Decreased Activation of the Visual Cortex in Unilateral Optic Neuritis Demonstrated by Near–infrared Spectroscopy

Abstract

Abstract: : Purpose: We applied near–infrared spectroscopy (NIRS) of the visual cortex to two patients with unilateral optic neuritis and investigated whether or not NIRS could detect visual dysfunction objectively in clinically affected eyes. Methods: We used an OM–100A (Shimadzu Corporation, Kyoto, Japan) near–infrared spectroscopy system to monitor changes in the oxyhemoglobin (oxy–Hb), deoxyhemoglobin (deoxy–Hb), and total hemoglobin (total–Hb) concentrations in the occipital lobe. NIRS was performed on two patients with acute unilateral optic neuritis during monocular visual stimulation. Each condition lasted for 30 seconds, and a pair of two conditions was repeated six times for each experiment. As controls, six normal subjects were also tested in the same manner. Results: In all six normal subjects, an increase in [oxy–Hb], a decrease in [deoxy–Hb], and an increase in [total–Hb] were observed following monocular visual stimulation. In these control subjects, there were no significant differences in activation between the right and left eyes. In the patients with optic neuritis, the changes in the hemoglobin concentrations ([oxy–Hb], [deoxy–Hb], and [total–Hb]) in the occipital lobe were found to be markedly reduced when the clinically affected eyes were stimulated as compared with the fellow eyes. The response induced by the stimulation of the affected eye was decreased even when the patient's visual acuity improved to 20/20 in the recovery phase. Conclusions: Our results demonstrate that a decreased activation of the visual cortex in patients with optic neuritis can be demonstrated when NIRS is used. NIRS may be useful in detecting visual dysfunction objectively and noninvasively in patients with visual disturbance, especially when used at the bedside.

Keywords: neuro-ophthalmology: diagnosis • visual cortex • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)