The effects of total lymphoid irradiation upon corneal vascularization in the rat following chemical cautery.

The effect of total lymphoid irradiation (TLI), a form of radiotherapy known to suppress the number of circulating lymphocytes, on corneal neovascularization was assessed in rats. The corneas of TLI-treated rats were cauterized with silver/potassium nitrate one day after delivering gamma irradiation in five equal fractions (10 Gy total dose). Corneal neovascularization was assessed quantitatively by computerized image analysis in corneal flat preparations 4 days after corneal injury following perfusion of the circulation with India ink. TLI reduced the total leukocyte, lymphocyte, neutrophil, and platelet counts below preirradiation levels. The number of circulating lymphocytes was reduced more than neutrophils and platelets. TLI caused a predominance of cytotoxic/suppressor lymphocytes. Tissue examinations 4 days after TLI disclosed an absence of the thymus, as well as a markedly reduced number and size of lymph nodes. TLI rats had less corneal vascularization than nonirradiated controls. Our findings are consistent with the hypothesis that leukocytes play an important role in the pathogenesis of corneal angiogenesis following chemical cautery, but this study does not indicate how TLI suppresses corneal neovascularization.