Radiation-induced leukocyte entrapment in the rat retinal microcirculation

PURPOSE. TO evaluate the effects of irradiation on leukocyte dynamics in th e rat retinal microcirculation. METHODS. Thirty-five Brown-Norway rats received a dose of 10 Gy irradiation in one fraction. Leukocyte dynamics were studied with acridine orange digi tal fluorography, in which a nuclear fluorescent dye of acridine orange is used and examined by scanning laser ophthalmoscope. This technique allowed visualization of fluorescent leukocytes in vivo. The leukocyte dynamics wer e evaluated at 0, 4, 7, 14, 30, and 60 days after the irradiation. RESULTS. Mean leukocyte velocity in the retinal capillaries decreased immed iately. It partially recovered on day 4 but then gradually decreased up to the 2-month mark. Low-dose irradiation induced entrapment of leukocytes in the retinal microcirculation. The number of entrapped leukocytes gradually increased with time. The major retinal vessels significantly constricted im mediately after irradiation. The diameter was reduced by 76% in arteries an d 75% in veins, 2 months after irradiation. CONCLUSIONS. Entrapped leukocytes may be activated and exacerbate vascular injury and microinfarction and thus may participate in the pathogenesis of radiation retinopathy.