**2. Principle**

Microcirculation consists of arterioles, capillaries, and venules. The main function of the microcirculation is capillary exchange—delivery of oxygen and nutrients to tissues and removal of carbon dioxide and waste products. In most areas of fingers, capillaries are oriented perpendicular to the skin surface and are thus not amenable to visualization. In the nailfold areas, however, they become parallel to the skin surface and thus are observable in full length in the distal row.

**Figure 1.** *Schematic representation of a capillary loop.*

Usually there are one to three capillaries in each dermal papilla [3]. Hence most of the examination of the capillaries is concentrated on this region. Each capillary loop consists of an arterial and a venous limb with the latter being wider (**Figure 1**). With the help of various instruments, we are able to visualize the column of blood within these capillaries. The density and morphology of these loops help in the diagnosis and follow-up of patients with rheumatic diseases. We shall address these in the below mentioned sections.
