Aging effects upon smooth pursuit induced by step–ramp stimulation

Objective: in predictable target movements, pursuit gains are extremely close to 1.0. Under these conditions, aging effects upon pursuit have not been detected. Step–ramp stimuli produced by unpredictable combinations would be favorable procedures to assess the properties of smooth pursuit between young and aged people. Methods: the target was a 0.5° red laser spot. Eye movements of 49 normal subjects (26 younger subjects less than 49 years old and 23 older subjects more than 50 years old) were recorded with infrared reflection oculography and sampled at 250 Hz. Step direction and distance (2, 4, 6, 8°) followed by 10°/s ramp speed movement in the same (onward stimulus) or opposite to the direction (backward stimulus) were programmed in an unpredictable way before each set of ten tests. Both onward and backward stimulation were randomly given for each subject. Results: in the onward study, there was a close correlation between retinal slip velocity (RSV) and eye acceleration (EA), which was expressed as a regression curve, being steeper in the younger group. This means that the younger subjects could produce faster velocity and greater acceleration than the aged group (P<0.05). Conclusion: subtle reduction in visual acuity, visual fields and contrast sensitivity will be one of possible causes, and the degradation of cortical areas crucial for visual processing might be one of possible causes of slowing of pursuit EA.