Effect of argon laser photoradiation on monkey retina treated with hematoporphyrin derivative--fluorescein angiographic and light microscopic study.

To determine the method of treating retinoblastoma by means of argon laser photoradiation and hematoporphyrin derivative (HpD), we gave HpD intravenously at a dose of 2.5 or 5.0 mg per kg to monkeys, and 40 minutes, one day or 3 days after this injection, argon laser photoradiation was performed at 2.0 mm diameter with a 10-minute exposure at intensities of 40, 100 or 200 mW. As photoradiation after HpD injection of 5.0 mg per kg induced severe retinal changes, 2.5 mg per kg was thought to be the dose for clinical application. Photoradiation 3 days after the injection of HpD was found to be the best choice of timing. One hundred to 200 mW intensity of laser beam was considered to be an appropriate range. Without HpD, changes in the retinal pigment epithelium and outer segment of the visual cells of the photoradiated eyes resembled those caused by conventional photocoagulation. Characteristic findings of the photoradiated retina were obstruction of the retinal vessels, fragility of the nerve fiber layer and attenuation of the inner nuclear layer. Photoradiation at a high intensity induced retention of subretinal fluid in the nonphotoradiated area. Therefore, at the time of photoradiation, light should be delivered only to the tumor.