To evaluate the efficacy of mecobalamin injection and tablet in the treatment of small fiber lesions in the early stage of diabetic peripheral neuropathy by corneal confocal microscopy.

Inclusion Criteria:

• diagnosis of type 1 or 2 diabetes for at least 1 year
• must be consistent with the diagnosis of distal, symmetrical, sensorimotor polyneuropathy
• according to the clinical judgment of the researchers, the blood glucose has been under the best control. Before screening visit, HbA1c level ≤ 9%. During the course of the study, the blood glucose was adjusted under the guidance of the researchers, and the blood glucose was kept stable as much as possible.
• Toronto clinical neuropathy score (TCSs) ≤ 5 at screening visit
• no history of eye injury and laser treatment
• no history of keratopathy or other intraocular and extraocular diseases
• no wearing history of corneal contact lens
• no drugs affecting corneal metabolism
• no Mecobalamin or lipoic acid in 3 months
• women of childbearing age (e.g. non-surgical contraception or menopause less than 1 year) must be negative in the gonadotropin pregnancy test (urine) during the screening period, and effective contraceptive measures must be taken during the treatment period and within 1 month after the end of the treatment
• the participant signs the informed consent, indicating that the subject has been informed of all research related contents
• participants are willing and able to follow study visit arrangements, treatment plans, laboratory tests and other research procedures

Exclusion Criteria:

• has been diagnosed as a malignant tumor in the past 2 years.
• the presence of other neurological disorders that the researchers believe may affect the evaluation of diabetic peripheral neuropathy
• presence of skin disease in the affected skin area, which, in the judgment of the researchers, may affect the evaluation of diabetic peripheral neuropathy
• amputations other than finger ends and toes
• participated in any other studies or post market drugs studies within 30 days prior to screening
• participants with clinically significant or unstable diseases, such as but not limited to acute cardiovascular disease, cerebrovascular disease, liver, kidney, respiratory system, blood system, immune system, inflammatory or rheumatic disease, uncontrolled infection, symptomatic peripheral vascular disease, untreated endocrine disease, etc
• have donated blood within 30 days prior to the start of the study treatment (if applicable); or have prepared blood donors during the study or within 30 days after the end of the treatment
• WBC < 4000 / mm3; neutrophil count < 1500 / mm3; platelet count < 100 × 103 / mm3
• clinically significant abnormal 12 lead ECG
• participants received combined transcutaneous electrical nerve stimulation (TENS) or acupuncture
• previous history of intolerance or allergies to study drugs or drugs with similar chemical structure
• has a history of alcohol and / or other drug abuse in the past year or is currently under the influence of alcohol or drug abuse
• the presence of other acute or chronic medical or psychiatric conditions or laboratory abnormalities that, in the judgment of the investigator, may increase the risk associated with participating in the trial or using the study product, or may affect the interpretation of the study results, may make the subject unsuitable for the trial
• inability and / or unwillingness to understand and / or comply with the program