AIM To assess the retinal phototoxicity hazards of and to provide safety margins for endoillumination during vitrectomy. METHODS The absolute power and spectral distribution from various light sources and filter combinations that are commercially available for vitreous surgery were measured. The maximal exposure times based on the ICNIRP safety guidelines for photochemical and thermal injury of the aphakic eye were calculated. Additionally, the effect of various measures that reduce the risk of phototoxicity was evaluated. RESULTS Measurements of the spectrum and energy indicated that the ICNIRP safety guidelines for photochemical retinal damage are exceeded within 1 minute for nine out of 10 combinations tested. With an additional 475 nm long pass filter, light levels below 10 mW, and a distance from light probe to retina of at least 10 mm, the allowable exposure time can be increased up to 13 minutes. Thermal damage can be anticipated when the light probe touches the retina. CONCLUSION Commercially available light sources for endoillumination during vitrectomy are not safe with respect to photochemical retinal damage. Even with maximal precautions macular phototoxic damage remains a factual danger during vitrectomy.

Objectives: The aim of this experimental study was to investigate the mechanism of action of endovenous laser ablation (EVLA) using an 810-nm diode laser. Methods: We compared intermittent and continuous delivery of laser energy and studied the absorption of laser light by blood, intravascular temperatures in ex vivo human vein segments using an intravascular thermography catheter and heat dissipation in a model tissue using the Schlieren technique. Results: Laser light is absorbed by blood and converted to heat leading to coagulation, vaporization and carbonization, and forming an isolating layer at the fibre tip. Laser energy is then absorbed into the isolating layer forming black patches that burned on the laser fibre. Intravascular temperature increased rapidly above carbonization temperatures (300°C) after the fibre tip reached the thermocouple, stayed at this temperature for a few seconds and decreased gradually to around 30°C, 10 s after the fibre tip passed the thermocouple. Schlieren techniques revealed that heat spread from the laser was locally distributed and closely around the laser fibre tip while heat dissipation is minimal and comparable for both exposures. Compared with intermittent exposure, continuous exposure results in more carbonization, higher mean maximum intravascular temperature (128 ± 7 vs. 75 ± 4°C), and long-lasting temperature of 100°C (1.2 ± 0.4 vs. 0.1 ± 0.1 s). Conclusion: In this experimental study, application of endovenous laser shows to be dominated by carbonization at the fibre tip. Although intraluminal laser-induced heat was heterogeneously distributed, with laser tip temperatures up to 1200°C, heat dissipation was minimal. Continuous exposure of laser light appears to be better suited in EVLA than intermittent.