A new technique developed by Canadian, British and American researchers allows near-infrared laser light to penetrate two or three times deeper into living tissue, shutting off blood vessels to treat certain tumors or age-related macular degeneration.

Using two-photon excitation, it is a significant upgrade to an existing treatment called photodynamic therapy (PDT), which involves injecting a light-sensitive compound into diseased tissue. Exposing the compound to laser light generates a high-energy form of oxygen that is toxic to cells.