Experimental external irradiation of corneal neovascularization

The clinical effect of ionidizing radiation on ocular neovascularizations i s controversial not only because of the variety of treatment modalities. Th e aim of our study was to investigate an experimental model which allows to evaluate radiation parameters and to study the mechanism of the inhibitory effect on neoangiogensis. Methods: Corneal angiogenesis was induced by use of a micropocket assay in NZW rabbits. Pellets with 500 ng bFGF in 2% methylcellulose were implanted into the stroma 2.0 mm from the limbus. initiation of vessel growth occurre d on day 3. At this time radiation was performed with different doses (sing le dose of 15 to 30 Gy or fractionated 5 x 5 Gy) using a 6 MeV linear accel erator Vascular growth was quantified. Results: Irradiation with a total dose of 25 Gy applied in a fractionated r egimen or as single-dose irradiation on the day of surgery or on day 6 afte r surgery did not significantly reduce neovascular growth. In contrast, pos toperative radiation therapy on day 3 was able to reduce the area of ingrow ing vessels significantly (P < 0.01). In spite of the relatively high dose there were no significant side effects during the observation period of 8 w eeks. Conclusion: Our results show that single-dose radiation (greater than or eq ual to 25 Gy) is sufficient to inhibit the growth of corneal neovasculariza tions. With this model it might be possible to investigate parameters for t h era py of ocular neovascularizations as well as the underlying mechanisms .