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Two-photon microperimetry with picosecond pulses

Two-photon vision is a phenomenon associated with the perception of short pulsesof near-infrared radiation (900-1200 nm) as a visible light. It is caused by the nonlinear processof two-photon absorption by visual pigments. Here we present results showing the influence ofpulse duration and repetition rate of short pulsed lasers on the visual threshold. We comparedtwo-photon sensitivity maps of the retina obtained for subjects with normal vision using acost-effective fiber laser (λc=1028.4 nm,τp=12.2 ps,Frep=19.17 MHz) and a solid-state laser(λc=1043.3 nm,τp=0.253 ps,Frep=62.65 MHz). We have shown that in accordance with thedescription of two-photon absorption, the average optical power required for two-photon visionfor a fiber laser is 4 times greater than that for a solid-state laser. Mean sensitivity measured forthe first one is 5.9±2.8 dB lower than for the second but still 17 dB away from the safety limit,confirming that picosecond light sources can be successfully applied in microperimetry. Thisdevelopment would dramatically reduce the cost and complexity of future clinical devices

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