Hyperspectral imaging measures retinal oxygen levels

Measuring the oxygen level of the retinal tissues may allow detection of retinal changes in patients with diabetes before structural changes in the capillaries occur, said Amani Fawzi, MD, Doheny Eye Institute, University of Southern California, Los Angeles.

Dr. Fawzi and colleagues are developing a hyperspectral oxygen camera to obtain color images of the retina that detail the level of oxygen saturation of the tissues. One snapshot captures spatial and spectral data and the oximetry information can be extracted and analyzed.

Investigators tested the accuracy of the instrument based on previous knowledge that there can be about a 30% difference in oximetry between the arteries and veins in the retina. Images confirmed the difference between the structures, with the arteries having about 90% oxygen saturation and the veins about 70% saturation, Dr. Fawzi said.

She showed images of the macula in patients with branch and central vein occlusions and diabetic retinopathy that showed capillary damage and zones of foveal avascularity. She also demonstrated the effect of treatment with bevacizumab (Avastin, Genentech) in a patient with central vein occlusion and that the oximetry increased after treatment, which explains the immediate increase in vision after injection.

"This technology is a robust means to image retinal oximetry," Dr. Fawzi said. "It is rapid and noninvasive. Low oxygen levels correlated with ischemia/nonperfusion in retinal vasculature disease. The hope is that imaging can detect changes before structural damage occurs and result in treatment algorithms before structural damage occurs."