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Application of femtosecond ultrashort pulse laser to photodynamic therapy mediated by indocyanine green

¹ Department of Ophthalmology and Visual Science, Osaka University Graduate School of Medicine, Osaka, Japan
² Institute of Free Electron Laser, Graduate School of Engineering, Osaka University, Osaka, Japan

Correspondence to:
Correspondence to:
Dr M Sawa
Department of Ophthalmology and Visual Science, Osaka University Graduate School of Medicine, Room E7, 2-2 Yamadaoka, Suita, Osaka, Japan 565-0871; sawamiki{at}ophthal.med.osaka-u.ac.jp

Backgrounds/aims: To evaluate treatment with high peak power pulse energy by femtosecond ultrashort pulse laser (titanium sapphire laser) delivered at an 800 nm wavelength for corneal neovascularisation using photodynamic therapy (PDT) mediated by indocyanine green (ICG).

Methods: Using a gelatin solid as an in vitro corneal model, the safety of laser power was studied to determine if it degenerated gelatin with or without ICG. The authors then induced corneal neovascularisation in rabbit eyes by an intracorneal suturing technique. Fluorescein angiography was used to evaluate occlusion before PDT and 0, 1, 3, and 10 days after PDT. The authors performed light microscopy with haematoxylin eosin staining and transmission electron microscopy to determine thrombosis formation in the neovascular regions.

Results: The threshold of peak laser power density ranged from 39 to 53 W/cm². Laser irradiation was started 30 seconds after a 10 mg/kg ICG injection, and all irradiated segments were occluded at 0, 1, 3, and 10 days at 3.8 J/cm². Light and electron microscopy documented thrombosis formation in the neovascular region.

Conclusion: Femtosecond pulse laser enhanced by ICG can be used for PDT. Because of effective closure of corneal neovascularisation at a low energy level, the high peak power pulse energy of the femtosecond pulse laser might be more efficacious than continuous wave laser for use with PDT.

Keywords: corneal neovascularisation; femtosecond pulse laser; indocyanine green; photodynamic therapy; photothrombosis

Abbreviations: ICG, indocyanine green; PDT, photodynamic therapy

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