THE EVOLUTION OF PHOTODYNAMIC THERAPY TECHNIQUES IN THE TREATMENT OF INTRAOCULAR TUMORS

Abstract The techniques of photodynamic therapy (PDT) and the indications for its use in the treatment of intraocular tumors have evolved during the years in which it has been assessed in patients at our institution. It is now clear that transcorneal PDT delivered at a subthermal dose-rate to the surface of a pigmented lesion such as choroidal melanoma has little effect. In the absence of pigment, however, as in the case of retinoblastoma or amelanotic melanoma of the iris or choroid, the tumor kill attributed to PDT alone is significant. Data from animal tumor models in our institution and from patient studies elsewhere suggest that the addition of heat with the light delivery will predictably improve the outcome of the treatment of pigmented lesions. Ocular PDT delivered in conjunction with heat will be useful clinically as an adjunct to scleral plaque therapy by reducing the height of a lesion and concurrently the dose of radiation necessary at the base of the tumor for sterilization. Since the clinical tumoricidal effect of PDT is now known to be due at least in part to vascular damage, trans-scleral application of light to the base of melanomas and occlusion of its blood supply holds significant promise of efficacy with continued improvement of the light delivery system. Finally, a transpupillary approach to occlusion of the choroidal vascular supply to a melanoma by surrounding the tumor with photodynamic lesions may provide the best approach for ocular PDT as a primary therapy.