Near-IR retinal laser Doppler velocimetry and flowmetry: new delivery and detection techniques

In laser Doppler velocimetry and flowmetry of the human ocular fundus, near infrared diode lasers, coupled with avalanche photodiode detectors, offer much improved signal-to-noise ratio compared to He-Ne laser delivery and photomultiplier tube detection. The increased signal-to-noise ratio is achieved through increased retinal irradiance and better quantum efficiency of the avalanche photodiode in the near infrared. Furthermore, the small size of the diode lasers allows delivery of two individually steerable beams for simultaneous measurements in different parts of the fundus. Applications are given as illustrations of the capabilities of the system: retinal laser Doppler velocimetry in humans without need for pupil dilatation and optic nerve head laser Doppler flowmetry in the cat using flicker as a stimulus to induce blood flow changes.