Purpose: Macular edema is one of the most serious adverse effects after retinal scatter laser photocoagulation. It has been suggested that the changes in the distribution of retinal blood flow or the inflammatory reaction after photocoagulation may be involved in the pathogenesis of macular edema, but little information is available about its exact mechanism. This study was designed to evaluate quantitatively leukocyte-endothelial cell interactions and vascular permeability in the nonphotocoagulated portions of the retina after partial scatter laser photocoagulation.
Methods: Argon laser photocoagulation was performed in one half of the retina in male pigmented rats (n = 90). In the other half of the retina, leukocyte dynamics after photocoagulation were evaluated in vivo with acridine orange digital fluorography. Retinal vessel permeability was quantified by using Evans blue dye.
Results: Scatter laser photocoagulation caused significant inflammatory leukocyte-endothelial interactions not only in the photocoagulated but also in the untreated half of the retina. In the nonphotocoagulated half of the retina, the number of leukocytes rolling along the major retinal veins increased after photocoagulation and peaked at 12 hours (14.3 +/- 4.5 cells/min per vessel). Leukocyte accumulation in the untreated half of the retina increased after photocoagulation, with a peak of 47.5 +/- 13.0 cells/mm(2) 24 hours after photocoagulation. Retinal vascular permeability in the untreated half of the retina gradually increased after photocoagulation.
Conclusions: Scatter laser photocoagulation increased leukocyte rolling and subsequent accumulation in both the photocoagulated and the untreated portions of the retina. The accumulated leukocytes may be involved in the augmented vascular permeability in the untreated retina, resulting in retinal edema after photocoagulation.