Effects of Aging on Smooth Pursuit Eye Movements Induced by Step-Ramp Stimulation

Step-ramp stimuli were used to distinguish the effects of aging on smooth pursuit eye movements in young and elderly subjects. In this experiment, step-ramp target motions which include four kinds of onward stimulus (2, 4, 6, 8° steps followed by 10°/s ramp) and three kinds of backward stimulus (2° step combined by 9°/s ramp, 4° step; 17°/s, 6° step; 27°/s), were used to test 26 subjects less than 49 years old and 23 subjects more than 50 years old. Eye movements were recorded by infrared reflection oculography with a sampling time of 250 Hz. Data on eye velocity and acceleration were processed with a personal computer. The latency of the response was determined at the time when mean eye acceleration along the base line intersected the line of 100°/s2. Eye acceleration corresponding to the retinal slip velocity (target velocity-eye velocity) was established in each 20 ms segment after pursuit initiation. The relationship between retinal slip velocity and eye acceleration was evaluated by plotting the regression curve for each stimulus. The latencies of smooth pursuit ranged from 145 to 169 ms, and were independent of stimulus conditions. There was a close correlation between retinal slip velocity and eye acceleration in the onward step-ramp target motion study. The x-coefficient of the regression curve in the younger group (y=211x+ 1671) was greater than that in the older group (y=98x+2045) in the step positions of 8° and 10°/s ramp stimulus. These results indicate that younger subjects could produce faster velocity and greater eye acceleration than elderly subjects. Among factors influencing aging effects, the cerebrum might be important, because visual recognition and eye acceleration involve the parietal lobe.