be seen with evidence that IGF-1 alone could not increase corneal ulcer healing and had only an effect combined with substance P (which is also ineffective when given alone) [252,253]. Here, INS is linked to corneal ulcer.