Counting capillaries in nailfold capillaroscopy: State of the art and a proposed method

Capillaries play a crucial role in the microcircu-latory system by exchanging metabolic substrates and waste products between blood and various tissues. The behavior of capillaries is affiliated with the number of capillaries per unit volume of tissue. Among the various noninvasive techniques available for analyzing skin microcirculation, nailfold capillaroscopy is considered to be a simple and easy-to-perform technique that allows a direct in-vivo visualization of the capillary network. Capillary density is one of the most important parameters in the studies involving capillaroscopy images. Capillary density in most of studies is defined as the number of capillaries in one millimeter span of the distal row in each finger or toe. This definition is silent about counting or excluding the number of capillary with different shapes. However, there is no single standard for counting the number of capillaries in a span of one millimeter. In this paper, a novel method is proposed for determining the nailfold capillary density. This method is a modified combination of two existing techniques: the direct observation and the 90° method. Compared to the two existing approaches, the proposed method is more straightforward and easy to use for cases in which the capillaries have different shapes and sizes. Through different examples, we have shown how this method can be used to select the apex point of capillary and subsequently count the number of capillaries with several papillae.