Leucocytes have a central role in the pathogenesis of retinal and choroidal inflammatory disease. The traffic of different leucocyte subsets such as neutrophils, lymphocytes, and monocytes into retinal and choroidal tissue greatly determines the type of immune response that is observed. Infiltration of these cells can lead to tissue destruction with resulting visual loss.1 To allow these cells to accumulate at these sites, leucocytes must pass from the intravascular compartment and into the extravascular space. Until recently, it has not been possible to observe this leucocyte traffic in the retina and choroid in vivo. Most of our understanding of the movement of leucocytes from the intravascular compartment to the extravascular space has been based on studies of leucocyte traffic in the rat mesentery2 or the mouse peripheral lymph node.3 Whether the observations made in these systems are applicable to the circulations of the retina and the choroid is not clear.

The scanning laser ophthalmoscope (SLO) provides real time imaging of the ocular fundus using low levels of illumination.4 This advantage has been used to perform real time fundus fluorescein and indocyanine green angiography but the use of SLO technology to perform these tasks has limited benefits. The real time imaging facility of the SLO, however, has the greatest application in visualising leucocyte traffic in the fundus in vivo. This development is becoming an important tool to study the circulation of leucocytes in different types of retinal and choroidal pathology and this review will describe the current methods of leucocyte angiography and their applications.