Pulmonary arterial hypertension (PAH) is a disease characterized by progressive loss and remodeling of the pulmonary arteries resulting in right heart failure and death. The majority of research has focused on endothelial dysfunction in the pulmonary circulation without much attention to whether similar pathology may be found in the rest of the circulatory system. However, there is growing evidence that PAH patients also exhibit systemic endothelial dysfunction as evidenced by impaired brachial artery flow-mediated dilation, abnormal cerebral blood flow and intrinsic kidney disease. Besides abnormalities in vascular function and metabolic processes, patients with systemic sclerosis and PAH have been reported to exhibit distinctive morphological changes in kidney, skin, nailfold capillaries and sublingual vessels.1 The eye is a highly vascularized organ that is sensitive to systemic changes in oxygen and blood flow. Interestingly, abnormally dilated episcleral vessels were found not only in PAH patients but also in unaffected carriers before the development of the disease. A more recent study by Chyou and colleagues using the Multi-Ethnic Study of Atherosclerosis database demonstrated that a higher right ventricular mass and volume by MRI correlated with a wider diameter in retinal vessels in women compared to men independent of body size, diabetes mellitus, cholesterol, age and alcohol use.2 While this study did not involve PAH patients, it is does allow speculation of a physiological communication between the retina and cardiopulmonary system that should be further explored. We sought to characterize the genetic and functional properties of human retinal endothelial cells (REC) along with anatomic characterization of healthy and PAH retinal vessels in human and a hypoxia mouse model of pulmonary hypertension (PH).