LASER ENERGY AND DYE FLUORESCENCE TRANSMISSION THROUGH BLOOD IN-VITRO

PURPOSE: Because of the potential usefulness of evaluating and treatin g choroidal neovascularization obscured by blood, we designed this stu dy to quantify the transmission of dye fluorescence and laser energy t hrough blood. METHODS: Blood preparations anticoagulated with ethylene diaminetetraacetic acid with hematocrits of 0% (plasma), 46%, and 99% were placed in open cuvettes with path lengths of 100, 200, or 500 mu m and were exposed for one minute to either 100% oxygen or 100% carbon dioxide, Each cuvette was then sealed. Photographs of the cuvettes of blood in front of a flask of fluorescein or indocyanine green solutio n were decoded and used to calculate the percent transmission of fluor escence through blood. Cuvettes of blood were also placed in the path of argon, krypton, and diode lasers for energy transmission measuremen ts. RESULTS: Plasma transmission of fluorescein and indocyanine green fluorescence and argon, krypton, and diode laser energy was 89% to 100 % for all samples tested, Transmission of fluorescein fluorescence and argon laser energy through 99% hematocrit samples were both less than 5%. Transmission of indocyanine green fluorescence through 100-, 200- , and 500-mu m thick cuvettes filled with 99% hematocrit blood was 57% , 34%, and 4%. Transmission of krypton laser energy was 50%, 25%, and 6%; and transmission of diode laser energy was 60%, 35%, and 12% throu gh 99% hematocrit blood. Intermediate transmission values were obtaine d for 46% hematocrit samples. CONCLUSIONS: Kryrpton and, to a slightly greater degree, diode laser energy penetrate a thin film of blood. In docyanine green fluorescence also penetrates a thin film of blood. If a layer of blood appears thinner than 500 mu m, then indocyanine green angiography may be useful in imaging underlying pathologic features. If a lesion can be imaged with indocyanine green, then it can probably be treated with a krypton or diode laser.