Retinal vascular imaging in clinical research

Toward the end of the nineteenth century, the introduction of the ophthalmoscope in clinical practice provided an ideal opportunity to assess in vivo the human retina, including the microcirculation, noninvasively. The Scottish physician Robert Marcus Gunn, who in 1898 presented a series of observations from patients with stroke, recognized changes seen in the retinal blood vessels as markers of systemic disease [1,2]. These retinal signs included generalized arteriolar narrowing, arteriovenous nicking, cotton-wool spots, intraretinal hemorrhages, and papilledema. These signs subsequently became known as markers of hypertensive retinopathy (Figure 1.1). Subsequently, from the 1930s onward, several classification schemes for hypertensive retinopathy were proposed, and their relationship with a wide spectrum of cardiovascular diseases and mortality was described [3–7].