Evaluation of Effect of Doxycycline Verses Placebo on Retinal Function and Diabetic Retinopathy

Inclusion Criteria: * age ≥ 18 years old * diagnosis of type 1 or type 2 diabetes mellitus (defined as current regular use of oral anti-hyperglycemia agents and/or insulin for the treatment of diabetes) * have a hemoglobin A1c \< 11% at pre-qualification visit * able and willing to give informed consent * best-corrected ETDRS visual acuity (10) in study eye ≥ 69 letters (20/40) * mild to moderate non-proliferative diabetic retinopathy (ETDRS levels 20 to 43) (11), and in whom retinal photocoagulation is not anticipated (by the investigator) within the subsequent 2 years * able to perform reliable visual field and dark adaptation testing * central subfield thickness on OCT ≤ 275 microns * media clarity and pupil dilation sufficient for high-quality fundus photographs * abnormal retinal function defined as: * abnormal FDP function as defined by a foveal sensitivity ≤ 30.91 dB Exclusion Criteria: * prior panretinal photocoagulation in the study eye * prior focal/grid laser photocoagulation in the macula in the study eye * intraocular pressure in the study eye \> 22 mmHg by Goldmann tonometry * history of pars plana vitrectomy in the study eye * systemic or intravitreal anti-VEGF agent to the study eye or the fellow eye within the past 3 months * peribulbar steroid injection to the study eye or the fellow eye within the past 6 months * intravitreal triamcinolone acetonide to the study eye within the past 4 months * expectation by the investigator that retinal photocoagulation …