Obstructive sleep apnea (OSA) causes intermittent nocturnal hypoxemia and is associated with obesity, diabetes, inflammation, endothelial dysfunction, and hypertension, possibly leading to micro- and macro-vascular disease. OSA has been associated with higher risk of clinical cardiovascular disease (CVD) independent of traditional risk factors and severity of atherosclerosis. Microvascular disease may be a potential mediator for the association of OSA with clinical CVD. However, evidence for the association between OSA and microvascular dysfunction is conflicting. Since the retinal microvasculature is structurally and functionally similar to microvasculature elsewhere in the body and can be directly visualized via ophthalmoscopy, several studies have assessed the relationship of OSA with retinal microvascular characteristics but shown inconsistent results. Notably, the multi-ethnic study of atherosclerosis (MESA) recently revealed that the associations of OSA severity with retinal microvascular signs may differ by sex. Moderate/severe OSA was associated with retinal vascular calibers in men, but not women.