In diabetes, chronic high blood sugar levels (hyperglycemia) damage the retina which may impair vision and even lead to blindness. This disease is referred to as diabetic retinopathy and treating it is difficult. In search for new treatment options, researchers have increasingly studied the molecular mechanisms that affect diabetic retinopathy, including microRNAs. microRNAs are small RNA molecules that regulate cellular protein expression by inhibiting their translation from the messenger RNA. In diabetic retinopathy, the expression of microRNAs is changed. This change in microRNA expression may drive a change in protein expression that is thought to sustain and aggravate diabetic retinopathy. Vice versa, correcting the ill-changed microRNA expression has the potential to ameliorate diabetic retinopathy, which is why microRNAs are considered promising molecules to treat diabetic retinopathy. To expand our knowledge on microRNAs in diabetic retinopathy, we studied the ocular microRNA expression during different stages of diabetic retinopathy in preclinical and clinical experiments and identified several microRNAs that are differentially expressed in diabetic retinopathy. We discovered that the change in microRNA expression can aggravate diabetic retinopathy through various mechanisms, including blood vessels destabilization and the concomitant decrease in retinal oxygen supply, a phenomenon well-known to culminate in blindness. Moreover, we observed that microRNA profiles are highly dynamic during diabetic retinopathy, suggesting that distinct stages of diabetic retinopathy require a distinct microRNA therapy. Altogether, the microRNAs described in this thesis extend our knowledge on the mechanisms underlying diabetic retinopathy and may aid in the development of novel treatments of diabetic retinopathy.