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Abstract

The visual system consists of several subsystems, which perform their task nearly independently of each other. One is the accessory-optic system, performing the gaze stabilisation by eye-nystagmus.
In humans two kinds of nystagmus can be discriminated: stare nystagmus and look nystagmus (smooth pursuit). The best known example for stare nystagmus can be seen on a
train journey. The vis-à-vis -staring out of the window- moves his eyes nystagmic. Without fixating any single object the eyes run over the landscape, most of the time following and bouncing back every now and then. In contrast, during look nystagmus single objects are fixated and pursued. Stare nystagmus is driven by the accessory-optic system, a set of subcortical nuclei, while cortical structures contribute to the look nystagmus.
In order to find out which cones contribute to both kinds of nystagmus, we measured their spectral sensitivity. Two different instructions were given to the observers, leading to either stare or look nystagmus, respectively. Spectral sensitivity turned out to be different for look and stare nystagmus. Spectral sensitivity of stare nystagmus corresponds basically to the V(l)-function, indicating that there is no or only a minor contribution of the short wavelength cones. Look nystagmus has a higher sensitivity at short wavelengths, demonstrating a contribution of short wavelength cones.