Propranolol for Diabetic Retinopathy

Inclusion Criteria: * Age \>=18 years * Eyes with proliferative diabetic retinopathy and neovascularization * Eyes with a history of panretinal photocoagulation treatment and persistent neovascularization deemed by the investigator to be a potential threat to visual acuity either by causing a vitreous hemorrhage or tractional retinal detachment. (Group 1 - maximum 5 eyes enrolled with these characteristics) * Eyes without a history of panretinal photocoagulation treatment, but that do not have high-risk proliferative diabetic retinopathy characteristics (i.e. these are eyes that have early proliferative diabetic retinopathy that are not yet at a high-risk for vitreous hemorrhage and tractional retinal detachment such that panretinal photocoagulation laser may be deferred). (Group 2 - maximum 5 eyes enrolled with these characteristics) Exclusion Criteria: * Either panretinal photocoagulation laser or focal/grid laser into study eye within 3 months of study enrollment * Anti-Vascular endothelial growth factor injection into study eye within 3 months of study enrollment * Contraindications to beta-blockers such as: allergy, previous intolerance, abnormally slow heart rates, asthma or chronic obstructive pulmonary disease, use of medications that have an effect on certain drug metabolic pathways that may cause interactions. * Known coronary arterial disease or left ventricular dysfunction, or known peripheral vascular disease * Resting heart rate \<60 or systolic blood pressure \<90 and/or diastolic blood pressure \<50 * Pregnancy * All patients will either be post-menopausal, have adequate birth control and, if of childbearing age, will have a urinary pregnancy test performed * Allergy to fluorescein dye * Media opacity obscuring adequate determination of neovascularization including dense cataract or dense vitreous hemorrhage * Patient is already taking an oral beta-blocker * Vulnerable populations such as prisoners and minors will also be excluded