Positron emission tomography to study the effect of eye closure and optic nerve damage on human cerebral glucose metabolism

Previous studies have shown that visual stimulation can influence the metabolism of the vision center or visual cortex of the brain. An evaluation of the effect of visual deprivation on the metabolism of glucose in the brain was undertaken. Positron emission tomography (PET) was used to evaluate subjects who were seated in a quiet, dimly lit laboratory. The rate of glucose metabolism in different areas of the brain was studied. Normal volunteers were used in this experiment. The metabolic rates of one group (11 people), who was evaluated with their eyes open, was compared with those of another group (seven people) who kept their eyes closed. Whole brain glucose metabolism was similar in both groups. There was an insignificant difference of decreased glucose metabolism in the calcarine posterior cortex with eye closure. In a second experiment, six patients with poor vision (20/200) due to bilateral optic nerve disease were studied, and compared with a group of 12 normal controls. Whole brain glucose metabolism was similar in both groups. However, in the patients with optic nerve disease, there were significant reductions in glucose metabolism found in several visual centers of the brain: the anterior calcarine cortex, posterior calcarine cortex, peristriate cortex, and lateral occipital cortex. The decreases in glucose metabolism did not correlate with the duration of optic nerve damage experienced by this group of patients. These findings indicate that the level of visual stimulation is not the only factor involved in visual cortex metabolism. This conclusion was reached because closing of the eye resulted in only minimal changes in glucose metabolism, but optic nerve damage was associated with major changes in glucose metabolism in the visual areas of the brain. (Consumer Summary produced by Reliance Medical Information, Inc.)