Inclusion Criteria:
1. Male or female subjects, age 18-70 years.
2. Participants who have been diagnosed with type 1 or type 2 diabetes for at least 1 year.
3. Meet the diagnosis of peripheral neuropathy according to neuroelectrophysiological examination.
4. According to the researchers' clinical judgment, blood glucose has been optimally controlled. The blood glucose was kept as stable as possible during the study. HbA1c level≤9% prior to screening, the variety is at least less than 2% within the 3-months before enrollment.
5. No history of eye trauma or corneal laser treatment.
6. No history of keratopathy or other intraocular ophthalmic disease.
7. No history of wearing contact lenses.
8. Have not taken medicines that affect corneal metabolism.
9. Did not take Mecbl or α-lipoic acid therapy within 3 months before screening.
10. Women of child bearing age (e.g., non-operative birth control or pausimenia less than 1 year) must be negative in the gonadotropin pregnancy test (urine) screening and receive effective contraception during treatment.
11. Signs the informed consent.
12. Subjects are willing and able to comply with the study visit schedule, treatment plan, laboratory tests and other study procedures.
Exclusion Criteria:
1. Have been diagnosed with a malignant tumor in the past 2 years.
2. The presence of other neurological disorders that researchers believe perhaps affect the evaluation of DPN.
3. The presence of skin diseases in the affected skin areas may affect the evaluation of DPN and injection according to the researcher's judgment.
4. Amputation of the ends of fingers and toes.
5. Participated in any other trials involving a study or post-marketing drug within 30 days of screening.
6. Subjects with clinically significant or unstable diseases, such as but not limited to acute cardiovascular diseases, cerebrovascular diseases, liver diseases, kidney diseases, respiratory diseases, blood diseases, immune system diseases, inflammatory or rheumatic diseases, uncontrolled infections, symptomatic peripheral vascular diseases, untreated endocrine diseases, etc.
7. Had donated blood within 30 days of the study treatment commencement (if applicable); or preparative blood donors during the study or 30 days after the end of treatment.
8. The WBC \< 4000 / mm\^2, neutrophils count \<1500/mm\^2, platelet count \<100×109 /mm\^2.
9. Clinically significant abnormalities in 12-lead ECG.
10. Subjects received combining transcutaneous electrical nerve stimulation (TENS) or acupuncture.
11. A history of intolerance or allergy to Mecbl or similar chemical compound.
12. Current or history presence of alcohol and/or other substance abuse within the past 1 year.
13. Other severe acute or chronic medical or psychiatric conditions or laboratory abnormalities that, in the determination of the investigator, may increase the risk associated with participating in the trial or using Mecbl, or that may affect the interpretation of the study results, may render the subject unfit to participate in the trial.
14. Inability and/or unwillingness to understand and/or comply with the plan.
