Visual function declines with age. Much of the decline may result from functional degradation in central visual areas. To investigate the physiological mechanisms underlying visual function declines during normal aging, we compared the response variability of cells in primary visual cortex (V1) and middle temporal visual area (MT) in young adult and very old macaque monkeys using single-neuron in vivo electrophysiology. We found that mean response and response variability in both V1 and MT of old monkeys are significantly higher than in young monkeys. And response-to-noise ratio in old monkeys is significantly lower than in young ones. The results are consistent with an age-related degradation of inhibitory intracortical circuits. The neural changes described here could contribute to declines in visual function during senescence.