The influence of age on optokinetic nystagmus.

The influence of age on optokinetic nystagmus (OKN) was studied in 63 healthy subjects, who were divided into three groups according to their age, group I (20-39 years), II (40-59 years) and III (60-82 years). It was found that on average maximal OKN velocity decreases considerably with age, from 114 degrees/s in group I to 93 degrees/s in group II and 73 degrees/s in group III. Two mechanisms participate in the generation of OKN, the so-called 'fast' component and 'velocity storage' component. The 'fast' component leads to immediate changes in slow phase nystagmus velocity and is related to smooth pursuit eye movements. The 'velocity storage' component causes more gradual velocity changes and expresses itself during optokinetic afternystagmus (OKAN). To study the relative contribution of these two components, maximal smooth pursuit and OKAN velocity were determined in addition to the maximal OKN velocity for the same individuals. It was found that both smooth pursuit and OKAN performance decrease with age. Consequently the maximal OKN velocity, which depends on both factors, is even more affected than smooth pursuit eye movements.