Encircling photothrombotic therapy for choroidal Greene melanoma using rose bengal

The photosensitizing dye rose bengal in combination with an argon green laser (514.5 nm) operated at low power was evaluated in 49 rabbit eyes for treatment of experimental choroidal Greene melanoma by circumferential occlusion of the choroidal vasculature. The effects of no treatment, laser alone, and rose bengal alone were observed in 16 control eyes, all of which showed rapid tumor growth. Immediately following rose bengal injection, 3 minutes of continuous irradiation at 20.4 W/cm2 (500-microns spot, 40 mW) applied in three to four circumferential revolutions around the base of tumor nodules, without direct tumor irradiation, produced peripheral vascular occlusion and consequent tumor inhibition. Similar therapy at higher laser intensity (30.6 W/cm2) and with multiple retreatment sessions (28.0 to 30.6 W/cm2) resulted in increased tumor-inhibiting effect. Low-dose rose bengal phototherapy did not appear to directly damage ocular tissues adjacent to treatment areas; however, when multiple irradiation sessions were given within a short interval, an increased incidence of retinal detachment was observed.