Evaluation of leukocyte dynamics in choroidal circulation with indocyaninegreen-stained leukocytes

PURPOSE. To develop a new method with which to visualize leukocytes moving through the choroidal vessels of pigmented animals and enable the evaluatio n of leukocyte dynamics in the choroidal microcirculation. METHODS. Pigmented rabbits and monkeys were used in this study. Leukocytes, collected by centrifugal separation of autologous blood, were stained with indocyanine green (ICG) dye. The ICG-stained leukocyte fluid was injected into the vein, and the fundus image was obtained with a scanning laser opht halmoscope. The image was recorded on videotapes and analyzed with a person al computer-based image analysis system. RESULTS. In pigmented rabbits, fluorescent leukocytes moving in the choroid al circulation were clearly visible for more than 1 hour. In monkeys, disti nct fluorescent dots were seen moving approximately 50 to 200 mu m in the f oveal avascular zone for more than 30 minutes after the injection of the IC G-stained leukocyte fluid. Dim fluorescent dots were seen moving in the fun dus. Although the movement of these dim dots was difficult to trace, they s eemed to be moving in the choroidal vessels. In the rabbits, the mean flow velocity of leukocytes moving without plugging was 0.48 +/- 0.14 mm/sec in the peripheral choriocapillaris. In the monkeys, the mean flow velocity of distinct fluorescent leukocytes without plugging was 2.45 +/- 0.48 mm/sec i n the posterior choroid. CONCLUSIONS. In pigmented rabbits and monkeys, this method allows visualiza tion of leukocytes passing through the choroidal vessels and provides a new way to investigate, noninvasively and in vivo, leukocyte dynamics in the c horoidal microcirculation.