Coupling between neuronal activity and retinal metabolism

Introduction The main goal of this grant was to establish a new, non-invasiv method to evaluate the so called neuro-vascular coupling (the coupling between augmented blood flow and increased neural activity) in the human retina. Furthermore, our studies aimed to investigate the influence of two ocular diseases, diabetic retinopathy and glaucoma, on flicker induced vasodilation. Methods The Zeiss Retinal Vessel Analyser, a fundus camera based system comprising a video camera and a personal computer, was equipped with a flicker light stimulation system. To avoid artifacts during the measurement, a wave length separation technique based on cut-off and interference filters was introduced in the optical system of the fundus camera. Flicker stimulation consisted of light flashed at a frequency of 8 Hz and provided a stimulus size of approximately 30 of visual angle on the central retina. Results The data of evaluation study revealed a very high statistically significant increase in retinal vessel diameters in the range of 3 to 5% during 60 seconds of flicker stimulation in healthy young humans. The reproducibility and sensitivity of these measurements were very high. (unpublished data, paper submitted) Evaluation and acquiring of measurement results in patients with diabetes mellitus and open angle glaucoma are still in progress. Discussion The new Zeiss retinal vessel analyzer has been proven to be an effective instrument to measure retinal vessel diameters in humans. In combination with a special flicker light stimulation system there is first indirect evidence that measurement of the neurovascular coupling is possible in humans. Additionally, measurements in patients have demonstrated a wide spectrum of applications in several diseases of the inner retina.