Inclusion Criteria:

• * Type 2 diabetes (clinically diagnosed, taking anti-diabetes medications or history of elevated A1C≥6.5%)
• * 40-65 years of age
• * Diabetic retinopathy of at least moderate degree

Exclusion Criteria:

• * use of melatonin
• * antidepressants or antipsychotics
• * illicit drug use
• * night shift work or travel beyond 2 time zones in the month before enrollment
• * end stage renal disease requiring renal replacement therapy
• * history of stroke or transient ischemic attacks
• * history of dementia or memory impairment
• * uncontrolled congestive heart failure or recent hospitalization for cardiac condition (6 months)
• * chronic obstructive pulmonary disease requiring oxygen
• * severe chronic liver disease such as cirrhosis
• * ongoing treatment for major medical problems such as cancer
• * history of severe hypoglycemia defined as hypoglycemic episodes requiring assistance from others within the past six months.
• * Significant depressive symptoms
• * untreated severe OSA (AHI≥ 30 events/hour),
• * uncontrolled hypertension (blood pressure ≥ 160/100 mmHg),
• * uncontrolled diabetes (A1C ≥ 11%),
• * abnormal TSH
• * abnormal liver function (AST or ALT\>3x upper limits of normal
• * use of sedatives and hypnotics.
• * clinically significant epiretinal membranes, clinically significant lens opacities, or cystoid macular edema, iris neovascularization, iris atrophy, or an asymmetrically shaped pupil, nuclear sclerotic, posterior subcapsular, or cortical lens opacities greater than 2+, a history of pan-retinal photocoagulation.
• * hemoglobin \<11.5 g/dL in women and \<13.5 g/dL in men.