IMPROVING THE EFFICIENCY OF HEMATOPORPHYRIN PHOTOTHERAPY OF OCULAR TUMORS

Malignant melanoma of the choroid is the most common primary intraocular tumor in adult humans. Controversy exists over which is the most effective therapy. One therapeutic modality that has not been thoroughly investigated is hematoporphyrin derivative phototherapy (HPdPRT), a technique used successfully in the clinic on many non‐ocular tumors. The effect of HPd PRT on an ocular, amelanotic melanoma was evaluated using Greene melanoma implanted on pigmented rabbit iris. The parameters used clinically on non‐ocular tumors (intravenous 2.5 mg HPd kg^‐1 body weight and irradiation at 633 nm 48 h later) were totally ineffective in killing Greene melanoma implanted on the iris. The dose of dye (2.5–5 mg kg^‐1), wavelength of light (500‐700 nm), and illumination intensity were varied to determine the most efficient parameters for treating this tumor. The most important parameter was dye dose; increasing it to 5 mg kg^‐1 resulted in some control of tumor growth. Administering 100% O₂ prior to and during irradiation also improved HPd PRT cytotoxicity. The use of pulsed light (pulses of 1 or 2 min) further enhanced killing and reduced the length of irradiation needed. These studies suggested that HPd PRT might be used efficiently on ocular melanomas.