Alterations of retinal microcirculation in response to scatter photocoagulation

To perform acridine orange digital fluorography on rats after scatter photocoagulation to investigate alterations of retinal microcirculation at the capillary level, the authors used leukocyte dynamics as a parameter.

Twenty-five pigmented rats (Long-Evans) were studied. Argon laser photocoagulation, extending 6 disc diameters from the optic disc, was delivered to one half of the retina, and the other half was untreated. The total number of burns was 200 +/- 10. Leukocyte hemodynamics in retinal microcirculation were evaluated 4, 7, 14, and 28 days after photocoagulation by acridine orange digital fluorography. The fundus image was obtained by using an argon laser in a scanning laser ophthalmoscope and was recorded on magnetic tapes at a video rate. The images were analyzed by a personal computer-based image analysis system.

Leukocyte velocities in the retinal capillaries were significantly decreased immediately after photocoagulation. In the laser-treated area, mean capillary leukocyte velocities were 0.73, 0.92, 1, and 1.3 mm/second on days 4, 7, 14, and 28, respectively (velocity in normal control animals 1.4 mm/second). In addition, leukocyte hemodynamics were compromised in the untreated retina: Mean capillary leukocyte velocities were 0.88, 1.1, 1.2, and 1.3 mm/second on days 4, 7, 14, and 28, respectively. Twenty-eight days after photocoagulation, the velocities recovered to normal values in the treated and the untreated areas of the retina.

Retinal capillary hemodynamics were impaired after scatter photocoagulation, and the hemodynamics in the untreated retina were also affected. Photocoagulation to the retina may influence capillary hemodynamics by diffusible chemical substances and by direct tissue injury.