Retinal vessel oximetry in glaucoma

Purpose We undertook retinal vessel oximetry, using spectral imaging, with both sequential and snapshot cameras. We have validated the values obtained using a model eye. We have explored the propagation of light through the retina using Monte Carlo modelling. Clinical retinal oximetry results are presented from normal volunteers, and glaucoma patients. Methods The sequential spectral camera employs a liquid‐crystal tunable filter. Images were captured using a cooled CCD camera, at wavelengths between 550nm and 680nm. The snapshot camera captures multiple spectral images simultaneously. We used the spectral images from these devices to calculate retinal vessel oximetric values, with the output displayed as a retinal oximetric 'map'. We obtained oximetric maps from normal volunteers, and compared these with the oximetric maps from glaucoma patients with a range of visual field loss. Results There were significant differences between oxygen saturation in the retinal venules of the most severely affected glaucoma patients, compared with the normals: the glaucoma patients had higher values of venous saturation, with a correlation between visual field mean deviation (MD) and venous saturation. There were no significant differences in ateriolar oxygen saturation between normals and glaucoma patients. Conclusion We have demonstrated retinal vessel oximetry using two types of spectral imager. We have attempted to validate our cameras using a model eye. We found higher venular oxygen saturation in glaucoma patients versus normals: these findings might suggest reduced inner retinal oxygen consumption in glaucoma. The venular oxygen saturation might represent an objective, clinically useful, measure of ganglion cell health.