Scanning laser ophthalmoscope imaging of fluorescein-labelled blood cells

• Purpose: To demonstrate the feasibility of a technique for the visualization by scanning laser ophthalmoscope (SLO) of fluores cein-labelled autologous leukocytes and platelets in retinal vessels. • Method: Individual blood samples from rats and rabbits were centrifuged to isolate platelets and leukocytes, then passively labelled with fluorescein and reinjected into the same animal. An SLO was used to visualize and record cell displacement in the retinal circulation. Labelled platelets were analysed by flow cytometry. • Results: By SLO, platelets appeared as a heterogeneous particle flow, and individual leukocytes appearing as brighter spots could easily be traced. Flow cytometry showed that after labelling platelets were well individualized and their size was slightly increased. • Conclusion: Circulating blood cells can be visualized in retinal vessels by a simple method consisting of passive labelling of autologous platelets and leukocytes by fluorescein. No platelet toxicity was detected. This method could be applied to the study of blood cell movement in human retinal vascular diseases.