Oximetry with a multiple wavelength SLO

Abstract

Oximetry may be useful for understanding pathologies of the eye. We use a prototype scanning laser ophthalmoscope capable of simultaneous multiple wavelength imaging to record fundus images. The system is run under non-confocal conditions in using slit apertures with a width of up to 600 µm. The laser lines launched into the SLO were the 633 nm line of a HeNe-laser, and the 815 nm line from a tunable (700 to 900 nm) cw Ti:Sapphire-laser. These wavelengths were selected because of their availability and absorption characteristics. The difference in absorption at these two wavelengths is used to assess blood oxygen content. Images were averaged to improve the signal to noise ratio.

This simultaneous method of measuring oxygen content may be preferred to other techniques such as sequential SLO imaging at different wavelengths, or spot analysis using a modified fundus camera. The advantages of this technique are that image registration is not required, and a large area of the retina can be assessed concurrently.