This study evaluates the effect of melatonin 4 mg on circadian rhythm and visual function of patients with diabetes mellitus. Half of the patients will receive melatonin (arm-1) and the other half will receive placebo (arm-2), both groups in 3 weeks. After a week of washout, the patients will cross over to the other treatment arm.

Inclusion Criteria:

• Diabetic patients
• Age range 40-75 years
• Participant should be legally competent

Exclusion Criteria:

• Other known eye disease.
• Eye disease manifestation during ocular examination.
• Competing neurologic and systemic conditions affecting retina.
• Use of any drugs influencing pupillary light reflex and sleep pattern.
• Refractive error with need of > 6 diopter lenses.
• Pregnancy
• Alcohol consumption during the trial
• Lack of cooperation
• Allergy to melatonin and/or preservatives in melatonin and placebo
• Reduced hepatic function
• Fluvoxamin intake due to drug interaction
• Consumption of Alpha-1 and beta-1 adnergic antagoists.
• Alcohol consumption during treatment

Melatonin and placebo tablets are identicle in terms of taste, colour, tablet-size etc. The tablets are packed and masked by external manufacturer.