Corneal sensitivity reduction is a common nerve conduction dysfunction due to a variety of causes. Although whether corneal sensitivity reduction is a symptom of diabetes is still controversial, it has strong correlation with the duration of diabetes,glycemic control and also diabetic peripheral neuropathy. In recent years, the corneal sensation as a monitoring indicator of diabetic peripheral neuropathy has been extensively researched. The mechanism may be the sugar metabolites accumulation in the nerve cells, the reduced number and the shortened length of nerve fibers, or immune mechanisms.